N-heterocycle regulation in robust imidazolate covalent organic frameworks for efficient photocatalytic hydrogen peroxide production

The development of covalent organic frameworks (COFs) with robust linkages is fundamentally important for the photocatalytic production of H₂O₂. In this work, a series of isostructural COFs with robust imidazole linkage were synthesized as photocatalysts for H₂O₂ production via the precise N-substituted microenvironment regulation (benzene, pyridine, pyrimidine, and triazine). The corresponding frameworks enable water and dissolved oxygen to reach the catalytic sites easily via planar skeletons and regulation of nitrogen-atom numbers. Additionally, the N-adjustment of heterocycle units in these COFs could significantly regulate the electronic band structures, light-harvesting capacity, and hydrophilic properties. The experimental investigation demonstrated that the photocatalytic process of COFs was composed of a dominant and indirect two-electron (2e⁻) oxygen reduction reaction (ORR). Notably, compared to H-COF (benzene), P-COF (pyridine), and M-COF (pyrimidine), T-COF with triazine unit exhibited the highest H₂O₂ production rate of 42,180 μmol·g⁻¹·h⁻¹ due to its wider visible light absorption and higher separation efficiency of photogenerated electron-hole pairs. Theoretical investigations confirmed that N-heterocycle units in COFs could precisely modulate the energy barrier related to the formation of *OOH and *O₂. This study is expected to provide a new way for rationally designing imidazole-linked COFs as promising photocatalysts for efficiently photocatalytic H₂O₂ generation.