A threefold approach to boost photo-harvesting efficiency in covalent organic frameworks via strategic N-centre regulation

Abstract

The strategic development of metal-free photocatalysts with efficient charge-carrier separation and transfer is crucial for high-performance solar-energy conversion. In this regard, covalent-organic frameworks (COFs) have emerged as promising candidates; however, achieving precise, rational control over excitonic separation remains a challenge often limited to incremental material optimization. To address this, we report a structurally distinct design strategy, achieved via a unified “Threefold-Approach” that systematically regulates the density and positional distribution of N heteroatoms across a series of imine-linked COFs. This precise regulation strategy systematically enhances the intramolecular polarity and strengthens donor–acceptor (D–A) interaction, fundamentally advancing beyond conventional donor–acceptor optimisation by establishing a clear correlation between heteroatom positioning and charge-carrier dynamics. To validate the influence of this design strategy on photoefficiency, we conducted photocatalytic H₂O₂ synthesis, given its growing significance for zero-carbon electricity generation in one-component fuel cells. Among the synthesised materials, one of the COFs (COF-C) featuring a strong intramolecular D–A system, maximises free charge generation and achieves an unprecedented H₂O₂ production rate of 9183 µmol h⁻¹ g⁻¹, along with a solar-to-chemical conversion efficiency of 1.3% in an oxygen-saturated aqueous system, without the use of any sacrificial agent. Furthermore, the practical efficacy of sunlight-driven, bulk-scale synthesised H₂O₂ was validated through advanced oxidation experiments, including the detoxification of a mustard-gas simulant. Overall, this study establishes a definitive architectural blueprint for the rational design of heteroatom-regulated COF photocatalysts, providing a new pathway toward highly efficient solar-driven synthesis and utilisation of value-added chemicals.