K₂Cu₃(Fe(CN)₆)₂ In Situ-Modified MXene Nanosheets for Selective Enrichment of Cs⁺ and the Mechanism

Selective enrichment of cesium ions (Cs⁺) at ultralow concentrations is essential for resource recovery and radioactive waste disposal, yet efficient adsorbents are lacking. Herein, we reported a Prussian blue analogue (K₂Cu₃(Fe(CN)₆)₂, Cu-PBA) decorated on MXene nanosheets by in situ fabrication, forming a composite material termed PMX, for enhanced adsorption of Cs⁺ in acidic solutions and seawater. The stable, negatively charged MXene effectively anchors Cu²⁺ precursors and promotes Cs⁺ adsorption. The synergistic interaction between MXene and the in situ-synthesized Cu-PBA significantly enhances the adsorption performance and water stability of PMX in both acidic solutions and seawater. PMX achieves rapid adsorption equilibrium within 5 min, with a high adsorption capacity of 408.2 mg/g at pH 1, surpassing conventional adsorbents. Moreover, PMX shows excellent Cs⁺ selectivity (<i>K_d</i> = 68,361.7 mL/g), cycle stability, and notable anti-irradiation ability, demonstrating superior efficiency in Cs⁺ enrichment from complex matrices. The adsorption mechanism involves electrostatic attraction and K⁺/Cs⁺ ion exchange, facilitated by MXene's functional groups and the Cu-PBA structure. These findings underscore the excellent potential of PMX as an efficient adsorbent for resource enrichment and the removal of radioactive elements such as Cs⁺.