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

Zinc oxide and titanium dioxide co-doped reduced graphene (ZnO - TiO2/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 TiO2 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 R2 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 k2 = 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 - TiO2/rGO ternary material exhibited its considerable potential for dye treatment in the industrial effluent.