Effects of crystallite structure and interface band alignment on the photocatalytic property of bismuth ferrite/ (N-doped) graphene composites

Bismuth ferrite/graphene (N-doped graphene) photocatalysts are successfully prepared by a facile and effective two-step hydrothermal method. Bismuth ferrite/graphene shows superior photocatalytic activity compared with bismuth ferrite/N-doped graphene and pure BiFeO₃. X-ray diffraction, scanning electron microscopy and energy-dispersive spectroscopy analyses indicate that Bi₂₅FeO₄₀ crystalline phase is obtained with the addition of graphene, while BiFeO₃ is formed under the same hydrothermal conditions in the presence of N-doped graphene. Core-level and valence-band X-ray photoelectron spectroscopy analyses reveal a downward band bending of bismuth ferrite (∼0.5 eV) at the interface of the bismuth ferrite/(N-doped) graphene composites, which facilitates the electron transfer from bismuth ferrite to (N-doped) graphene and suppresses the recombination of photo-generated electron–hole pairs. This downward bending band alignment at the interface supposes to be the main mechanism underlying the enhanced photocatalytic activity of the bismuth ferrite/graphene composites that are currently of great interest in the photocatalysis field. - Highlights: • Bismuth ferrite/(N-doped) graphene composites were prepared by a hydrothermal method. • Bi₂₅FeO₄₀ and BiFeO₃ were obtained with presence of graphene and N-graphene, respectively. • Bi₂₅FeO₄₀/graphene shows superior photocatalytic activity over BiFeO₃ and BiFeO₃/N-graphene. • A downward band bending (∼0.5 eV) of bismuth ferrite exists at the composites interface. • The downward band bending supposes to be the mechanism for the enhanced photocatalytic activity.