Optimising a green approach to the synthesis of silver nanoparticles

Abstract

Although nanochemistry is viewed as a relatively new frontier of knowledge in the science and technology world, our own evolution and existence has its basis in nanostructures and processes. Apart from serving as a point of reference for the chemical, physical and functional nature of nanoparticles, biological material can be utilised for nanoparticle production. Biological methods for nanoparticle synthesis can be simpler, cheaper, and an environmentally friendlier alternative to chemical and physical synthesis. Recently, research on the biosynthetic routes using biomolecules present in plant water extracts is gaining impetus. Synthesis of silver metal nanoparticles was carried out using quercetin and botanical extracts; particularly olive leaf extract and caper leaf extract to serve as both the reducing and stabilising agents. Only quercetin and olive leaf extract were found to produce silver nanoparticles. Experimental conditions including pH, time, temperature, reducing/stabilising agent and final concentration of quercetin or extract and sequence of the addition of reagents were varied to manipulate the size and properties of Ag nanoparticles. The produced metal nanoparticles were characterised through Dynamic Light Scattering. UV-vis analysis detected Ag nanoparticles with an absorption wavelength in the 440 nm region and 535 nm wavelength for Au nanoparticles. Ag nanoparticles were produced employing olive leaf extract as the reducing and stabilising agent. The particle sizes were measured using Dynamic Light Scattering. The dispersions generally contained particles in two size distributions. The smaller particles had mean diameters in the order of 2 - 10 nm whilst the larger particles had mean diameters of the order of 80 nm. Particle sizes did not vary significantly with time but the fraction of larger particles did grow at the expense of the smaller ones. By varying one parameter at a time, it was found that the olive leaf extract method to produce the particles showed no significant change in particle size by varying the silver ions or olive leaf extract by ± 20% or the temperature by ± 7 °C. The optimum pH was found to be pH 10, with the smallest average Ag nanoparticle diameter detected being 2.5 nm. In this study, the synthesis of copper and gold nanoparticles was also investigated using olive leaf extract. Synthesis of Cu nanoparticles was unsuccessful but gold nanoparticles can be produced using olive leaf extract at pH 10.