Statistical screening and optimization of photocatalytic degradation of methylene blue by ZnO–TiO2/rGO nanocomposite

Abstract

Zinc oxide and titanium dioxide co-doped reduced graphene (ZnO − TiO 2 /rGO) was synthesized via two-step solvothermal method for effective treatment of methylene blue (MB) solution. The characterization of synthesized materials has shown the nanoscale sizing of the TiO 2 particles of 5.57 nm and low band-gap energies of 2.7 eV. The process variables were screened by Plackett-Burman model and then optimized via response surface methodology, using Box-Behnken model. The efficiency of MB treatment reached 0.994 under the optimal condition of 63.5 min of irradiation, 25.25 mg photocatalyst, and 20 mg/L MB, with a high adjusted R 2 of 0.9889. Finally, the kinetics studies proved that the MB adsorption of the synthesized materials follows the pseudo-second-order model with the highest rate constant of k 2 = 0.0185 g/mg min. The MB photocatalytic degradation process has the highest rate constant of k = 0.0707 min −1 following the pseudo-first-order model. With the simple synthesis procedure and promising degradation efficiency, the ZnO − TiO 2 /rGO ternary material exhibited its considerable potential for dye treatment in the industrial effluent. A proposed mechanism of MB photocatalytic degradation by ZnO − TiO 2 /rGO nanocomposite.