Cross-Linking of Polyamidoxime Nanofibers by a Hyperbranched Macromolecule for Enhancing [UO₂(CO₃)₃]^4- Ion Capture

Polyamidoxime fibers have been widely studied for uranium extraction from seawater, but improving the amidoxime (AO) group utilization and increasing the selectivity toward uranium remain challenging. Herein, a hyperbranched macromolecular cross-linking strategy was employed to construct hyperbranched polyethylenimine (PEI) among the molecular chains of polyamidoxime nanofibers (PAN/PEI-AO nanofibers). This approach simultaneously suppressed chain entanglement and effectively reduced hydrogen bond formation between amidoxime groups, thereby significantly enhancing the utilization efficiency of AO groups. Moreover, the PEI structure also facilitated the dissociation of CO₃^2- from uranyl tricarbonate ([UO₂(CO₃)₃]^4-) and comprised amino groups as assistant groups for enhanced uranium uptake. The above cross-linking effect by PEI was confirmed by experimental data and theoretical calculation, resulting in high uranium uptake (474.8 mg g^-1) alongside good deep removal capability (k_d = 7.7 × 10⁵ mL g^-1) from [UO₂(CO₃)₃]^4- solution. Moreover, PAN/PEI-AO nanofibers also exhibited good selectivity and reusability toward uranium and showed a uranium extraction capacity of 8.24 mg g^-1 after 20 days' testing from natural seawater. The obtained adsorption performance of PAN/PEI-AO nanofibers exceeded traditional polyamidoxime nanofibers and many reported uranium adsorbents. Overall, this work offers a strategy to improve the performance of polyamidoxime fibers, which possess the potential to extract real uranium species from natural seawater.