Photocatalytic decolorization of methylene blue in aqueous solutions using coupled ZnO/SnO2 photocatalysts

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 with ZnSO4·7H2O and SnCl4·5H2O concentrations of 0.10 mol/kg and 0.05 mol/kg, respectively, an NaOH concentration of 0.40 mol/kg, a rotational speed of 600 rpm, and liquid flow rates of 500 mL/min. Coupled ZnO/SnO2 photocatalysts were formed by calcining these precursors (Zn(OH)2/Sn(OH)4) at 600 °C for 10 h. This investigation evaluates the effectiveness of coupled ZnO/SnO2 photocatalysts in the decolorization of methylene blue in aqueous solutions. The effects of addition of oxygen, ZnO/SnO2 dosage, and pH on the decolorization efficiency of methylene blue were studied experimentally. Adding oxygen increased the decolorization efficiency of methylene blue, as measured after 120 min. The optimum dosage of coupled ZnO/SnO2 photocatalysts was 0.5 g/L for the decolorization of methylene blue. Additionally, a higher pH was associated with a higher decolorization efficiency of methylene blue. With the addition of oxygen, the decolorization efficiency of methylene blue was around 96% at a ZnO/SnO2 dosage of 0.50 g/L and pH 12, as measured after 60 min.