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

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.