Design of a direct Z-scheme photocatalyst: Preparation and characterization of Bi₂O₃/g-C₃N₄ with high visible light activity

Graphical abstract: - Highlights: • A direct Z-scheme photocatalyst Bi₂O₃/g-C₃N₄ was prepared. • The photocatalyst exhibited a much higher activity than pure g-C₃N₄. • Bi₂O₃/g-C₃N₄ as a typical Z-scheme photocatalyst was proved. • e⁻ in the CB of Bi₂O₃ and h⁺ in the VB of g-C₃N₄ are quickly combined. • e⁻ in the CB of g-C₃N₄ and h⁺ in the VB of Bi₂O₃ participate in redox reaction. - Abstract: A direct Z-scheme photocatalyst Bi₂O₃/g-C₃N₄ was prepared by ball milling and heat treatment methods. The photocatalyst was characterized by X-ray powder diffraction (XRD), UV–vis diffuse reflection spectroscopy (DRS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) surface areas, photoluminescence technique (PL), and electron spin resonance (ESR) technology. The photocatalytic activity was evaluated by degradation of methylene blue (MB) and rhodamine B (RhB). The results showed that Bi₂O₃/g-C₃N₄ exhibited a much higher photocatalytic activity than pure g-C₃N₄ under visible light illumination. The rate constants of MB and RhB degradation for Bi₂O₃(1.0 wt.%)/g-C₃N₄ are about 3.4 and 5 times that of pure g-C₃N₄, respectively. The migration of photogenerated carriers adopts a Z-scheme mechanism. The photoexcited electrons in the CB of Bi₂O₃ and photogenerated holes in the VB of g-C₃N₄ are quickly combined, so the photoexcited electrons in the CB of g-C₃N₄ and holes in the VB of Bi₂O₃ participate in reduction and oxidation reactions, respectively. ·O₂⁻, ·OH and h⁺ are the major reactive species for the Bi₂O₃/g-C₃N₄ photocatalytic system