Tuning the interlayer stacking of a vinylene-linked covalent organic framework for enhancing sacrificial agent-free hydrogen peroxide photoproduction

Abstract

The layer-stacking mode of a two-dimensional (2D) material plays a dominant role either in its topology or properties, but remains challenging to control. Herein, we developed alkali-metal ion-regulating synthetic control on the stacking structure of a vinylene-linked covalent triazine framework (termed sp²c-CTF) for improving hydrogen peroxide (H₂O₂) photoproduction. Upon the catalysis of EtONa in Knoevenagel polycondensation, a typical eclipsed stacking mode (sp²c-CTF-4@AA) was built, while a staggered one (sp²c-CTF-4@AB) was constructed using LiOH. The AB stacking might be induced by the Li⁺ promoted Lewis acid–base interactions with the nitrogen atoms of s-triazine units which would endow the s-triazine units with a charged state and enlarge the total crystal stacking energy. Specifically, the shift in the stacking mode speeds up electron transfer within each layer and along interlayers, thereby improving the photocatalytic activity. sp²c-CTF-4@AB features superior activity over the eclipsed stacking counterpart (sp²c-CTF-4@AA) in sacrificial agent-free H₂O₂ generation, comparable to the state-of-the-art COF photocatalysts, which has not been demonstrated in this field before. This work demonstrates that regulating the interlayer-stacking mode of COFs can endow them with high photocatalytic activity, further inspiring the development of heterogeneous catalysis.