Efficient adsorption of U(VI) from seawater on tannin-immobilized conjugated micro-mesoporous poly(aniline)s

The development of adsorbents capable of simultaneously achieving high uranium(VI) adsorption capacity, rapid kinetics, and exceptional selectivity remains a critical challenge for sustainable uranium(VI) extraction from seawater, essential for nuclear energy sustainability. Herein, we report the synthesis of a novel ellagic acid immobilized conjugated micro-mesoporous poly(aniline)s (CMP-E) via a Buchwald-Hartwig coupling strategy incorporating ellagic acid prefunctionalization. This synergistic combination of molecular confinement and pore engineering maximizes the density of accessible adsorption sites, overcoming the long-standing trade-off between adsorption site uniformity and surface coverage in conventional adsorbents. The resulting CMP-E showed exceptional uranium(VI) extraction performance, achieving a record adsorption capacity of 515 ± 14 mg g −1 , and the initial adsorption kinetics ( h ) reached 6.5 ± 0.3 mg g −1  min −1 , both exceeding pristine CMP by over 1.5 times. Notably, CMP-E demonstrated outstanding selectivity for uranium(VI), with a selectivity coefficient over 6.8 for uranium(VI)/other ions in the presence of various co-existing ions. This enhanced performance was attributed to the stable negative surface charge of CMP-E across a wide pH range, which promoted efficient electrostatic enrichment of uranium(VI) species. The subsequent coordination of uranium(VI) with lone pair electrons from nitrogen atoms (-NH- and = N-) in the poly(aniline) skeleton and oxygen atoms (-OH and C O) in the ellagic acid moiety further enhanced the uranium(VI) capture. Dynamic adsorption tests in real seawater demonstrated promising performance, achieving >86.3 ± 0.9 % uranium(VI) recovery with negligible capacity loss. Furthermore, a 7-day marine field test conducted in Pingtan revealed an adsorption capacity of 2.32 ± 0.02 mg g −1 under real marine conditions. These results suggested that CMP-E held significant potential as a material for the efficient extraction and recovery of uranium(VI) from seawater.