Abstract: Photocatalytic CO₂ reduction provides a promising strategy for the alleviation of greenhouse effect and energy shortage problem. Metal single atom modification is an effective method to improve the CO₂ reduction performance of covalent organic framework (COF) photocatalysts, while the intrinsic mechanism is not revealed in depth. Herein, a Pt-COF photocatalytic system was constructed by embedding Pt single atom in TFPT-TMT-COF (TFPT: 1,3,5-tris(4-formylphenyl)-triazine, TMT: 2,4,6-trimethyl-1,3,5-triazine). Based on density functional theory (DFT) calculation, the geometric structure and electronic property of Pt-COF were investigated, and the CO₂ adsorption and reduction reaction process on Pt-COF were simulated. The results show that the Pt atom can be steadily anchored in COF via the formation of Pt-N and Pt-C bonds. Moreover, there is strong electronic interaction between Pt and COF. The incorporation of Pt atom benefits the CO₂ reduction activity of COF from multiple aspects: (ⅰ) reducing the band gap and improving light absorption; (ⅱ) enhancing CO₂ adsorption and activating the CO₂ molecule; (ⅲ) decreasing the energy barrier in the hydrogenation step of CO₂→COOH, thus facilitating CO₂ conversion to CO; (ⅳ) inhibiting the hydrogenation of CO, thereby increasing the selectivity of CO. This work brings a novel insight into the excellent CO₂ reduction performance of Pt modified COF, and provides useful references for the design of single atom photocatalysts.

Key words: Photocatalysis, Carbon dioxide reduction, Covalent organic framework, Pt single atom, Theoretical calculation