Nickel-iron Prussian blue composite membranes with ion-sieving channels for targeted cesium ion capture in aquatic...

This study successfully fabricated Ni-Fe Prussian blue analogues (PBAs) on polytetrafluoroethylene (PTFE) membranes (Ni-Fe PBAs@M) through interfacial functionalization and in situ crystal growth. Structural and compositional analyses confirmed the formation of a hierarchical porous structure with uniformly distributed PBA nanocubes (55-80 nm), cyanide-bridged coordination, and a 2.1-fold increase in surface area. Under optimized synthesis conditions (Ni/Fe molar ratio 3:2, 60 °C, Ni(NO₃)₂ precursor), the membranes achieved over 99 % Cs⁺ removal from 0.05 ppm solutions within 60 min, with a considerable and promising adsorption capacity of 444.00 mg·m⁻² at 5.0 ppm Cs⁺. Performance remained stable across transmembrane pressures (0.1 MPa) and pH levels (5-10), with slightly enhanced kinetics under acidic conditions. The membrane exhibited strong selectivity, retaining over 92 % Cs⁺ removal efficiency even in the presence of high concentrations of competing ions (Na⁺, K⁺, Ca²⁺, Mg²⁺, 10²-fold excess), which is attributed to the favorable hydration radius of Cs⁺. Water-based regeneration maintained >97.5 % removal efficiency over three cycles. In real-world applications, the membrane achieved >90 % Cs⁺ removal from Pearl River water and ∼50 % removal from salt-lake brine, despite extreme ionic competition exceeding Cs⁺ concentrations by >10⁴-fold. Mechanistic investigations revealed that Cs⁺ immobilization involves surface proton exchange (derived from polarized water molecules), subsequent diffusion into the lattice structure, the formation of Fe/Ni-NC-Cs⁺ coordination bonds accompanied by a 0.6 % lattice contraction, and redox-mediated stabilization for enhanced retention. These findings demonstrate that Ni-Fe PBAs@M is a promising, scalable membrane for efficient Cs⁺ decontamination and resource recovery.