Highly selective capture of Ni from complex environments by a sandwich-like layered metal sulfide ion exchanger.

Radionickel ion (Ni) remediation is critical for public health and the environment, but selectively capturing of Ni from complex environments like seawater presents a challenge. Metal sulfide ion exchangers (MSIEs) are emerging as efficient adsorbents for radionuclides; however, the study of MSIEs for selectively removing Ni is still in its infancy. Herein, the layered metal sulfide KCuSnS (CTS-1) with a unique sandwich-like anionic framework was synthesized by the hydrothermal method for the first time, representing a novel approach in the selective capture of Ni from complex environments. Single-crystal structural analysis confirmed the sandwich-like framework, in which a [Cu-S] sublayer is sandwiched by two [Sn-S] sublayers with parallel grooves. The charge-balancing K ions are located within these grooves. Due to its special structure, CTS-1 exhibits remarkable adsorption capacities for Ni with rapid kinetics (a high rate constant k of 7.26 ×10 g/(mg·min)), broad pH durability (removal rates >97 % at pH 3-12), and high selectivity (separation factors for Ni >700 against various cations). Impressively, it can efficiently remove Ni from multiple complex environments, achieving a 90.28 % removal rate even in seawater (C ∼5 mg/L). CTS-1 is environmentally friendly and suitable for use in fixed-bed columns for the practical application. Moreover, Ni ions are captured through ion exchange with K, and the high selectivity stems from the strong affinity of S for Ni and the trapping effect of the grooves within the structure. In summary, this pioneering study demonstrates the highly selective capture of Ni by a sandwich-like layered MSIE, potentially inspiring the development of efficient scavengers for radionuclides.