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

- Bi4O5Br2 with various morphologies was firstly synthesized by emulsion templating.
- The shape and size of Bi4O5Br2 could be regulated by changing the amount of TX-100.
- The layered/hollow structure and Bi-rich strategy result in enhanced photoactivity.
- The direct h+ transfer and O2− mediated pathway for OPP removal is proposed.

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.

161The Bi-rich Bi4O5Br2 with various morphologies of 2D nanosheets, 3D monodisperse layered microspheres and hollow spheres were firstly synthesized via an emulsion-mediated method, and displayed excellent photoactivity for the removal of OPP under visible light.