Shape stable poly(vinyl alcohol) hydrogels with immobilized metal hexacyanoferrates for cesium removal from waters

The metal hexacyanoferrates with transition metal ions to replace ferric ions in the face center cubic structure of Prussian blue (PB) crystals are candidate adsorbents for radioactive cesium ions in waters. This study for the first time synthesized the shape stable poly(vinyl alcohol) (PVA) hydrogels with immobilized metal hexacynoferrate (PB analogue) that can be stored at dry and can efficiently adsorb cesium ions from waters after rewetting. A total of eight PB analogue particles in two families M₃[Fe(III)(CN)₆]₂ (MFe(III)) or M₄[Fe(II)(CN)₆]₂ (MFe(II)) with M=Zn, Ni, Cu, or Co were synthesized and were immobilized in the PVA hydrogels following boric acid and sulfate crosslinking. The produced PVA-PB analogue hydrogels are all stable in shape after dry and rewet, and the rewet hydrogels can adsorb cesium ions from waters at much higher rates. As predicted by the diffusion-reaction model, the apparent reaction constants for cesium ion adsorption are 4.2×10⁻⁴ 1/s, 3.4×10⁻⁴ 1/s, 3.9×10⁻⁴ 1/s, 4.1×10⁻⁴ 1/s, 4.1×10⁻⁴ 1/s, 3.8×10⁻⁴ 1/s, 1.1×10⁻³ 1/s, and 9.6×10⁻⁴ 1/s, for ZnFe(III), ZnFe(II), NiFe(III), NiFe(II), CuFe(III), CuFe(II), CoFe(III), and CoFe(II), respectively. The corresponding maximum adsorption capacities based on Langmuir isotherm model at 25 °C are 232.6 mg/g, 389.0 mg/g, 193.9 mg/g, 256.8 mg/g, 388.2 mg/g, 395.1 mg/g, 297.3 mg/g, and 391.2 mg/g, respectively. The use of PVA-CoFe(III) is the candidate for enhanced Cs removal from waters comparing the use of other PB analogues as adsorbent.