Hydroxyl-based donor-acceptor covalent triazine frameworks as efficient platforms for in-situ photocatalytic U(Ⅵ) reduction

Developing stable and efficient catalysts for artificial photoreduction of soluble hexavalent uranium (U(VI)) into less mobile complexes is of considerable value to U enrichment and environmental sustainability. However, the pursuit of high-performance U(VI) photoreduction is greatly plagued by inferior charge separation and utilization for semiconductors. Herein, the multipolar donor-acceptor (D-A) interface and hydroxyl groups are rationally integrated into covalent triazine frameworks (CTFs) for enhancing U(VI) photoreduction without sacrificial agents. Once incorporating phenolic hydroxyl (Ph-OH) groups as electron donors, the targeted CTF-HUST-OH displays high efficiency (∼100 %) for U(VI) removal with a brilliant enrichment capacity (681.15 mg·g −1 ) under visible light irradiation, superior to most reported metal-free catalysts. Experimental and density functional theory (DFT) results validate that the polarized internal micro-electric field is formed in CTF-HUST-OH with an oriented charge transfer from Ph-OH to triazine units, thus achieving efficient electron separation and utilization. Impressively, the introduced -OH groups promote U(VI) adsorption via increase of pore hydrophilicity, and create reaction sites towards H 2 O 2 production, thereby facilitating in-situ generation of UO 2 O 2 ·4H 2 O(s). This study highlights a new strategy on the molecular-level design of D-A type CTF photocatalysts for efficient uranyl removal and extraction from uranium-bearing aqueous environments.