Engineering intermolecular charge transfer in covalent organic frameworks for photocatalytic hydrogen peroxide generation

Abstract

Intermolecular charge transfer (ICT) plays a crucial role in photocatalysis, particularly in donor–acceptor systems. Thorough investigation of charge transfer within the photocatalyst framework is essential to achieving highly effective, unprecedented photocatalytic performance. In this regard, covalent organic frameworks (COFs) have recently garnered attention because their building blocks (linkers) can be easily modified to influence their structure–activity relationships. Herein, we present a pair of donor–acceptor COFs with distinct acceptor strengths in their constituent moieties and examine how this impacts the photosynthesis of hydrogen peroxide (H₂O₂). TTT–DTDA COF, a donor–acceptor system, exhibited an optimal intermolecular charge-transfer efficiency, demonstrating a maximum H₂O₂ yield of 1265 µmol g⁻¹ h⁻¹ in pure water and in the presence of natural air. Photocatalytic H₂O₂ generation in the biphasic benzyl alcohol/water system reached 21 541 µmol g⁻¹ h⁻¹, exceeding the performance of most reported photocatalysts. Furthermore, we modified the backbone by inserting a phenyl ring into the TTT–DTDA framework to create the extTTT–DTDA COF. We then analysed the impact of this modification on the photocatalytic H₂O₂ generation. Thorough experimental and theoretical investigations were conducted to study intermolecular charge transfer in COFs and explore the potential of metal-free COFs for photocatalytic H₂O₂ generation.