Regulation of Charge Carrier Transportation in D-π-A Type Covalent Organic Frameworks for Promoting Photocatalytic H2O2 Production

Abstract

Covalent Organic Frameworks (COFs) with diverse conjugated structures are extensively utilized as promising photocatalyts for hydrogen peroxide (H2O2) production. However, the current applications are constrained by the rapid recombination of photogenerated carriers and the slow reaction kinetics. To address these issues, in this study, we design and prepare four COFs photocatalysts with a distinct Donor-π-Acceptor (D-π-A) structure to regulate the photogenerated charge carrier transportation. Significantly, the Tf-TAPT-COF containing triazine units shows the most elevated rate of H2O2 evolution. This is primarily attributed to the electron-withdrawing capacity of N centers in COFs following the order: triazine > pyrimidine > pyridine > benzene, leading to the enhanced transportation of electrons along the π-bridge from the donor to the acceptor. In the absence of sacrificial agent, the photocatalytic H2O2 production of Tf-TAPT-COF can reach 2700 μmol g-1 h-1, surpassing most of the reported similar photocatalysts. A series of experimental characterizations and theoretical calculations indicate that increasing the number of N atoms in the N-heterocycles of COFs can enhance the transportation of photogenerated carriers along the π-bridge. It enables COFs to facilitate the oxygen reduction reaction (ORR) via both π-bridges and acceptor dual sites, and the water oxidation reaction (WOR) occurs on the donor, thereby significantly improving their activity in photocatalytic H2O2 production. This research provides a promising approach for the regulation of charge carrier transportation in COFs and the performance improvement in full photosynthesis of H2O2 based on COFs.