Electrochemical Behaviour Of Dyes On Platinum And Activated Carbon Fiber Electrodes

The decolorization of dye wastewater has been concerned. Electrochemical technology is a promising wastewater treatment method since it is environmental benign. Activated carbon fiber (ACF) is a kind of porous, three dimensional electrode with prospective application in dye wastewater treatment. Three dyes, Amaranth, Reactive Blue 19 and Mordant Orange R, were chosen as model compounds for the research of decolorization of simulated dye wastewater on ACF and platinum (Pt) electrodes. Potentiostatic and galvanostatic models were applied for the research.The decolorization kinetics of Amaranth and Reactive Blue 19 on ACF electrode was first investigated with the discussion of chemical oxygen demand (COD) and total organic carbon (TOC) removals. It was found that there were three mechanisms based on different potentials and current densities. They are electrooxidation, electroreduction and adsorption. Not only electrooxidation could remove COD and TOC, but the COD and TOC could be removed during the process of electroreduction. Furthermore, the electroreduction was prior to the electrooxidation for the removal of COD and TOC. It was deduced that azo bond in the Amaranth was destroyed with the electroreduction. Besides, the energy consumption for the whole electrochemical process and current efficiency for the electroreduction process were analyzed.The processes of electroreduction and electrosorption of Mordant Orange R on Pt and ACF were examined respectively. It can be seen that electrosorption is effective on the removal of Mordant Orange R for its hydrophobic characters. Both positive and negative polarization can enhance the capacity of the dye on ACF. Of course, positive polarization, which can make the capacity 3.4 times of that under open circuit, was better than negative one. However, if the positive potential was lower than the potential of zero charge (E_zpc) of ACF, the electrosorption of the dye was prohibited. The processes of electroreduction ofMordant Orange R on ACF and Ft follow pseudo-first order kinetics. Also, it can be confirmed that no 4-nitroaniline and 1,4-aniline were produced for the Mordant Orange R on ACF and Pt based on the HPLC analysis.By analyzing the electrochemical behavior of Mordant Orange R, Pt has little effect on the electrochemical process within the discussed potential and current density. So it is successful to choose Pt as the power collector for ACF.The onset oxidation and reduction potentials for the dyes on Pt or ACF were obtained. For the process of adsorption/electrosorption, the decolonzation and COD or TOC removals resulted from the adsorption of the dye. For the process of electrooxidation, the color, COD and TOC removals resulted from the carbonization of the dye and the adsorption of the electrooxidation products. COD and TOC removals during the process of electroreduction resulted from the adsorption of the electroreduction products. In fact, for the processes of electrooxidation and electroreduction, an adsorption process was included for the first stage under galvanostatic model before the potential was up to the onset potentials.The increase of specific surface area for ACF was not distinct when it was polarized. The increase of active carbon atoms benefits the decolonzation of dye. The quantity of carboxyl (COOH) or ester (COOR) groups increased with the positive polarization and the increased of carbonyl (C=O) or quinone groups with the negative polarization. As a result, more active sites were provided and did good to the electrochemical process.It was shown from the electrochemical impedance spectroscopy that the process of decolorization was controlled by both kinetics and mass transfer diffusion. Also, two time constants were included when polarized negatively.