Influence of chemical structure of dyes on capacitive dye removal from solutions

Polypyrrole nanofibers (PPy-NF) were prepared by an oxidative template assembly method and utilized for the fabrication of N-doped activated carbon nanofibers (N-AC-NF). Capacitor cells, containing N-AC-NF electrodes were used for capacitive dye removal (CDR) from aqueous solutions. It was found that CDR method can be used for the removal of triphenylmethane and chromotropic acid family dyes from aqueous solutions. The analysis of cyclic voltammetry, galvanostatic charge-discharge and impedance spectroscopy data, coupled with results of quartz crystal microbalance studies, provided an insight into the influence of chemical structure, size, charge-to mass ratio, concentration and redox-active ligands of the dyes on the capacitive behavior, dye removal efficiency, reversibility and cyclic stability of the cells. The CDR method offers advantages for the dyes of chromotropic acid family, due to larger voltage window, good capacitive behavior, improved cyclic stability and higher power-energy characteristics. It was found that charge storage mechanism is mainly attributed to double layer capacitance. CDR is a promising method for water purification, which offers advantages of energy saving and simple electrode regeneration.