Efficient capture of Sr2+ ions by a layered crystalline zirconium phosphate fluoride

Abstract

The effective remediation of radioactive strontium-90 (⁹⁰Sr) from complex aqueous environments remains challenging due to the inherent high solubility and migration propensity of Sr²⁺ ions. Herein, we synthesized hydrothermally a new two-dimensional (2D) crystalline zirconium phosphate fluoride [(CH₃)₂NH₂][Zr(PO₄)F₂] featuring a layered anionic architecture of [Zr(PO₄)F₂]_nⁿ⁻ with intercalated [(CH₃)₂NH₂]⁺ cations, which shows exceptional Sr²⁺ remediation capability. It possesses a high maximum Sr²⁺ adsorption capacity (q^Sr_m) of 161.48 mg g⁻¹ (higher than that of many inorganic crystalline adsorbents) and fast kinetics for Sr²⁺ capture (Sr²⁺ removal rate (R^Sr) of 94.89% within 1 min). Specifically, it maintains Sr²⁺ removal efficiency in the presence of competing Cs⁺, K⁺, Na⁺, Ca²⁺, Mg²⁺ ions and in actual aqueous systems including seawater (R^Sr = 79.06%). X-ray photoelectron spectroscopy (XPS) and thermodynamics confirm that spontaneous Sr²⁺ capture occurs through ion exchange processes, where the interlayered [(CH₃)₂NH₂]⁺ cations in [(CH₃)₂NH₂][Zr(PO₄)F₂] are exchanged with Sr²⁺. The compound [(CH₃)₂NH₂][Zr(PO₄)F₂] represents the first crystalline inorganic zirconium phosphate fluoride ion exchange material for radionuclide capture. This work provides a high-performance ion exchanger as a candidate for radiostrontium capture.