Effect of Optimized Precursor Concentration, Temperature, and Doping on Optical Properties of ZnO Nanoparticles Synthesized via a Green Route Using Bush Tea (Athrixia phylicoides DC.) Leaf Extracts.

Nanoparticles possess several properties, such as antimicrobial, anti-inflammatory, wound healing, catalytic, magnetic, optical, and electronic properties, that have allowed them to be used in different fields. Among them, zinc oxide (ZnO) has received copious consideration due to its technological and medicinal applications. Plant-mediated synthesis of ZnO nanoparticles has provided a cost-effective and eco-friendly method. Therefore, the objective of the study is to assess the effect of the precursor concentration and silver and cerium doping on the optical properties of ZnO nanoparticles synthesized via a green process using bush tea leaf extract as the chelating agent. Zinc nitrate hexahydrate was used as the precursor. Quasi-spherical-shaped ZnO nanoparticles were obtained with an average crystallite size ranging between 24.53 and 63.02 nm. The crystallite size was found to decrease with the increase of precursor concentration at 43.82 nm (0.05 g), 37.25 nm (0.10 g), 26.53 nm (0.50 g), and 24.53 nm (1 g); thereafter, the size increases with an increase in precursor concentration. The optimum precursor concentration was 1 g with the smallest grain size and a high purity level. The increase in annealing temperature induced an increase in the crystallite size of ZnO nanoparticles from 24.53 nm (600 °C) to 34.24 nm (800 °C), however, increasing the level of purity of the nanopowders. The band gap energies were 2.75 and 3.17 eV as calculated using the Tauc plot with variations due to the precursor concentrations. Doping with both silver and cerium increased the band gap of ZnO nanoparticles up to 3.19 eV and the increase in annealing temperature slightly augmented the band gap energy from 3.00 and 3.16 eV, respectively. Hence, doping with Ag and Ce induced the formation of nanorods at higher concentrations. This study successfully demonstrated that the natural plant extract of bush tea can be used in the bioreduction of zinc nitrate hexahydrate to prepare pure ZnO nanoparticles, thus extending the use of this plant to the nano producing industry.