Selective capture of Cs(I) from aqueous solution by synergistic effects of size-compatible lattice confinement and ion exchange using kaolinite-derived sodalite

Efficient capture and separation of Cs + from nuclear wastewater remains a central challenge in nuclear chemical engineering. Here, a solvent-free solid-state conversion strategy is developed to directionally transform natural kaolinite into sodalite under thermally driven solid-state conditions, yielding a Cs + -selective capture material with intrinsic ion-sieving properties. The resulting sodalite exhibits a high Cs + adsorption capacity of up to 242.96 mg/g in weakly acidic solutions and reaches adsorption equilibrium within approximately 50 min, demonstrating fast uptake kinetics. Isotherm and kinetic analyses demonstrate that Cs + adsorption proceeds via a monolayer, chemisorption-dominated process governed by ion exchange. Multiscale characterization combined with theoretical calculations reveals that Cs + capture arises from the synergistic effects of size-matched pore confinement and spatially confined ion-exchange sites within the sodalite framework. These findings establish kaolinite-derived sodalite as a viable inorganic platform for the efficient separation and long-term management of radionuclides in nuclear wastewater.