Highly Efficient and Recyclable Uranium Extraction via Amidoxime-Functionalized Amphiphilic Block Copolymer Nanomicelles

Escalating global demand for nuclear energy has made uranium (U(VI)) an indispensable strategic resource. Limited terrestrial uranium reserves and widespread uranium-contaminated wastewater have spurred research into uranium recovery and remediation technologies. Adsorption is the most promising approach, yet conventional amidoxime (AO)-functionalized adsorbents suffer from low AO group utilization, sluggish adsorption kinetics, and poor structural stability in cyclic use. Herein, we report the rational design and synthesis of a novel amphiphilic block copolymer (polystyrene-block-polyamidoxime, PS-b-PAO) via reversible addition–fragmentation chain transfer (RAFT) polymerization and subsequent amidoximation. This copolymer spontaneously self-assembles into core–shell nanomicelles in aqueous media, with a hydrophobic polystyrene (PS) core and a hydrophilic PAO shell, ensuring full exposure of AO groups to enhance coordination with uranyl ions (UO22+). Systematic adsorption tests showed that PS-b-PAO nanomicelles exhibit an ultrahigh uranium adsorption capacity of 916.14 mg·g–1 in uranium-spiked aqueous solutions, 4.27 times higher than that of linear polyamidoxime (PAO) under the same conditions and 4.01 times higher than that of poly(styrene-co-acrylonitrile) under identical conditions. Kinetic and isotherm analyses indicated the adsorption follows the pseudo-second-order kinetic model and Langmuir isotherm model, dominated by chemisorption and monolayer coordination between AO groups and UO22+. The adsorbent also has excellent selectivity for U(VI) over interfering metal ions (V5+, Fe3+, Cu2+, and Co2+), superior recyclability (retaining over 87% uranium removal efficiency after 5 adsorption–desorption cycles), and a satisfactory uranium adsorption capacity of 5.28 mg·g–1 in natural seawater. X-ray photoelectron spectroscopy (XPS) confirmed that the adsorption mechanism involves chelation of UO22+ by nitrogen and oxygen atoms in the AO moieties of PS-b-PAO.