Preparation and characterization of Fe_(2)O_(3)/Bi_(2)WO_(6)composite and photocatalytic degradation mechanism of microcystin-LR

摘要

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,Fe_(2)O_(3)/Bi_(2)WO_(6)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),ultravioletevisible(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 Fe_(2)O_(3)/Bi_(2)WO_(6)composite had an average diameter of approximately 4 nm,with smaller specific surface area and larger pore diameter than those of pristine Bi_(2)WO_(6).The results of XRD and SEM analyses confirmed that the composite was composed of Fe_(2)O_(3)and Bi_(2)WO_(6).The absorption edge of Bi_(2)WO_(6)was at a wavelength of 460 nm.By contrast,the absorption edge of Fe_(2)O_(3)/Bi_(2)WO_(6)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 Fe_(2)O_(3)and Bi_(2)WO_(6)can improve the charge transfer rate and effectively separate the photoinduced electrons and holes.Compared with Bi_(2)WO_(6),Fe_(2)O_(3)/Bi_(2)WO_(6)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 Fe_(2)O_(3)/Bi_(2)WO_(6)and Bi_(2)WO_(6)reached 80%and 56%,respectively.The degradation efficiency of MC-LR was affected by the initial pH value,initial Fe_(2)O_(3)/Bi_(2)WO_(6)concentration,and initial MC-LR concentration.