Mesoporous rGO@ZnO composite: Facile synthesis and excellent water treatment performance by pesticide adsorption and catalytic oxidative dye degradation

Abstract

This study describes the facile fabrication, characterization and applications of mesoporous reduced graphene oxide@zinc oxide (rGO@ZnO) composite for the adsorptive removal of the toxic organophosphorus pesticide chlorpyrifos (CPF) and catalytic oxidative degradation of the crystal violet (CV) dye from their respective aqueous solutions. The physical properties of the as-synthesized composite were evaluated by various state of the art techniques like powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infrared (FT-IR) spectroscopy. The adsorption efficacy of the rGO@ZnO composite was evaluated by conducting adsorption isotherm studies, kinetics studies and thermodynamic studies. The effect of solution pH, adsorbent dosage, solvent polarity, contact time and regeneration ability of the adsorbent on the adsorptive removal efficiency were also studied. Excellent removal efficiency of 95.4% was achieved within 70min of contact time with the rGO@ZnO composite and more than 75% of the pesticide was adsorbed at the end of the fifth adsorption cycle. Batch adsorption results fitted well with the Freundlich adsorption isotherm with a high coefficient of determination (R2). The adsorption kinetics was best described by a pseudo-second-order model with an R2 value of 0.93. Thermodynamic parameters corroborate the physisorption nature of the adsorption owing to the spontaneous and exothermic adsorption process. Pesticide contaminated water was used to determine the field applicability of the rGO@ZnO composite. The catalytic efficiency was evaluated by the oxidative dye degradation performance of rGO@ZnO based on the activation of oxone to produce sulfate radicals which degraded the CV dye within 30min. Results indicate that mesoporous rGO@ZnO is an excellent candidate and possesses huge potential in water treatment.