Photocatalysis of dichlorvos using graphene oxide-TiO2 nanocomposite under visible irradiation: process optimization using response surface methodology

Abstract

Graphene oxide-TiO2 nanocomposite (GOT) was used for degradation and mineralization of dichlorvos, an organophosphorus pesticide, from aqueous solution under visible irradiation. The nanocomposite was characterized by scanning electron microscopy, transmission electron microscopy, UV-DRS, Fourier-transform infrared spectroscopy, Raman spectroscopy, and x-ray photoelectron spectroscopy. Anatase phase TiO2 nanoparticles (10–20 nm in diameter) were present in the nanocomposite. The nanoparticles were uniformly distributed on reduced GO sheets. A three-factor face-centered central composite design with response surface methodology was used for modeling and optimization of various variables that may potentially affect photodegradation, i.e. pH, catalyst loading, and initial dichlorvos concentration. A quadratic model was built to predict degradation, mineralization efficiency, and reaction rate constant. The experimental and predicted values depicted a good correlation and the utility of the models was confirmed by the high F-values observed for the degradation and mineralization models. High coefficient of determination (R 2) was obtained for the degradation (R 2 = 0.95) and mineralization (R 2 = 0.93) models. Pareto analysis was carried out to determine the effect of each variable on photocatalytic degradation and mineralization. The predicted results suggested that the optimum conditions for obtaining maximum degradation (69%) and mineralization (64%) were: initial dichlorvos concentration of 0.5 mg l−1 with a catalyst dose of 110 mg l−1 at pH 6.5. The main effect plots also suggested a significant influence of the variables used in the photocatalysis of dichlorvos by GOT.