Electrosorption of Cu(II) and Zn(II) in Capacitive Deionization by KOH Activation Coconut-Shell Activated Carbon

Capacitive deionization (CDI) is a simple, cost-efficient, and environmentally friendly method for brackish water desalination, and CDI technology also refers to heavy metal removal through the non-Faraday-process. In order to develop the highly electro-adsorptive electrode for heavy metal electrosorption via CDI process, a combination of biomass-derived activated carbon (AC) and nano-carbonaceous materials have been considered as a sustainable approach. In this study, the composite coconut-shell-derived AC@CNTs electrode with low CNTs content (1 wt%) was utilized for Cu(II) and Zn(II) removal. The surface properties of pristine AC and KOH-activated AC with nitrogen adsorption technique (BET) and scanning electron microscopy (SEM) are characterized. As calculated from BET measurements, surface area are 581 m(2)/g, 560 m(2)/g, and 552 m(2)/g, corresponding to AC-KOH-2@CNTs, AC-KOH-4@CNTs, and AC-KOH-6@CNTs. After KOH activation, a specific capacitance of AC-KOH-2@CNTs is significantly increased up to 133.7 F/g in comparison with 78.0 F/g of pristine AC. Furthermore, in the Cu(II) and Zn(II) removal performance, AC-KOH-2@CNTs achieved a significant average salt adsorption rate of 29.87 mg/g min and 25.27 mg/g min with a high salt adsorption (SAC) of 7.31 mg/g and 12.55 mg/g at the operation voltage of 1.2 V in 200 ppm CuSO4 solution and 200 ppm ZnSO4 solution, respectively.