Adsorption properties of V(IV) on the resin-activated carbon composite electrodes in capacitive deionization

The composite electrodes prepared by cation exchange resins and activated carbon (AC) were used to adsorb V(IV) in capacitive deionization (CDI). The electrode made of middle resin size (D860/AC M) has the largest specific surface area and mesoporous content than other two composite electrodes. Electrochemical analysis showed that D860/AC M presents higher specific capacitance and electrical double layer capacitor, and significantly lower internal diffusion impedance, thus it exhibits the highest adsorption capacity and rate for V(IV) among three electrodes. The intra-particle diffusion model fits well the initial adsorption stage, while the liquid film diffusion model is more suitable for the fitting at the later stage. The pseudo-second-order kinetic model is fit for the entire adsorption process. The adsorption of V(IV) on the composite electrode follows the Freundlich isotherm, and thermodynamic analysis indicates that this is an exothermic process with entropy reduction and the electric field force plays a dominant role in the CDI process. This work is conducive to peep at the ions adsorption behaviors and mechanisms on the composite electrodes in CDI.