Flux synthesis of Bi2MO4Cl (M = Gd and Nd) nanosheets for high-efficiency photocatalytic oxygen evolution under visible light

The Bi2MO4Cl (M = Gd and Nd) nanosheets were prepared by a molten salt flux method for the first time. The resulted Bi2GdO4Cl (F-BG) nanosheets showed the highest photocatalytic activity for oxygen (O2) evolution and trypan blue (TB) degradation than Bi2NdO4Cl (F-BN), Bi2GdO4Cl (S-BG) and Bi2NdO4Cl (S-BN) synthesized by a solid-state method. The F-BG nanosheets showed the larger specific surface areas and abundant pores, which could provide more reactive sites. The photoelectrochemical and photoluminescence (PL) results revealed that F-BG sample had the excellent separation and transfer rates of photogenerated charge carriers, leading to the highly photocatalytic performance for both O2 evolution and TB degradation. The UV–Vis diffuse reflectance spectra (DRS) showed all samples had the visible-light-responsive characteristic. The radical trapping experiment revealed hole (h+) played a major role, while superoxide radical (\(\cdot {\text{O}}_{{2}}^{ - }\)) contributed a little to photocatalytic degradation process. Thus, a possible photocatalytic mechanism was proposed based on the radical trapping experiment. This work shows us a useful insight into the preparation of highly active bismuth-based oxyhalide nanosheets photocatalysts by a molten salt synthesis through surface modification and morphology control and provides the possibility of water splitting under visible light.