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Review—Multifunctional Copper Nanoparticles: Synthesis and Applications

Madhulika Bhagat 1 , Rythem Anand 1 , Pooja Sharma 1 , Prerna Rajput 1 , Neha Sharma 1 and Khushwace Singh 2

Published 28 June 2021 • © 2021 The Author(s). Published on behalf of The Electrochemical Society by IOP Publishing Limited ECS Journal of Solid State Science and Technology , Volume 10 , Number 6 Focus Issue on Solid State Reviews Citation Madhulika Bhagat et al 2021 ECS J. Solid State Sci. Technol. 10 063011 DOI 10.1149/2162-8777/ac07f8

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1 School of Biotechnology, University of Jammu, Jammu and Kashmir 180006, India

2 Yogananda College of Engineering & Technology (YCET), Department of Civil Engineering, (affiliated to University of Jammu), Jammu and Kashmir-181123, India

Madhulika Bhagat https://orcid.org/0000-0001-5539-7090

  • Received 5 January 2021
  • Revised 5 May 2021
  • Published 28 June 2021

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Copper nanomaterials due to their unique properties are rapidly finding place as an important component of next-generation material in various sectors such as electronics, machinery, construction, engineering, pharmaceutical, agriculture, energy, environment etc In fact in past decades, researchers have devoted several studies to Cu nanomaterials, and have achieved many innovative results from synthesis to applications, highlighting its immeasurable potential for extensive practical and theoretical applications holding great promises. This review emphasises on the recent progress made in synthesis of copper nanoparticles by various techniques such as physical, chemical and biological methods. The application section describes their utility in several sectors including agriculture, environment, construction, electronics etc Moreover, the emphasis was also laid to understand the uptake mechanism of the copper nanoparticles by plants, the toxicity caused at higher concentrations and the associated implications of exposure to both human and environmental health, including the challenges and difficulties to be addressed in the future.

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With recent advancement in nanotechnology, the nano sized structures have emerged as a powerful tool and in the current scientific era these tiny structures have received lots of attention in various fields such as physics, chemistry, biology, nanomedicine, electronics etc. 1 , 2 A nanometer (nm) is an International System of Units (SI) unit that represents 10 −9 meter in length, whereas in principle, nanomaterials are described as materials with length of 1–1000 nm in at least one dimension; however, they are commonly defined to be of diameter in the range of 1 to 100 nm including the several other definitions available with special reference to nanomaterials. However, a single internationally accepted definition for nanomaterials still does not exist, as different organizations have different opinions in defining nanomaterials. According to the US Food and Drug Administration (USFDA) nanomaterials are referred as "materials that have at least one dimension in the range of approximately 1 to 100 nm and exhibit dimension-dependent phenomena". 3 At this range nanomaterials act as a bridge between bulk materials, atomic or molecular structures 4 and capable of possessing unique, interesting properties owing to their very small sizes, large surface area with free dangling bonds, diffusion rate and higher reactivity compared to their bulk counterparts. 5 – 7 As the material size decreases, approaches towards nano-scale physical properties of bulk-sized materials, such as optical, magnetic, catalytic, thermodynamic, electrochemical properties etc also gets dramatically changed. 8 These exceptional properties of the nanosized materials have found role for diverse applications in various sectors such as textiles, pharmaceuticals, cosmetics, environmental, agricultural, electronic, aerospace, construction etc. 9 , 10 Till date many different types of nanoparticles have been fabricated using various approaches such as physical, chemical, biological or hybrid methods. 11 Lots of different types of nanoparticles have been explored for various purposes that includes, carbon based (Fullerenes (C60), carbon nanotubes (CNTs), carbon nanofibers, carbon black, graphene (Gr), carbon onions etc), others types like core–shell nanoparticles, polymer-coated magnetite nanoparticles, organic-based nanomaterials (dendrimers, micelles, liposomes and polymer NPs), metal oxide nanoparticles (CeO 2 , TiO 2 , ZrO 2 ), inorganic nanoparticles (AgNPs, CoNPs, FeNPs, AuNPs, PdNPs) and metal oxide nanoparticles (FeONPs, CuONPs, MgONPs, ZnONPs) etc. 2 , 7 Among several nanomaterials, the copper nanoparticles (Cu NPs) are particularly attractive option and being explored in various sectors mostly as catalysts in organic synthesis, for drug delivery, agriculture, food preservation, paint, water treatment, agrochemicals like antimicrobial products, semiconducting compounds, sensors, sintering additives, capacitor materials, in metal-metal bonding process, construction materials, nanometal lubricant additives etc. 12 – 15

Copper (Cu) is the 8th abundant metallic element of the Earth's crust, once solubilised from the Earth's crust, is neither created nor destroyed and therefore their homeostatic regulation is under strict control. 16 Copper (Cu) is a transition metal with a distinct red–orange color and metallic luster having atomic number 29, atomic mass 63.546, with density greater than 5 g cm −3 . It has several interesting properties including good ductility, malleability, high thermal, electrical conductivity, high corrosion resistance, low chemical reactivity etc. 17 , 18 All these unique properties of copper have been applied in several essential functionalities of the societal structure for thousands of years. Moreover, copper (Cu) is also a key trace element for humans, plants, and animals. For humans, it is needed in a minimal amount (<100 mg/day). 19 The property of Cu that drives its diverse roles in structure and catalysis, is its existence in either a reduced, Cu + , or oxidized, Cu 2+ , state through multiple pathways. 20 Since Cu + has an affinity for thiol and thioether groups viz ., cysteine or methionine and Cu 2+ exhibits preferred coordination to oxygen or imidazole nitrogen groups viz ., aspartic, glutamic acid, histidine, the interactions of the metal ions with proteins led to derivation of diverse structures and various biochemical reactions such as neuropeptides synthesis, regulator of cell signalling pathways, antioxidant defense, immune cells (macrophage, neutrophils, helper T cells) activation for killing of pathogens, maintaining the immune system constituents of hair and of elastic tissue contained in the skin, bone and other body organs. 21 – 23 In plants copper can be present as Cu 2+ and Cu + under natural conditions with optimum concentrations ranging from 10 −14 to 10 −16 M respectively. Being a cofactor for numerous enzymes, responsible for proper functioning of various vital proteins/enzymes such as amino oxidase, cytochrome c oxidase, plastocyanin etc and certain concentrations are responsible to formation of structural components of numerous regulatory proteins and take part in the photosynthetic electron transport chain, mitochondrial respiration, oxidative stress response, cell wall metabolism, hormone signalling, iron mobilization etc. 24 , 25 Based on the current information, the present review discusses the various methodologies for the synthesis of Cu NPs followed by its characterizations; it's mechanism of uptake in plant system, their recent applications in different areas followed by highlighting its probable toxicity and future challenges to be addressed.

Synthesis of Copper Nanoparticles

The preparation of copper nanoparticles is much more difficult in comparison with noble metals as copper particles have the tendency to get oxidized when they are exposed to air, leading to agglomeration of particles due to surface oxidation. To avoid this problem nano copper particles are produced in an inert gas atmosphere. 26 In some cases, protective polymers 27 , 28 or surfactants 29 are utilized to inhibit oxidation. A wide range of copper nanoparticles can be produced using different physical, chemical and biological methods (Fig. 1 ).

Figure 1.

Figure 1.  Different approaches in synthesis of copper nanoparticles.

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Copper nanoparticles can be produced by using various techniques typically classified as bottom-up or chemical methods and top-down or physical methods. The structure of copper nanoparticles are composed of atoms and clusters or molecules in a bottom-up approach whereas in the case of top-down approach a bulk piece of required material is diminished to nanoscale dimensions using mechanical milling, cutting, etching and grinding techniques. Some of the methods like chemical reduction, sonochemical reduction, microemulsion techniques, electrochemical, hydrothermal, sol–gel synthesis, polyol process and microwave-assisted methods are the major techniques for preparing copper nanoparticles from bottom-up approach. Biological syntheses are also treated as a bottom-up approach. Top-down methods for synthesis of copper nanoparticles are laser ablation, vapor phase synthesis, mechanical milling, vacuum vapor deposition and pulsed wire discharge (PWD). 30 – 33 Similarly, a wide range of nanoparticles can also be produced using top-down or physical methods with little alterations but the quality of product is not good when compared to chemical methods and it requires special equipment and vacuum systems to produce nanoparticles. But in the case of chemical methods the size, growth, morphology and distribution of particles can be controlled by optimizing reaction conditions such as reaction time, pH and ratio of electrolyte to the surfactant, protective agent, type of solvent and capping ag conditions it is very easy to obtain narrow particle size distribution in chemical methods. Large-scale syntheses are not possible by using chemical methods. These physical or chemical methods for the synthesis of copper nanoparticles have various limitations such as generation of hazardous toxic chemicals, utilization of expensive reagents, and more tedious processes to isolate nanoparticles etc Hence, the researchers had to look out for alternative approaches for the synthesis of nanoparticles which involve utilization of inexpensive reagents that can be developed safely with less drastic reaction conditions and are eco-friendly in nature. Thus, synthesis using bio-organisms/plants considered more compatible with the green chemistry principles as the Green synthesis of nanoparticles involves usage of non-toxic, environmentally friendly and safe reagents. 34 However, green synthesis by using plant extracts in addition to bacteria, fungi and algae is considered the most convenient method as the phytochemicals present in the plants can act as both reducing agent and stabilizing agent in the synthesis of metal nanoparticles.

Physical Methods

Pulse laser ablation/deposition.

Pulse laser ablation is a physical method that is done in a vacuum chamber in presence of inert gas/some background. It helps to generate copper nanoparticles in colloidal form with a variety of solvents to prevent oxidation. 35 Number of parameters like type of solvent, duration of pulses, type of laser can be controlled to change the final product. For example, Cu NPs synthesised using 2-propanol as solvent produce 5–15 nm, 36 polysiloxane produced 2–20 nm, 37 and pure acetone/water formed 10–30 nm sized particles. 38

Mechanical/Ball milling method

It is a solid state processing technique for the preparation of copper nanoparticles. There are many different types of mechanical mills available for the copper nanoparticles synthesis and are classified according to their applications and capacity. Most commonly used mechanical mills for the copper nanoparticles synthesis are planetary, vibratory, uniball and attritor. Following factors control the size of the particles such as type of mill, design of container or chamber, milling speed and time, heat treatment temperature, atmosphere, process control agent, size distribution of grinding medium and weight ratio of ball to powder. The size of the particle depends upon the capacity of the mills. 39 , 40

Pulse Wire Discharge Method

Pulse wire discharge (PWD) method is a physical method for the synthesis of copper nanoparticles. 41 , 42 In this method pulsed current is guided through a copper solid wire, here the Joule heating causes electrical energy deposition that can turn the whole copper solid wire into plasma. By cooling this plasma with ambient gas, we can obtain a large number of very fine solid copper nanoparticles. 43 , 44 Dash et al. prepared copper nanoparticles of 16 nm by applying 22KV with 3 F capacitance and pressure of 0.1 MPa. 45 , 46 Muraia and his coworkers prepared copper nanoparticles of 20–25 nm by evaporation of copper wire on oleic acid vapor/mist by using pulse wire technique. 47 , 48

Chemical Synthesis Method

Chemical reduction method.

The chemical reduction method for the synthesis of copper nanoparticles is the easiest, simplest and most commonly used method where reduction of copper salts by using reducing agents such as polyols, 49 , 50 sodium borohydride, 51 , 52 hydrazine, 53 , 54 ascorbic acid. 55 , 56 Some capping agents can also be used which include polyethylene glycol 57 , 58 and poly(vinylpyrrolidone). 49 , 59 Copper nanoparticles of <10 nm were produced by reduction of Cu 2+ in solution of poly(acrylic acid) and pluronic blends. 60 Copper nanocolloids of 70–80 nm were synthesized by the reduction of dioxane solution copper salt which was further reduced with hydrazine. 61

Photochemical Method

The photochemical method utilizes light intensity to produce copper nanoparticles. Photochemical techniques provide several advantages over conventional chemical means, such as the reduction of metal ions can be carried out without using reducing agents and so avoiding undesired by-products of the reductant, selection of suitable wavelength and concentration helps to control rate of reaction, light (reducing agent) is uniformly distributed in the solution, irradiation can be performed at room temperature. For example by using poly (N-vinylpyrrolidone) (PVP) as a stabilizer, the copper nanoparticles with an average size of 15 to 20 nm were produced by this technique. 62

Electrochemical Method (Electrolysis)

In this method an electric current between the anode and cathode electrodes in the electrolyte solution is applied to produce copper nanoparticles, so synthesis takes place at the electrode/electrolyte interface. 63 The electrochemical method is a simple, fast, economical, clean, non-toxic flow process that can be done at room temperature and in an environmentally friendly manner. Raja et al. synthesized copper nanoparticles of 40–60 nm using copper sulfate and sulfuric acid as electrolytic solutions with 4 V, 5 A supply of electricity for 30 min. 64

Thermal Decomposition Method

Thermal decomposition method is carried out in pressurized containers and controlled temperatures such as autoclaves, where the solvent reaches a temperature above its boiling point. 64 , 65 Different solvents such as hydrothermal and solvothermal such as copper chloride, sodium oleate and phenyl ether are used to produce copper nanoparticles. 40 , 66 Baco-Carles et al. used this method for the synthesis of copper nanoparticles of 3.5–40 nm. 67 Chen et al. also applied a hydrothermal method to synthesize copper nanoparticles with different sizes. 68

Sonochemical Method

In sonochemical method, ultrasound radiation (frequency 20 kHz to 10 MHz) is used in the copper salt electrolyte solution. The chemical effects of ultrasound do not originate from a direct coupling of the acoustic field to the molecular species. Instead, they come from nonlinear acoustic phenomena, primarily acoustic cavitation. 69 For example, using copper hydrazine carboxylate as a precursor for 30 min, synthesized 50–70 nm sized copper nanoparticles. 70

Microemulsion Method

Microemulsion is a process which involves two immiscible fluids for the synthesis of copper nanoparticles i.e. water in oil or oil in water with the addition of surfactant. An emulsion is a single phase having three components: water, oil and surfactant 71 , 72 making them to possess unique properties, namely, ultralow interfacial tension, large interfacial area, thermodynamic stability and the ability to solubilize otherwise immiscible liquids.

Microwave Method

A microwave method involves electromagnetic energy with the frequency range between 300 MHz to 300 GHz. In the microwave method, microwaves are passed into the reaction solution. Interactions between materials and microwaves are based on two specific mechanisms: dipole interactions and ionic conduction. Both mechanisms require coupling between components of target material and the oscillating electric field of the microwave. The microwave-assisted synthesis of copper nanoparticles allowed to increase the efficiency of materials by providing rapid heating and rapid reaction time. 73 It can accelerate volumetric heating and kinetics, rapid volumetric heating and kinetics, short reaction periods and increasing yields of products compared to conventional heating methods. Blosi et al. reported microwave assisted polyol synthesis of crystalline copper nanoparticles with radius in between 90 nm–260 nm. 74

Biological Synthesis Method

This method is environmentally friendly and has a cost effective approach for the production of nanoparticles. Biomolecules found in these plant extracts and microbial extracts function as both reducing and stabilizing agents during the synthesis of CuONPs and other metal nanoparticles. 75 Biomolecules such as flavonoids, proteins, tannins, phenols and terpenoids have been reported as good reducing and stabilizing agents for CuONPs synthesis. The biosynthesis of copper nanoparticles has been accomplished by utilizing microbes 76 , 77 algae, 78 fungi, 79 angiosperm plant extracts, 80 phytochemicals such as sinapic acid 81 are utilized for the nanoparticles production. Various examples are enlisted in literature like Usha et al. reported copper nanoparticles synthesis with average size of 29 nm by aqueous leaf extract of Ocimum sanctum . 82 Similarly, CuNPs were synthesised by leaf extract of Capparis zeylanica , 83 aqueous extract of Syzygium aromaticum (Cloves) synthesis Cu NP with 5–40 nm, 84 Datura metel leaf extract with 5 nm, 85 Papaya extract with 20 nm, 86 , 87 other examples where plant leaf have explored for copper nanoparticle synthesis are Catha edulis, Enicostemma axillare (Lam.), Juglans regia, Abutilon indicum, Daturameta, Carica papaya, Thymus vulgaris L., Malus domestica, Thymbra spicata, Ginkgo biloba Linn., Hagenia abyssinica, Ageratum houstonianum Mill. Jatropha curcas, Camelia sinensis, Uncaria gambir, Eclipta prostrata etc. 85 , 88 – 96 , 97 – 99 . The synthesized particles have shown a size range of 1.5 nm–40 nm. 100 – 103 Similarly, other parts of plant such as seed extract of Caesalpinia bonducella , 104 fruit of Phyllanthus emblica (Gooseberry) with 15–30 nm, 105 flower of Anthemis nobilis with 18 nm, 106 flowers of Lantana camara , 93 peel of Musa acuminate , 107 whole plant extract by Adiantum lunulatum with 6.5 ± 1.5 nm, 108 seaweeds Sargassum polycystum with size of 17nm. 109 Additionally, several reports are available reporting synthesis of copper nanoparticles from the microorganisms. Like cell-free culture extract of Pseudomonas fluorescens MAL2,(metal copper-resistant bacteria) was used to synthesize spherical CuNP with a size range of 10:70. 110 Other examples include extracellular synthesis of copper nanoparticles using supernatants of Salmonella typhimurium form culture reported to produce 40–60 nm sized copper nanoparticles. 111 Similarly, synthesis by other bacteria reported are Phormidium cyanobacterium 112 Escherichia coli and Morganella morganii , 113 Serratia sp 114 had been reported. Additionally biosynthesis by other microbes such as green alga Botryococcus braunii synthesised spherical 10–70 nm CuNP, 78 Stereum hirsutum (white rot fungus) with 5–20 nm, 115 dead biomass of Hypocrea lixii synthesised spherical with 24.5 nm, 116 Aspergillus niger strain STA9 synthesized 398.2 nm copper nanoparticles, 117 Pseudomonas stutzeri, Shewanella oneidensis 118 , 119 and genus like Serratia and Lactobacillus have also been reported to synthesize nano sized copper oxide particles. 120 , 121

Characterization of Cu Np

The synthesized nanoparticles can be characterized using different tools (Table I ). In this category UV–visible spectroscopy is used to confirm the bioreduction of the nanoparticle through the obtained surface plasmon resonance (SPR) peak as well as to determine shape, size, band width, and possible aggregation state of nanoparticles. 122 TEM, SEM, STM, AFM analysis are conducted to study the size, shape, morphology, topography, roughness of the surface, texture of the nanoparticle. XRD analysis is used to find the crystalline structure of the nanoparticle. 123 , 124 DLS (referred to as quasi-elastic light scattering) helps in size determination and aggregation of NPs. Biomolecules and a functional group involved in the reduction and stabilization of nanoparticles are identified by Fourier transform infrared spectroscopy (FTIR). 125 The functional groups present on the surface of the nanoparticle and the presence of protein, carbonyl groups, and CH bonds in amines, which is the source for the biosynthesis can also be determined by FTIR. EDAX analysis could be used to determine elemental composition, purity of synthesized nanoparticles. 126

Table I.  Common characterization techniques and parameters obtained.

Characterization TechniquesParameters Assessed
Scanning Electron MicroscopyTopology, Size, Morphology, Crystallography and structure
Transmission Electron MicroscopyTopology, Size, Morphology, Crystallography
Atomic Force MicroscopySize, morphology, surface roughness and texture
Scanning Tunneling MicroscopyTopology, surface modifications, chemical analysis
Dynamic Light ScanningSize distribution
UV spectroscopyTransmission, shape, size, composition and concentration
Fourier Transform Infrared SpectroscopyFunctional group and chemical bonding
X-ray DiffractionStructure type and crystallinity
Differential Scanning CalorimetryPolymorphism and amorphous content
Thermo Gravimetric AnalysisKinetic, chemical and physical properties
X-Ray Photoelectron MicroscopyChemical analysis, uniforming of composition and binding energy

Mechanism of Uptake Cu Nanoparticles by Plants

Mostly, the nanoparticles are supplied to the plants either through foliar route or via root system. Both the routes involve certain binding or carrier proteins, ion transport channels or endocytosis in order to enter the plant cells. The foliar entry involves cuticles, trichomes, stomata, stigma, and hydathodes and once the particles enter, these travel to the entire plant via phloem tissue. 138 The uptake of metallic nanoparticles from the soil matrix is an active transport mechanism that includes transfer of metal ions from the rhizosphere to the central vascular tissue. The uptake of CuO nanoparticles in plants occurs from root hairs via the vascular system to the upper parts of plants. The pathway followed by the particles is either symplastic or apoplastic pathways according to the size, shape and nature of the particle (Fig. 2 ). Although not much research is done in the transport of copper in the cell, there are reports of presence of certain heavy metal transporters within the plants which work along the chelator or sequester transporters. P-type ATPase Cu transporter has been identified in plants in the transport of essential and toxic metals across the cellular membrane. They are subgroups of large P-type ATPase that use ATP to pump a variety of substrates across biological membranes. COPT1 among the copper transporters (COPT) are the important ones that help in copper transport and entry of Cu into cells. 139 , 140 Copper chaperones, another important biological transporter, transport copper in the cytosol to their target sites. CCH, CCS, COX17 are the three different members of copper chaperones identified in the plants. All these metal nanoparticles are regulated at the transcriptional level and by different proteins. 141

Figure 2.

Figure 2.  Probable mechanism of Copper nanoparticles uptake in plants. (A). Upward movement of CuNPs in plants through xylem (B). Uptake of CuNPs via root hairs to the vascular system (C). Two pathways for movement of CuNPs in the plant cells.

Mitogen activated protein kinase (MAPS) was observed to be activated in response to excess of copper. MAPS were found to be involved in signal transduction and phosphorylation events. 142

Applications of Copper Nanoparticles

The use of copper nanoparticles in agriculture is cost effective and their small size facilitates easy absorption by plants. It has proved its antagonism against fungi, insects, pests of crop plants etc. Therefore, it has a potential to be explored as nanoherbicides, nanopesticides, nanofertilizers with several cost benefits. Using copper nanoparticles (CuNPs) alone serves as fungicide, pesticide, micronutrient and a fertiliser thereby solving the extra cost incurred by the separate use of fungicide, pesticide, fertilisers in conventional agriculture. Copper nanoparticles being economical and eco friendly, it is used as an antimicrobial agent in food packaging as well. It forms an impermeable food packaging material protecting from UV radiation increasing their shelf life for a longer time. Copper nanoparticles have also been reported to suppress diseases during stress and drought conditions, thus increasing the drought tolerance and production efficacy. It is also reported to enhance anthocyanin, chlorophyll and carotenoid content 143 responsible to increases seed number, grain yield under stress environment, waste water management and in biomedical applications. The various applications of CuNPs are explained under separate headings as follows:

Agriculture Perspective

Cunps as antimicrobial agents.

According to reports of The Environment Protection Agency (EPA), copper has been approved as an effective antimicrobial agent reducing around 99.9% of the microbial concentration responsible for the deadly diseases. The biosynthesized CuNPs of size 5–45 nm showed an effective antibacterial activity against Enterococcus and Staphylococcus species. 78 These nano copper particles have also reported to show antimicrobial effects against pathogenic microbes such as Vibrio cholerae, Bacillus subtilis, Pseudomonas aeruginosa, Staphylococcus aureus . 83 This antimicrobial activity depends upon several factors such as temperature, pH, aeration and also the microbial concentration. 144 Not only bacteria, but the viruses and yeasts have also been inhibited by CuNPs. 145 Grass (2011) have reported the copper as self sanitising metal thereby its potential could be applied in killing the microorganisms at a high rate 146 Copper nanoparticles release a very high amount of reactive oxygen species (ROS) against E.coli which causes lipid oxidation, DNA degradation and ultimately leading to cell death 147 (Fig. 3 ). The antimicrobial activity of the particles could be easily observed on solid media by visualising colony forming units and optical density in case of liquid media wherein growth inhibition is observed. 148 , 149 The morphological changes such as the change in shape or the cavity formation in cell walls are observed in microbes when treated with CuNPs and this can be observed through scanning electron microscopy (SEM). Moreover, the concentration of CuNPs also plays an important role in growth inhibition or delaying the lag phase of microbes. 150 A study also reported the enhancement of antimicrobial activity of CuNPs by the use of electric power in air filtration, water purification and antibacterial packaging. 151 , 152 In 2012, a study reported that copper nanoparticles prepared from reducing copper chloride and gelatin as a stabiliser have increased antimicrobial activity against E. coli even at a low concentration. 153 There has been significant antimicrobial and antioxidant activity of CuNPs synthesized from thermal decomposition having a free radical activity of around 85% much higher than other metal oxide nanoparticles. 154 Research studies have also shown the use of carbon nanotubes along with CuNPs forming multiwalled carbon nanotubes with CuNPs (MWCNT) wherein the nanotubes increases the surface area of nanoparticles. This composition enhances their antimicrobial activity much more than pure CuNPs and it involves the release of copper ions that enters the microbial cells causing their killing. 155 Among the fungal species, Penicillium chrysogenum is the most affected species by CuNPs with the lowest minimum inhibitory concentration than Alternaria alternata and Fusarium solani . 156 The antifungal activity of CuNPs was also observed against red-root rot disease in tea plants wherein it increased the amounts of organic carbon, total nitrogen, potassium and phosphorus content as well. 157 Similar studies are reported against the fungal species of Colletotrichum treated with different concentrations of Copper and its oxide nanoparticles. 158 Similarly, CuNPs with varying time of exposure and concentration showed antifungal activity against Saprolegnia sp found on white fish ( Rutilus frisii kutum ) eggs. The green synthesized copper nanoparticles have shown a high mycelial inhibition against Fusarium oxysporum with an antifungal activity of 76.29 ± 1.52. 159

Figure 3.

Figure 3.  Probable antimicrobial mechanism of copper nanoparticles.

Copper nanoparticles as pesticides and for insect management

Copper nanoparticles show a positive and profound effect on pest management in different plants. In cotton plants, CuNPs of different concentrations minimised the effect of cotton leaf worm Spodoptera littoralis attacking cotton (Gossypium hirsutum ) plants. 160 These have increased the mortality rate in Tribolium castaneum with increased concentrations of CuNPs. 110 These particles pass through epithelial cells, endothelial cells, dendritic cells and also through blood and lymphatic systems causing oxidative stress. 161 , 162 Similarly, copper nanoparticles inhibited the growth of Skeletonema costatum, an alga at a concentration of more than 0.15 mg l −1 affecting its density and chlorophyll content. 163

Copper nanoparticles as plant nutrient and fertilizer

In the agriculture system, plants require some essential mineral elements in the form of macro and micronutrients for the proper growth of vegetative, reproductive tissues and development. The essential macronutrients include magnesium (Mg), potassium (K), nitrogen (N), calcium (Ca), sulfur (S), and phosphorus (P), that are required at higher concentrations by plants (>0.1% of dry tissue weight). Whereas,essential micronutrients are copper (Cu), nickel (Ni), iron (Fe), molybdenum (Mo), manganese (Mn), boron (B), zinc (Zn), and chlorine (Cl) and require at <0.01% of the dry tissue weight. These macro- and micronutrients are responsible for various functions as structural components in macromolecules. Plants require Cu as a micronutrient, which is evident by the presence of its high concentration in chloroplasts and plays an important role in the synthesis of chlorophyll and other plant pigments and is also responsible for protein and carbohydrate metabolism. 138 Taking into view, CuNPs have been used as nano-biofertilizers in the growth of Cajanus cajan L. (Pigeon pea). The copper nanoparticles of size 20–30 nm showed an increase in plant height, root length, weight and germination of seedlings of pigeon pea. 164 Additionally, slow release of micronutrients in agricultural systems was observed through nano-fertilisers that influence the plant growth and biochemical cycles of the nutrients. Moreover, at different concentrations of CuNPs the enhanced productivity, quality, bioactive compounds, protein content and firmness was observed in tomatoes. 165 , 166 Also CuNPs encapsulated in chitosan hydrogels showed the improved the yield of tomato crop as well as the beneficial compounds of the tomato fruits. 167 Similarly, the effect of CuNPs have also been reported in maize crops under normal and stress conditions, the result showed enhanced growth under normal conditions whereas less curling and wilting of leaves under drought conditions was observed. In addition to this increased pigments, seed number, yield, water retention was reported in maize plants under stress conditions. 168 , 169 Likewise, increased yield in wheat on treatment CuNPs was also reported. 170 Under stress conditions, there are increased levels of Reactive oxygen species (ROS), which causes damage to the protein and nucleic acids of the cells. The CuNPs treated plants have shown reduced levels of ROS due to the increased activity of SOD and APx enzymes in several studies. 65 , 171 The treatment of plants with copper increases vitamin C content which plays an important role in photosynthesis and improves fruit quality. 172 Various reports also highlight the increase in lycopene, flavonoids content, growth, yield, shelf life in several plants. 173

Environmental Perspective

Copper nanoparticles in wastewater management.

CuNPs have been in use for the removal of pollutants from wastewater samples collected from water treatment plants consisting samples and particles mixed. 174 Additionally found effective in removal of pollutants especially phosphorus and sulfur responsible for eutrophication that affect aquatic lives. 175 Also, applied to remove the pollutants from domestic wastewater industries and coal mines. 176 , 177

Biocatalyst and bioremediation

Copper, a low cost metal with least toxicity can be used as a catalyst to degrade the chemical effluents mostly the dyes from the industrial areas. Since dyes are the major pollutants of the water bodies in the industrial areas, their discharge can lead to alterations in aquatic life. Organic dyes such as methyl red, methylene blue, congo red, methyl orange, eosin Y etc are widely used in various textile, leather tanning, paper, cosmetics, pharmaceutical industries (Fig. 4 ). 178 Therefore, bioremediation of such pollutants is important otherwise, these being highly toxic, carcinogenic and non-degradable can cause serious health issues in many people. 159 , 179 CuNPs synthesized from the leaves of Celastrus paniculatus showed degradation of methylene blue dye. 159 Moreover, CuNps have also been reported to show photocatalyst activity against methylene blue. Similar studies by Khan et al. showed the degradation of organic dyes by CuNPs and nano clay supported CuNPs. 180 It was demonstrated the degradation of cationic and anionic dye by CuNPs. 181 Although the degradation efficiency of CuNPs have been higher against congo red, methylene blue under uv radiation. 182 The reducing effect of xanthene dye by CuNPs along with fluorescence quenching is observed by Mandal and De. 183

Figure 4.

Figure 4.  Photocatalysis of Pollutants (Dyes) by CuNPs by release of ROS.

Some Other Applications

Copper nanoparticles in the construction sector.

Steel products are one of the extensively used building materials due to its durability, high strength to weight ratio, fire resistance and can be continuously recycled making it a comparatively better choice than other construction material. 17 However, when used as reinforcement bars for concrete construction the stronger steel types are produced by adding nanoparticles into paints for steel coating These bars are known as micro-composite multi-structural formable (MMFX) steel and are preferred over conventional steel due to their corrosion-resistance and durable properties. 184 Copper nanoparticles enhance the weldability, corrosion resistance, and formability properties in steel. Hegazy et al. studied the influence of colloidal copper nanoparticles as a modifier for steel anti-corrosion paints. 185 Colloidal solution of copper nanoparticles that was prepared by chemical reduction method. The steel anti-corrosion coating shows maximum inhibition when exposed to 0.5%wt copper nanoparticles solution, thus indicating the efficacy of modified coating for protection against corrosion and good carbon steel coverage. Additionally, due to the excellent electrical and thermal conductivities of Cu-based nanoparticles, they were found to be beneficial as fillers in the metal–metal bonding process. 186 The metal metal bonding processes is an important process were solders or fillers have conventionally been used for efficient bonding. The solders are melted at high temperatures and spread between metallic surfaces; thus, bonding the surfaces together. A decrease in temperature solidifies the metallic materials and completes the metal-metal bonding. These Cu-based nanoparticles found to be beneficial as fillers in the metal–metal bonding process.

Copper nanoparticles in the electronic sector

Copper nanowire based functional electrodes are being used in electronics due to their superior electrical conductivity, remarkable mechanical flexibility and wearable properties. These immeasurable potential found its place in the field of electronic devices, including flexible transparent electrodes for optical devices, current collectors for lithium-ion batteries, and stretchable electrodes for wearable devices owing to significantly lower price as an abundance source for large scale production. 187 Most of the electronic devices use the Cu as the wire material to ensure the rapid transmission of signals due to their high electron transfer speed. Kang et al. prepared copper (Cu) nanoclusters that were electrochemically deposited on the film of a Nafion-solubilized multiwall carbon nanotube (CNTs)-modified glassy carbon electrode (CNTs-GCE), and fabricated a Cu-CNTs composite sensor (Cu-CNTs-GCE) to detect glucose with non enzyme. 188 Copper based nanowires film has been also studied as the one of the most promising materials for next-generation current collectors for lithium-ion batteries (LIBs) due to their low cost, excellent conductivity, high flexibility, solution processability, light weight and three dimensional (3D) structure. 189

Toxicity of Copper Nanoparticles

Although CuNPs have applications in different areas, these are associated with some toxicity effects as well (Fig. 5 ). Copper, being a less toxic element, has its severe toxic effects only at high concentrations and varies with different conditions and organisms. The toxicity of Cu-based NPs is influenced by their composition, capping/coating material, size, and interactions with environmental components such as abiotic factors (e.g. pH) and microbial/plant secretions, and naturally occurring organic matter etc Since nonmaterial's are used in agrochemicals and other industrial based products, after application they eventually find their way into different ecosystems thereby emerging as potential pollutants at some point of time. 13 For example, during wastewater treatment or being applied as nano-pesticides or nano-fertilisers, CuNPs if applied at higher doses enter the terrestrial ecosystem as a pollutant that can effect agricultural land, associated microorganisms and terrestrial animals. Similarly, when used as antimicrobial agents, CuNPs have a potential to affect microbial processes such as increasing soil fertility, various biogeochemical cycles influenced by different soil parameters 14 here at higher concentrations of Cu ions they becomes harmful at higher doses and at lower doses, it works as essential micronutrients for the plants. Furthermore, the human impact of CuNPs is less severe and acute toxicity appears only at high concentrations where it leads to the accumulation of Cu causing alteration in structure and physiology of liver leading to Wilson's disease as well as generate increased oxidative stress thus, affecting the whole endocrine system. According to the reports of the WHO, 190 excess Cu in humans causes nausea, vomiting, weakness, anorexia, gastrointestinal damage and kidney necrosis. It results in mitochondrial damage, DNA breaks, and neurological disturbances as well. Overall, Cu accumulation affects humans and plants depending on their recommended doses.

Figure 5.

Figure 5.  Toxicity of copper nanoparticles (CuNPs).

Future Perspective and Challenges

Copper and copper based nanoparticles have a promising role in various applications, owing to their excellent physicochemical properties, high electrical conduction, biocompatibility, surface activity etc. Different process of synthesis has been highlighted in this review and much more emphasis is required for easy and efficient synthesis of CuNPs. Mostly it can be achieved by manipulating the different reaction parameters such as temperature, pressure, time, pH etc that are majorly involved in controlling the shape, size and morphology of the nanoparticles that are of paramount importance in order to design, optimize and develop copper nanoparticles with specific characteristic tailored to develop an product.

CuNPs as agrochemical when applied are either taken up by organisms (internal efficiency) or adsorbed on external structures (external efficiency). The adherence and bioaccumulation may also be changed by physicochemical properties of Cu-based NPs, plant genotypes, and physical/chemical/biological transformation. It is important to understand the uptake and toxicity mechanisms in order to establish guidelines and ensure safe usage of these nanoparticles. Also, many studies highlighted the potential activity of CuNPs against fungi and insect-pests of crop plants, thus can be used to develop as novel formulation for plant protection as in the form of CuNP-based nanopesticides, nanoherbicides, and nanofertilizers, which will be required in lower quantity, thus can minimize the toxicity problem generated due to excessive use of pesticides. Additionally, CuNP-based biosensors can also be explored for the management of pests and in the detection of pathogens responsible for food spoilage. However there is still need to understand the fate, exposure and toxicity of these applied CuNPs. Therefore, large trials in forwarding and developing futuristic investigations based on perceived gaps of knowledge is required to be executed as well as various support from researchers and funding from the government to utilise the benefits of CuNPs in sustainable production in industries is also needed.

Conclusions

This review paper has highlighted recent advances in methods for the preparation of copper nanoparticles and their applications in various areas. Various process such as physical, chemical and biological methods have been discussed indicating that physical and chemical remain expensive methods involving the usage of higher temperatures and toxic by products. However several studies indicated biological methods as safer, economical and eco-friendly in nature. Owing to the various unique properties the CuNPs have find potential applications in various sectors such as in pest management, pollution management, electronic etc. Additionally, copper based nanoparticles have both positive and negative effects on the biotic and abiotic factors of the environment. However, in higher concentrations copper nanoparticles may prove toxic to the environment and other organisms. Conclusively, to ensure that the safety of Cu NPs to environment and organisms, the toxicity of CuO NPs must be reduced to the non‐significant level. To reduce the toxicity factors various investigation on surface modification, incorporating new low toxicity substances, size, dissolution factor, selection of adequate exposure route are to be explored in order to minimise the toxicity of metal oxide NPs. Henceforth, Cu NPs environmental fate must be determined carefully, and criteria for sustainable applications in different fields must be defined.

Acknowledgments

Authors would like to acknowledge the grants from SERB (EEQ/2016/000478) and also to the center faciltiy created by the fund allocated by RUSA, DST-FIST, UGC-SAP grantof School of Biotechnology, University of Jammu.

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Copper and copper nanoparticles applications and their role against infections: a minireview.

research paper on copper nanoparticles

1. Introduction and History of Copper Applications in the Prevention and Treatment of Infections

2. methods for the synthesis of copper nanoparticles, 3. green synthesis of copper nanoparticles, 4. copper ions and nanoparticles, 5. gene expression after nanoparticle interaction, 6. combinations between copper, copper oxide, and other nanoparticles, 7. combination of copper with polymers for antimicrobial effect, 8. copper oxide’s biological effects, 9. mechanisms of antimicrobial activity, 10. conclusions, 11. future directions, author contributions, data availability statement, conflicts of interest.

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Ivanova, I.A.; Daskalova, D.S.; Yordanova, L.P.; Pavlova, E.L. Copper and Copper Nanoparticles Applications and Their Role against Infections: A Minireview. Processes 2024 , 12 , 352. https://doi.org/10.3390/pr12020352

Ivanova IA, Daskalova DS, Yordanova LP, Pavlova EL. Copper and Copper Nanoparticles Applications and Their Role against Infections: A Minireview. Processes . 2024; 12(2):352. https://doi.org/10.3390/pr12020352

Ivanova, Iliana A., Dragomira S. Daskalova, Lilia P. Yordanova, and Elitsa L. Pavlova. 2024. "Copper and Copper Nanoparticles Applications and Their Role against Infections: A Minireview" Processes 12, no. 2: 352. https://doi.org/10.3390/pr12020352

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An Overview of Copper Nanoparticles: Synthesis, Characterisation and Anticancer Activity

Affiliations.

  • 1 Department of Mathematics and Sciences, College of Arts and Applied Sciences, Dhofar University, Salalah 211, Oman.
  • 2 Department of Chemical Engineering, College of Engineering, Dhofar University, Salalah 211, Oman.
  • 3 Department of Biochemistry, Aligarh Muslim University, U.P., India.
  • 4 College of Engineering, Dhofar University, Salalah 211, Oman.
  • 5 Department of Urology, Masonic Cancer Center, University of Minnesota, MN55455,, United States.
  • 6 Department of Chemistry, Khalifa University of Science and Technology, Main Campus, Abu Dhabi, PO Box 127788, United Arab Emirates.
  • 7 School of Mathe- matics and Physics, College of Science, University of Lincoln, Lincoln, LN6 7TS, United Kingdom.
  • 8 Department of Chemistry, Faculty of Sci- ence, King Abdulaziz University, Jeddah 21589, Saudi Arabia.
  • 9 Department of Pharmaceutics and Pharmaceutical Technology, Fac- ulty of Pharmacy, Yarmouk University, Irbid 566, Jordan.
  • 10 School of Pharmacy and Pharmaceutical Science, Ulster University, Coleraine, County Londonderry, BT52 1SA, Northern Ireland, United Kingdom.
  • PMID: 34348615
  • DOI: 10.2174/1381612827666210804100303

In this review, we summarised the different methods for copper nanoparticle synthesis, including green methods. We highlighted that the synthesis of the copper nanoparticles from green sources is preferable as they serve as stable and reducing entities. Furthermore, we critically reviewed the effectiveness of copper- based nanoparticles in oncogenic treatments emphasizing breast, lung, colorectal, and skin cancers. Finally, we have summarised the recent progress made in copper-based nanoparticles and their applications to amplify and rectify present cancer treatment options. The synthesis, characterization, stabilization, and functionalization techniques of various copper-based nanoparticles have also been highlighted in each section. In conclusion, the review provides the outlook of copper nanoparticles in cancer diagnostics and therapeutics.

Keywords: Cancer; cancer treatment; copper nanoparticles; diagnostics; nanomaterials.; nanomedicine; therapeutics.

Copyright© Bentham Science Publishers; For any queries, please email at [email protected].

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Structural and optical properties of copper oxide nanoparticles: A study of variation in structure and antibiotic activity

  • Published: 19 April 2021
  • Volume 36 , pages 1496–1509, ( 2021 )

Cite this article

research paper on copper nanoparticles

  • Ankush Chauhan 1 ,
  • Ritesh Verma 1 ,
  • Khalid Mujasam Batoo   ORCID: orcid.org/0000-0001-8264-8203 2 ,
  • Swati Kumari 3 ,
  • Rahul Kalia 1 ,
  • Rajesh Kumar 1 , 4 ,
  • Muhammad Hadi 5 ,
  • Emad H. Raslan 5 &
  • Ahamad Imran 3  

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In this paper, we study the synthesis dependence of structural, optical and antimicrobial properties for copper oxide nanoparticles on, synthesized using microwave irradiation CuO(M), co-precipitation CuO(P) and hydrothermal CuO(H) protocols. Structural and morphological properties were studied using XRD, SEM, TEM and SAED techniques. XPS studies confirmed the presence of copper ions in Cu 2+ oxidation state, and Raman spectroscopy confirmed the presence of nanostructured phase in all the samples. The synthesized CuO(M), CuO(P) and CuO(H) nanoparticles were investigated for antimicrobial activity against different pathogenic bacteria including methicillin-resistant Staphylococcus aureus . The result showed that maximum inhibition zone was detected in CuO(M) nanoparticles against Gram-negative bacteria i.e. Klebsiella pneumoniae (20 mm). CuO(H) and CuO(P) nanoparticles have antibacterial inhibition zone of 17 mm and 13 mm against K. pneumoniae and S. aureus , respectively. The CuO(P) and CuO(H) nanoparticles displayed mild antimicrobial activity as compared to the CuO(M) nanoparticles.

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Precursor-dependent structural properties and antibacterial activity of copper oxide

Chemical synthesis, characterization and evaluation of antimicrobial properties of cu and its oxide nanoparticles, synthesis, characterization, and antibacterial activity of copper(ii) oxide nanoparticles prepared by thermal decomposition, data availability.

All data generated or analysed during this study are included in this published article and in supplementary file.

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Author K M Batoo is thankful to the Deanship of Scientific Research at King Saud University for financial support through the project Code (RG-1437-030).

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School of Applied Science and Biotechnology, Shoolini University of Biotechnology & Management Sciences, Bajhol-Solan, HP, 173212, India

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Chauhan, A., Verma, R., Batoo, K.M. et al. Structural and optical properties of copper oxide nanoparticles: A study of variation in structure and antibiotic activity. Journal of Materials Research 36 , 1496–1509 (2021). https://doi.org/10.1557/s43578-021-00193-7

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  • Published: 15 June 2021

Green copper oxide nanoparticles for lead, nickel, and cadmium removal from contaminated water

  • Alaa El Din Mahmoud 1 , 2 ,
  • Khairia M. Al-Qahtani 3 ,
  • Sahab O. Alflaij 3 ,
  • Salma F. Al-Qahtani 4 &
  • Faten A. Alsamhan 3  

Scientific Reports volume  11 , Article number:  12547 ( 2021 ) Cite this article

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  • Nanoscience and technology

Environmentally friendly copper oxide nanoparticles (CuO NPs) were prepared with a green synthesis route without using hazardous chemicals. Hence, the extracts of mint leaves and orange peels were utilized as reducing agents to synthesize CuO NPs-1 and CuO NPs-2, respectively. The synthesized CuO NPs nanoparticles were characterized using scanning electron microscopy (SEM), Energy Dispersive X-ray Analysis (EDX), BET surface area, Ultraviolet–Visible spectroscopy (UV–Vis), and Fourier Transform Infrared Spectroscopy (FT-IR). Various parameters of batch experiments were considered for the removal of Pb(II), Ni(II), and Cd(II) using the CuO NPs such as nanosorbent dose, contact time, pH, and initial metal concentration. The maximum uptake capacity (q m ) of both CuO NPs-1 and CuO NPs-2 followed the order of Pb(II) > Ni(II) > Cd(II). The optimum q m of CuO NPs were 88.80, 54.90, and 15.60 mg g −1 for Pb(II), Ni(II), and Cd(II), respectively and occurred at sorbent dose of 0.33 g L −1 and pH of 6. Furthermore, isotherm and kinetic models were applied to fit the experimental data. Freundlich models (R 2  > 0.97) and pseudo-second-order model (R 2  > 0.96) were fitted well to the experimental data and the equilibrium of metal adsorption occurred within 60 min.

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Introduction.

Nanotechnology has gained more attention since the synthesized materials are on the nanoscale that differ in chemical and physical properties from those of bulk materials. This allows the integration of nanomaterials in environmental 1 , 2 , medicinal 3 , and agricultural 4 applications.

Several synthesis approaches have been used to produce metallic oxide nanoparticles, including physical and chemical routes. In literature, there are many reported techniques for the synthesis of Copper oxide nanoparticles (CuO NPs) via thermal reduction and microwave irradiation 5 , chemical vapor deposition 6 , polyol 7 , photochemical 8 , 9 , and electrochemical methods 10 . Most of these mentioned techniques have potential environmental impacts because they involve the use of  harsh, dangerous, and toxic chemicals in addition to being very expensive with costly reaction conditions. Akintelu et al. 11 recommended that more research work should be conducted to minimize the toxicity of CuO NPs synthesis route while maintaining and/or improving their performance in environmental or medical applications. Therefore, green chemistry routes have attracted researchers’ interest for producing environmentally friendly metal nanoparticles that are free from the use of expensive, harsh, and toxic chemicals.

As there is a fast progress in the field of nanotechnology, the green synthesis of metallic oxide nanoparticles using plant extract has presented as an eco-friendly science by which there exists an ability to control the size, shape, and material quality 12 , 13 . The green synthesis technique is dependent on eco-friendly reducing and capping agents so it eliminates the generation of toxic intermediate during chemical reactions 14 . This would prompt researchers to develop non-toxic green synthesis methods for producing CuO NPs.

Water pollution is a global problem with the increasing usage of chemical compounds 15 . This can be due to the progress in industrialization and technological development, and the runoff of household wastes 16 , 17 . It is believed that heavy metal pollution is one of the serious factors affecting water bodies because of their toxic, non-biodegradable, and persistent nature when released into the environment through natural sources (weathering, erosion) and anthropogenic sources (car exhausts, industrial discharges, and mining) 18 .

The burgeoning demand for obtaining high-quality water has become a reason for researchers to develop advanced technology to deliver clean water. There are many conventional wastewater treatment techniques including precipitation, flocculation, electrocoagulation, ion exchange, etc. Ion exchangers are classified into organic and inorganic. However, composite ion exchangers are preferable to be applied in the removal of heavy metals because of their mechanical stability and enhanced ion exchange capacity which are lacked in organic or inorganic resins. For instance, Mohammad et al. 19 found that the poly (3,4-ethylenedioxythiophene): polystyrene sulfonate-Zr(IV) phosphate enhanced the ion exchange capacity of Cd(II) to be 2.34 meq g −1 . Whereas the composite of carbon nanotubes with cerium(IV) phosphate possesses Cd(II) exchange capacity of 1.64 meq g −1 20 . Polyvinyl alcohol Ce(IV) phosphate composite proved its efficiency as ion exchange for the mixture of Cu(II)–Zn(II), Cu(II)–Cd(II), and Cu(II)–Ni(II) 21 . However, the synthesis routes require many chemical reagents which harm the environment and most of the above-mentioned techniques cannot remove heavy metals from wastewater completely.

The most common adsorbents used in removal of a wide range of heavy metals are activated carbon and zeolite, but their costs are still high at large scale applications 22 , 23 . Accordingly, agricultural or plant byproducts can be an alternative for the preparation of adsorbents or nanosorbents. This has led to the integration of various nanomaterials in the adsorption process for the removal of heavy metals from water and/or wastewater.

Nanomaterials possess the potential of heavy metal removal from water over conventional techniques because of their high surface area (surface/volume ratio) 24 . As an example, metallic oxide nanoparticles can be used to provide a long-term solution to/for water quality and make possible water reuse 25 .

Plant extracts assisted CuO NPs have attracted much attentions because green synthesis techniques hold several advantages over chemical ones, which are using non-toxic solvents such as biological extracts in addition to their simplicity. For instance, aqueous black bean extract 26 , fruit extract of Duranta erecta 27 , Eclipta prostrata leaves extract 28 , clove extract 29 , Solanum lycopersicum leaf extract 30 , and Hawthorn berries extract 31 .

Herein, we focus on green preparation of CuO NPs due to the abundance of copper, its cost effective preparation, and its excellent optical, mechanical, thermal, electrical and catalytic properties 11 , 12 . Recently, CuO NPs have been made available for various applications. This led the researchers to apply alternative sustainable synthesis techniques. Singh et al. 32 synthesized CuO NPs synthesized using Psidium guajava leaf extract as reducing agent as well as capping agent. They confirmed its potential for photocatalytic degradation of Nile blue (93%) and reactive yellow 160 (81%) dyes in 120 min. Khani et al. 33 used the fruit extracts of Ziziphus spina-christi (L.) as reducing agents to prepare CuNPs and tested in crystal violet (CV) adsorption. CV removal reached 95% with a high adsorption capacity (37.5 mg g −1 ) in 7.5 min. Currently, CuO NPs were successfully synthesized using the seed extract of Caesalpinia bonducella but evaluated for electrochemical detection of riboflavin 34 .

Most literature are focused on the application of chemically synthesized CuO NPs in heavy metals removal from contaminated water. Fakhri 35 prepared CuO NPs by sol–gel method and its uptake capacity for Hg(II) reached 46.10 mg g −1 at pH of 9 and nanosorbent dose of 0.05 g. Another CuO NPs were prepared by chemical precipitation technique and applied for Ni(II) removal from water 36 . Its adsorption capacity was 15.4 mg g −1 with nanosorbent dos of 0.2 g L −1 , pH of 7.0, and contact time of 90 min.

Consequently, the objective of our work is to synthesize nontoxic CuO NPs by using the extracts of mint leaves and orange peels as green reducing agents. The obtained CuO NPs are tested as an adsorptive nanomaterial to purify polluted water from heavy metals such as Pb(II), Ni(II), and Cd(II) as well as modelling the experimental results with isotherm and kinetic models.

Results and discussions

Characterization of nanoparticles.

The SEM micrographs of the CuO NPs-1 (synthesized using the extract of mint leaves) and CuO NPs-2 (synthesized using the extract of orange peels) are illustrated in Fig.  1 . Figure  1 a,b shows that the prepared CuO NPs-1 were mostly spherical in shape, while CuO NPs-2 appear with more aggregates (Fig.  1 c,d). This can be due to the coating of different surface functional groups from the prepared extracts (see Fig.  3 b). The same issue was observed with Khani et al. 33 . The SEM micrographs revealed that the synthesized CuO NPs were in the nanometer range of ~ 150 nm. Sankar et al. 37 found that the size of CuO NP was 140 nm when it is synthesized with the extract of Carica papaya leaves. On the other hand, Prasad et al. 38 obtained spherical CuO NPs with sizes of 40–70 nm when the leaves extract of Saraca indica was utilized.

figure 1

SEM micrographs of ( a,b ) CuO NPS-1 and ( b,c ) CuO NPs-2 at different magnifications.

The BET surface area of the synthesized CuO NPs were found ~20 m 2  g −1 . In literature, the prepared CuO NPs with a precipitation technique has surface area of 34 m 2  g −1 with a size of 196 nm 39 . Another study found that the BET surface area of the prepared CuO NPs with the same technique was 1.7 m 2  g −1 with a size of 140 and 180 nm 40 . On the other hand, Dörner et al. 41 found the BET of sol–gel synthesized CuO NPs was 16 m 2  g −1 with a size of 100–140 nm.

The elemental compositions of the prepared CuO NPs were confirmed using Energy-dispersive X-ray (EDX) and the peaks obtained are illustrated in Fig.  2 a,b. It is observed that the prepared CuO NPs are mainly composed of Cu, O and C without any trace of other materials. In both samples, EDX patterns show a strong signal peak at 1.0 keV representing Cu atoms. The detected carbon and high oxide peaks must be due to the phytochemicals already present in both plant extracts which are added in large volume. There are no other elements were detected even from the extract. The same findings were found with using the leaf extract of Psidium guajava as a reducing agent for the synthesis of CuO NPs 32 .

figure 2

EDX spectra of ( a ) CuO NPs-1 and ( b ) CuO NPs-2.

The phytochemicals in the extracts are responsible for the formation of complexes with the copper salt that is reduced the ions to form nanoparticles. Hence, we observed the color transformation in the prepared Solutions and UV–Vis spectroscopy is used in the range of 200‒600 nm. Figure  3 a indicates a noticeable peak at 325 nm due to the inter band transition of the core electrons of the CuO NPs. Aziz et al. 42 used also mint leaf extract for the synthesis of CuO NPs and detected its absorption peak at 346 nm. Sankar et al. 37 detected a strong absorbance peak between 250 and 300 nm suggesting the formation of CuO NPs.

figure 3

( a ) UV–Vis spectra and ( b ) FT-IR Spectra of CuO NPs using mint extract (CuO NPs-1) and orange peel extract (CuO NPs-2).

The result of FT- IR spectrum of synthesized CuO NPs using the extract of mint and orange leaves were shown in Fig.  3 b. The broad peaks at 3290 cm −1 correspond to the O–H stretching of the Phenols and alcohols. The most intense bands between 1603 and 1627 cm −1 represent C=O stretching band. The peak value at 1273 cm −1 shows the presence of C–O stretching of alcohols. The peak at 1100 cm −1 stands for C–N stretching aliphatic amines, or 1150–1085 cm −1 for strong C–O stretching aliphatic ether. The absorption at 1743 cm −1 was caused by C=O stretching esters, saturated aliphatic, aldehydes. The peaks at ~ 590 cm −1 and ~ 610 cm −1 exhibit the CuO phase. Similar characteristic peaks were observed by Priya et al. 43 with Aerva lanata -mediated CuO NPs at 580 cm −1 and 525 cm −1 . This indicated that the synthetic method conditions reflect the CuO phase.

Metal ions treatment experiments

Effect of nanosorbents dose.

The dose of nanosorbents has a great effect on the adsorption performance. Various dose concentrations (0.17, 0.33, 0.67, 1.00, 1.33, 1.67, and 2.00 g L −1 ) of CuO NP-1 and CuO NP-2 were used to evaluate the efficiency of removing the studied metal ions. Figure  4 Shows an increase in the removal efficiency of Pb(II), Ni(II), and Cd(II) with increasing in the dose of nanosorbents. The reason is due to the availability of more binding sites on the surface of the nanosorbents to the complexity of the metal ions. The selectivity sequence of CuO NPs for the adsorption process was Pb(II) > Ni(II) > Cd(II). Thus, the adsorption of Cd(II) is the least due to its lower electronegativity (1.69) and its bigger radius hydrated radius (0.404 nm) than Ni(II) (1.91 nm) and Pb(II) (0.401 nm).

figure 4

Effect of nanosorbent doses on the removal of the studied metal ions using ( a ) CuO NPs-1 and ( b ) CuO NPs-2 at initial concentration: 20 mg L −1 , pH: 6, and contact time: 60 min.

Our results indicated that 0.33 g L −1 of CuO NPs can be used for further experiments because the nanosorbent dose is a key parameter in the cost analysis of the adsorption process. Therefore, it is recommended to use the lower nanosorbent dose but if have high adsorption performance. This nanosorbent dose is much less than one stated in literature. Sreekala et al. 44 observed that the optimum dose of CuO NPs (synthesized with Simarouba glauca leaf extract) for 10 mg L −1 Pb(II) was 1.00 g L −1 .

Effect of contact time

Figure  5 shows that the removal efficiency of the selected metal ions on CuO NPs required 60 min contact time to reach equilibrium. It is observed that the adsorption rate became almost fixed after 60 min and had a little effect on its rate. This can be attributed to the saturated capacity of the studied nanosorbents.

figure 5

Effect of contact time on the removal of the studied metal ions using ( a ) CuO NPs-1 and ( b ) CuO NPs-2 at initial concentration: 20 mg L −1 , pH: 6, and dose: 0.33 g L −1 .

The removal efficiency of CuO NPs-1 was compared to CuO NPs-2 with the studied metal ions. The removal % of Cd (II), Ni(II) and Pb (II) were 18%, 52.5%, 84% and 11%, 48%, 80.5% when using CuO NPs-1 and CuO NPs-2, respectively. The variation in the removal % of heavy metals is due to the types of the used extracts and their volumes. They can influence the application of CuO NPs in the heavy metals removal. Due to the high intensity of the surface functional groups of CuO NPs-1 as detected in FT-IR (Fig.  3 b), the highest percentage removal of the studied metal ions was obtained using CuO NPs-1. The reason for that can be the richness of mint leaves extract with various phytochemical constituents as reported in Alexa et al. 45 and Thawkar 46 compared to the orange peels extract 47 . Hence, we can conclude that CuO NPs-1 are effective in removing heavy metals.

Effect of pH

Removal of heavy metals from contaminated water depends largely on the pH of the solution. Consequently, the effect of pH on the adsorption of Pb(II), Ni(II),and Cd(II) on CuO NPs was evaluated with pH values, ranging from 3 to 9 at the equilibrium time. The results are shown in Fig.  6 . When pH is increased from 3 to 6, the removal efficiency of Cd(II), Ni(II) and Pb(II) increased from 6.5, 11.5 and 24% to 18, 52.5 and 84%, respectively in the case of CuO NPs-1 which were higher than  those values of CuO NPs-2. Subsequent to these values,the adsorption rate decreased.

figure 6

Effect of pH on the removal of the studied metal ions using ( a ) CuO NPs-1 and ( b ) CuO NPs-2 at initial concentration: 20 mg L −1 , contact time: 60 min, pH: 6, and dose: 0.33 g L −1 .

With increasing the pH values till 6, the removal % of the studied metal ions increased because of the decrement of the positive charge of the nanosorbent resulted in a lower electrostatic repulsion between the nanosorbents surface and metal cations as well as the competition decrement between the metal cations and protons of hydrogen ions for the functional groups of the nanosorbents 48 . In addition, pH values beyond 6 resulted in the precipitation of metal ions.

Effect of initial concentration of the selected metal ions

As shown in Figure  7 , the adsorption of the metal ions at different concentrations indicates the removal % decreases with increasing the concentration of the metal ions. Utilizing CuO NP-1 nanosorbent in the removal of Pb(II), Ni(II), and Cd(II) that are ranging from 5 to 40 mg L −1 cause the removal % of Pb(II), Ni(II), and Cd(II) decreased from 92.0, 58.0, and 28.0% to 74.0, 45.7, and 13.0%, respectively. While the nanosorbent of CuO NP-2 led to the decrement of Pb(II), Ni(II), and Cd(II) removal from 89.0, 54.0, and 20.0% to 71.0, 40.0, and 7.0%, respectively. Similar findings were reported with CuO NPs in Jain et al. 36 and Singh et al. 32 . This phenomenon illustrates a significant relationship between the adsorption efficiency and the metal concentration. At low metal concentrations, more absorbable vacant sites are available which lead to an increase in the prevalence of metal ions on the nanosorbent. At a higher concentration of metal ions, the available adsorbed sites become less and thus the removal rate of these ions decreases 23 .

figure 7

Effect of initial metal concentration on the removal of the studied metal ions using ( a ) CuO NPs-1 and ( b ) CuO NPs-2 at contact time: 60 min, and dose: 0.33 g L −1 .

In this work, the understanding mechanism of the studied metal ions removal could be predicted using FT-IR for the spent CuO NPs. After the metal ions adsorption, the O–H stretching bands get weaker and we observed new peaks as well as shifts in the intensities and positions of FT-IR bands as shown in Fig.  8 . The band of CH 2 and CH 3 groups appeared which might be induced by C–H stretching vibration of CH 2 and CH 3 groups 49 . It became more intense and shifted with each metal ions removal. This band of CuO NPs is shifted to 2960, 2928, and 2956 cm −1 after removal of Pb(II), Ni(II), and Cd(II), respectively. Other shifts were observed in the bands of C–O stretching aliphatic ether to be 1063, 1068, 1070 cm −1 after removal of Pb(II), Ni(II), and Cd(II), respectively. The intense peaks appeared in the range of 1424–1416 cm −1 are attributed to –C–OH deformation. This indicates that the functional groups present on the synthesized CuO NPs were involved in the adsorption process of the studied metal ions.

figure 8

FT-IR Spectra of CuO NPs after adsorption of ( a ) Pb(II), ( b ) Ni(II), and ( c ) Cd(II).

Adsorption models

Adsorption isotherms.

Two isotherm models (Langmuir and Freundlich) were applied to describe the adsorption process. Their linear equations are expressed in Eqs. ( 3 ) and ( 4 ), respectively. The differentiation between the two models is that the Langmuir model suggests homogeneity of the surface of the nanosorbent and no further adsorption occurs once the available adsorption sites are filled, while the Freundlich model proposes heterogeneous of the surface of the nanosorbent.

As shown in Figure  9 , R 2 values of the Freundlich models are higher than the Langmuir models. This indicates that the adsorption of metal ions to the surface of the CuO NPs is carried out by multiple, heterogeneous layers of the nanosorbent surface. Therefore, the adsorption of metal ions using CuO NPs can be described by the Freundlich model. On the other hand, the chemically synthesized CuO NPs (precipitation method) showed monolayer adsorption with Ni(II) 36 .

figure 9

( a,b ) Langmuir plots, ( c,d ) Freundlich plots, and ( e,f ) separation factor for the adsorption of metal ions; Pb(II), Ni(II), and Cd(II) using ( a,c,e ) CuO NPs-1 and ( b,d,f ) CuO NPs-2 at contact time: 60 min, dose: 0.33 g L −1 , and pH: 6.

Table 1 illustrates the isotherm parameters for the adsorption of Pb(II), Ni(II), and Cd(II). The adsorption intensity (n) indicates the sorption driving force’s magnitude. n values are usually in the range of 0–1. The calculations of n values indicated that the adsorption isotherm is favorable because their values are < 1. The adsorption intensity can be also checked using separation factor (SF; Eq. ( 5 )). Their values confirmed the findings of n values as illustrated in Fig.  9 e,f. Furthermore, the SF values of CuO NP-1 were less than CuO NP-2 so the CuO NP-1 adsorption of the studied metal ions is expected to be more as confirmed from the experimental work. Desta 50 found the adsorption of Cr(VI), Cd(II), Pb(II), Ni(II), and Cu(II) is favorable using teff straw waste due to the SF values were in the range of 0.298 to 0.986.

The maximum uptake capacity, q m of Pb(II) was 88.80 and 82.80 mg g −1 using CuO NP-1 and CuO NP-2, respectively. Faisal et al. 22 estimated the q m of Pb(II) using sludge to be 20.41 mg g −1 under similar our experimental conditions except for the dose of 6 g L −1 . The Langmuir affinity constant (K L ) of CuO NPs-1 and CuO NPs-2 for Pb(II) adsorption was higher than K L of Ni(II) and Cd(II). The high K L value estimates the studied metal ions affinity to the available adsorption sites of CuO NPs. Such findings are attributed to the behavior of Pb(II) in the aqueous solutions. For instance, the high electronegativity of Pb(II) which is 2.10 and its small radius hydrated radius 0.401 nm 51 .

Adsorption kinetics

Figure  10 a,b provides a straight line with slope (K 1 ; min −1 ) and intercept equal to log q e . It is worth noting that the values of q e exp are different from the calculated ones obtained from the pseudo-first order which indicates that this model is not valid to represent the adsorption process. On the other hand, Figure  10 c,d represents linear plots of (t/q t ) versus time . Its linear fit gives a straight line with slope of the rate constant (1/q e ) and intercept 1/k 2 q e 2 .

figure 10

( a,b ) Pseudo-first order and ( c,d ) Pseudo-second order for the adsorption metal ions using ( a,c ) CuO NPs-1 and ( b,d ) CuO NPs-2 at initial concentration: 20 mg L −1 , dose: 0.01 g, and pH 6.

The highest correlation coefficients (R 2 ) were obtained for pseudo-second order kinetic models (Table 2 ). The validation of pseudo-second order indicates that the adsorption capacity is related to the available active sites on nanosorbents 23 . Farghali et al. 52 found the same behavior for Pb(II) kinetics removal by CuO NPs which assume the adsorption process is rate limiting process. However, they estimated the optimum contact time is 240 min for using CuO NPs synthesized from microwave radiation which is more than our reported optimum contact time (60 min). Both models’ parameters are summarized in Table 2 . In addition, the values of initial adsorption rate (h; Eq. ( 8 )) indicated that Pb(II) possesses the high rate compared to Ni(II) and Cd(II).

Conclusions

The preparation of green CuO NPs was successful with the mint leaves and orange peels extracts as reducing agents. This proposed method holds several merits such as easy preparation, cost-effective, and safe compared to the chemical methods as well as the green synthesis method could be applicable for preparing other metal oxide nanoparticles. The EDX and UV–Vis spectroscopy confirmed the preparation of CuO NPs using both extracts. The adsorption application of CuO NPs on the removal of Pb(II), Ni(II), and Cd(II) is found to be dependent on the nanosorbent dose, the metal ions concentration, pH and the contact time. The optimum equilibrium contact time (60 min) and nanosorbent dose (0.33 g L −1 ) are less than those stated in literature for the adsorption of the studied metal ions. The affinity of these metal ions to CuO NPs followed the sequence Pb 2+  > Ni 2+  > Cd 2+ .

The optimum removal efficiency of Pb(II), Ni(II), and Cd(II) were found 84.00, 52.50%, and 18.00%, respectively and obtained at pH 6 for simulating wastewater under normal environmental conditions. The experimental data indicated that the Freundlich isotherm model fitted to the adsorption process as well as pseudo-second order. The maximum adsorption uptakes were 88.80, 54.90, and 15.60 mg g −1 for Pb(II), Ni(II), and Cd(II) with CuO NPs-1. These findings revealed that CuO NPs can be a good nanosorbent to purify water contaminated with heavy metals and its regeneration and reusing should be studied in the future. Furthermore, the environmental application performance of metallic oxide nanoparticles relies on the type of the used extract and its volume for the green synthesis method that influence the morphological properties of the produced nanoparticles and reflect its application performance.

Materials and methods

Preparation of plant extracts.

Orange peels and mint leaves were collected from a local vegetable market. Then, we prepared the orange peel extract and mint leaves extract by washing them with double distilled water and drying at room temperature for 48 h. Each one was grinded, and we added 25 g in a standard beaker filled with 500 mL of double distilled water, the solution is boiled for 5 min (Fig.  10 ). Subsequent to boiling and leaving to the solution to cool down, we filtered and stored each extract at 4 °C and used it within a week as a reducing agent for preparing CuO NPs.

Preparation of CuO NPs

In the green synthesis technique, 20 mL of either orange peel extract or mint leaves extract were added to 80 mL of copper sulfate (CuSO 4 ) at a concentration of 0.01 M in a 250 mL Erlenmeyer flask and placed on a magnetic stirrer and heated to 50 °C, then the extract is slowly added to the solution for 20 min and then left stirred for 2 h where the solution changes when adding the mint leaves extract to the brown color,  the obtained nanoparticles denoted as CuO NPs-1, and when adding the orange peel extract, the color changed to the light green color, and the obtained nanoparticles denoted as CuO NPs-2. The two mixtures were left for 24 h at room temperature then separated using a centrifuge (12,000×g cycles) for 15 min and the nanoparticles were obtained after drying in an oven at 45 °C for 24 h. The schematic diagram for both nanoparticles synthesis is shown in Fig.  11 .

figure 11

Schematic diagram for the green synthesis of CuO NPs.

Detection and characterization of CuO NPs

The primary detections of CuO NPs were carried out by visual observation of the change in the color of the precursor. The synthesized nanostructures have been characterized by UV–Vis spectroscopy using Shimadzu UV-1700, Japan. The BET surface area of CuO NPs were measured with a Belsorp-miniX (Germany). Prior to this measurement, the samples were degassed at 140 °C. Scanning Electron Microscopy (SEM) coupled with Energy dispersive X-ray (EDX) was used to examine the surface morphology and size of the synthesized CuO NPs as well as its elemental composition. Fourier transform infrared spectroscopy (FT-IR) spectroscopy is used to identify the stretching and bending frequencies of molecular functional groups attached to CuO NPs surface 49 . Its spectra record was conducted in the range of 500–4000 cm −1 .

We have prepared artificial wastewater containing lead, nickel, and cadmium. Several factors were studied. For instance, the doses of CuO NPs-1 and CuO NPs-2 were 0.17, 0.33, 0.67, 1.00, 1.33, 1.67, and 2.00 g L −1 . The optimum dose was fixed at 0.33 g L −1 when studying the other factors. The second factor was contact time at different times (5–90 min) and the time was fixed at 60 min when studying other factors. The third factor was studying the effect of the different metal concentrations (5–40 mg L −1 ) and the concentration was fixed at 20 mg L −1 . The fourth factor was the pH of the solutions. It was adjusted in the range of 3–9 by 0.1 M NaOH or 0.1 M HCl and the pH was fixed at 6.00 when studying the other factors.

The experimental experiments were carried out by shaking 0.33 g L −1 of either CuO NPs-1 or CuO NPs-2 in 30 mL solution of each metal ions, with concentration range from 5 to 40 mg L −1 , onto a bath shaker at 120 rpm. The adsorption capacity and removal percentage of the nanosorbents can be estimated with the following equations  53 , 54 , 55 .

where q e is the equilibrium adsorption capacity (mg g −1 ), C o is the metal ion initial concentration (mg L −1 ), C e is the metal ion concentration (mg L −1 ) at equilibrium, V is the volume of solution (mL) and W is the weight (g) of nanosorbent, R is the removal percentage of the studied metal ions.

Isotherm and kinetics models are investigated to get the optimum conditions of the batch adsorption process. Langmuir and Freundlich models were used as they are most used isotherm models and can be compared to literature based on Eqs. ( 3 ) and ( 4 ). In addition, separation factor (SF; Eq. ( 5 )) is calculated at different initial metal ion concentrations to express the adsorption process feasibility 23 , 56 .

where K L is the Langmuir adsorption equilibrium constant related to the affinity between the metal ions and nanosorbents (L mg −1 ), n is the measure of adsorption intensity and it indicates the relative distribution of energy sites. K f (mg g −1 ) (L mg −1 ) n constant is concerned with the ability of nanosorbent to adsorb. SF is the separation factor (dimensionless).

The kinetics removal of the studied metal ions can be explained using pseudo-first order (Eq. ( 6 )) and pseudo-second order (Eq. ( 7 )). Initial adsorption rate (h) is calculated using Eq. ( 8 ).

where q t is adsorption capacity at contact time (t), K 1 is the pseudo first order rate constant (min −1 ), K 2 the pseudo second order rate constant (g mg −1  min −1 ).

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Acknowledgements

This research was supported by the Chair of Environmental Pollution Research at Princess Nourah bint Abdulrahman University (Grant No. EPR-013).

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Khairia M. Al-Qahtani, Sahab O. Alflaij & Faten A. Alsamhan

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Conceptualization, A.E.D.M. and K.M.A.-Q.; visualization, A.E.D.M.; project administration, K.M.A.-Q.; writing—original draft preparation, A.E.D.M., S.O.A. and S.F.A.-Q.; writing—review and editing, A.E.D.M., methodology, A.E.D.M. and F.A.A.; Formal analysis, A.E.D.M. All authors have read and agreed to the published version of the manuscript.

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Mahmoud, A.E.D., Al-Qahtani, K.M., Alflaij, S.O. et al. Green copper oxide nanoparticles for lead, nickel, and cadmium removal from contaminated water. Sci Rep 11 , 12547 (2021). https://doi.org/10.1038/s41598-021-91093-7

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DOI : https://doi.org/10.1038/s41598-021-91093-7

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Copper-containing nanoparticles: Mechanism of antimicrobial effect and application in dentistry-a narrative review

1 Department of Stomatology, Sichuan Provincial People’s Hospital, University of Electronic Science and Technology of China, Chengdu, China

2 Department of Stomatology, Hospital of Chengdu Office of People's Government of Tibetan Autonomous Region (West China Hospital Sichuan University Tibet Chengdu Branch Hospital), Chengdu, China

Xiaoling Xu

3 School of Materials Science and Engineering, Southwest Jiaotong University, Chengdu, China

Copper has been used as an antimicrobial agent long time ago. Nowadays, copper-containing nanoparticles (NPs) with antimicrobial properties have been widely used in all aspects of our daily life. Copper-containing NPs may also be incorporated or coated on the surface of dental materials to inhibit oral pathogenic microorganisms. This review aims to detail copper-containing NPs’ antimicrobial mechanism, cytotoxic effect and their application in dentistry.

Introduction

Copper is a common metal with unique physical and chemical properties. Copper is the 26th most abundant element in the Earth's crust ( 1 ). Copper has been used in coins, jewelry, and utensils since ancient times, and the potential of copper to promote health effects was recognized as early as 3,000 BC ( 2 , 3 ). A large variety of dental restorative materials contain copper, such as dental amalgam, porcelain-fused-to-metal crowns, implants, and partial denture attachments and frameworks ( 4 – 7 ). Copper is an essential trace element for humans and can promote angiogenesis, bone formation, wound healing, and the activities of various enzymes ( 8 – 10 ). Additionally, it also catalyzes the formation of crosslinks in collagen and elastin precursors ( 11 – 13 ). Moreover, copper is essential for maintaining the normal physiological functions of microorganisms. But high concentrations of copper can be used as microbicides ( 14 – 16 ). Prior to the development of antibiotics, inorganic antibacterial agents, such as silver and copper, were used to treat microbial infections ( 17 ). The paper reported copper as an antimicrobial coating as early as 1962 ( 18 ). Also, current research has shown that copper has a much less toxic effect on mammalian cells than silver ( 19 ).

With the progress of nanotechnology, copper has been increasingly used in the medical field, such as the latest copper-containing Nanoparticles (NPs), which have been proven to inhibit a variety of oral microorganisms, such as Streptococcus mutans ( S. mutans ) ( 20 – 22 ), Porphyromonas gingivalis ( P. gingivalis ) ( 23 ), and Candida albicans ( C. albicans ) ( 20 , 24 – 26 ). In 2008, the International Organization for Standardization (ISO) defined NPs as discrete nano-objects with all three external dimensions less than 100 nm. In 2011, the European Commission set a more technical but wider ranging definition: a natural, incidental, or manufactured material containing particles in an unbound state, as an aggregate, or as an agglomerate and where, for 50% or more of the particles in the number size distribution, one or more external dimensions is within the size range 1–100 nm. Under this definition, nanomaterials can be classified as NPs only if one of their characteristic dimensions is within the range of 1–100 nm. NPs have many unique physical and chemical properties, such as tunable size, biocompatibility, and singlet oxygen generation, which allows them to be widely used ( 27 , 28 ).

In recent years, the application of nanomaterials in dentistry has gradually increased, and copper NPs can be used as a new type of antimicrobial material ( 28 ). This paper reviews the antimicrobial mechanisms of copper-containing NPs and their application in dentistry.

Different types of copper-containing NPs

Various types of copper-containing NPs are successfully synthesized, such as copper NPs (Cu NPs), copper oxide NPs (Cu x O NPs), and copper-containing bimetallic NPs. Cu x O NPs are widely used in the fields of biomedicine, environmental restoration, and industry ( 29 – 31 ). In biomedicine, cuprous oxide (Cu 2 O) and cupric oxide (CuO) are often used as antimicrobial agents ( 32 – 34 ). Compared with organic antimicrobial agents, copper oxide has the advantages of stable physical and chemical properties, solidity, and a relatively long shelf life. Moreover, copper oxide has physical properties that allow it to be easily mixed with polymers, which enables Cu x O NPs to be prepared into a variety of composite materials. Compared with Cu x O NPs, Cu NPs are relatively unstable and easily oxidized. Copper (Cu) is easily oxidized to form Cu 2 O and CuO when exposed to the air, making it difficult to synthesize Cu NPs in an ambient environment. Therefore, it is usually necessary to synthesize Cu NPs in the presence of polymers and surfactants and form coatings on the surface of Cu NPs ( 25 ). Copper-containing bimetal NPs are NPs containing copper and another metal element. The combination of two metal elements will have a synergistic effect and may have better antimicrobial performance than single metal. For example, Perdikaki et al. ( 35 ) have shown that synthesized Ag/Cu bimetallic NPs have stronger antimicrobial properties than Ag and Cu monometallic NPs.

These different types of copper-containing NPs can be incorporated into supporting materials (chitosan, cellulose polymers, hydrogels, etc .), which are biocompatible and retain antimicrobial activity ( 36 – 40 ). Tran CD et al. ( 41 ) synthesized composites containing cellulose, chitosan, and CuO NPs. This composite can prevent the aggregation, coagulation, and changes in size and morphology of CuO NPs without changing the unique properties of the NPs. Moreover, they can exert superior antibacterial activity against a variety of bacteria and fungi, and the antibacterial activity is related to the content of CuO NPs. As chitosan is a biocompatible, biodegradable, and non-toxic polymer, copper-containing NPs can be incorporated into chitosan and used in dental materials. Chitosan can interact with hydroxyapatite and the bacterial cell walls of teeth to improve the adhesion of copper on the tooth surface and the anti-biofilm action of copper ( 42 ). Chitosan not only has a good inhibitory effect on Gram-negative bacteria, Gram-positive bacteria, and fungi ( 43 ), but also interferes with oral microbial adhesion, inhibit biofilm formation and maturation, and promote wound and oral ulcer healing ( 43 – 46 ). Mishra et al. ( 47 ) synthesized biocompatible thiol-functionalized cellulose-grafted copper oxide nanoparticles, which alleviated colitis conditions and recovered damaged colon structure. Cellulose enhances the biocompatibility of copper oxide NPs and avoids the adverse effects of CuO NPs on the biological systems. The Cu-NP-embedded hydrogels also possessed remarkable antibacterial ability, and reduced the inflammatory response and promoted angiogenesis in vivo to accelerate the wound healing process ( 48 ). By preparing copper-containing NPs and other materials into composites, the original physical and chemical properties of copper-containing NPs can be retained while giving composites new characteristics, making them more suitable for clinical application.

Antimicrobial mechanism of copper-containing NPs

Copper can cause damage to various cell functions and exert cytotoxicity, making it an effective microbial inhibitor. In general, copper damages microbial cells by generating reactive oxygen species (ROS) and replacing or binding the native cofactors in metalloproteins ( 49 ). Besides, copper is also involved in innate immunity and can catalyze the formation of ROS in the blasting reaction taking place within phagocytes, enhancing the bactericidal activity during bacterial phagocytosis ( 14 , 50 ).

Copper-containing NPs can inhibiting microorganisms through the same mechanism as other types of copper materials mentioned above ( 51 – 53 ). Many studies have shown that NPs can exert stronger antimicrobial properties than ordinary size materials, but the reason for this is not completely clear at present. Compared with other copper molecular materials, Copper-containing NPs has higher surface area and different crystal structure, and can affect different cellular components of microbial cells through some unique mechanisms to exert better antibacterial activity ( 54 – 59 ). Copper-containing NPs can dissolve faster in solutions, release more metal ions, and exert a stronger antimicrobial effect ( 60 ). In addition, Copper-containing NPs can bring multiple antibacterial mechanisms simultaneously, but it is difficult for the same microorganism to have multiple gene mutations to cope with various antimicrobial mechanisms of NPs, so the probability of antimicrobial resistance is low.

In general, Copper-containing NPs added to many dental materials inhibits microorganisms mainly through the release of the NPs and copper ions. The antimicrobial process of copper-containing NPs is to produce ROS, destroy cell walls and cell membranes, and react with proteins and DNA ( 61 ). In this process, copper-containing NPs can damage different microbial cell components through a variety of mechanisms ( Figure 1 ).

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Illustration of possible antibacterial mechanism of Copper-containing NPs.

Generation of ROS

Oxidative stress caused by ROS is crucial in the antibacterial effect of copper. ROS are oxygen-containing derivatives composed of highly unstable oxygen radicals, such as superoxide (O 2 •− ), hydroxyl (OH • ), hydrogen peroxide (H 2 O 2 ), and singlet oxygen (O 2 ) ( 62 ). The atomic or molecular orbitals of ROS contain one or more unpaired electrons, which makes them highly reactive ( 63 ). Transition metals, such as copper, iron, and silicon, can generate ROS through Fenton type and Haber-Weiss reactions:

During these reactions, copper accepts and donates an electron during cycling between the Cu + and Cu 2+ oxidation states, producing O 2 •− and hydroxyl OH • , which are highly reactive and have strong damaging potential, leading to lipid peroxidation, protein oxidation, and DNA damage ( 64 – 66 ).

In the presence of water and oxygen molecules, copper can only dissolve a small amount of copper ions ( 67 ). In fact, the metal ions released by dissolution outside the cell are not the main antibacterial mechanism of copper-containing NPs. A recent study showed that dissolved copper ions contributed less than half of the total cytotoxicity induced by CuO NPs ( 68 ). A possible reason for this is that metal-based NPs enter the acidic lysosomal environment (pH 5.5) in cells, which promotes the formation of free radicals and the degradation/corrosion of NPs, thereby converting the core metal into an ionic form and resulting in the intracellular release of metal ions. This process of the internalization of NPs is often referred to as “the Trojan horse mechanism”, which promotes the formation of intracellular ROS ( 69 , 70 ). The formation of ROS is an important part of the antimicrobial mechanism of copper-containing NPs. Copper-containing NPs can not only generate ROS by directly leaching ions but may also generate ROS through multiple mechanisms, such as the disruption of mitochondrial membrane potential, and produce singlet oxygen to mediate the degradation of DNA ( 71 , 72 ). However, these mechanisms have not been fully clarified, and relevant microbial cytotoxicity studies are lacking.

Disruption of microbial cell walls and cell membranes

The early stage of copper-containing NPs damage to microbials is their direct contact with the microbial surface, which leads to the alteration of the microbial cell wall and cell membrane ( 73 ). Metal-based NPs and their leached metal ions are positively charged, and the surface of both Gram-positive and Gram-negative bacteria are negatively charged. Therefore, through electrostatic interaction, metal-based NPs will be adsorbed onto the surface of bacteria and build strong bonding leads for the destruction of the cell wall. This process increases cell permeability and allows metal-based NPs to enter the cell easily ( 74 ). Besides, copper ions can be combined with negatively charged areas on the cell membrane to reduce the potential difference and cause depolarization. When the potential difference drops to zero, it will cause membrane leakage or even rupture, exposure of the cellular components, and, eventually, bacterial death ( 75 ). Many studies have shown that the cell membrane is a direct target of copper exposure ( 76 , 77 ). Hong et al. ( 78 ) found that E. coli died after 45 min of copper alloy contact, but no degradation of genomic DNA was observed. Copper ions can cause oxidative damage to the unsaturated fatty acids of bacterial cell membrane phospholipids through the production of extracellular ROS, while OH· can drive the non-enzymatic peroxidation of the unsaturated double bonds of fatty acids, thereby triggering a series of reactions and leading to extensive changes in the structure of the phospholipid bilayer and destroying the biophysical properties of the membrane, which ultimately leads to a loss of membrane integrity, exposure of the cell components, and cell death.

However, the bactericidal effect of copper-containing NPs on Gram-positive bacteria is stronger than that of Gram-negative bacteria, which may be due to the difference in the cell wall structure of these two classes. Compared with lipids, copper has a higher affinity for proteins, so Gram-positive bacteria with higher levels of peptidoglycan and protein content in the cell wall is more easily destroyed by copper-containing NPs ( 44 ).

Replace or bind the native cofactors in metalloproteins

Previous studies believed that copper toxicity was mainly related to the production of ROS, but later studies found that, under anaerobic conditions, copper accumulation can also increase cytotoxicity to bacteria ( 79 , 80 ). Moreover, recent studies have shown that copper's cytotoxicity to microorganisms is also closely related to its ability to replace or bind to the native cofactors in metalloproteins. Intracellular copper accumulation promotes mismetallation, which is mainly related to the iron-sulfur cluster protein and its assembly process ( 81 ). Specifically, the copper accumulated in bacterial cells mainly exists in the form of highly toxic Cu + , which coordinates with the thiolate or inorganic sulfur ligands of the solvent-exposed dehydratase and replaces the iron atom, rapidly inactivating Fe/S cluster dehydratases to cause cell dysfunction ( 82 , 83 ). In addition, copper and iron in Escherichia coli ( E. coli ) cells seem to share the same binding site in the Iron-sulfur cluster assembly protein (IscA), and excessive copper can also compete with iron for metal binding sites in IscAs and effectively inhibit the IscA-mediated assembly of [4Fe-4S] clusters ( 81 , 84 ).

Damage of intracellular components

As described above, the uniqueness of the toxicity of copper-containing NPs to microorganisms is due to that they can directly enter the cells, and are internalized into complete intracellular particles in microbial cells through the Trojan horse mechanism. Studies by Kaweeteerawat et al. ( 85 ) showed that, at low concentrations, copper ions mainly inhibit microorganisms by damaging cell membranes rather than by causing oxidative stress in cells. However, they found that, even at lower concentrations, copper-containing NPs are also sufficient to promote the production of large amounts of intracellular ROS. In general, copper-containing NPs entering cells can directly damage oxidative organelles, such as mitochondria, and lead to increased intracellular ROS, protein oxidation, and DNA degradation ( 86 , 87 ). Studies by Chatterjee et al. ( 87 ) showed that the oxidation of proteins in cells is mediated by ROS, but the degradation of DNA is a ROS-independent phenomenon caused by the intracellular release of copper ions. Studies by Giannousi et al. ( 33 ) have also found that copper-containing NPs induce DNA degradation in a dose-dependent manner and extensively degrade double-stranded calf thymus DNA (dsCT-DNA) at low concentrations. In general, the exact mechanism of the antimicrobial effect of copper-containing NPs is unclear and needs to be elucidated.

Factors affecting antimicrobial effect

The main physical factors affecting the antimicrobial activity of copper-containing NPs are include the size, morphology and environmental conditions (temperature) of the NPs., Chemical factors include environmental conditions (PH value, dry or wet, and composition of the surrounding medium), the doping modification of other elements, and the oxidation state of copper.

Size and morphology

It has been suggested that due to the small size and high surface-to-volume ratio, metallic NPs can exert better antimicrobial activity than ordinary metals ( 88 – 91 ). At similar surface area doses, copper NPs and copper microparticles have similar effects on cell membrane damage, reflecting the fact that the damage of the cell membrane is related to the surface area of NPs ( 60 , 89 ). Different sizes of copper-containing NPs have different inhibitory effects on Gram-positive and Gram-negative bacteria ( 92 ). Azam et al. ( 93 ) found that the small size CuO NPs is more stable than the large size CuO NPs and has significantly stronger antibacterial properties. Some studies have also proved that the antibacterial activity of CuO NPs and Cu 2 O NPs are size-dependent: the reduction in the size of the NPs leads to an increase in antibacterial properties ( 93 – 95 ). Applerot et al. ( 94 ) believed that the reason for the stronger antibacterial effect of small-size CuO NPs is due to their stronger ability to penetrate cells. The high surface-to-volume ratio and small size of copper-containing NPs enhance their interaction with microbial membranes, enabling them to exert stronger antimicrobial activity than copper ions.

The antimicrobial activity of NPs is also related to morphology, and different morphologies of NPs can cause different degrees of bacterial cell damage through interactions with periplasmic enzymes ( 96 ). Copper-containing NPs with different crystal planes have different surface energies, and this difference may also be responsible for the morphologically dependent antimicrobial activity of copper-containing NPs. The higher surface energy of the exposed facets of copper-containing NPs may generate copper ions more effectively and lead to stronger antimicrobial activity ( 97 , 98 ). Xiong et al. ( 99 ) synthesized polyhedral, flower-like, and thumbtack-like Cu/Cu x O NPs. And they proved that, among the three kinds of Cu / Cu x O NPs, the main exposed facets {111} of the flower-like Cu / Cu x O NPs had the highest surface energy, dissolved the most copper ions in the culture medium, and had the best antibacterial ability. Studies by Feng et al. ( 100 ) have shown that {100} facets of the Cu 2 O nanocrystals can release more copper ions and produce more ROS in a shorter amount of time than {111} facets of the Cu 2 O nanocrystals, resulting in stronger toxicity in the short term. Besides, some studies believe that {110} facets of the Cu 2 O microcrystals have better antibacterial activity against E. coli than that of {111} facets ( 101 , 102 ). However, on the contrary, some studies also believe that {111} facets of the Cu 2 O microcrystals have stronger antibacterial properties ( 103 ). In addition, studies by Pang et al. ( 97 ) have shown that the antibacterial activity of cubic Cu 2 O has a broad spectrum, while the antibacterial activity of octahedral Cu 2 O has high selectivity ( Figure 2 ).

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Different morphology of Copper-containing NPs.

Ambient conditions

The ambient conditions of copper-containing nanoparticles are one of the factors that affect the antibacterial effect ( Figure 3 ). The temperature and pH of the solvent affect the rate at which copper inhibits microorganisms. Studies by Sharan R et al. ( 17 ) showed that copper can cause the rapid inactivation of E. coli at higher temperatures and exhibit a faster inactivation at pH 6.0 and 9.0 than at pH 7.0 and 8.0. However, the effect of pH on bacterial inactivation is not as significant as that of temperature. The dissolution of copper ions is also an important part of the antimicrobial activity of copper-containing NPs. Usually, copper-containing NPs release more copper ions in an acid lysosomal environment than in a neutral environment ( 104 , 105 ). Dry conditions bring about faster microbicidal effects to copper, as the contact killing caused by dry copper surfaces can kill microorganisms in a short amount of time. Tian et al. ( 106 ) demonstrated that the Enterobacter cell structure was severely degraded after exposure to the dry copper surface for 30 s. Moreover, compared to wet conditions, copper kills Enterococcus 80% to 90% faster under dry conditions ( 77 ). In the case of contact killing, the antimicrobial effect of copper is not related to the dissolution of copper but the copper content on the contact surface ( 107 ).

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Ambient conditions affecting the antibacterial effect of Copper-containing NPs ( A ) temperature: the higher the temperature, the faster the sterilization; ( B ) PH value: the sterilization of acidic and alkaline conditions is faster than that of neutral conditions; ( C ) Dry or Wet: dry conditions kill bacteria faster than wet conditions; ( D ) composition of the surrounding medium: interaction of NPs with other molecules in the medium).

Besides, the interaction of copper-containing NPs with other molecules present in biological and environmental media may greatly affect the solubility, aggregation state, and surface properties of the NPs, resulting in changes of the toxicity ( 108 ). Studies by Badetti et al. ( 109 ) found that CuO NPs can react with some natural amino acids to affect their antimicrobial properties. L-Glutamic can be bonded to the surface of CuO NPs to enhance their antibacterial activity, while L-Asparaginase, L-Leucine, l-Phenylalanine, and L-Tyrosine can weaken the antibacterial activity of CuO NPs by forming complexes with copper ions. Ruparelia et al. ( 110 ) found that the chloride-containing nutrient media can promote the dissolution of Cu NPs, so as to release copper ions, which may be due to the interaction between the chloride ions and the oxide layer of the NPs.

Doping modification

Doping modifications can modulate the interaction between NPs and microorganisms. Some studies have shown that doping other materials into Cu NPs and Cu x O NPs can improve their antimicrobial ability. For example, studies by Lv et al. ( 111 ) have shown that the doping of Mg, Zn, and Ce ions can promote the release of Cu 2+ in the doped CuO NPs and promote their antibacterial activity. Studies by Malka et al. ( 112 ) have shown that Zn-doped CuO NPs can generate more ROS than pure CuO NPs or ZnO NPs and thus exert stronger antibacterial activity. After being exposed to E. coli and Staphylococcus aureus ( S. aureus ) for 10 min, the antibacterial activity of Zn-doped CuO NPs was 10,000 times greater than that of pure CuO NPs or ZnO NPs. Besides, other metal component of copper-containing bimetal NPs, such as iron, can promote the conversion of Cu 2+ to more toxic Cu + and Cu 3+ , which makes bimetallic iron-copper NPs exhibit a stronger antimicrobial activity than Cu NPs and iron NPs (Fe NPs) ( 113 ).

Oxidation state

Copper has different antimicrobial properties under different oxidation states. The surface of pure copper is susceptible to oxidation and forms both CuO and Cu 2 O. Oxidative conditions (e.g., clean water in the air, upper hatched areas) contribute to the formation of CuO, while reducing conditions (e.g., the presence of organic matter and bacteria) contribute to the formation of Cu 2 O. These changes in oxidation state may affect the antibacterial properties of copper-containing NPs ( 105 ). Studies by O Akhavan et al. ( 114 ) have shown that Cu NPs exhibit greater antibacterial activity than CuO NPs, which may be attributed to the stronger electron-accepting ability and better electron transfer with bacteria of Cu NPs. The electron transfer between the negatively charged bacteria and the metal NPs is one of the effective mechanisms that cause the bacterial membrane rupturing and exerting antibacterial activity. Studies by Hans M et al. ( 115 ) have shown that Cu NPs and cuprous oxide NPs (Cu 2 O NPs) have strong contact killing activity against bacteria, while CuO NPs significantly inhibit contact killing. This difference is roughly related to the release of copper ions: pure copper releases the most copper ions, followed by Cu 2 O and CuO. Studies by Giannousi et al. ( 33 ) have also shown that the antibacterial activity of Cu 2 O NPs against a variety of Gram-negative and Gram-positive bacteria strains is stronger than CuO NPs. However, CuO NPs can induce higher ROS than Cu 2 O NPs, which is probably because CuO NPs can generate ROS through Haber-Weiss and Fenton type reactions, while Cu 2 O NPs can only generate ROS through Fenton type reactions. Moreover, CuO NPs have a higher degree of internalization and better antifungal activity at lower concentrations ( 24 ).

Host tissue interaction of copper-containing NPs

Although copper-containing NPs are highly anticipated new materials, it is necessary to ensure their biosafety to human bodies ( 116 – 120 ). Copper is an essential trace element for the human body, participating in various kinds of physiological activities. Copper containing enzymes and transcription factors are essential for cellular integrity, energy production, signalling, proliferation, oxidation and radiation defence ( 121 ). The liver, brain, heart and kidneys have the highest copper concentration in the body, followed by the lungs, intestines and spleen.

Research concerning acute or chronic toxicity of copper due to its deficiency or excess is growing rapidly and interest in the subject is pervasive ( 122 – 129 ). The four major routes of human exposure to engineered NPs include inhalation, dermal penetration, ocular exposure, and ingestion. Studies have shown that oral exposure of copper containing NPs in rats mainly accumulates in liver, kidney, stomach, intestine, lung, brain and blood, among which liver and kidney are the main organs most affected by Cu NPs ( 130 , 131 ) ( Figure 4 ). Exposure to NPs induces an inflammatory response and activates the immune system ( 132 ). The toxicity mechanism of copper-containing NPs to human cells is similar to that of microbial cells. Copper-containing NPs will dissolve and release copper ions, generate ROS, disrupt normal cellular functions and cause DNA damage. Changing the physicochemical properties of copper-containing NPs can change the induced toxic response/mechanism of action, such as size (aerodynamic, hydrodynamic), surface (surface area:mass ratio), chemical composition (core structure, surface functionalization, coatings), solubility (hydrophobic, hydrophilic) ( 133 ).

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Main routes of transfer (blue) and accumulation (green) in organs of copper-containing NPs in the body through oral intake.

In dentistry, copper-containing NPs are expected to be used in restorative materials, prosthodontic materials, dental implants and orthodontic appliances. Researchers tried to explore safe forms to reduce toxicity of copper-containing NPs ( 116 , 118 ). In fact, copper-containing NPs applied to dental materials rarely enter the body,and the concentration and morphological characteristics of copper-containing NPs can be controlled so that they will not be cytotoxic to normal cells ( 134 ). In addition, since copper-containing NPs can exert better microbial inhibition effect than copper native, addition amount of copper-containing NPs can be lower ( 44 ).

Inhibitory effect of copper-containing nps on oral pathogenic microorganisms

Since microorganisms are less susceptible to resistance against metal antibacterial substances, the application of metals as antibacterial substances to control oral plaque has become a research hotspot. Studies have shown that copper-containing NPs can inhibit various oral pathogens, such as S. mutans ( 20 , 21 ), P. gingivalis ( 23 ), and C. albicans ( 20 , 24 – 26 ) ( Table 1 ).

The inhibitory ability of some copper-containing nanoparticles on oral microbes.

Nanoparticles (Diameter and morphology)Test oral microbesAnti-microbial test methodAntimicrobial efficiencyMechanism of actionReference
CuO NPs (40 nm) (PTCC 1683)

( )
( )
 MIC (37°C, 48 h) : 1–10 µg/ml (MIC )
,
and : 1000 µg/ml (MIC )
Produce ROS( )
CuO NPs (39.87 nm, spherical)Oral bacteria from the teeth crown surfaceCuO NPs (10, 50, and 100 µg /ml) were treated with 10 CFU/ml bacterial cells (37°C,16 h)10 µg/ml: 66% (NA agar plates) and 59% (MRS agar plates) inhibition of bacteria
50 µg/ml: Inhibits 82-92% of bacteria
The EC values:
22.5 µg/ml (NA agar plates)
25 µg/ml (MRS agar plates)
Unclear( )
CuO NPs (18–20 nm, spherical) (700610)Sonochemical coating of CuO NPs on artificial tooth surface treated with 10 CFU/ml bacterial cells (37°C, 24 h)Biofilm formation is reduced by 70%
Bacteria in the medium was not affected.
Produce ROS( )
CuCh NPs (131 ± 36 nm) (ATCC 25175)MIC and MBC (37°C , 48h)MIC: 35 µg/ml
MBC: 60 µg/ml
Produce ROS
Inhibit the activity of glucosyltransferase (GTF)
( )
CuO (10.7 nm, nanobar)
Cu O (36 nm, nanocube)
(ATCC 90028)CuO and Cu O were treated with 5 × 10 CFU/ml bacterial (37°C , 24 h)The MIC of CuO and Cu O is 150 µg/ml and 250 µg/ml respectively, and biofilm inhibitory concentration (BIC) for both NPs is 1 µg/mlProduce ROS
Destroy cell membranes
Inhibits ergosterol and causes loss of virulence
Inhibits yeast-to-hyphal transition
( )
CuO
Cu O
Ag + CuO composite [70% (w/w) Ag]
(10–50 nm)
(W83)
( , ATCC 25611)
( ) subsp. nucleatum (ATCC 25586)
( , ATCC33384)
CuO, Cu O and Ag + CuO composite (100, 250, 500, 1,000 and 2,500 µg/ml ) were treated with 5 × 10 CFU/ml bacterial cells (37°C , 48 h)For CuO: : 500 µg/ml (MIC), 2500 µg/ml (MBC)
: 250 µg/ml (MIC), 250 µg/ml (MBC)
: 250 µg/ml (MIC), 250 µg/ml (MBC)
: 250 µg/ml (MIC), 250 µg/ml (MBC)
For Cu O: : <100 µg/ml (MIC), <100 µg/ml (MBC)
: <100 µg/ml (MIC), <100 µg/ml (MBC)
: <100 µg/ml (MIC), <100 µg/ml (MBC)
:1,000 µg/ml (MIC), 1,000 µg/ml (MBC)
For Ag + CuO composite: : <100 µg/ml (MIC), <100 µg/ml (MBC)
: <100 µg/ml (MIC), 100 µg/ml (MBC)
: 500 µg/ml (MIC), 500 µg/ml (MBC)
: 250 µg/ml (MIC), 250 µg/ml (MBC)
Damage to cell membrane permeability
Produce ROS
( )
Fe doped CuO NPs (Rectangular shape assembled from approximately 23 µm microspheres and sheets with an average thickness of 150 nm) Fe doped CuO NPs were treated with 1% overnight cultures of (30°C, 24 h)20 µg/ml: inhibited biofilm formation by 7.2%.
100 µg/ml: reduced the growth OD to 0.28 and inhibited the formation of biofilms by 76.4%
Release metal cations
Combine with bacterial cells
The Trojan horse mechanism
( )
chitosan-copper NPs (The diameters of NPs containing 0.05, 0.1, 0.2 and 0.5 wt% chitosan are 50–300 nm, 50–270 nm, 5–50 nm and 2 nm, respectively) chitosan-copper NPs (2,500 µg/ml) were treated with 1 × 10 CFU/ml fungal cells (37°C, overnight)The inhibition rates of 0.05, 0.1, 0.2 and 0.5 wt% of NPs on were 82.75, 82.2, 81.37 and 65.86%, respectivelyThe Trojan horse mechanism( )

It is well-known that S. mutans is the main pathogen of dental caries, which can adhere to the surface of tooth or dental prosthesis to form plaque biofilm, produces acid, and causes dental caries ( 135 – 139 ). Numerous studies have shown that copper can inhibit the growth of S. mutans and caries formation ( 140 – 143 ). In the case of extracellular high concentrations of copper, copper ions enter S. mutans cells and inhibit the transcription of glucosyltransferase ( gtf ) genes and glucan binding protein ( gbp ) genes to reduce cell adherence and biofilm biomass ( 144 , 145 ).

Generally, bacteria have a “copper transport system” to cope with fluctuating copper ion concentrations in complex ecosystems and maintain copper homeostasis ( Figure 5 ). S. mutans can tolerate extracellular high concentrations of copper through a conserved P-type ATPase, a copper-transport operon ( 146 , 147 ). S. mutans can also oxidize intracellular Cu + to less toxic Cu 2+ . Despite a certain degree of resistance to copper, copper-containing NPs can still effectively inhibit S. mutans through various mechanisms. Studies by Amiri et al. ( 20 ) have shown that the MIC 50 value for CuO NPs with a size of 40 nm is 1–10 µg/ml for S. mutans , and higher concentrations of CuO NPs (100–1,000 µg/ml) can significantly inhibit bacterial growth. Similarly, Khan et al. ( 21 ) also demonstrated that CuO NPs at a size of 40 nm can significantly inhibit the growth of human oral pathogens (such as S. mutans ), the extracellular polysaccharide production, and the multispecies biofilm formation at a concentration of 50 µg/ml. In another study, Eshed et al. ( 148 ) used the sonochemistry method to coat CuO NPs on the teeth surface, and the biofilm formation on the teeth coated with CuO NPs was significantly reduced by 70%. Similarly, Covarrubias et al. ( 42 ) synthesized hybrid NPs of chitosan-coated copper NPs (CuCh NPs), which can significantly inhibit the growth of S. mutans and significantly reduce biofilm formation.

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Copper transport system in bacteria.

P. gingivalis

P. gingivalis is the main periodontal pathogen and is closely related not only to the occurrence of periodontal disease but also to the occurrence of systemic diseases, such as atherosclerosis, diabetes, and rheumatoid arthritis ( 149 – 153 ). Studies have shown that copper and copper alloys can inhibit the growth of P. gingivalis by contact killing, such as the Ti-Cu alloy, which can exert good antibacterial activity by killing the bacteria as well as reducing the activity of any surviving bacteria ( 154 , 155 ). In addition, copper ions can inhibit the coaggregation of P. gingivalis with other bacteria, thereby reducing the accumulation of P. gingivalis in plaque biofilm and also reducing the pathogenicity and occurrence of periodontal disease ( 156 ). P. gingivalis is a Gram-negative bacterium with a lipopolysaccharide on the cell membrane surface that can prevent copper-containing NPs entering the cell. However, copper-containing NPs still have a significant inhibitory effect on P. gingivalis . Vargas-Reus et al. ( 23 ) found that the MICs of CuO NPs, Cu 2 O NPs and Ag + CuO composite with a size ranging between 10 nm and 50 nm were 500 µg/ml, <100 µg/ml and <100 µg/ml for P. gingivalis , respectively, suggesting that they have good antibacterial activity. Additionally, CuO NPs, Cu 2 O NPs and Ag + CuO composite has better antibacterial ability to P. gingivalis than ZnO NPs, TiO 2 NPs and Ag NPs.

C. albicans

C. albicans is the most common fungus in the oral cavity and is a conditional pathogen that often causes fungal infections in the elderly population or in denture patients. ( 157 , 158 ) C. albicans can form a biofilm on the oral mucosa against external antifungal agents, which makes it pathogenic ( 159 ). Copper-containing NPs have also exhibited considerable antimicrobial activity against C. albicans . Padmavathi et al. ( 24 ) found that both CuO NPs and Cu 2 O NPs have fungal inhibitory activity. They can destroy the cell membrane of C. albicans by inhibiting the production of ergosterol, which lead to the loss of virulence. They can also alter the expression of the genes involved in the morphogenesis of C. albicans . CuO NPs can inhibit mycelial growth, while Cu 2 O NPs can distinctively inhibit morphological switching. Moreover, CuO NPs have a stronger inhibitory effect on C. albicans than Cu 2 O NPs and exhibit better antifungal activity at a low concentration. Amiri et al. ( 20 ) found that CuO NPs with a size of 40 nm couldreduce the growth of C. albicans , Candida krusei , and Candida glabrata , and the MIC 50 value of CuO NPs was 1,000 µg/ml for these three species of oral Candida. Pugazhendhi et al. ( 26 ) synthesized Fe-doped CuO using a sol-gel method, which has a rectangular shape and agglomerates at an average size of 21 nm. The Fe-doped CuO has excellent antimicrobial and anti-biofilm properties to C. albicans , which can reduce the growth OD of C. albicans to 0.28 at 30°C for 24 h and reduce the biofilm by 76.4% at a concentration of 100 µg/ml. In another study, Lara et al. ( 159 ) synthesized chitosan-copper NPs with a size between 2 nm and 350 nm and proved that they had good antimicrobial activity against C. albicans.

Application of copper-containing NPs in dentistry

Copper-containing NPs can be applied to various aspects of dentistry. Applying NPs to the surface of dental materials or incorporating them in dental materials can not only impart different antibacterial activity to the material, but also improve or maintain the mechanical properties of the material ( 22 , 160 , 161 ). When applied to dental materials, they can also play a variety of beneficial roles by inhibiting metalloproteinases (MMPs) ( 146 ). Many current studies have synthesized different types of copper-containing NPs that can be used for dental materials, including dental adhesive es and filling materials, implant and bracket coatings, etc. ( Figure 6 ) and ( Table 2 ).

Antibacterial application of copper-containing nanoparticles in dentistry.

Nanoparticles (Diameter and morphology)Oral materials descriptionTest oral microbesAnti-microbial test methodAntimicrobial efficiencyFeaturescytotoxicityReference
Cu NPs (40–60 nm, spherical)
ZnO NPs (10–30 nm)
Add 5 /0.1 wt% and 5/0.2 wt% of ZnO / CuNp respectively to two commercial adhesives (ATCC 25175)Disc diffusion method (37°C , 48 h)Non-polymerized: Significantly higher antibacterial properties
Polymerized: only the 5/0.2 groups showed significantly higher antibacterial properties.
Provides anti-MMPs properties without affecting its mechanical properties, thereby improving the integrity of the hybrid layer on caries-affected dentin.Data not shown( )
Cu NPs (63–154 nmAdd 0.0075, 0.015, 0.06, 0.1, 0.5 and 1.0 wt% Cu NPs into the simplified etch and-rinse adhesive system (ATCC 25175)Prepare disk-shaped adhesive specimens and place on BHI agar plates cultured with (37°C , 96 h)Improved antibacterial performance, with the highest antibacterial effect at 0.1, 0.5 and 1.0 wt%Increase the immediate and 2-year bond strength of the resin-dentin interface, as well as the mechanical properties of the adhesive formulation after 2-years of water storage.Data not shown( )
PAA-CuI NPs (20 nm–1.5 µm)Mix PAA CuI powder with two commercial binder resins (XP Bond and Optibond XTR) to prepare PAA-CuI adhesive concentrations of 0.5 mg/ml or 1.0 mg/ml (ATCC 25175)Resin composite discs are fabricated and coated with adhesive, and is inoculated on the surface (37°C , 18 h; 37°C , 1y)After18 h: Bacteria reduced by 99.99% (XP Bond) and 79.65% (XTR – 1.0 mg/ml)
After 1y: Bacteria reduced by 99.99% (XP Bond)
Does not affect shear bond strengthNo cytotoxicity ( human gingival fibroblast-like cells)( )
Cu NPs (Uncharacterized)Add 0.01, 0.5 and 1 wt% of Cu NPs to the orthodontic composite Disk-shaped adhesive specimens were prepared and placed in medium with (37°C , 24 h)Shows a significant antibacterial effect. The antibacterial effect was enhanced with the increase of NPs concentrationDoes not affect shear bond strengthData not shown( )
PAA-CuI NPs (59–88 nm)0.263 wt% of PAA-CuI NPs were added to fluoroaluminosilicate glass powdersto generate Generation of PAA-CuI modified glass ionomer (GI) and PAA-CuI modified resin-modified glass ionomer (RMGI) Disk-shaped specimens were prepared,inoculated with 100 µl of (1 × 10 cells/ml) on the surface (37°C , 18 h)Reduce bacterial concentration by 99.999%Does not affect mechanical properties Reduce the degradation of collagen in the dentin matricesData not shown( )
Cu NPs (10.87 nm)Add1, 2, 3 and 4 wt% of Cu NPs to the glass ionomer cement (ATCC 25175)
( , ATCC 10556)
Modified glass ionomer cement discs were prepared and placed in medium with and (1 × 10 cells/ml, 35°C, 48 h)Significantly inhibited the growth of and (2–4 wt%)Data not shownAfter 72 h of exposure to modified glass ionomer (2–4 wt%) extract, the viability of human dental pulp fibroblasts remained above 68%.( )
CuO NPs (40–60 nm)
TiO NPs (40–60 nm)
ZnO NPs (20 nm)
Ag NPs (50–60 nm)
The NPs were added to a water based-solution (PTC 1683)
(PTCC 1449)
Mix 50 ml of each sample with 50 ml of bacterial suspension (5 × 10 CFU) and incubate for 1 and 5 minBoth ZnONPs and CuONPs mouthwashes significantly reduced after 1 and 5 min of exposure
The colonies in all NPs groups after 5 min treatment was comparable to that of chlorhexidine
Data not shownData not shown( )
Cu NPs (50–100 nm)The mussel-inspired dendritic polyglycerol (MI-dPG) surface coating doped with Cu NPs was prepared

kanamycin-resistant
The sample was incubated with the various bacterial suspension for 24 h to detect the antibacterial rate.
The same sample and its extract have been tested for long-term antibacterial activity against for 3d.
After 40d of incubation, the sample was immersed in PBS or MilliQ for one month to test the durable antibacterial activity against .
Anti-biofilm activity was assessed by incubating the sample with for 24 h.
The antibacterial rate against various bacteria is over 99.99%.
 In the three-day continuous antibacterial experiment, the antibacterial rates were 99.99%, 99.52% and 93.50%, respectively, and the antibacterial rate of the extract was less than 90%.
After 40 days of culture, the Cu NPs in the coating can still effectively kill the attached bacteria and inhibit biofilm formation.
Excellent, long-lasting and broad-spectrum antibacterial properties with "attract-kill-release" characteristics80% cell viability after 24 h (NIH/3T3 cells )( )
Cu NPs (20–30 nm, cubic geometry)Deposition of Cu NPs on the surface of TiO nanotubes to form nCu–nT-TiO surface (ATCC 25922)
(ATCC 6538)
Immerse the modified surface in the bacterial suspension (150 rpm, 37°C, 2 h)100% reduction of surface adhesion of and Prevent early infection
Enhance the adhesion of osteoblast
Promote the colonization of bone cells
Data not shown( )
Cu NPsDepositing Cu NPs on the surface of HA coating to obtain Cu-HA composite coatings (JM109)
(ATCC 27217)
In the presence of coated titanium plates placed in bacterial suspension ( 1 × 10 cells/Ml, 37°C), monitor and measure several time points (0, 2, 4, 6, and 8 h) bacterial growth in the bacterial suspension.The antibacterial rate gradually increases with the increase of copper content. The highest resistance rates to and were 78% and 83%, respectively.Enhance the osseointegration
Provide a continuous antibacterial effect
Data not shown( )
ZnO NPs (45 nm)
CuO NPs(37 nm)
CuO-ZnO NPs
Deposited NPs on the orthodontic brackets (ATCC 35668)Glue the brackets to the center of the buccal surface of each tooth. Add 1 ml of bacterial suspension (1.5 × 10 CFU/ml, 37°C ,180 shakes per minute), and detect the amount of bacteria at 0, 2, 4, 6 and 24 h.Brackets oated with CuO NPs and ZnO-CuO NPs reduced the number of to zero after 2 h.Brackets coated with CuO NPs and ZnO-CuO NPs have excellent antibacterial effects on Data not shown( )

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Object name is fsurg-09-905892-g006.jpg

Application of copper-containing NPs in dentistry.

Dental adhesives

Many recent studies have shown that copper-containing NPs in dental adhesives can not only effectively inhibit bacteria but also improve the performance of the adhesive. Copper ions released by copper-containing NPs can be used as an effective dentin metalloproteinase (mainly on the Matrix metalloproteinase's subtypes −2 and −9) inhibitor, which can stimulate the secretion of the tissue inhibitors of MMPs ( 162 ). Matrix metalloproteinase 2 (MMP-2) is involved in the destruction of periodontal tissue and the development of oral squamous cell carcinoma, and it also plays an important role in the destruction of dentin during the progression of caries ( 162 – 165 ). MMPs can also mediate the degradation of adhesives, while inhibiting MMP can increase the longevity of the adhesive-hard tissue interface and improve the bonding effect of adhesives ( 166 – 169 ). Besides, MMPs inhibitors can prevent dental caries, reduce dentinal caries progression, and promote remineralization ( 170 – 172 ). Studies by Gutiérrez et al. ( 173 ) have shown that the addition of Cu NPs and ZnO NPs to the universal adhesive system can provide the adhesive with antibacterial activity against S. mutans and anti-MMPs properties without affecting its mechanical properties, thereby improving the integrity of the hybrid layer on caries-affected dentin. The addition of copper-containing NPs to the adhesive may also improve its mechanical properties. Vidal Oet al. ( 174 ) incorporated copper nanoparticles (CuNp) into a universal adhesive and applied it to dentin surfaces. The addition of copper nanoparticles can significantly enhance the antibacterial activity of the resin-dentin interface, showing higher bond strength and mechanical properties, even under cariogenic challenges. Javed et al. ( 175 ) incorporated CuO NPs and CuO-chitosan NPs into dentin adhesives, which can significantly inhibit Lactobacillus acidophilus ( L. acidophilu ) and S.mutans and effectively treat secondary caries. The addition of NPs also improved the mechanical properties, water absorption and solubility of the adhesive without affecting the shear bond strength.

Many studies have also shown that adhesives with copper-containing NPs can exhibit long-lasting and effective antimicrobial effects. For example, studies by Gutiérrez et al. ( 176 ) have shown that the addition of Cu NPs at a concentration of 0.1 wt% in the adhesive system can provide antibacterial properties without reducing the mechanical and optical properties of the adhesive formulations. Moreover, compared with copper-free adhesives, copper-containing adhesives can significantly reduce the dentin degradation of the resin-dentin bonded interfaces dentin after two years of water storage. In addition, a sufficient concentration of copper still exists in the adhesive interface, which can exert anti-MMPs effects. In another study, Jun et al. ( 177 ) synthesized novel copper-doped bioactive glass NPs (CuBGn NPs) and added them to the resin-dentin adhesive system. Although there are no antibacterial experiments to prove its antibacterial properties, the adhesive can release up to 0.5 ppm copper ions over a 28-day period, which is sufficient to deactivate MMPs, promote remineralization, and extend the longevity of resin-dentin interfaces dentin regeneration.

Other studies have shown that adding copper-containing NPs to adhesives will not cause additional cytotoxicity to the pulp or oral soft tissues. For example, Sabatini et al. ( 178 ) synthesized polyacrylic acid coated copper iodide NPs (PAA-CuI NPs) and incorporated them into adhesives. After ageing for 18 h or one year, the adhesive can exert effective antibacterial effects without affecting the bond strength and cytotoxicity. A study by Matos et al. ( 179 ) also confirmed that the addition of 0.1 wt% Cu NPs to the adhesive can improve the clinical performance of universal adhesive systems in non-carious cervical lesions without increasing cytotoxicity.

Moreover, Cu NPs and CuO NPs can also be added to orthodontic adhesives to exert a certain antibacterial effect. Studies have shown that the addition of Cu NPs can significantly improve the material shear bond strength, while the addition of CuO NPs will not adversely affect the shear bond strength ( 180 ).

Dental filling materials

Copper-containing NPs can also be used in dental filling materials. Studies by Renné et al. ( 181 ) have shown that the incorporation of polyacrylic acid coated copper NPs (PAA-CuI NPs) into glass ionomer-based materials can improve their antibacterial properties and reduce collagen degradation without affecting the mechanical properties, which can help increase the longevity of adhesive restorations. Aguilar-Perez et al. ( 182 ) synthesized copper-containing NPs composed of metallic copper and cuprous oxide and added them to commercial glass ionomer cement, confirming that they can inhibit oral anaerobic bacteria strains. In addition, the glass ionomer cement doped with copper-containing NPs has no cytotoxic effect and will not damage the dental pulp.

Antimicrobial coatings

NPs can be used to control the formation of microbial biofilms in the oral cavity, which allows them to be incorporated into coatings and applied to a variety of dental materials ( 183 , 184 ). Although dental implants have a high success rate, there are still failures. Poor osseointegration and infection are important reasons for implant failure ( 185 ). Coatings containing copper-containing NPs are commonly used in dental and orthopedic implants to increase their success rates by improving bone binding capacity and reducing the incidence of post-surgery infections ( 186 , 187 ). Copper-containing NPs reduce the formation of biofilms on the surface of titanium implants. Moreover copper is involved in enzyme-based processes for bone metabolism and stimulates the formation of new blood vessels, which, in turn, reduces implant-related infections ( 90 ). Therefore, coating the titanium surface of the implant with copper-containing NPs can reduce the use of prophylactic antibiotics, which may cause the development of antibiotic resistant strains ( 188 – 190 ). Besides, the incorporation of an appropriate amount of Cu NPs on the implant surface not only has no cytotoxicity to endothelial cells and osteoblasts but also promotes osteoblast proliferation and adhesion as well as extracellular matrix mineralization ( 191 ).

Many studies have confirmed that the coatings containing copper-containing NPs can exert antimicrobial activity and be used in dentistry ( 192 – 194 ). For example, Li et al. ( 195 ) prepared an antibacterial coating material based on mussel-inspired dendritic polyglycerol embedded with Cu NPs, which not only has a bacteriostatic rate of over 99.99% against S. aureus , E. coli , and kanamycin-resistant E. coli , but also can exert effective long-term and durable antibacterial properties against E. coli . Rosenbaum et al. ( 196 ) prepared copper nanocubes with an average size of 20 nm on the surface of TiO nanotubes. This copper derived TiO surfaces could cause the death of E. coli and S. aureus and exert a powerful bactericidal ability. Ghosh et al. ( 197 ) used a two-stage electrochemical method to synthesize copper-hydroxyapatite (Cu-HA) composite coatings on titanium surfaces, which can slowly release copper ions while enhancing implant osseointegration to provide a sustained bacteriostatic effect. In addition, CuO NPs can be coated on the surface of orthodontic brackets. Studies have also shown that the CuO NPs and ZnO-CuO NPs coatings on the surface of orthodontic brackets have stronger antibacterial effects on S. mutans than ZnO NPs coatings ( 198 ).

Mouthwashes

Copper-containing NPs also have the potential to be added to mouthwashes for antimicrobial action. In one study, CuO NPs were prepared in colloidal solutions as mouthwashes, and it was found that, although not as good as chlorhexidine mouthwash, CuO NPs can also have a certain antibacterial effect on S. mutans ( 199 ).

Soft denture liners

The intrinsic porosity of soft denture pads facilitates the adhesion and colonization of microorganisms and promotes the formation of biofilms. A study by et al. ( 200 ) showed that the incorporation of CuO NPs at a concentration of 500 µg/ml into soft denture liners exerted an effective prevention of oral microbial infection. The biofilm inhibition rates of soft denture liners containing CuO NPs against C.albicans , Streptococcus sobrinus ( S. sobrinus ), S. mutans , and Streptococcus salivarius ( S. salivariu ) were 75%, 66%, 30%, and 60%, respectively.

Many current studies indicate that copper-containing NPs can be used in dentistry due to their antimicrobial and anti-biofilm properties. Copper-containing NPs are a new type of ideal antimicrobial material, which can inhibit or kill a variety of oral pathogenic microorganisms without causing microbial resistance, and can also produce a certain degree of beneficial effects on oral tissues. Various forms of copper-containing NPs are still being explored for use in dental filling materials, prosthetic devices and implant coatings, and oral antimicrobial agents. However, many of these studies have been performed under in vitro conditions, and further in vivo studies are needed to assess their safety and clinical efficacy.

This work was supported by The Applied Foundation in Science and Technology office of Sichuan Province (No. 2021YFG0230)

Author contributions

XM contributed to the motivation, the interpretation of the methods, the data analysis and results; SZ provided the draft versions and revised versions, references; XX provided the data and results, the revised versions and references; QD provided the related concepts and minor recommendations, extracted the conclusion and discussion. All authors contributed to the article and approved the submitted version.

Publisher's note

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

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Enhancing diesel engine performance with different concentrations of copper oxide nanoparticles in biodiesel blends.

© 2024 The authors. This article is published by IIETA and is licensed under the CC BY 4.0 license ( http://creativecommons.org/licenses/by/4.0/ ).

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This study explores the impact of adding copper oxide (CuO) nanoparticles to biodiesel derived from sunflower oil on the performance of a diesel engine. Various concentrations of CuO nanoparticles were tested. Using a Korean-origin KiaBongo2701 Model 12 diesel engine, seven fuel types were examined, including pure diesel and biodiesel blends with different ratios. The effects of these blends and the performance of CuO nanoparticle additives were evaluated at various speeds and loads. Both mechanical mixing and ultrasonic devices were employed to prepare the fuel blends for comparison. Copper oxide nanoparticles significantly enhanced the performance of the D85B15 fuel blend, narrowing the performance gap with pure diesel. The results demonstrated that increasing the nanoparticle concentration led to a marked improvement in thermal efficiency at 1600 RPM, with D85B15PPM50 showing a 4.63% increase, D85B15PPM75 achieving a 6.41% improvement, and D85B15PPM100 experiencing a 7.54% boost. Diesel-like performance was attained using D85B15PPM100. D85B15's reduced calorific value raised fuel consumption, but nanoparticle integration improved brake-specific fuel consumption, especially at full load with 100 ppm copper oxide. The emissions tests showed that biodiesel blends containing nanoparticles produced less carbon monoxide and nitrogen oxides than the basic mix, reducing environmental impact. At the highest concentration (100 ppm), nanoparticles virtually equaled pure diesel performance, suggesting a way to produce biodiesel with equivalent performance and reduced environmental effects. These findings demonstrate the potential of nanoparticle additions to bridge the performance gap between biodiesel and conventional diesel and make biodiesel usage in diesel engines more sustainable and efficient.

biodiesel, sunflower oil, copper oxide nanoparticles, diesel engine, thermal efficiency, brake-specific fuel consumption, engine performance

Efforts to find cleaner and more efficient fuels for diesel engines have prompted the investigation of different additives and mixtures. Biodiesel generated from sunflower oil has become an attractive alternative since it is sustainable and can reduce greenhouse gas emissions significantly [1, 2]. Researchers are using nanotechnology, namely copper oxide nanoparticles, to improve the efficiency of biodiesel mixes [3, 4]. Nanoparticles enhance the efficiency of combustion and decrease emissions, therefore tackling environmental issues and advocating for more sustainable energy sources in the transportation industry [5, 6]. The physiochemical features of biodiesel blends may be significantly enhanced by the presence of copper oxide nanoparticles, leading to a notable interest in their use [7, 8]. The researchers aim to enhance engine efficiency and reduce the ecological footprint by incorporating nanoparticles into biodiesel made from sunflower oil. Nanoparticles can boost combustion efficiency, improve thermal efficiency, decrease fuel consumption, and increase lubricity. This has the potential to cut engine wear and maintenance costs [9, 10].

Recently, several researchers have explored alternative fuels to reduce the use of diesel fuel and mitigate the pollution caused by diesel engines. Biodiesel and alcohol are attractive choices because of their renewable nature and ability to decrease greenhouse gas emissions [11-13]. Researchers are studying the qualities and combustion characteristics of alternative fuels such as biodiesel and alcohols to make it easier for them to be used in the transportation industry. These studies try to determine the most effective fuel formulas and mixes via thorough testing and analysis. The goal is to find environmentally friendly options while maintaining or enhancing engine performance. A key focus is on the viability of sunflower oil-derived biodiesel as a promising replacement for traditional petroleum-based diesel fuels. Azad et al. [14] explored the sustainability of biodiesel from mustard oil, testing blends from B20 to B50 in a diesel engine according to British standards. Yasin et al. [15] assessed the effects of palm oil methyl ester (PME) blends on diesel engine performance, demonstrating improved combustion and lower emissions without engine modifications. Moom et al. [16] studied fuel blends, including biodiesel-ethanol from waste cooking oil in a single-cylinder engine, noting a 7.26% increase in brake thermal efficiency and a 14.9% rise in brake-specific fuel consumption compared to pure diesel. Sayin Kul and Kahraman [17] analyzed a diesel engine using a biodiesel and bioethanol blend, achieving nearly the same performance as traditional diesel. Şanli [18] examined biodiesel from microalgae in a four-cylinder engine, finding it comparable to conventional diesel, especially at higher speeds, and supporting its use in internal combustion engines.

Several researchers are focusing on the impact of nanoparticles in biodiesel to enhance diesel engine performance. This includes increasing efficiency and environmental compatibility by integrating nanoparticle additives into biodiesel blends. These studies examine the impact of nanoparticles on the efficiency of combustion, emissions, and overall performance of engines. They provide valuable insights for the development of more environmentally friendly diesel technology. Santhanamuthu et al. [19] conducted experiments using iron oxide nanoparticles in diesel fuel mixed with polenta oil. The results showed enhanced fuel efficiency and a 27% brake thermal efficiency (BTE) boost. Venu and Appavu [20] discovered that the presence of zirconium oxide nanoparticles enhances the fuel's calorific value and improves combustion efficiency. Al-Kayiem et al. [21] found that adding iron oxide nanoparticles improved the characteristics of fuel and the performance of engines while si multaneously decreasing emissions in a mixture of diesel and biodiesel. D’Silva et al. [22] observed that adding copper oxide nanoparticles to a biodiesel mix enhanced the engine's performance and decreased emissions. The most effective outcomes were achieved with higher concentrations of the nanoparticles. Uday and Simhadri [23] investigated the impact of titanium dioxide nanoparticles in bio-sesame oil blends. They observed significant enhancements in engine torque and a decrease in fuel consumption. The word by Sajeevan and Sajith [24], which focused on nanoparticles such as cerium oxide, demonstrated that these particles enhance the thermal efficiency of fuel by increasing oxygen levels. Shadidi et al. [25] and Zhang et al. [26] investigated the effects of several nanoparticle additions and indicated possible advantages in engine performance. They also emphasized the need for more studies on these additives' environmental and health implications. John et al. [27] used iron oxide nanoparticles to augment the generation of biodiesel from waste cooking oil. They found notable enhancements in combustion efficiency and thermal performance. Ağbulut et al. [7], Perumaland and Ilangkumaran [28] tested 1000 and 2000 ppm copper oxide (CuO) nanoparticles in diesel fuel in a diesel engine. These nanoparticles improved combustion efficiency, decreased hydrocarbon, carbon monoxide, and nitrogen oxide emissions, and boosted fuel heating value. Kalaimurugan et al. [29] tested a compression-ignition engine using CuO 2 nanoparticles (25, 50, 75, and 100 ppm) in a B20 diesel mix at different loads without altering the engine. All evaluated criteria revealed that CuO 2 improved combustion, engine performance, and emissions. Channappagoudra [30] examined the effects of incorporating copper oxide (CuO) nanoparticles at 25, 50, and 75 ppm concentrations into a DSOME-B20 diesel mix. The results showed that the 75-ppm blend had a notable positive influence on engine performance, efficiency, and emissions, surpassing the effects seen in the other blends. Chatur et al. [31] experimented on a regular diesel engine with adjustable compression ratios. They added copper oxide nano additives to a waste cooking oil methyl ester blend. This resulted in a 6.3% improvement in thermal efficiency and a 4.9% reduction in fuel consumption. Additionally, the experiment decreased CO and HC emissions by 26.1% and 4.3%, respectively. These findings collectively underscore the potential of nanoparticle-enhanced fuels to advance diesel engine efficiency and sustainability.

Governments worldwide are implementing stricter regulations on diesel engines due to their high levels of harmful emissions. Tackling these pollutants is a substantial problem for both engine makers and consumers. Given the circumstances, the development and utilization of sunflower oil biodiesel is imperative to diminish conventional energy use and mitigate environmental contamination. This study addresses a significant method to improve diesel engines' efficiency and decrease emissions using sunflower oil biodiesel infused with CuO nanoparticles. Biodiesel, mainly when produced from sunflower oil, is a sustainable and possibly less detrimental substitute for conventional diesel fuel. It frequently performs poorly compared to diesel. This work examines using copper oxide nanoparticles to address this performance difference. At increased nanoparticle concentrations and full load, thermal efficiency, fuel consumption, and emissions improved significantly. These findings suggest that this strategy might boost biodiesel's profitability and make fuels more sustainable.

This study investigated the performance of various fuels in a Korean-made diesel engine, specifically the KiaBongo2701 model 12, featuring a 2.7-liter capacity, four-stroke design, and water-cooling system. The technical specifications of the engine are detailed in Table 1. The experiment occurred in the engineering workshop at the College of Agricultural Engineering Sciences, University of Baghdad, and utilized direct injection and water-cooling technology. To evaluate how different fuels impacted the engine, seven fuel types were tested:

  • Conventional diesel (D) served as the baseline for comparison.
  • Mixtures of conventional diesel and biodiesel:
  • D85 B15 (85% diesel, 15% biodiesel)
  • D90 B10 (90% diesel, 10% biodiesel)
  • D95 B5 (95% diesel, 5% biodiesel)
  • Biodiesel with copper oxide nanoparticles:
  • D85 B15 PPM 50 (85% diesel, 15% biodiesel with 50 ppm CuO nanoparticles)
  • D85 B15 PPM 75 (85% diesel, 15% biodiesel with 75 ppm CuO nanoparticles)
  • D85 B15 PPM 100 (85% diesel, 15% biodiesel with 100 ppm CuO nanoparticles)

The engine was tested at three speeds (1200, 1400, and 1600 rpm) across three progressive stages and load levels. The primary performance indicators examined were brake-specific fuel consumption and brake thermal efficiency.

Diesel fuel sourced from a local gas station in Salah al-Din/Iraq underwent three stages of preparation for the experiment. Initially, biofuels were produced, followed by blending these biofuels with diesel fuel. In the final stage, nanomaterials were added to the mixture. In the first stage of the experiment, the biofuels were synthesized through a specific transesterification process, leveraging catalytic activity to convert vegetable oil into usable biofuel. Initially, the vegetable oil was placed in a large metal jar and heated to a temperature range of 55℃ to 60℃. Then, potassium hydroxide was added as a catalyst to facilitate the chemical reaction. A mixture of methyl alcohol (methanol) and the catalyst was then introduced to the heated oil, ensuring the oil's temperature was maintained to prevent the alcohol from evaporating. The container was securely sealed to avoid any loss of alcohol through evaporation. Mixing was performed using an electric drill equipped with a fan blade, operating at a low speed for two hours. This facilitated the thorough integration of the oil with the catalyst and alcohol. After mixing, the mixture was left to sit for 24 hours, allowing the glycerin to precipitate. This glycerin was then separated using the traditional method, where it settled at the bottom of the jar and was removed, leaving the biofuel product above.

Table 1. Technical specifications of the diesel engine

1

Type of engine

J2 2701

2

Engine cylinder number

4

3

Cooling system

Water type

4

Piston Displacement

2,694cm3

5

Stroke

95mm

6

Bore

95mm

7

Engine oil type

SAE 10W-30

8

Nominal Output

59.656kW at 4,000rev/min.

9

Maximum Torque

164.75Nm at 2,400rev/min.

In the second stage of the experiment, the process involved mixing biofuels with diesel fuel. The diesel was combined with biofuels in three specific mixing ratios: 85% diesel to 15% biofuel (D85 B15) at a ratio of 8 liters diesel to 1.5 liters biofuel, 90% diesel to 10% biofuel (D90 B10) at a ratio of 9 liters to 1 liter, and 95% diesel to 5% biofuel (D95 B5) at a ratio of 9.5 liters to 0.5 liters. A graduated bowl was utilized to ensure precise measurements of each sample. After combining the components, the mixture was shaken vigorously for one minute to achieve a homogeneous blend.

In the third stage of the experiment, nanomaterial addition, each diesel fuel sample previously mixed with biofuels underwent further processing by incorporating copper oxide. The copper oxide was added in varying concentrations: 100 ppm, 75 ppm, and 50 ppm. These specific amounts were meticulously measured using a sensitive electronic balance to ensure precision. Three samples were prepared for each concentration to facilitate detailed analysis and comparison. The nanomaterial was blended with the fuel through ultrasound application via the GT SONIC apparatus depicted in Figure 1. This process aimed to disperse copper oxide particles uniformly within the fuel, ensuring a thorough mixture and minimizing their accumulation in the container.

The engine's velocity was electronically determined and monitored using a magnetic sensor connected to a speed-measuring apparatus on the experimental engine's control panel. The sensor was positioned close to the pilot wheel, detecting its rotation and converting this magnetic sensing into electronic signals. These signals were then displayed on the speed-measuring device depicted in Figure 1.

The North Refineries Company's Laboratories and Quality Control Department, specifically the Division of Evaluation and Analysis of Products and Materials, analyzed all fuel types utilized in the experiment. The outcomes detailing the properties of the tested fuels are depicted in Table 2.

research paper on copper nanoparticles

Figure 1. Ultrasound and motor speed measuring devices

Table 2. The properties of the tested fuels

Density@ 15ckg/L

0.845

0.831

0.833

0.837

0.832

0.8335

0.8336

API

41.6

38.7

38.3

37.5

38.2

37.9

38.2

Sulphur Content wt%

0.83

0.713

0.685

0.617

0.699

0.6952

0.6991

Cetane Index

53

54

54

52

54

53

54

Gross Calorific Value (kcal/kg)

10.95

10.87

10.86

10.85

10.86

10.867

10.870

Viscosity@40c

2.1

2.60

2.66

2.70

2.65

2.67

2.69

An uncertainty analysis is essential for ensuring the tests' reliability, aiming to achieve the highest confidence level in the obtained results. This involves repeating the tests and ensuring accuracy in data collection. The variability in the performance factors' values is utilized to calculate uncertainty, typically expressed as the relative standard error percentage ( Φ ), as depicted in Eq. (1) [32].

$\emptyset \%=\left(\frac{S}{Y}\right) \times 100$                (1)

Here, S represents the standard error, while Y denotes the average of the gathered data. The standard error is computed following equation [32]:

$s=\frac{\alpha}{\sqrt{k}}$                (2)

Here, α represents the standard deviation, and k represents the repeated measurements of the performance characteristics. The uncertainties associated with the measured parameters are outlined in Table 3.

Table 3. Uncertainties of the measured parameters

Speed (rpm)

1600

±0.09

BSFC (kg/kWh)

0.576

±1.50

BTE %

17.2

±1.42

This section presents and discusses the experimental results of scientific tests conducted on the engine. Seven fuel mixtures were used, including conventional diesel fuel (D100) and various blends of sunflower biodiesel (D95 B15, D85 B15, D90 B10). Copper oxide particles were added to the D85 B15 mixture to enhance its performance and bring it closer to that of pure diesel. Thermal performance, particularly brake efficiency and fuel consumption, was the primary focus of the research. The data are visualized through graphs, and performance charts were meticulously analyzed to understand the performance characteristics of the diesel engine under different conditions, including fuel mixtures and nanoparticle concentrations, across various speeds and loads. The tests were conducted three times to ensure accuracy and minimize errors.

research paper on copper nanoparticles

Figure 2. BTE vs. engine load with different mixtures at 1200rpm

research paper on copper nanoparticles

Figure 3. BTE vs. engine load with different mixtures at 1400rpm

research paper on copper nanoparticles

Figure 4. BTE vs. engine load with different mixtures at 1600rpm

research paper on copper nanoparticles

Figure 5. BTE rated for fuel mixture with engine speeds at load 13500W

Figures 2-4 illustrate the relationships between engine load and Brake Thermal Efficiency (BTE) for different blends. Overall, adding sunflower biodiesel to diesel decreases engine BTE across rotational speeds of 1600rpm, 1400rpm, and 1200rpm. This decline in BTE can be primarily attributed to the lower calorie content of mixtures containing 5%, 10%, and 15% sunflower biodiesel compared to pure diesel.

It is observed from Figure 5 that the BTE values for blends D85B15, D90B10, and D95B15 at speeds of 1200, 1400, and 1600rpm are slightly lower than those of pure diesel fuel. This decrease is attributed to the reduced calorific value and cetane number resulting from adding vegetable sunflower oils compared to pure diesel. Previous research consistently supports the notion that biodiesel blends exhibit lower BTE than pure diesel [33-36].

research paper on copper nanoparticles

Figure 6. BSFC vs. engine load in different mixtures at 1200rpm rotational speed

research paper on copper nanoparticles

Figure 7. BSFC vs. engine load in different mixtures at 1400rpm rotational speed

research paper on copper nanoparticles

Figure 8. BSFC vs. engine load in different mixtures at 1600rpm rotational speed

Figures 6-8 illustrate the relationship between engine loads and brake-specific fuel consumption (BSFC) at speeds of 1200rpm, 1400rpm, and 1600rpm. The graphs reveal a clear trend: as engine load increases, fuel consumption rises. Notably, excess sunflower oil-derived biodiesel leads to increased fuel consumption. This change is influenced by the calorific value of both biodiesel and diesel. Interestingly, true diesel consistently exhibits the lowest BSFC values across all engine loads due to its inherent fuel characteristics. Similar trends were observed in a previous study [37].

research paper on copper nanoparticles

Figure 9. BSFC rated for fuel mixture with engine speeds at load 13500W

Figure 9 illustrates how brake-specific fuel consumption (BSFC) varies as the engine operates at speeds of 1200rpm, 1400rpm, and 1600rpm, with a load of 13500W. All fuel mixtures exhibit a consistent trend, with the lowest BSFC values occurring at 1600rpm and the highest at 1200rpm. Notably, diesel consistently achieves the lowest BSFC levels across the entire speed range. Researchers have observed a similar deviation in BSFC for sunflower biodiesel compared to diesel [27]. This discrepancy is attributed to the lower calorific value of biodiesel. Compromising measures are necessary to achieve the same energy output due to this lower calorific value. As anticipated, the addition of biodiesel to diesel leads to increased fuel consumption, dependent on load and operating conditions.

Mixing biodiesel with CuO nanoparticles increased brake thermal efficiency (BTE), as illustrated in Figures 10-12, in comparison to diesel blended with biofuels (D85B15) across engine speeds of 1200rpm, 1400rpm, and 1600rpm. The addition of copper oxide nanoparticles notably and reasonably enhanced brake thermal efficiency by boosting brake force and increasing heat transfer efficiency. This enhancement can be attributed to the high surface-to-volume ratio of nanoparticles, which promotes efficient fuel oxidation, and the excellent conductivity of copper oxide nanoparticles, which facilitates enhanced heat transfer, thereby contributing to improved brake thermal efficiency. These observations align with the findings reported by Man et al. [35].

research paper on copper nanoparticles

Figure 10. BTE offers different nano dosages compared to elegant diesel and a combination of 15% biodiesel at 1200rpm

research paper on copper nanoparticles

Figure 11. BTE variation with comparison of nanodoses to pure diesel and a mixture of 15% biodiesel at 1400rpm

research paper on copper nanoparticles

Figure 12. Variation in BTE appears at a different nano dose compared to the pure diesel and 15% biodiesel blend at 1600rpm

research paper on copper nanoparticles

Figure 13. BTE rated for fuel mixture with engine speeds at load 13500W

research paper on copper nanoparticles

Figure 14. Change in BSFC appears using varying nano quantities of the diesel-biodiesel mixture at 1200rpm

research paper on copper nanoparticles

Figure 15. Change in BSFC appears using varying nano quantities of the biodiesel mixture at 1400rpm

The brake thermal efficiency (BTE) was calculated while the engine operated under a load capacity of 13,500 watts and variable motor speeds of 1200rpm, 1400rpm, and 1600rpm, as depicted in Figure 13. As the engine speed increases, BTE improves due to more work being done with lower fuel consumption. The highest BTE percentage occurs at 1600rpm, reaching 17.20% for pure diesel. When CuO nanoparticles are added to the fuel mixture, the BTE values are 17.06%, 15.93%, and 14.15% at different nanoparticle concentrations. Notably, the addition of nanoparticles enhances overall engine efficiency. These nanoparticles act as oxidizing agents, leading to better thermal efficiency and an overall increase in engine performance.

Figures 14-16 illustrate the relationship between brake-specific fuel consumption (BSFC) and engine load. The base fuel mixture, known as D85B15 (a blend of 15% biodiesel and 85% pure diesel), was enhanced with nano copper oxide particles at concentrations of 50, 75, and 100 ppm. The addition of nanoparticles led to improved BSFC, especially as nanoparticle concentration increased. Optimal outcomes were achieved when the system operated at maximum capacity. Notably, adding 100 ppm of copper nanooxide resulted in a significant boost in fuel efficiency, allowing the engine to generate more power with less fuel consumption. Overall, including nanoparticles enhanced combustion efficiency compared to fuel combustion without copper nanooxide. Similar findings were also reported by Atmanlı et al. [36].

research paper on copper nanoparticles

Figure 16. Variation in BSFC at different nano doses of diesel and biodiesel blend at 1600rpm

research paper on copper nanoparticles

Figure 17. BSFC rated for fuel mixture with engine speeds at load 13500W

The engine's Brake-Specific Fuel Consumption (BSFC) was evaluated under a 13,500-watt load, with speeds ranging from 1200 to 1600rpm, as depicted in Figure 17. Optimal performance was observed at 1600rpm. Notably, adding 50ppm, 75ppm, and 100ppm of copper nanoparticles significantly improved fuel efficiency, enabling the engine to generate more power while consuming less fuel. Overall, including nanoparticles enhanced combustion efficiency compared to fuel combustion without copper nanoparticles, consistent with findings from prior research [36].

All fuel blends exhibit an increase in CO₂ emissions with an increase in engine speed (RPM), as seen in Figure 18. This is consistent with the general understanding that higher engine speeds result in more complete combustion, thus producing more CO₂. Pure diesel shows the lowest CO₂ emissions across all RPM ranges. At 1600 RPM, it reaches about 0.064%. The D85B20 biodiesel blend shows higher CO₂ emissions than pure diesel and the CuO-added blends. It peaks at around 0.10% at 1600 RPM. Adding CuO nanoparticles to the biodiesel blend (D85 Bi15) seems to increase the CO₂ emissions slightly than the pure diesel. This could be due to enhanced combustion efficiency provided by the catalytic properties of CuO, resulting in more complete combustion and, therefore, higher CO₂ output.

research paper on copper nanoparticles

Figure 18. Variation of CO with engine speeds at load 13500W

research paper on copper nanoparticles

Figure 19. Variation of HC with engine speeds at load 13500W

Figure 19 shows that CuO nanoparticles reduce HC emissions in biofuel compared to diesel. This reduction is due to the homogeneous mixing of fuel blends with air, increased surface/volume ratio aiding complete combustion, and CuO nanoparticles acting as oxidation catalysts [28, 38-40]. At 1600 RPM, D85B15CuO100 emits 11.43% less HC than diesel, similar to D80B20 fuel blends. Including 15% biodiesel (D85 Bi15) leads to higher HC emissions levels than 100% diesel (D100%) at all speeds. This may be due to the distinct combustion properties of biodiesel. Adding CuO nanoparticles to biodiesel blends significantly decreases HC emissions, and larger concentrations of CuO result in even more significant reductions.

research paper on copper nanoparticles

Figure 20. Variation of NO x with engine speeds at load 13500W

research paper on copper nanoparticles

Figure 21. Variation of smoke opacity with engine speeds at load 13500W

Figure 20 depicts the correlation between nitrogen oxide (NO x ) emissions, measured in parts per million (PPM), and engine speed, measured in revolutions per minute (RPM), for various fuel mixtures. NOx emissions positively correlate with engine speed, rising from 1200 RPM to 1600 RPM across all fuel mixes. This phenomenon is anticipated since higher engine speeds often lead to elevated combustion temperatures, which in turn cause an increase in the generation of NOx. At all engine speeds, using 15% biodiesel (D85 Bi15) results in lower NO x emissions than using 100% diesel (D100%). The decrease in NO x emissions may be ascribed to the oxygen content in biodiesel, which facilitates enhanced combustion and thus reduces NO x emissions. Adding CuO nanoparticles to biodiesel blends leads to an additional decrease in NO x emissions [28]. The decline is more noticeable with greater concentrations of CuO. At 1600 RPM, D85B15 CuO100 emits 521 ppm NO x , a 17.3% reduction compared to the 611 ppm from the D85B15 blend.

Figure 21 illustrates that smoke emissions from CuO nanoparticle additive fuel blends are lower than those from diesel. At 1600 RPM, smoke emissions were 39 HSU for D85B15, 34.5 HSU for D85B15 CuO100, and 32 HSU for diesel. The reduction in smoke emissions for D85B15 CuO100 compared to D85B15 is attributed to the high surface-to-volume ratio of CuO nanoparticles, which improve mixture formation, evaporation, and ignition characteristics, leading to a shorter ignition delay. This finding aligns with other research [28, 41-43], showing a 13.04% reduction in smoke emissions for B20CuO100 compared to B20.

In an experimental investigation, the performance of sunflower oil-based biodiesel as an eco-friendly fuel alternative was examined, with a specific focus on its effects on engine efficiency. Blends comprising higher concentrations of sunflower biodiesel demonstrated diminished efficiency, necessitating greater fuel consumption for equivalent power output than pure diesel. Nevertheless, introducing minute copper oxide (CuO) nanoparticles notably improved efficiency. This discovery implies that nanoparticles could bolster the feasibility of sunflower biodiesel for future utilization. In conclusion, the study produced encouraging findings, outlined as follows:

  • Biodiesel blends (D85B15, D90B10, D95B15) show lower thermal efficiency than pure diesel due to their reduced calorific value and cetane number.
  • Higher engine speed leads to lower fuel consumption (BSFC) for all fuels, with the most significant benefit occurring at 1600rpm.
  • Pure diesel consistently has the lowest BSFC compared to sunflower biodiesel blends due to its higher calorific value. This necessitates increased fuel consumption with biodiesel blends despite similar energy output.
  • Adding copper oxide nanoparticles (50-100ppm) to a biodiesel blend (D85B15) significantly improved brake-specific fuel consumption (BSFC), especially at high engine loads.
  • While biodiesel blends, such as D85 Bi15, generally produce lower NOx emissions levels than pure diesel (D100%), adding CuO nanoparticles further decreases these emissions.
  • Utilizing nanoparticles significantly decreased carbon monoxide, indicating a dual advantage of improved performance and less environmental impact.
  • Adding copper oxide nanoparticles (50-100 ppm) significantly enhanced fuel efficiency at all speeds, enabling more power generation with less fuel consumption than fuel without nanoparticles.

Future studies might examine nanoparticle materials like titanium dioxide or iron oxide, which may have different or better advantages than CuO. Studying nanoparticles in biodiesel from additional plant sources or waste oils might broaden its use and enhance blends for certain engine types or operating circumstances. Research into their long-term impacts on engine wear and maintenance and lifetime environmental impact is essential for commercial and industrial use of nanoparticle additives.

CuO

Copper oxide

D85 B15

85% diesel, 15% biodiesel

D85 B15 PPM 100

85% diesel, 15% biodiesel with 100 ppm CuO nanoparticles

D85 B15 PPM 50

85% diesel, 15% biodiesel with 50 ppm CuO nanoparticles

D85 B15 PPM 75

85% diesel, 15% biodiesel with 75 ppm CuO nanoparticles

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research paper on copper nanoparticles

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Micropatterned superhydrophobic meshes coated with low-cost carbon nanoparticles for efficient oil/water separation †.

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* Corresponding authors

a Materials Science and Engineering Program, College of Arts and Sciences, American University of Sharjah, Sharjah 26666, United Arab Emirates E-mail: [email protected]

b Department of Chemical and Biological Engineering, American University of Sharjah, Sharjah, United Arab Emirates

c Department of Physics, American University of Sharjah, Sharjah 26666, United Arab Emirates

d Materials Research Center, American University of Sharjah, Sharjah 26666, United Arab Emirates

Superhydrophobic and superoleophilic meshes have gained considerable attention in oil/water separation in recent years. To fabricate such meshes, surface roughness features can be introduced, and the surface free energy can be lowered, preferably, by utilizing low cost, safe, and readily available materials. Herein, we report a novel approach for fabricating a superhydrophobic copper mesh using low-cost carbon nanoparticles embedded within surface micropatterns. To create the micropatterns, a femtosecond laser was employed. The fabricated mesh exhibited a water contact angle of 168.9° and a roll-off angle of only 5.9°. Additionally, the mesh was highly durable and effectively retained its superhydrophobicity during water jet impact and tape-peeling tests. After 50 cycles of the water jet impact test and 5 cycles of the tape-peeling test, the water contact angle reduced by only 0.3° and 2.3°, respectively. When tested for separating n -hexane/water mixtures, the mesh exhibited a separation efficiency of up to 98%. The separation efficiency remained essentially constant after 10 cycles of n -hexane/water separation. It was observed that the surface micropatterns played a significant role in achieving superhydrophobicity and imparting high durability to the mesh. Meshes lacking these laser-induced micropatterns showed higher wettability, lower durability, and decreased separation performance with repeated use.

Graphical abstract: Micropatterned superhydrophobic meshes coated with low-cost carbon nanoparticles for efficient oil/water separation

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research paper on copper nanoparticles

Micropatterned superhydrophobic meshes coated with low-cost carbon nanoparticles for efficient oil/water separation

M. Qasim, A. Ali and A. Alnaser, RSC Adv. , 2024,  14 , 20426 DOI: 10.1039/D4RA03275F

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  • DOI: 10.1186/s12866-024-03358-6
  • Corpus ID: 270522616

In Vivo and in Vitro activity of colistin-conjugated bimetallic silver-copper oxide nanoparticles against Pandrug-resistant Pseudomonas aeruginosa

  • Asmaa Abdul Hak , H. Zedan , +2 authors Mai M. Zafer
  • Published in BMC Microbiology 17 June 2024
  • Medicine, Chemistry, Environmental Science

90 References

Rifampicin conjugated silver nanoparticles: a new arena for development of antibiofilm potential against methicillin resistant staphylococcus aureus and klebsiella pneumoniae, inhibitory effect of biosynthesized silver nanoparticles from extract of nitzschia palea against curli-mediated biofilm of escherichia coli, cefotaxime incorporated bimetallic silver-selenium nanoparticles: promising antimicrobial synergism, antibiofilm activity, and bacterial membrane leakage reaction mechanism, in vivo activity of silver nanoparticles against pseudomonas aeruginosa infection in galleria mellonella, antibacterial effect of silver nanoparticles on staphylococcus aureus, gentamicin-assisted mycogenic selenium nanoparticles synthesized under gamma irradiation for robust reluctance of resistant urinary tract infection-causing pathogens, gamma rays-assisted bacterial synthesis of bimetallic silver-selenium nanoparticles: powerful antimicrobial, antibiofilm, antioxidant, and photocatalytic activities, microbial synthesized cadmium oxide nanoparticles induce oxidative stress and protein leakage in bacterial cells., antibacterial activities of bacteriagenic silver nanoparticles against nosocomial acinetobacter baumannii., promising antimicrobial and antibiofilm activities of orobanche aegyptiaca extract-mediated bimetallic silver-selenium nanoparticles synthesis: effect of uv-exposure, bacterial membrane leakage reaction mechanism, and kinetic study., related papers.

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    Today, different types of nanoparticles (NPs) are being synthesized and used for medical and agricultural applications. In this study, copper nanoparticles (CuNPs) were synthesized using the aqueous extract of mint (Mentha longifolia L.).For the characterization of CuNPs, UV-visible spectroscopy, scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectrometry were ...

  14. Copper Nanoparticles: Synthetic Strategies, Properties and

    International Journal of Nanoscience. Vol. 13, No. 2 (2014) 1430001 (22 pages) #. . c. World Scienti¯c Publishing Company. DOI: 10.1142/S0219581X14300016. 1430001-1. PDF | Copper nanoparticles ...

  15. Copper and Copper-Based Nanoparticles in Medicine—Perspectives and

    Copper nanoparticles have not received as much attention in biomedical research compared to other metallic nanoparticles such as gold, silver, or platinum. Although there is a steady expansion of the body of scientific literature concerning the biomedical use of copper nanomaterials, it is necessary to overcome significant challenges before ...

  16. PDF Copper Nanoparticles: Synthesis and Characterization, Physiology

    3. Copper and Copper Nanoparticles Copper is one of the most abundant elements found on Earth. It has played an important part in history, given its many properties, like good electrical and thermal conductivity, high corrosion resistance and increased malleability. It has been used in ornaments, weapons and coins since the early 14th century [13].

  17. 7840 PDFs

    Explore the latest full-text research PDFs, articles, conference papers, preprints and more on COPPER NANOPARTICLES. Find methods information, sources, references or conduct a literature review on ...

  18. Structural and optical properties of copper oxide nanoparticles: A

    Abstract In this paper, we study the synthesis dependence of structural, optical and antimicrobial properties for copper oxide nanoparticles on, synthesized using microwave irradiation CuO(M), co-precipitation CuO(P) and hydrothermal CuO(H) protocols. Structural and morphological properties were studied using XRD, SEM, TEM and SAED techniques. XPS studies confirmed the presence of copper ions ...

  19. Copper nanoparticles: Synthesis methods and its light harvesting

    The metallic nanoparticles have a unique optical property known as surface plasmon resonance (SPR) which can be utilized to enhance the light harvesting performance in solar cells. Efficiency of the solar cell strongly depends on various deposition methods, band structure, light absorption and electronic properties of the material being used.

  20. Copper-Based Nanoparticles as Antibacterial Agents

    With the wide application of copper-based nanoparticles antibacterial agents, more and more studies on their preparation and application have been proposed in recent years. In this paper, the synthetic methods, antibacterial principles, and research progress on antibacterial copper-based nanoparticles are reviewed for further research reference.

  21. A Comprehensive Investigation of Methanol Electrooxidation on Copper

    Here, we comprehensively investigated methanol electrooxidation on Cu-based catalysts, allowing us to build the first microfluidic fuel cell (μFC) equipped with a Cu anode and a metal-free cathode that converts energy from methanol. We applied a simple, fast, small-scale, and surfactant-free strategy for synthesizing Cu-based nanoparticles at room temperature in steady state (ST), under ...

  22. Direct formation of copper nanoparticles from atoms at ...

    As copper nanoparticles restructure during the reaction the crystal facet likely changes from Cu(111), and hence affects the selectivity and faradic efficiency for CO 2 reduction products, as ...

  23. Green copper oxide nanoparticles for lead, nickel, and cadmium ...

    Environmentally friendly copper oxide nanoparticles (CuO NPs) were prepared with a green synthesis route without using hazardous chemicals. Hence, the extracts of mint leaves and orange peels were ...

  24. Copper recovery by solvent extraction for nanoparticle ...

    From this purified liquor, nanoparticles containing copper and metallic copper oxides and hydroxides were produced, with an average size of 84 nm, at pH 11, 3 h of hot stirring, volume of 0.015 L of ascorbic acid (0.50 M) and 0.015 L of precursor solution (0.03 M Cu), and temperature (343 K). ... Similar Papers Volume Content Graphics ...

  25. Synthesis, characterization, and study of photocatalytic ...

    The photocatalytic degradation of aniline blue dye by copper oxide nanoparticles (NPs) was analyzed under sunlight. Copper oxide NPs were synthesized by green synthesis using the Santa Maria leaf extract. The phases were identified by X-ray diffraction. The morphology of the material was observed by field-emission scanning electron microscopy, and the elemental information was confirmed by ...

  26. Copper-containing nanoparticles: Mechanism of antimicrobial effect and

    The paper reported copper as an antimicrobial coating as early as 1962 . Also, current research has shown that copper has a much less toxic effect on mammalian cells than ... The addition of copper nanoparticles can significantly enhance the antibacterial activity of the resin-dentin interface, showing higher bond strength and mechanical ...

  27. Enhancing Diesel Engine Performance with Different Concentrations of

    Notably, adding 50ppm, 75ppm, and 100ppm of copper nanoparticles significantly improved fuel efficiency, enabling the engine to generate more power while consuming less fuel. Overall, including nanoparticles enhanced combustion efficiency compared to fuel combustion without copper nanoparticles, consistent with findings from prior research [36].

  28. Micropatterned superhydrophobic meshes coated with low-cost carbon

    d Materials Research Center, ... Herein, we report a novel approach for fabricating a superhydrophobic copper mesh using low-cost carbon nanoparticles embedded within surface micropatterns. To create the micropatterns, a femtosecond laser was employed. The fabricated mesh exhibited a water contact angle of 168.9° and a roll-off angle of only 5 ...

  29. (PDF) The Synthesis of Copper Nanoparticles for Printed Electronic

    When the prepared copper nanoparticles are spread on a polyimide substrate and sintered at 250 °C for 120 min, the resistivity can be as low as 23.5 μΩ·cm, and at 350 °C for 30 min, the ...

  30. In Vivo and in Vitro activity of colistin-conjugated bimetallic silver

    The synthesis of bimetallic Ag-CuO NPs conjugated with colistin presents a promising alternative treatment for combating the challenging P. aeruginosa pathogen in hospital settings. Background Addressing microbial resistance urgently calls for alternative treatment options. This study investigates the impact of a bimetallic formulation containing colistin, silver, and copper oxide on a pandrug ...