A Two-Dimensional Thiotitanate Ion Exchanger with High Cs+ Removal Performance

137Cs is a persistent β/γ-emitter (t1/2 = 30.1 years) generated from 235U and 239Pu fission. It is a critical challenge to efficiently capture 137Cs+ for nuclear waste management due to its high solubility, environmental mobility, and propensity for biological accumulation. Herein, we prepare a two-dimensional (2D) thiotitanate Rb0.32TiS2·0.75H2O (denoted Rb-TiS2) using a special molten salt synthesis method, “Mg + RbCl”. Rb-TiS2 can selectively capture Cs+ from aqueous solutions. Its structure features a flexible anionic thiotitanate layer with Rb+ as counter ions located at the interlayer spaces. As an ion exchanger, it possesses high adsorption capacity (qmCs = 232.70 mg·g−1), rapid kinetics (the removal rate R > 72% within 10 min), and a wide pH tolerance range (pH = 4–12) for Cs⁺ adsorption. Through a single-crystal X-ray structural analysis, we elucidated the mechanism of Cs⁺ capture, revealing the ion exchange pathways between Cs⁺ and Rb+ in Rb-TiS2. This work not only provides an important reference for the synthesis of transition metal sulfides with alkali metal cations but also proves the application prospect of transition metal sulfides in radionuclide remediation.