Boosting selective Cs⁺ uptake through the modulation of stacking modes in layered niobate-based perovskites

Selective separation of ¹³⁷Cs is significant for the sustainable development of nuclear energy and environmental protection, due to its strong radioactivity and long half-life. However, selective capture of ¹³⁷Cs⁺ from radioactive liquid waste is challenging due to strong coulomb interactions between the adsorbents and high-valency metal ions. Herein, we propose a strategy to resolve this issue and achieve specific Cs⁺ ion recognition and separation by modulating the stacking modes of layered perovskites. We demonstrate that among niobate-based perovskites, ALaNb₂O₇ (A = Cs, H, K, and Li), HLaNb₂O₇ shows an outstanding selectivity for Cs⁺ even in the presence of a large amount of competing Mⁿ⁺ ions (Mⁿ⁺ = K⁺, Ca²⁺, Mg²⁺, Sr²⁺, Eu³⁺, and Zr⁴⁺) owing to its suitable void fraction and space shape, brought by the stacking mode of layers. The Cs⁺ capture mechanism is directly elucidated at molecular level by single-crystal structural analyses and density functional theory calculations. This work not only provides key insights in the design and property optimization of perovskite-type materials for radiocesium separation, but also paves the way for the development of efficient inorganic materials for radionuclides remediation.