Selective Capture of Cu2+ Using a Redox-Active CuS Cathode Material in Hybrid Capacitive Deionization

Abstract

Resource shortage and industrial wastewater pollution are important problems concerning environmental safety. Copper is not only an important industrial metal but also a common heavy metal contamination in water. Selective extraction of copper from wastewater is a huge challenge. Here, an environmentally friendly hybrid capacitive deionization method was used to selectively remove Cu²⁺ from wastewater by using the redox-active CuS electrode for the first time. CuS as a cathode material can significantly reduce the concentration of Cu²⁺ in wastewater with the high adsorption capacity (350.04 mg·g^–1) and excellent selective adsorption. The removal efficiency for Cu²⁺ is greater than 90%, and the distribution coefficient K_d is over 10⁴ mL·g^–1 in a variety of salt ions and heavy metal-ion mixtures. Additionally, the electrode shows high cyclic stability in the adsorption of Cu²⁺. Importantly, CuS exhibits an outstanding copper extraction performance in real water samples (e.g., industrial wastewater and natural lake water), which confirms the high applicability of CuS in real-world scenarios. Ex situ XRD and XPS tests were used to unveil the Cu²⁺ removal mechanism. This work provides a new direction for the removal of copper from wastewater and a possibility for the application of copper resource extraction from wastewater.