Visible-light-driven 2D/2D Bismuth oxyhalides/covalent organic framework heterojunctions for synchronous photocatalytic U(VI) reduction and bisphenol A degradation

Bismuth oxyhalides (BiOX, X = Cl, Br, I) with two-dimensional (2D) layered structures have strong photocatalytic properties. 2D covalent organic frameworks (COFs) are metal-free photocatalysts with extended π-conjugated layer structure, high specific surface area and chemical stabilities, and have extraordinary application potential. Here, the novel double layer of BiOX@TpPa-1 composites were constructed to integrate the advantages of narrow bandgap and efficient separation of photogenerated carriers. After TpPa-1 modification, the bandgap of BiOX can be adjusted from 2 to 3 eV to 1.5–1.84 eV due to electronic rich π-conjugated system of TpPa-1, which remarkably increased the utilization of solar energy. The optimal doping ratio of BiOX@TpPa-1–5% manifested the highest catalytic activity for simultaneous U(VI) reduction (48.6%~81.2%) and bisphenol A (BPA) (43.4%~57.6%) degradation under visible light, which can be attributed to the existence of oxygen vacancies and the efficient production of electrons and •O 2 − radicals. After deducting the dark adsorption reaction, compared with the single BiOX (10%~30%), the removal efficiencies of BiOX@TpPa-1 (42.6%~53.6%) for photoreduction U(VI) were significantly improved, especially for BiOCl@TpPa-1. The enhanced photocatalytic performance of BiOX@TpPa-1 was systematically identified by photoelectrochemical characterizations, such as PL, Mott-Schottky plots, EIS, I - t . Furthermore, the efficiency of BiOX@TpPa-1 for the photocatalytic U(VI) reduction and BPA degradation remained relatively stable after recycling, exhibiting the good reusability and stability. Therefore, this study provided the construction of inorganic-organic composite photocatalysts with excellent performance and stability for the extensive application prospect in the field of environmental purification. • Simultaneous photocatalytic reduction of U(VI) and BPA degradation on BiOX@TpPa-1. • TpPa-1 broaden light absorption range and narrow bandgap of BiOX@TpPa-1. • The extended π-conjugated system improved the photocatalytic performance. • Type-II heterojunction is formed at the interface between BiOX and TpPa-1. • BiOX@TpPa-1exhibited the high removal efficiency and reusability.