Removal of methylene blue dye by green synthesized NiO/ZnO nanocomposites

Abstract

In this study, Justicia adhatoda leaf extract was used as both a reducing agent and a capping agent in a straightforward, environmentally friendly, and low-cost approach for the green synthesis of NiO/ZnO nanocomposites (NCs). The synthesized NiO/ZnO NCs were characterized by XRD, Rietveld refinement, UV–visible, FTIR, and SEM. The XRD and Rietveld Refinement studies have revealed the presence of two phases corresponding to hexagonal wurtzite ZnO and cubic NiO. The optical energy band gap (EGap) of prepared NiO/ZnO was 3.27 eV. SEM analysis revealed that the NiO-ZnO NCs have a cauliflower-like surface morphology with an average size of 89 nm. Under sunlight and UV illumination, the ability of NiO/ZnO NCs was evaluated to decompose methylene blue. NiO/ZnO NCs are very effective for methylene blue dye degradation under UV light following pseudo-first-order reaction kinetics, with a rate constant of 0.04625 min−1. Further, the scavenger study, hot filtration test, and reusability assessment were conducted to evaluate the catalyst's applicability and performance.