One-pot microemulsion-mediated synthesis of Bi-rich Bi4O5Br2 with controllable morphologies and excellent visible-light photocatalytic removal of pollutants

The novel Bi-rich Bi4O5Br2 with tunable morphologies of two-dimentional (2D) nanosheets (NSs), three-dimentional (3D) monodisperse layered microspheres (LMs) and hollow spheres (HSs) have been successfully synthesized via an ionic liquid-in-water (IL/W) microemulsion method. Surfactant TX-100 served as the stabilizer of the IL/W microemulsion, and its concentration significantly influenced the morphology and size of the resulting Bi4O5Br2 crystal. Possible formation mechanisms have also been discussed. UV–vis diffuse-reflectance spectra and Density function theory (DFT) calculations indicated that Bi4O5Br2 possessed stronger visible light adsorption and more negative conduction band minimum (CBM), which is beneficial to effectively activate molecular oxygen to produce O2−. The photocatalytic activity of Bi-rich Bi4O5Br2 with varied shapes was investigated and compared with BiOBr for the removal of fungicide o-phenylphenol (OPP) and antibacterial agent norfloxacin (NOR) and tetracycline hydrochloride (TC) under visible light irradiation. The as-prepared Bi4O5Br2 HSs and LMs possess higher photocatalytic efficiency than Bi4O5Br2 and BiOBr NSs, which is attributed to the hollow/layered spherical structures and Bi-rich strategies. The O2− and h+ are identified to be the major photoactive species during the photo-degradation process by scavenger experiments and EPR methods. This study is expected to provide a stepping stone to purposively design and explore other novel hollow structures with controllable morphology and enhanced photocatalytic activity.