Solvent-assisted synthesis of potassium copper hexacyanoferrate embedded 3D-interconnected porous hydrogel for highly selective and rapid cesium ion removal

Potassium copper hexacyanoferrate-embedded poly(vinyl alcohol)-citric acid hydrogel film (HPC) was prepared via a two-step method of Cu immobilization, followed by the diffusion of potassium hexacyanoferrate accelerated by acetone evaporation. The diffusion-derived KCuHCF formation in the preformed hydrogel facilitated the preservation of the 3D-interconnected hydrogel structure and dispersion of the KCuHCF nanoparticles. Using acetone as a non-solvent, reverse diffusion of the incorporated Cu in the hydrogel matrix was hindered; hence a large amount of KCuHCF was loaded in the matrix. The HPC exhibited substantially enhanced Cs+ removal properties in terms of adsorption capacity, kinetics and selectivity. From the adsorption isotherm, the HPC showed a very high Cs+ uptake of 667 mg/g KCuHCF. Moreover, the adsorbent revealed stable and high Cs+ removal efficiency of 99.9% across a wide pH range from 2 to 10. The kinetics of Cs+ removal was remarkably rapid with 99.5% removal achieved within 30 min from a dilute Cs+ solution (9.18 ppm). When using seawater, the HPC exhibited almost unaltered Cs+ removal efficiency above 99.5%, and high distribution coefficient Kd value of 7.7 × 105 ml/g at an extremely low Cs+ concentration (0.67 ppm, V/m = 1000 ml/g), which highlighted the tremendous affinity for Cs+.