Photocatalytic Efficacy of Green Synthesized ZnO/CuO Nanoparticle Using Anacardium occidentale leaf extract for Anthocyanin Degradation in Wastewater

Abstract

The successful synthesis of ZnO/CuO bimetallic nanoparticles was carried out utilizing the phytochemical-rich extract of Anacardium occidentale (cashew) leaves as both the reducing and stabilizing agent. The primary objective of this research work was to evaluate the efficacy of novel nanoparticles as high-performance adsorbents and photocatalysts for the removal of aqueous anthocyanin pigment extracted from Hibiscus sabdariffa calyces, a common natural pigment contaminant in wastewater. Characterization via UV-VIS, X-Ray Diffraction (XRD), and Scanning Electron Microscopy (SEM) confirmed the successful fabrication of the bimetallic system. The material exhibited a face-centered cubic (FCC) crystalline structure with a calculated average size of 39.60 nm. The fusion of CuO within the ZnO matrix resulted in significant band gap engineering, yielding a reduced optical band gap of 2.33 eV. This reduction promotes high photocatalytic activity under visible light irradiation, attributing the enhanced efficiency to synergistic electronic effects within the heterojunction. Batch photodegradation experiments revealed exceptional performance, achieving removal efficiencies exceeding 95% under optimal conditions. The key optimal parameters identified were a solution pH of 8, an initial ACYN concentration of 10 mg/L, an adsorbent dose of 0.4 g, a contact time of 40 minutes, and a reaction temperature of 60oC. Mechanistic modeling provided deep insights into the degradation pathway. The adsorption equilibrium data were best described by the Freundlich isotherm (R2 = 0.9889), confirming strong, favorable, and multilayer adsorption onto the heterogeneous surface. Furthermore, kinetic analysis was definitively governed by the pseudo-second-order model (R2 = 0.9999), indicating that chemisorption, involving valence forces and electron exchange, is the rate-limiting step in the overall degradation process. These findings substantiate the potential of green-synthesized ZnO/CuO nanoparticles as a highly efficient and sustainable adsorbent/photocatalyst for industrial wastewater treatment.