Magnetic Bi25FeO40-graphene catalyst and its high visible-light photocatalytic performance

Abstract

Magnetic Bi₂₅FeO₄₀-graphene visible-light photocatalysts were prepared by a one-step alkaline hydrothermal method and were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) surface area analysis, Raman spectroscopy, X-ray photoelectron spectra (XPS) and magnetic hysteresis loop measurements. XRD characterization indicated that under identical hydrothermal conditions, perovskite type bismuth ferrite (BiFeO₃) was obtained without graphene addition, while the presence of graphene led to the formation of sillenite type bismuth ferrite (Bi₂₅FeO₄₀). In contrast to BiFeO₃, the Bi₂₅FeO₄₀-graphene composite was superparamagnetic, and could be readily recovered in an external magnetic field. Additionally, Bi₂₅FeO₄₀-graphene photocatalyst exhibited higher catalytic activity for the degradation of methylene blue (MB) under visible-light irradiation than BiFeO₃ and Bi₂₅FeO₄₀. This is due to enhanced MB adsorption and effective suppression of electron-hole recombination via preferential electron transfer from Bi₂₅FeO₄₀ to graphene. Moreover, increasing graphene content enhanced the catalytic activity of the composite catalyst. Accordingly, the photocatalytic MB degradation over Bi₂₅FeO₄₀-(20) graphene followed the Langmuir–Hinshelwood model, indicative of an adsorption controlled reaction mechanism.