Redox-assisted electrosorption pathways for nickel removal and recovery using carbon nanotubes modified iron based MOF in capacitive deionization

The development of efficient and sustainable technologies for heavy metal recovery is critical for addressing environmental pollution and resource scarcity. In this study, a redox hybrid electrode comprising MIL-88A, multi-walled carbon nanotubes (MWCNTs), and activated carbon (AC) was designed for enhanced Ni 2+ removal via capacitive deionization (CDI). The synergistic integration of high surface area AC, conductive MWCNT networks, and Fe-based metal-organic framework (MIL-88A) enables improved charge transport, ion accessibility, and surface reactivity. Under optimized conditions (1.2 V, pH 4, 10 mL min −1 ), the electrode achieved a high salt adsorption capacity (SAC) of ∼75.6 mg g −1 with rapid adsorption kinetics. Kinetic analysis revealed that the process follows a pseudo second order model (R 2 = 0.998), indicating surface-controlled electrochemical adsorption. Mass transfer studies confirmed a multi-step mechanism involving film diffusion, intraparticle diffusion, and surface electrosorption. The system exhibited excellent electrochemical stability, with coulombic efficiency exceeding 99.99% and capacity retention above 95% over repeated cycles, demonstrating high reversibility and minimal parasitic reactions. Comparative analysis with reported CDI systems shows that the developed electrode significantly outperforms conventional carbon-based materials. Techno-economic evaluation indicated a low specific energy consumption ∼2.2 kWh m −3 for the CDI application and a total treatment cost of ∼1.32 $ m −3 , highlighting its economic feasibility. Furthermore, the system enables chemical-free regeneration and efficient Ni 2+ recovery, minimizing secondary waste generation. The MIL-88A/MWCNT/AC hybrid electrode offers a high-performance, energy efficient, and scalable solution for heavy metal removal and resource recovery from aqueous systems, advancing CDI technology beyond conventional desalination applications.