Linkages conversion of imine to amide promotes photocatalytic overall water splitting in Two-Dimensional covalent organic frameworks: The role of polarity effects

Imine-based covalent organic frameworks (Im-COFs) have attracted extensive attention in photocatalytic Overall Water Splitting (OWS) due to their facile synthesis and structural stability. However, most of the Im-COFs photocatalysts face the challenge of rapid recombination of photogenerated carriers, leading to low Solar-To-Hydrogen (STH) conversion efficiency. Here, we propose that the oxidation of imine to amide linkages in two-dimensional (2D) Im-COFs would be an effective strategy to enhance the in-plane polarity and thus facilitate the separation of photogenerated carriers. Based on first principles calculations, Two amide-linked 2,4,6-triphenyl-1,3,5-triazine (TST) and Triphenylamine (TA) monolayers (Am-TST, Am-TA) were used as model to compare the photocatalytic performance with the imine-linked ones (Im-TST, Im-TA). Interestingly, both the amide-linked COFs exhibit type-II band alignments, which is absent in the imine-linked ones. Moreover, the Non-Adiabatic Molecular Dynamics (NAMD) simulations reveal the photogenerated carriers’ lifetime Am-TST monolayer (13.41 ns) is 3.45 times longer than that of Im-TST monolayer, indicating the superior ability of amide linkages in suppressing the recombination of photoexcited carriers. In addition, the Am-TST monolayer can also achieve visible-light-driven photocatalytic OWS activity, and the light absorption capability can be further improved by using the Am-TST bilayer. These findings reveal the role of imine-to-amide linkages conversion in promoting the separation of photogenerated carriers, providing a promising strategy for designing amide-based COFs photocatalysts towards OWS.