An unsaturated bond strategy in covalent organic frameworks for enhanced simultaneous photocatalytic uranium recovery and hydrogen peroxide production

Abstract

The photocatalytic uranium extraction process in the presence of oxygen is often accompanied by the production of hydrogen peroxide (H₂O₂). However, simultaneous visible light-driven efficient uranium extraction and enhanced H₂O₂ photosynthesis remain challenging. In this work, an unsaturated bond (UB) regulation strategy was utilized in COFs to modulate uranium extraction and H₂O₂ production. Compared with the vinyl group (–CC–), the azo group (–NN–) anchored to the skeleton (Azo COF) can promote charge separation/transport in COFs. Under visible light and in open air, Azo COF could achieve a uranium extraction efficiency of 95.0% and an enhanced simultaneous H₂O₂ production of 77.5 μmol L⁻¹ h⁻¹ without sacrificial agents in uranyl aqueous solution. Furthermore, Azo COF also showed 90.9% uranium extraction efficiency in simulated uranium containing wastewater and showed excellent UO₂²⁺ selectivity and recycling performance. The presence of the azo group promoted H₂O₂ photosynthesis through one-step oxygen reduction and 4 e⁻ water oxidation reactions. The experimental and theoretical calculation results revealed that the introduction of the azo group could effectively improve the O₂ adsorption and regulate the charge distribution, facilitating H₂O₂ production and the conversion of soluble uranium into insoluble metastudtite ((UO₂)O₂·2H₂O). This work provides insight into the UB photocatalyst design strategy for simultaneous uranium recovery and high value-added chemicals.