Constructing molecular junction in covalent organic frameworks for efficient uranium(VI) photoreduction

Constructing heterojunction photocatalysts is widely regarded as an effective strategy to improve photocatalytic reduction efficiency of U(VI) to U(IV). However, the traditional heterojunctions fabricated by the multiphase hybridization generally present inhomogeneous junction distribution and low connectivity, which is not beneficial for the migration of photogenerated charges. Here, Cu-N cluster as oxidative site and Ti-O cluster as reductive site are covalently coupled to fabricate Cu3-Ti6-COF molecular junction. Importantly, the resulting Cu3-Ti6-COF not only possesses high connectivity but also exhibits well-defined crystalline structure and monophasic periodic distribution, thus effectively boosting the directed transport and separation of charge carriers. As a result, the excellent photocatalytic performance is achieved with the U(VI) removal efficiency of up to 94.8 % without any sacrificial reagents. As far as our knowledge, this is the first work about constructing COF molecular junction for photoreduction U(VI), which may simulate the exploration of novel COFs photocatalysts toward photoinduced radionuclide removal.