Controllable synthesis of uniform BiOF nanosheets and their improved photocatalytic activity by an exposed high-energy (002) facet and internal electric field

To date, it still remains a big challenge to develop a new photocatalyst for photocatalysis technologies. Herein, a BiOF photocatalyst with a regular nanosheet shape has been, for the first time, prepared by a simple hydrothermal method. The samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), ultraviolet-visible diffuse reflectance spectroscopy (UV-DRS), electrochemistry impede spectroscopy (EIS) and nitrogen sorption isotherms. Also, ab initio density functional theory (DFT) calculations have been carried out to give insight into the energy band and electronic structures of BiOF. Furthermore, rhodamine B (RhB) is chosen as the representative dye pollutant to evaluate the photocatalytic activity of BiOF. The results show that the uniform BiOF nanosheets grow preferentially along the [110] and [100] orientation, and 75.4% of the (002) facets are exposed. After 60 min of ultraviolet light irradiation (<420 nm), 79.3% of RhB is degraded by BiOF, while only 33.7% of RhB is degraded by the commercial rutile TiO₂. The apparent kinetic rate constant (0.02534 min⁻¹) of BiOF is 3.88 times higher than (0.00652 min⁻¹) rutile TiO₂. Moreover, the calculation results demonstrate that the high-energy (002) facets are more active than the low-energy (020) and (200) facets. For the layered BiOF there is an internal electric field (IEF) perpendicular to the [Bi₂O₂]²⁺ slabs and fluorine anionic slabs, which is favorable for the efficient separation of the photogenerated electrons and holes. It is the synergetic effect of the surface structure and bulk IEF that greatly improves the activity of the BiOF nanosheets. We expect that bulk IEF adjustment is another new strategy to develop new, efficient photocatalysts for layered materials.