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. (C) 2016 Elsevier B.V. All rights reserved.