Copper hexacyanoferrate/carbon sheet combination with high selectivity and capacity for copper removal by pseudocapacitance.

The efficient capture of copper ions (Cu) in wastewater has dual significance in pollution control and resource recovery. Prussian blue analog (PBA)-based pseudocapacitive materials with open frameworks and abundant metal sites have attracted considerable attention as capacitive deionization (CDI) electrodes for copper removal. In this study, the efficiency of copper hexacyanoferrate (CuHCF) as CDI electrode for Cu treating was evaluated for the first time upon the successful synthesis of copper hexacyanoferrate/carbon sheet combination (CuHCF/C) by introducing carbon sheet as conductive substrate. CuHCF/C exhibited significant pseudocapacitance and high specific capacitance (52.92 F g) through the intercalation, deintercalation, and coupling of Cu/Cu and Fe/Fe redox pairs. At 0.8 an applied voltage and CuSO feed liquid concentration of 100 mg L, the salt adsorption capacity was 134.47 mg g higher than those of most reported electrodes. Moreover, CuHCF/C demonstrated excellent Cu selectivity in multi-ion coexisting solutions and in actual wastewater experiments. Density functional theory (DFT) calculations were employed to elucidate the mechanism. This study not only reveals the essence of Cu deionization by PBAs pseudocapacitance with promising potential applications but also provides a new strategy for selecting efficient CDI electrodes for Cu removal.