Producing nanomaterials, using plant extracts, is emerging as a promising approach to create metal oxide nanoparticles with potential applications in optoelectronics, nanosensors, nanodevices, nanoelectronics, information storage, and catalysis.
Among the various metal oxide nanoparticles, copper nanoparticles are of great interest, because of their low cost of preparation and excellent physical and chemical properties. Copper nanoparticles have wide applications as heat transfer systems, antimicrobials, sensors, and catalysts.
Although neem leaf broth has been used to synthesise silver, gold, and silver-gold alloy nanoparticles, there are no reports on the synthesis of copper nanoparticles using neem leaf broth. Now researchers from the Janki Devi Bajaj Government Girls College Rajasthan, report synthesising copper nanoparticles using neem leaf broth as reducing and capping agent.
The research team collected fresh, healthy neem leaves, cleaned them with deionized water and dried them in an oven. They prepared the neem leaf broth by heating a mixture of small pieces of leaves and deionized water. Then, they filtered the leaf broth through a Whatman filter paper.
The plant biomolecules induce the reduction of copper (Cu2+) ions to copper nanoparticles and also act as a capping and stabilising agents. The team monitored the formation of copper nanoparticles using the absorbance spectra of an ultraviolet-visible spectrophotometer at different stages, during the synthesis process.
The copper nanoparticles were highly crystalline, cubical in shape with an average size of 48 nm and stable for 2 months at 4 °C due to a high zeta potential that makes the nanoparticles repel each other in a dispersion. The biomolecules, present in the nem leaf broth, not only reduce metal ions but also stabilise metal nanoparticles.
The rate of reduction of metal ions by neem leaf broth is much faster than in earlier studies using microorganisms, highlighting the fact that biological nanoparticle synthesis methodologies can achieve a rate of synthesis comparable to those of chemical methods.
This biological technique of synthesising copper nanoparticles is simple and environmentally benign. It is cost-effective and doesn’t involve any harmful, toxic chemicals.
Materials Chemistry and Physics, 213: 44-51 (2018)
Mahadeva swamy H M
STEAMindiaReports 
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