Nano-manganese oxide and reduced graphene oxide-incorporated polyacrylonitrile fiber mats as an electrode material for capacitive deionization (CDI) technology

Capacitive deionization (CDI) is a trending water desalination method during which the impurity ions in water can be removed by electrosorption. In this study, nano-manganese dioxide (MnO 2 ) and reduced graphene oxide (rGO)-doped polyacrylonitrile (PAN) composite fibers are fabricated using an electrospinning technique. The incorporation of both MnO 2 and rGO nanomaterials in the synthesized fibers was confirmed by transmission electron microscopy (TEM), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX). The electrochemical characteristics of electrode materials were examined using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and constant current charge-discharge cycles (CCCDs). The specific capacitance of the PAN electrode increased with increasing MnO 2 and rGO contents as well as when thermally treated at 280 °C. Thermally treated composite fibers with 17% (w/w) MnO 2 and 1% (w/w) rGO (C-rGOMnPAN) were observed to have the best electrochemical performance, with a specific capacitance of 244 F g −1 at a 10 mV s −1 scan rate. The electrode system was used to study the removal of sodium chloride (NaCl), cadmium (Cd 2+ ) and lead (Pb 2+ ) ions. Results indicated that NaCl showed the highest electrosorption (20 472 C g −1 ) compared to two heavy metal salts (14 260 C g −1 for Pb 2+ and 6265 C g −1 for Cd 2+ ), which is most likely to be due to the ease of mass transfer of lighter Na + and Cl − ions; When compared, Pb 2+ ions tend to show more electrosorption on these fibers than Cd 2+ ions. Also, the C-rGOMnPAN electrode system is shown to work with 95% regeneration efficiency when 100 ppm NaCl is used as the electrolyte. Hence, it is clear that the novel binder-free, electrospun C-rGOMnPAN electrodes have the potential to be used in salt removal and also for the heavy metal removal applications of water purification. Capacitive deionization (CDI) is a trending water desalination method during which the impurity ions in water can be removed by electrosorption.