Electrocatalytic Oxidation Of Dyes Using Cobalt Phthalocyanine Modified Activated Carbon Fiber Electrode

Textile dyeing wastewater is known to contain strong color and toxic. Most dyes are resistant to microbial attack and the disposal of organic pollutants brings many problems to environment. Therefore, the dyes must be treated before discharge. The traditional treatment technologies include physical adsorption, biological treatments and chemical treatments. Recently, the advanced oxidation processes (AOPs) of the chemical treatments, which have high degradation rates, have been applied for the most. The primary advantage of electrochemical technique is that there is practically no consumption of chemicals since electron is a clean reagent. Another advantage is that the processes are commonly performed at room temperature and atmospheric pressure. It has been developed for its alternative use on the wastewater removal and drawn considerable attention in recent years.Metallophthalocyanines are planar electron-rich aromatic macrocycles which have both electron donor and electron acceptor properties. They have been used in the simulation of oxidase enzyme, photo catalytic oxidation, electro catalytic chemistry field, etc. Activated carbon fiber, a comparatively modern form of carbon fiber material, has an excellent physical adsorption capability and conductivity property. A novel catalytic electrode CoPc-ACF was designed to facilitate dye molecule migrate to the electrode surface, which possessed favorable electro catalytic activity. Furthermore, hydrogen peroxide was generated in the electrochemistry progress and CoPc-ACF/H₂O₂ system was formed. The main research contents are as follows:1. Acid red 1(AR1), one of the azo dyes, was studied in an undivided reaction cell at the different conditions. The results showed that the degradation ratio of AR1 reached at 92% with the electrode CoPc-ACF after 120min reaction, while the AR1 removal ratio was 62% under the reaction of bare ACF electrode, which was due to the adsorption ablity. It confirmed that AR1 was effectively garthered onto the CoPc-ACF firstly, then it was degraded rapidly with the reaction of CoPc in the electro chemistry system. Moreover, the influence of potential, initial pH and the electrolyte were investigated to optimize the operating parameters for the electro catalytic oxidation of AR1. The research suggested that CoPc-ACF exhibited high catalytic activity at a lower potential 3V and across a wide pH. Repetitive tests presented that CoPc-ACF can maintain high catalytic activity over four cycles, indicating that CoPc was completely immobilized by ACF.2. The other two dyes Rhodamine 6G (Rh6G) and Basic Green 1 (BG1) were investigated at the same electrochemical reaction cell. It was found that the degradation rate of BG1 was nearly 100% after 60min, while the Rh6G was 74% after 180min at the same reaction condition. The cyclic voltammetry (CV) curves of the dyes of AR1, Rh6G and BG1 were examined at the electro-chemistry work station. The initial oxidation potential of the three dyes (0.222 V versus standard hydrogen electrode (SHE)) occurred approximately at +1.118V, +1.263V and +1.068V respectively. Besides, the initial oxidation potential was related with the structure of dye, and it was clear that the most refractory dye was Rh6G, followed by AR1 and finally BG1. This showed that the catalytic oxidation ability of CoPc-ACF was affected with the structure and stability of dyes, However, all of the three dyes were effectively degraded by the CoPc-ACF catalytic electrode.3. A possible pathway for AR1 oxidation by the CoPc-ACF catalytic electrode was proposed by monitoring the reaction products with analytic techniques including Ultra-Performance Liquid Chromatography (UPLC), Total organic carbon (TOC), Fourier Transform Infrared (FTIR) and Gas Chromatography & Mass Spectrometry (GC/MS). It can be assumed that AR1 was adsorbed onto ACF firstly, and the decolorization characterized by degradation of azo linkage. The next stage was that naphthalene and benzene rings were destroyed with the reaction of CoPc-ACF electrode, and AR1 was oxidized to organic acids, such as latic acid, maleic acid, adipic acid and other ring opening products. Finally, the intermediates were mineralized to CO2 and H2O.4. The catalytic mechanism of oxidation AR1 with the CoPc-ACF electrode was investigated by using Cyclic Voltammetry (CV) and Electron Paramagnetic Resonance (EPR) spectroscopy. Compared with the bare ACF electrode, the CoPc-ACF catalytic electrode showed a very strong anodic wave with a peak potential lowered about 0.6V for the AR1 oxidation. It demonstrated that CoPc-ACF electrode had an excellent electro catalytic activity toward the ovidation of AR1. The EPR combined with spin trap technique was employed to probe the possible mechanism in the electro-chemistry progresses. No DMPO-·OH signals were detected in the electrocatalytic oxidation system when AR1 was treated when using CoPc-ACF as the electrode both at pH 3 and pH 7, which suggested that·OH didn't play a key role in the electrocatalytic system. As a result, CoPc-ACF catalytic electrode was quite different from the traditional Electro-Fenton technology. Therefore, it presents potential application in the organic pollutants process and provides an alternative to wastewater treatment.