The efficient removal of Sr2+ using two thiostannates via ion exchange

⁹⁰Sr is one of the most hazardous radionuclides in spent fuel, as it releases high energy β radiation accompanied by the release of a large amount of heat. Its easy environmental mobility and calcium-like bioconcentration properties pose a serious threat to the ecological environment and human health. Therefore, the efficient removal of ⁹⁰Sr from complex aqueous environments is of great significance. Herein, two new isomorphic thiostannates K₂Sn₂S₅·H₂O and K_1.1Rb_0.9Sn₂S₅·H₂O, namely FJSM-KSnS and FJSM-KRbSnS, respectively, were prepared by the solvothermal method. Their structures feature a two-dimensional (2D) wavy anionic layer of [Sn₂S₅]_n^2n- with big windows of ten-membered rings. Alkali metal cations (K⁺/Rb⁺) as charge balancers as well as H₂O molecules are located in the interlayer spaces. They exhibit efficient Sr²⁺ removal performance with high adsorption capacities (qSrm = 59.88 mg g^-1 for FJSM-KSnS, qSrm = 62.82 mg g^-1 for FJSM-KRbSnS). FJSM-KSnS as a representative exhibits fast kinetics (equilibrium within 10 minutes) and good selectivity for Sr²⁺ removal in the presence of excessive Na⁺, and even in actual environmental water samples. In addition, the Sr²⁺ capture mechanism is revealed by energy-dispersive X-ray spectroscopy, elemental distribution mapping, and X-ray photoelectron spectroscopy characterization. The efficient capture of Sr²⁺ is attributed to the ion exchange between Sr²⁺ and interlayered alkali metal ions of thiostannates. This work expands the structural types of thiostannates and provides new efficient ion exchange materials for radiostrontium remediation.