Radionickel　ion　(63Ni2+)　remediation　is　critical　for　public　health　and　the　environment,　but　selectively　capturing　of　Ni2+　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　Ni2+　is　still　in　its　infancy.　Herein,　the　layered　metal　sulfide　K2Cu2Sn2S6　(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　Ni2+　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　Ni2+　with　rapid　kinetics　(a　high　rate　constant　k2　of　7.26　×10−2　g/(mg·min)),　broad　pH　durability　(removal　rates　＞97　%　at　pH　3–12),　and　high　selectivity　(separation　factors　for　Ni2+　＞700　against　various　cations).　Impressively,　it　can　efficiently　remove　Ni2+　from　multiple　complex　environments,　achieving　a　90.28　%　removal　rate　even　in　seawater　(C0Ni　∼5　mg/L).　CTS-1　is　environmentally　friendly　and　suitable　for　use　in　fixed-bed　columns　for　the　practical　application.　Moreover,　Ni2+　ions　are　captured　through　ion　exchange　with　K+,　and　the　high　selectivity　stems　from　the　strong　affinity　of　S2−　for　Ni2+　and　the　trapping　effect　of　the　grooves　within　the　structure.　In　summary,　this　pioneering　study　demonstrates　the　highly　selective　capture　of　Ni2+　by　a　sandwich-like　layered　MSIE,　potentially　inspiring　the　development　of　efficient　scavengers　for　radionuclides.　©　2024　Elsevier　B.V.