Preparing CNTs/Ca-Selective zeolite composite electrode to remove calcium ions by capacitive deionization

Electrophoretic deposition (EPD) method was used to fabricate Carbon nanotubes (CNTs) and Ca-Selective zeolite composite electrode. The prepared electrode was employed in electrosorption of calcium ions in capacitive deionization. The morphology, porous size distribution, pore volume and electrochemical properties were characterized by scanning electron microscopy, N2 adsorption at 77K and Cyclic Voltammetry (CV), respectively. The results obtained from experiments showed that the optimum proportion between CNTs and zeolite was 1:4. It was also found that the optimum applied electrosorption voltage was 2.0V and the maximum equilibrium electrosorption capacity was 25mg/g with initial Ca2+ concentration of 750mg/L. The electrosorption process could be validated by both of pseudo first and second order kinetic models. Furthermore, the selective ion electrosorption experiments were repeated in solution with different ions, and it was observed that the electrosorption capacities of cations on the CNTs composite electrode followed the order of Ca2+>Mg2+>Na+. Finally, the prepared electrode can be reused in long-term electrosorption process. •The CNTs composite electrodes were fabricated by using EPD method for the first time.•The CNTs composite electrodes could remove Ca2+ by CDI progress.•The CNTs composite electrodes have excellent selectivity for Ca2+ than Mg2+ and Na+.