Synergistically enhanced nitrate removal by capacitive deionization with activated carbon/PVDF/polyaniline/ZrO2 composite electrode

Abstract

• Mixture design to optimize composite electrode toward nitrate removal in CDI cell. • 75.13% increase of Cs and 55.47% reduction in R ct for composite vs. AC electrode. • E3 as optimum electrode with ion electrosorption capacity of 6.01 mg g −1 at 2.0 V. • Maximum specific capacitance of 58.67F g −1 and Rct of 1.26 Ω for E3 electrode. • Highest water recovery of 72.94% and nitrate removal efficiency of 60.01% in the CDI. This work aims to introduce a novel ternary composite electrode to improve the performance of the capacitive deionization process toward nitrate removal from water through enhancing the specific capacitance of the carbon-based electrode. The mixture design methodology was utilized to find the optimum composite electrode containing activated carbon (AC), PVDF, ZrO2, and polyaniline as emeraldine salt (PANi-ES) with the highest specific capacitance. The morphology, specific surface area, functional groups and wettability, electrochemical behavior, specific capacitance, and charge transfer resistance of the electrode were evaluated by field emission scanning electron microscopy, Brunauer–Emmett–Teller analysis, Fourier-transform infrared spectroscopy, contact angle, cyclic voltammetry, and electrochemical impedance spectroscopy, respectively. The optimum E4 electrode containing 80 wt% AC, 6.0 wt% ZrO 2 , and 6.0 wt% PANi–ES and 8 wt% PVDF was compared to E1 (AC/PVDF), E2 (AC/PVDF/PANi-ES) and E3 (AC/PVDF/ZrO 2 ) electrode. The addition of ZrO 2 into AC as the E3 electrode could attain 19.43% increase in specific capacitance and 34.27 %decrease in charge transfer resistance. In comparison, incorporating both PANi-ES and ZrO 2 into AC led to 75.13% and 51% increase of specific capacitance and wettability, respectively, and 55.47% reduction in charge transfer resistance. This behavior was attributed to the synergistic improvement of specific capacitance by increasing its electrical conductivity and wettability (hydrophilic) and consequently improved the performance of nitrate ion separation by mesoporous structure. Based on the optimum applied voltage of 2.0 V on the E3 electrode, the electrosorption capacity, the maximum nitrate removal efficiency, the water recovery, and specific capacitance were calculated 6.01 mg g −1 , 60.01%, 72.94%, and 58.67F g −1 in the batch mode CDI cell, respectively.