Malachite Green Dye Degradation by Adsorption-Assisted Photocatalysis Employing Nano ZnO impregnated on GAC Derived from Unused Coconut Shells (nZnO/CSGAC)

Abstract

Wastewater containing malachite green (MG) dye has the potential to destroy the aquatic ecology and endanger human health. Therefore, an integrated adsorption and photocatalytic degradation technique was established to eliminate its presence in wastewater. In this study, ZnO photocatalytic nanoparticles (nZnO) supported on an adsorbent granular activated carbon (GAC) derived from waste coconut shells (nZnO/CSGAC) composite was used as an integrated photocatalytic adsorbent (IPCA). Various techniques such as SEM with EDX, powder XRD, pHpz analysis, and FTIR spectra were used to characterize these materials. The performance of nZnO/CSGAC was assessed by varying the operating variables such as solution pH, particle size, photocatalyst loading, reaction temperature, contact time and initial dye concentration. Kinetic studies at various initial MG dye concentrations show that the adsorption and photocatalytic degradation kinetics of MG dye obey the pseudo-second-order and the Langmuir–Hinshelwood (L–H) pseudo-first-order kinetic model, respectively. The Freundlich isotherm model fits the MG dye adsorption nicely. The spontaneous and endothermic adsorption of MG dye onto CSGAC and nZnO/CSGAC is demonstrated by the negative values of ΔG°and positive value of ΔH°. The photocatalyst's reusability study asserted that it could be used five times without noticeably losing its catalytic activity or shape.