A synergistic ligand complexation and photocatalytic precipitation strategy for efficient uranium extraction from...

The development of multifunctional materials capable of simultaneously capturing and immobilizing uranium(VI) [U(VI)] in complex saline environments remains a significant challenge for sustainable uranium recovery. In this study, a novel phosphate covalent organic framework (TFPD-COF-HP) that integrates both adsorption and photocatalytic functions was successfully constructed. The introduced phosphate groups function as a "dual-engine," orchestrating both thermodynamic coordination stability and kinetic excited-state dynamics to increase U(VI) adsorption capacity. The U(VI) adsorption capacity of TFPD-COF-HP increased by 28% compared to that of unmodified COF (TFPD-COF) with 390 ± 20 mg g^-1 under light irradiation at pH 5. Importantly, in the untreated Mahai salt lake (Qinghai), TFPD-COF-HP nearly reached adsorption equilibrium after 20 days, with a uranium uptake of approximately 2.6 ± 0.1 mg g^-1 and an average uptake rate of approximately 0.13 mg g^-1 d^-1. Combined experimental characterizations and theoretical calculations were employed to elucidate the coordination behavior and orbital interactions between the adsorbent and uranyl ions. Extended transition state-natural orbital for chemical valence (ETS-NOCV) analysis uncovers a unique push-pull electron adsorption mechanism, where U to O σ polarization and O to U π back-donation synergistically stabilize the uranium complexes. Excited-state charge transfer studies confirm that phosphorylation extends hole-electron separation, suppresses radiative recombination, and promotes interfacial charge transfer. Based on the above analysis, the robust adsorption performance of TFPD-COF-HP stems from the synergy between its high-affinity uranium binding capability and efficient photocatalytic-induced uranium precipitation, highlighting its potential for sustainable uranium recovery.