Electrosorption removal of cesium ions with a copper hexacyanoferrate electrode in a capacitive deionization (CDI) system

Capacitive deionization (CDI) is a promising technique that can be applied to the removal ions of radioactive liquid waste. Carbon-based electrodes, which are mainly used in CDI systems, show limited characteristics due to their inferior selectivity and adsorption performance of target components present in feed water. Prussian blue analogues (PBAs) are proposed as an electrode material that operates by a reversible redox reaction, and provides a strategy to efficiently remove cesium (Cs) ions from aqueous solutions owing to its excellent ion adsorption capacity. In this research, copper hexcacyanoferrate (CuHCF) was utilized to improve the electrosorption performance in terms of Cs+ ions removal capacity and charging efficiency, and to achieve the selective electrosorption of Cs+ ion in cation mixtures. An outstanding electrosorption capacity of 397 mg g−1 (qmax) and high selectivity were obtained at an optimum voltage of 1.4 V, and significant adsorption performance was maintained in the pH range of 1.0–5.6. The isotherms and adsorption kinetics employed to study the adsorption mechanism obey the Langmuir adsorption model and pseudo-first-order model, respectively. The Fe3+/Fe2+ and Cu2+/Cu+ redox couples are highly stable and reversible, providing outstanding cycling stability of CuHCF electrode. Our study demonstrates that the amount of Cs+ ions in an aqueous solution can be remarkably reduced by an electrochemically driven adsorption/desorption process using a CuHCF. Therefore, the proposed CDI system with CuHCF is a promising candidate for the efficient removal of cesium from wastewater and its large-scale application.