Preparation and characterization of Fe2O3/Bi2WO6 composite and photocatalytic degradation mechanism of microcystin-LR

The long-standing popularity of semiconductor photocatalysis, due to its great potential in a variety of applications, has resulted in the creation of numerous semiconductor photocatalysts, and it stimulated the development of various characterization methods. In this study, Fe2O3/Bi2WO6 composite with a flower-like microsphere and hierarchical structure was synthesized with the facile hydrothermal-impregnation method without any surfactants. X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet–visible (UV–Vis) diffuse reflectance spectroscopy, and photoluminescence spectroscopy were used to characterize the structures of the samples. The specific surface area was estimated with the Brunauer-Emmett-Teller (BET) method, and pore size distribution was determined using the Barrett-Joyner-Halenda (BJH) method. The synthesized Fe2O3/Bi2WO6 composite had an average diameter of approximately 4 nm, with smaller specific surface area and larger pore diameter than those of pristine Bi2WO6. The results of XRD and SEM analyses confirmed that the composite was composed of Fe2O3 and Bi2WO6. The absorption edge of Bi2WO6 was at a wavelength of 460 nm. By contrast, the absorption edge of Fe2O3/Bi2WO6 to visible light was redshifted to 520 nm, with narrower bandgap width and stronger visible light response. It was also found that the main active substances in the degradation of microcystin-LR (MC-LR) were hydroxyl radicals (·OH) and electron holes (h+). Consequently, the results further showed that the heterojunction between Fe2O3 and Bi2WO6 can improve the charge transfer rate and effectively separate the photoinduced electrons and holes. Compared with Bi2WO6, Fe2O3/Bi2WO6 had no significant difference in the adsorption capacity of MC-LR and had more efficient photocatalytic degradation activity of MC-LR. The degradation rates of MC-LR by Fe2O3/Bi2WO6 and Bi2WO6 reached 80% and 56%, respectively. The degradation efficiency of MC-LR was affected by the initial pH value, initial Fe2O3/Bi2WO6 concentration, and initial MC-LR concentration.