Interfacial N-Ti bond modulated COFs-TiO2 type-II heterojunctions with directional charge transfer for efficient photocatalytic uranium reduction

Abstract

Constructing organic–inorganic heterojunctions with high-efficiency interfacial charge transfer is a promising strategy to promote photocatalytic uranium reduction, but it is still a major issue and challenge. In this work, a series of COFs-TiO₂ type-II heterojunctions (Ph-COF-TiO₂, Th-COF-TiO₂, and TTh-COF-TiO₂) are synthesized via in-situ N-Ti bridging method for efficient photoreduction uranium. The optimized TTh-COF-TiO₂-2 exhibits a superior U^VI removal rate of 99.8 % within 40 min visible-light irradiation and achieves a record-breaking reduction rate constant (k = 0.142 min⁻¹, T = 293.15 K). Meanwhile, the TTh-COF-TiO₂ shows good stability under multiple cycles. The theoretical calculation combined with experimental results confirms that the directional migration of photogenerated electrons from TTh-COF to TiO₂ under irradiation through N-Ti “bridge” bonding, which greatly promotes the separation of electron-hole pairs at the interface to foster efficient uranium photoreduction. Our work opens a bright way for design and preparation of novel COFs-TiO₂ type-II heterostructure photocatalysts for solar energy to uranium resources.