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 remains challenging. In this work, an unsaturated bonds (UBs) regulation strategy was utilized in COFs to modulate uranium extraction and H2O2 production. Compared with vinyl group (-C=C-), azo group (-N=N-) anchored to the skeleton (Azo COF) can promote charge separation/transport in COFs. Under visible light and open air, Azo COF could achieve uranium extraction efficiency of 95.0% and 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 had excellent UO22+ selectivity and recycling performance. The presence of azo group promoted the H2O2 photosynthesis through one-step oxygen reduction and 4e-1 water oxidation reactions. Experimental and theoretical calculation results revealed that the introduction of azo group could effectively improve the O2 adsorption and regulate the charge distribution, facilitating the H2O2 production and the conversion of soluble uranium into insoluble metastudtite ((UO2)O2·2H2O). This work provides insight into the UBs photocatalyst design strategy for simultaneous uranium recovery and high value-added chemicals.