Nano-manganese oxide and reduced graphene oxide-incorporated polyacrylonitrile fiber mats as an electrode material...

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 (MnO₂) and reduced graphene oxide (rGO)-doped polyacrylonitrile (PAN) composite fibers are fabricated using an electrospinning technique. The incorporation of both MnO₂ 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 MnO₂ and rGO contents as well as when thermally treated at 280 °C. Thermally treated composite fibers with 17% (w/w) MnO₂ 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 (Cd²⁺) and lead (Pb²⁺) 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 Pb²⁺ and 6265 C g^-1 for Cd²⁺), which is most likely to be due to the ease of mass transfer of lighter Na⁺ and Cl^- ions; When compared, Pb²⁺ ions tend to show more electrosorption on these fibers than Cd²⁺ 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.