Synergistic adsorption-reduction by ZIF-8 immobilized Ni0 nanoparticles for ultrahigh-capacity uranium extraction from seawater: Integrated experimental and DFT studies

This study reported a Ni 0 @ZIF-8 nanocomposite synthesized via co-precipitation that synergistically integrated the high adsorption capacity of ZIF-8 with the redox activity of zero-valent nickel (Ni 0 ) for efficient uranium(VI) extraction. The composite with an optimized 1:1 ZIF-8:Ni 0 molar ratio achieved an exceptional adsorption capacity of 830.5 mg/g. Kinetic and thermodynamic analyses confirmed chemisorption-dominated monolayer adsorption following pseudo-second-order kinetics (R 2  > 0.999) and spontaneous endothermic behavior. Mechanistic investigations through spectroscopy and density functional theory (DFT) calculations revealed a dual-function mechanism that ZIF-8 facilitated U(VI) capture through electrostatic/coordination interactions, while Ni 0 mediated partial reduction of U(VI) to U(IV) via electron transfer, enhancing immobilization stability. Notably, only Pb 2+ , Cu 2+ , Cr 6+ , and organic ligands inhibited adsorption through redox competition and solution complexation. Comparative studies demonstrated minimal matrix interference-deionized water versus seawater systems exhibit merely 4.7 % deviation in adsorption efficiency at trace U(VI) concentrations (0.1–0.6 mg/L). Critically, direct uranium extraction from unprocessed natural seawater (ambient U: 4.27 μg/L) with only pH adjustment (5.0) achieves 86.02 % efficiency at ultra-low adsorbent dosage (0.001 g/L), yielding residual uranium concentrations of 0.597 ± 0.04 μg/L. By harmonizing adsorption and redox pathways, Ni 0 @ZIF-8 overcome limitations of conventional materials, establishing itself as a paradigm-shifting solution for uranium remediation in complex ionic matrices and real marine environments.