Enhanced photocatalytic activity of TiO2/γ-Fe2O3 by using H2O2 as an electron acceptor under visible light radiation.

Abstract

TiO2 is a photocatalyst widely used for the degradation of organic compounds in aqueous media; however, it presents some difficulties for application on larger scales. The biggest limitations are its bandgap value of 3.2 eV which corresponds to the UV range of the spectrum and its difficult removal from the reaction medium after the reaction. An alternative to enhance the photocatalytic activity of TiO2 consists in design heterojunctions with semiconductors that are active under visible light irradiation. Some reports have described the magnetic property and synthesis procedures based on inexpensive and abundant raw material. In this work, we synthesized photocatalysts based on γ−Fe2O3impregnated with different levels of TiO2. This may contribute to improving the wide application of TiO2 in water, since γ-Fe2O3 has magnetic features that facilitate the removal of the catalyst after the reaction run. The materials were characterized by X-ray diffraction, analysis of adsorption/desorption of N2, reflectance diffuse, and 57Fe Mössbauer spectroscopy. The photocatalytic activity of the materials was tested for removing rhodamine under visible or visible light in the presence of H2O2. From the X-ray diffraction and 57Fe Mössbauer spectroscopy data, it was observed the formation of γ-Fe2O3 phase with small particle. Without visible light, only 45% of RhB was adsorbed, and with the light on, there is no increase in removal after 60 min. However, after adding H2O2, the photocatalytic activity of material was significantly improved, reaching 80% of dye removal. Tests using scavengers of reactive species revealed that − O2 and OH are the main species in this system. Moreover, the H2O2 retards the electron−hole recombination, thus increasing its photocatalytic activity. The ESI-MS analysis revealed that in 15 min of reaction, deethylation (m/z = 415, 388), deamination (m/z = 301 and 279), and rhodamine B severe oxidation products (m/z < 250) were present in solution, and TOC analysis confirms the mineralization of the rhodamine.