Synthesis of potassium copper hexacyanoferrate and cellulose hydrogel composites for effective cesium adsorption

Abstract

Potassium copper hexacyanoferrate (KCuHCF) was synthesized and immobilized in a cellulose-based hydrogel made of carboxymethyl cellulose (CMC) and hydroxyethyl cellulose (HEC) for the adsorption of cesium ions in aqueous solutions. The immobilization with the cellulose-based hydrogel facilitated the dispersion of nano-sized KCuHCF particles, showing the unprecedented adsorption capacity of the composite. In $Cs^+$ removal experiments, KCuHCF-cellulose hydrogel composites (HCF-gels) exhibited exceptional Cs+ adsorption capacities ($2.06-2.32 mmol g^{-1}$) which was attributed to the presence of ion-exchangeable sites ($COO-Na^+$) in the cellulose hydrogel. The HCF-gels also exhibited a rapid Cs+ removal (90.1% removal for $0.15 mmol L^{-1}$ of $Cs^+$ in 1 h) with the uptake reaction kinetics expressed by a pseudo-second order kinetics model. Notably, the HCF-gels could adsorb $Cs^+$ selectively (>90%) in seawater containing $0.11 mmol L^{-1} Cs^+$. Such specificity with fast kinetics is due to the high ion accessibility from the inherent nature of hydrogels and the highly dispersed KCuHCF nanoparticles in the composites.