The effect of reaction and annealing temperatures on physicochemical properties of highly stable ZnO nanoparticles synthesized via a green route using Plumeria obtusa L.

Abstract

ZnO NPs are promising options due to their versatile application range in almost every field of science and technology including biomedical sciences. Obtaining stable and structured ZnO NPs is still challenging. The aim of this research is to produce highly stable and structured ZnO NPs through an economic and nontoxic approach. For this purpose, a green route using aqueous leaf extract of Plumeria obtusa L. as a reducing agent at different reaction temperatures (t) and annealing temperatures (T) is implemented. The structural, optical, and thermal properties of ZnO NPs were investigated using various analytical techniques (XRD, SEM, TEM, UV-vis, FTIR, Raman, zeta potential, photoluminescence, and TGA) and validated for their biological applications. The increase in both the temperatures ‘t’ and ‘T’ resulted in an increase in crystallite size from 20 to 42 nm with a wurtzite structure and the change was observed from the flower to sphere shape. The zeta-potential values between 35.1 and 47.8 mV suggested higher stability and the excess amount of oxygen over zinc depicted the occurrence of p-type semiconducting behaviour in ZnO NPs. The optical bandgap was found to decrease from 3.48 to 2.96 eV with an increase in ‘t’ and ‘T’ temperatures. More importantly, the ZnO NPs exhibited promising antimicrobial effects on pathogenic bacteria (Klebsiella pneumoniae) and fungi (Aspergillus niger and Rhizopus stolonifer) with inhibition zones of 19 to 26 mm. This study presents an efficient green synthesis route for ZnO NPs with remarkable physicochemical and antimicrobial properties.