Fabrication of hollow-catalytic microspheres (HCMs) with double-sided materials and their application on wastewater treatment

The hollow catalytic microspheres (HCMs) with double-sided structures were fabricated, in which the external and internal sides are TiO2–Ag and MgO–ZnO respectively. For a hollow catalytic microsphere (HCM), the visible-light-driven (VLD) photocatalysts (TiO2–Ag) can receive light, while the non-light-driven catalysts (MgO–ZnO) are in shadow. The characterizations demonstrated that metal oxides were loaded on the biochar microspheres and the hollow microspheres were fabricated. Moreover, the adsorption and photocatalytic behaviors of HCMs for methylene blue (MB) were explored. The results indicate that the removal rate of MB (100 mL, 25 mg/L) and chemical oxygen demand (COD) by HCMs (0.04 g) were 96.9% and 92.9% under Xe-lamp light (150 W, 8 h) irradiation, respectively. Besides, the HCMs exhibited high catalytic efficiency and stable photocatalytic capability after being utilized for five times. The possible degradation pathway of MB by HCMs was proposed.