Selective removal and utilization of copper from electroplating wastewater by modified MXene-based capacitive deionization

Capacitive deionization (CDI) technology has promising potential for the removal of copper ions from electroplating wastewater. In this study, a new kind of FeS₂ modified MXene electrode material with three-dimensional mutual support structure was synthesized, which has excellent hydrophilicity, electrical conductivity, and specific redox activity for copper ions. Therefore, this material was applied for the selective removal of copper ions from electroplating wastewater through the use of CDI. The FeS₂/MXene electrode demonstrated excellent electrosorption performance, with an electrosorption capacity (EC) of 80.02 mg g⁻¹ and a removal efficiency of 96.02 %. The electrosorption mechanism involves three synergistic pathways: (1) Faradaic redox reactions between Fe²⁺/Fe³⁺ and Cu²⁺/Cu⁺, (2) ion intercalation, and (3) capacitive adsorption. Notably, the material exhibited remarkable selectivity for Cu²⁺ even in mixed ion systems, with distribution coefficients exceeding 10⁴ mL g⁻¹. Additionally, Cu²⁺ in the actual electroplating wastewater was efficiently removed (99.97 %), meeting the water quality standard for metal plating and chemical coating process. Furthermore, the electrosorption-saturated electrodes with copper ions were reused as raw materials to prepare Cu@FeS₂/MXene electrocatalysts for nitrate (NO₃^–-N) reduction. The electrocatalytic efficiency of NO₃^–-N was 86.9 %, and the selectivity for nitrogen (N₂) reached 98.3 %. This study opens up a promising approach not only for selectively removing copper from wastewater but also for utilizing copper-saturated electrodes, demonstrating a sustainable and efficient strategy for water treatment and resource recovery.