Vertical Growth of Covalent Organic Frameworks on Poly(triazine imide) Nanosheets: Constructing an Efficient S-Scheme van der Waals Heterojunction for H2O2 Photosynthesis.

Photocatalytic synthesis of H2O2 from oxygen and/or water offers a sustainable alternative to conventional production routes but remains challenging for industrial application due to limited light harvesting and insufficient charge separation. Herein, two van der Waals heterojunctions were constructed by integrating ultrathin poly(triazine imide) (PTI) nanosheets with two structurally distinct covalent organic frameworks (COFs), giving rise to distinct interfacial growth behaviors for TTB-COF and TTT-COF on the PTI surface. Compared with the lateral (face-to-face) stacking in PTI-TTT, the predominantly vertical interfacial contact in PTI-TTB is associated with a more intimate interface, stronger internal electric field, and more abundant accessible active sites. As a result, the optimized PTI-TTB delivers a superior H2O2 production rate of 4402 μmol g-1 h-1 with an apparent quantum yield of 2.61% at 420 nm, which are 23.4 and 4.8 times higher than those of pristine PTI and TTB-COF, respectively. Experimental results and density functional theory (DFT) calculations support that the superior photocatalytic performance is related to an efficient S-scheme charge transfer pathway established at the strongly coupled interface. Mechanistic investigations further indicate that the synergistic coupling of the two-electron oxygen reduction reaction (2e- ORR) and two-electron water oxidation reaction (2e- WOR) accounts for the enhanced H2O2 photosynthesis.