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 0.10mol/kg and 0.05mol/kg, respectively, an NaOH concentration of 0.40mol/kg, a rotational speed of 600rpm, and liquid flow rates of 500mL/min. Coupled ZnO/SnO₂ photocatalysts were formed by calcining these precursors (Zn(OH)₂/Sn(OH)₄) at 600°C for 10h. 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 120min. The optimum dosage of coupled ZnO/SnO₂ photocatalysts was 0.5g/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 0.50g/L and pH12, as measured after 60min.