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 and rational control over charge separation remains a significant challenge. To address this, we design a series of imine-linked COFs through a unified “Threefold-Approach” that integrates (i) N-centre variation, (ii) enhancement of intramolecular polarity, and (iii) strengthening of intramolecular donor-acceptor (D-A) interactions, to promote efficient charge-separation and improved photocatalytic performance. 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 synthesized materials, one of the COFs (COF-C) featuring a strong intramolecular D-A system, maximizes 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 aqueous system. Furthermore, the practical efficacy of sunlight-driven, bulk-scale synthesized H2O2 was validated through advanced oxidation experiments, including the detoxification of a mustard-gas simulant. Overall, this study establishes a clear correlation between the design strategy of regulating heteroatom density in COF-based photocatalysts and their photocatalytic efficiency towards the synthesis of value-added products.