Copper nanoparticle synthesis has been gaining attention due to its availability. However, factors such as agglomeration and rapid oxidation have made it a difficult research area. Pure copper nanoparticles were prepared in the presence of a chitosan stabilizer through chemical means. The purity of the nanoparticles was authenticated using different characterization techniques, including ultraviolet visible spectroscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and field emission scanning electron microscopy. The antibacterial as well as antifungal activity of the nanoparticles were investigated using several microorganisms of interest, including methicillin-resistant Staphylococcus aureus, Bacillus subtilis, Pseudomonas aeruginosa, Salmonella choleraesuis, and Candida albicans. The effect of a chitosan medium on growth of the microorganism was studied, and this was found to influence growth rate. The size of the copper nanoparticles obtained was in the range of 2–350 nm, depending on the concentration of the chitosan stabilizer.
Copper nanoparticles are very interesting, not only because they show unique nanoscale phenomena like plasmonic absorption and high surface to volume ratio, but also due to useful properties like antibacterial and fungicidal activity. Copper nanoparticles and metal oxide nanoparticles of copper have widespread commercial presence, especially as fungicides. Copper fungicides are extremely effective against certain species of fungi that are common agricultural pathogens. Copper nanoparticles show good to great antimicrobial property against many pathogenic microbes and also used as a commercial antimicrobial agent. Liquid copper dispersions are used as an antimicrobial spray or to prepare antimicrobial surfaces. Other copper nanoparticle applications include conductive ink, chemical sensors, bio sensors etc. Some of these applications may be difficult for you to reproduce at home.
In acidic conditions, copper metal (Cu) in the anode (copper rod attached to the positive wire of the power supply) oxidizes (loses electrons) to form copper ions (Cu+2). These copper ions are released to the solution and will slowly travel towards the cathode (copper rod attached to the negative wire of the power supply). At the cathode, these copper ions will gain electrons and reduces back to copper metal, leaving a metal deposit on the cathode side. This is the main concept behind, electrodeposition.
However, our system is bit different. We have ascorbic acid; a reducing agent (chemical that can donate electrons to induce reduction) in our solution. Also we heat up the solution to spice things up. Now, for the copper ions that are traveling across the solutions, the journey would not be as easy. This is because, copper ions present the ideal opportunity for ascorbic acid molecules to give off their electrons and reduce the copper ions to copper metal. Therefore, in our system copper particles will be formed well before copper ions reach to the cathode.
Ascorbic acid, will not only function as a reducing agent but also as a capping agent. This means that when small copper particles are formed, ascorbic acid molecules will cap or surround the particle making it difficult for similar copper particles to come near to each other. This prevents the uncontrolled growth of the particles to micron sized dimensions.
Related reading: Copper Oxide Nanoparticles Nickel Oxide Nanoparticles