Bifunctional lignin-based hydrogel membrane with enhanced structural stability for synergistic uranium uptake

Developing biomass-based adsorbents with superior uranium uptake performance is imperative yet challenging for the sustainable development of nuclear energy. Herein, we constructed a novel lignin-based adsorbent (DLP@PAO) with dual functional groups and enhanced structural stability via ingenious integration of lignin and polyamidoxime. The two-step modification strategy was innovatively employed to phosphorylate lignin, significantly enhancing the phosphorylation efficiency and achieving an over eight-fold increase in the U(VI) uptake capacity of lignin. Benefiting from its double-crosslinked network and the strong electrostatic repulsion of phosphate groups, the DLP@PAO membrane, featuring a porous honeycomb structure, exhibits favorable shrinkage resistance even in acidic aqueous environments, facilitating the diffusion and mass transfer of U(VI) ions within the adsorbent. Notably, the synergistic effect of DLP and PAO components on U(VI) uptake was comprehensively verified through experimental data combined with density functional theory (DFT) calculation, which endows DLP@PAO with exceptional uptake capacity (701.02 mg g- 1 ) and selectivity (Kd = 1.45 x 105 mL g- 1 ) towards U(VI) ion. Moreover, DLP@PAO achieved a high U(VI) uptake efficiency of over 91.07 % in a dynamic column device with 10 L of simulated wastewater, indicating its immense potential for practical wastewater treatment. Mechanistic studies revealed that the synergistic coordination between UO 2 2+ ions and O as well as N atoms in the phosphate and amidoxime groups is primarily responsible for the U(VI) uptake by DLP@PAO. This work opens a new direction for the value-added utilization of lignin and advances the devel- opment of lignin-based adsorbents for U(VI) uptake.