Solvent-mediated construction of phosphate/carboxyl bifunctional hyper-cross-linked polymers for highly efficient...

In this study, through a one-pot Friedel-Crafts reaction, the solvent-mediated bifunctional hyper-crosslinked polymer (denoted as DP-PD1) containing phosphate and carboxyl groups was successfully synthesized, via the use of diphenyl phosphate (DP) as a functional monomer, pyromellitic dianhydride (PMDA) as a crosslinking agent, and 1,2-dichloroethane (DCE) which served dual roles as both solvent and reactant. The control experiments and characterizations confirmed that the multiplier effect of the bifunctional groups, combined with the solvent-driven synergic effect, endowed DP-PD1 with exceptional uranium(VI) adsorption performance. The DP-PD1 sorbent achieved a maximum adsorption capacity of 458.1 mg/g for U(VI) at pH = 7.0. Within the concentration range of 5.0-1000.0 μg/L U(VI), the removal efficiency exceeded 96.9 %. The residual U(VI) concentration in the treated simulated wastewater was reduced to below 40 μg/L, easily meeting the discharge standards. In addition, DP-PD1 also demonstrated the outstanding practical applicability, which retained > 95.0 % uranium removal efficiency after five consecutive adsorption-desorption cycles, exhibited the stable adsorption performance after 500 kGy γ-ray irradiation (highlighting its excellent radiation resistance), and achieved > 85.0 % U(VI) removal efficiency even under high ionic strength (Na/U molar ratio of 4762:1) and competing ion conditions. The mechanism studies revealed that the adsorption primarily relied on electrostatic interactions and complexation. DFT calculations suggested that U(VI) preferentially formed a 1:2 bidentate coordination mode with the ligands of DP-PD1. Therefore, the proposed "solvent-structure-functional group" integrated design strategy offered a novel approach for the development of advanced uranium adsorbents.