Combination of covalent-organic framework and Bi2O2S by covalent bonds to form p-n heterojunction for enhanced photocatalytic CO2 conversion

The objective of current photocatalysis research is to increase the separation efficiency of photogenerated carriers and convert CO2 into useful resources for human beings. In the present study, TpPa-2-COF was successfully grown in situ on Bi2O2S nanosheets by hydrothermal and thermal solvent two-step experimental method, and a typical p-n heterojunction was constructed by covalent-bond between TpPa-2-COF and Bi2O2S, which significantly improved the photocatalytic activity of CO2. When Bi2O2S@TpPa-2-COF-15 heterojunction was illuminated with 300 W xenon lamp for 3 h, the CO yield reached 19.5 μmol·g−1·h−1, while the CH4 yield reached 6.2 μmol·g−1·h−1. Compared with pure TpPa-2-COF and Bi2O2S, the photocatalytic activity of the Bi2O2S@TpPa-2-COF-15 increased 66.8 and 3.96 times, respectively. Meanwhile, the Bi2O2S@TpPa-2-COF-15 composite showed good stability under multiple cycles. Furthermore, the mechanism of Bi2O2S@TpPa-2-COF heterojunction enhanced photocatalytic reduction of CO2 was also proposed. The experimental and characterization findings have shown that the transit of photo-generated electron-hole pairs via TpPa-2-COF to Bi2O2S may be greatly promoted to achieve the effect of electron hole separation under visible-light irradiation.