Redox-Capacitive Coupled Electrosorption for Selective Copper Recovery from Industrial Wastewater Using GO/MIL-88A/AC Electrodes

Abstract

Abstract Selective removal and recovery of Cu2+ ions from industrial effluent was accomplished by a new redox-accelerated capacitive deionization (CDI) electrode with a hierarchical graphene oxide/MIL-88A/activated carbon composite (GO/MIL-88A/AC). The optimal electrode (E4, 6 wt %) exhibits a well-balanced charge storage mechanism with 81.7% capacitive and 18.3% diffusion-controlled sorption contributions, which facilitates fast mass transport accompanied by faradaic redox mechanisms of the systematic composite loading variation (0–8 wt %). The high specific capacitance (142 F g–1), low charge transfer resistance (1.3 Ω), and high Coulombic efficiency (99.99% for 500 cycles) via electrochemical measurements confirmed enhanced conductivity and reversibility. At optimum CDI operating conditions (1.2 V, 20 mL min–1, pH 4), the electrode exhibited an impressive electrosorption capacity (58.03 mg g–1, 95% removal). Kinetic studies showed a pseudo-first-order model (k1 = 0.0658 min–1, R2 = 0.9934) with high consistency between experimental (58.03 mg g–1) and theoretical capacities (64.01 mg g–1), and the linear driving force model gave a high mass transfer coefficient (kLDF = 0.0962 min–1), confirming efficient ion diffusion within the hierarchical structure. The improved performance is due to the combined contribution of pseudocapacitive property (GO), active Fe3+/Fe2+ sites of MIL-88A, and electric double-layer capacitance (AC) for the coupled electrosorption–desorption process. This work demonstrates the potential of a hybrid redox-capacitive system for energy-efficient Cu2+ recovery from industrial wastewater treatment.