Elucidating the Interlayer Regulation Mechanism on Uranium Capture Over Octacalcium Phosphate Carboxylate

ABSTRACT The extraction of uranium from seawater is crucial for sustaining the nuclear fuel supply, yet it remains challenging due to the slow kinetics of uranium capture. In this study, we systematically regulate the intra‐particle diffusion kinetics of octacalcium phosphate (OCP) and unveil the structure‐property relationship. The interlayer spacing of OCP is precisely modulated from 1.9 to 2.6 nm via intercalating dicarboxylic acids of different chain lengths. Concurrently, the localized chemical microenvironment is tuned from weakly alkaline to neutral and weakly acidic by functionalizing the interlayer with tris‐base, alkyl, and carboxylic acid groups. The optimized suberic acid‐intercalated OCP (OCPC‐sub) demonstrates an exceptional uranyl capture capacity, reaching 2820 mg‐U/g in simulated solution and 34.2 mg‐U/g in natural seawater, along with high selectivity. The performance enhancement stems from the expanded interlayer spacing that facilitates uranyl diffusion and chelation, as well as the localized acidic environment promoting the dissociation of [UO 2 (CO 3 ) 3 ] 4− into mobile [UO 2 ] 2+ ions. These synergistic effects improve intra‐particle diffusion kinetics and promote the subsequent reaction with apatite layers, ultimately converting OCP into calcium uranyl phosphate. This design strategy and modulation mechanism offer novel insights for developing high‐efficiency uranium capture materials, while deepening the fundamental understanding of diffusion‐reaction synergy in governing extraction kinetics.