Preparation of coupled ZnO/SnO2 photocatalysts using a rotating packed bed

Zn(OH)2/Sn(OH)4 was prepared by continuously pumping two aqueous solutions of ZnSO4/SnCl4 and NaOH into a rotating packed bed (RPB), where co-precipitation occurred to form Zn(OH)2/Sn(OH)4. Coupled ZnO/SnO2 photocatalysts were formed by calcining these precursors (Zn(OH)2/Sn(OH)4) at 600 °C for 10 h. The photocatalytic activity of coupled ZnO/SnO2 photocatalysts, evaluated using the photocatalytic degradation of methylene blue, was found to be related to the molar ratio of zinc salt to tin salt, the concentrations of the reactants, the concentration of the precipitant, the rotating speed of the RPB, the flow rates of the reactants and precipitant, and the zinc source. The photocatalytic activity of coupled ZnO/SnO2 photocatalysts was highest at ZnSO4 and SnCl4 concentrations of 0.10 mol/kg and 0.05 mol/kg, respectively, an NaOH concentration of 0.40 mol/kg, a rotating speed of 600 rpm, and flow rates of the solutions of ZnSO4/SnCl4 and NaOH of 500 mL/min. The photocatalytic degradation of methylene blue using coupled ZnO/SnO2 photocatalysts obeyed the pseudo-first-order kinetic model.

► Coupled ZnO/SnO2 photocatalysts can be prepared in RPB with co-precipitation.
► Optimum ZnSO4 concentration for preparing coupled photocatalysts is 0.10 mol/kg.
► Optimum SnCl4 concentration for preparing coupled photocatalysts is 0.05 mol/kg.
► Optimum rotating speed for preparing coupled photocatalysts is 600 rpm.
► Optimum liquid flow rates for preparing coupled photocatalysts are 500 mL/min.