Fluorenone-Based COFs with Electron-Relay Function for Highly Efficient Photocatalytic Uranium Extraction from Wastewater

The remediation of uranium-contaminated wastewater is crucial, given the severe environmental and health risks associated with uranium's chemical toxicity and radioactivity. Photocatalytic reduction of soluble U(VI) to insoluble U(IV) represents a promising strategy, yet its efficiency is often hampered by sluggish electron transfer kinetics, particularly at the catalyst-uranium interface. While covalent organic frameworks (COFs) are attractive photocatalysts, a significant challenge lies in simultaneously promoting intramolecular charge separation and interfacial electron injection. To address this, we constructed "electron relay stations" within a conjugated COF skeleton by incorporating fluorenone units. This design not only enhances intramolecular charge dissociation by strengthening the donor-acceptor interaction but also provides specific binding sites for UO₂²⁺, thereby effectively bridging bulk electron migration and surface reduction reactions. The optimized Py-FO-COF achieves a remarkable uranium removal rate of 99.6% and an exceptional adsorption capacity of 1057.1 mg g^-1 under visible light, significantly outperforming its control counterparts. Crucially, it maintains high efficiency (>98%) in treating real uranium-containing tailings wastewater and exhibits excellent selectivity and recyclability. This work underscores the importance of integrative molecular design in developing high-performance photocatalysts for radioactive environmental remediation.