Bifunctional hyper-cross-linked polymer with phosphorylated-amidoximated groups for efficient uranium extraction from water

Designing and developing a uranium adsorbent with high adsorption capacity and good selectivity is highly significant. We synthesized a novel hyper-cross-linked polymer adsorbent with bifunctional groups, (PHCP-4-AO), such as phosphate and amidoxime groups, via simple Scholl reaction and subsequent functionalization for the first time highly efficient extraction of U(VI) from aqueous solution. Due to its unique molecular structure design, it can enhance the selectivity and adsorption capacity of uranium by using two different functional groups. The maximum uranium adsorption capacity of PHCP-4-AO was 424.33 mg/g, which was higher than the single-functional group phosphorylated (PHCP-4) (315.43 mg/g) and amidoximated (HCP-4-AO) (260.38 mg/g) adsorbents. The combination of phosphate and amidoxime groups improves the adsorption effect. PHCP-4-AO has good selectivity and affinity for uranyl ions. In simulated wastewater, the Kd of PHCP-4-AO for uranium was 7266.3 mL/g, which was more than 15 times that of other ions. After three adsorption–desorption cycles, the adsorption capacity of PHCP-4-AO can still be maintained above 300.00 mg/g. Through XPS analysis, it is speculated that the sorption of uranium by PHCP-4-AO is owing to the lone pair electrons found on the oxygen atom of the phosphate groups, as well as the oxime oxygen and amino nitrogen atoms of the amidoxime groups entering the uranium's empty orbit to form the coordination bonds. These findings demonstrated that this new hyper-cross-linked polymer could be considered as a valuable material in the extraction and recovery of uranium from uranium-containing aqueous solutions.