Synthesis of Fe2O3–TiO2/fly-ash-cenosphere composite and its mechanism of photocatalytic oxidation under visible light

Fe2O3–TiO2/fly-ash-cenosphere (FAC) is a composite photocatalyst that was prepared by depositing Fe2O3 onto floating TiO2/FAC. Scanning electron microscopy, X-ray diffraction analysis, UV–Vis diffuse reflectance spectroscopy, N2 absorption–adsorption, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy were used to characterize the properties of the composites. Results showed that the modified methods could maintain the metastable anatase phase of TiO2. The crystalline phase of Fe2O3 was attributed to hematite. The band gap absorption edge of Fe2O3–TiO2/FAC was approximately 650–700 nm, and the absorption of the photocatalysts had an evident redshift. The composite displayed excellent photocatalytic oxidation activity. The degradation ratio of methylene blue was 86.81 % within 60 min under visible light by using Fe2O3–TiO2/FAC/H2O2. This ratio is 2.25 and 1.38 times higher than those of TiO2/FAC and Fe2O3/FAC, respectively. The excellent catalytic ability was attributed to Fe3+ doping combined with Fe2O3–TiO2 heterojunction structure. Finally, a mechanism for the photocatalytic oxidation was proposed based on experimental results by using Fe2O3–TiO2/FAC under visible light.