Characterisation of zinc oxide nanoparticles-herbal synthesised coated with Ocimum tenuiflorum

Various applications of nanoparticles stimulates the need for synthesising them. But, the conventional methods are usually hazardous and energy consuming. This lead to focus on "green synthesis "of nano particles that was a efficient and eco friendly approach. Biological reduction agents are being explored worldwide to minimise the effects of toxic chemicals used in nanoparticles fabrication. The present study states a green approach for the synthesis of zinc oxide nano particles via complex formation with plant extracts of ocimum tenuiflorum (black Tulasi). Leaf extract was used as the biological reduction agent for synthesising zinc oxide nano particles from zinc sulphate. The resultant nanopowder was characterised using various analytical techniques, such as X-ray diffraction, SEM, XRF, particle size analyser, The size range of nano particles obtained upon synthesis at optimum conditions was 50-63 nm as reported by TEM. X-ray diffraction studies confirmed the crystalline nature of the nanoparticles indicating particle size within the range provided by electron microscopy data. Due to the large rate of toxic chemicals and extreme environment employed in the physical and chemical production of these NPs, green methods employing the use of plants, fungus, bacteria and algae have been adopted. This review is a comprehensive study of the synthesis and characterisation methods used for the green synthesis of ZnO NPs using different biological sources.