Plant leaves extract assisted eco-friendly fabrication of ZnO-SnO2@Chitosan for UV-induced enhanced photodegradation of single and ternary mixtures of Rhodamine B

Abstract

The inadequate handling and uncontrolled discharge of organic dyes into aquatic environments can result in elevated toxicity levels and have adverse effects on both human health and the overall ecosystem. The present work investigated the photodegradation efficiency of the ZnO-SnO2@chitosan nanocomposite (NC) for Rhodamine B (RhB) under ultraviolet (UV) irradiation. The ZnO-SnO2@chitosan nanocomposite (NC) was synthesized via a simple, eco-friendly, and less energy-intensive route, i.e., the co-precipitation method. The synthesized NC was extensively characterized using X-ray diffraction (XRD), Fourier transform-infrared spectroscopy (FTIR), UV–Vis spectroscopy, Brunauer-Emmett-Teller (BET) analysis, field emission scanning electron microscope (FE-SEM), energy dispersive X-ray (EDX) spectroscopy, and UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS). The chitosan-modified nanocomposite (NC) exhibits a moderate surface area of 79 m2/g with a low band gap value of 2.72 eV. The photodegradation process depended on operational parameters, such as pH, irradiation time, temperature, dye concentration, and dosage of the photocatalyst. The degradation data of RhB dye was interpreted through a kinetic model, and the data agreed well with the pseudo-first-order kinetics. The rate constant values deciphered from the kinetic model were found to fall in the range of 0.0281–0.0182 min–1 for 25–100 mg/L of dye concentration, suggesting that the synthesized photocatalysts facilitate the dye mineralization process by reducing the activation energy barrier. The interpretation of the reaction intermediates was accomplished with the help of a GC-MS profile to understand the underlying reaction mechanism. The photodegradation potential of the synthesized NC was explored for individual dyes such as RhB, MB and CV and the mixed dye system (RhB+MB+CV). The NC performs better for individual dyes (RhB, CV, and MB), and the degradation performance diminished slightly in the case of mixed dye solution. The reusability study of the synthesized nanocomposites portrayed the successful utility of the recycled NC up to four times without any significant loss in the degradation capacity, thus making the overall degradation process economical and sustainable. The E–factor (a green chemistry metric) study infers that the NC synthesis process imposes no significant threat to the environment and can be safely used in wastewater treatment.