| The advanced electrocatalysis oxidation process has attracted a great deal of attention recently, mainly because of its ease of control, amenability to automation, high efficiency and environmental compatibility. Since 1990s, the processes of indirect electrooxidation of organic compounds by hydrogen peroxide (H2O2) generated by the reduction of oxygen on the cathode have much promise for treating organic toxicants. Generally, the electro-Fenton process can be realized in the no-diaphragm electrolysis system, where H2O2 is produced on the cathode in an acid medium and Fe2+ is added or offered by Fe anode. In this thesis, a new electrochemical oxidation system was used to treat the aqueous organic pollutant. It was constructed by a Ti/IrO2/RuO2 anode, a self-made carbon/ polytetrafluoroethylene (C/PTFE) O2-fed cathode and an organic synthetic diaphragm between the anode and the cathode. In this electrolysis system, the degradation of organic pollutants is realized by the simultaneous oxidation of active anode and oxidant species electrogenerated on the cathode. It is expected to increase notably the degradation rate of organic pollutants without adding metal catalyst.Electrochemical oxidation of methyl orange wastewater was studied using Ti/IrO2/RuO2 anode and a self-made carbon/polytetrafluoroethylene (C/PTFE) O2-fed cathode in the divided cell with a terylene diaphragm. The result indicated that appropriate aeration rate was favorable of improving the methyl orange removal efficiency. The decolorizing efficiency of methyl orange in the divided cell increased with increasing in current density, and it was slightly affected by initial pH. When the current density was 46 mA/cm2 and aeration rate was 30 mL/s, after 60 min, the color removal efficiency was 100%, the average COD removal efficiency was 80%.Chlorophenol pollutants, having high toxicity biorefractory, bioaccumulation and carcinogenic potential are widely found in the environment and are significant contaminants at many sites selected for cleanup on the USEPA top priority toxic pollutants list. There is need to treat such contaminants in concerning of environmental protection. In present work, we present a detailed study on the degradation of chlorophenol pollutants in the diaphragm cell with an organic synthesized diaphragm, a Ti/IrO2/RuO2 anode, and home-made gas-diffusion cathodes, and developing an effective and friendly method to treat chlorophenol pollutants by using a combination process of reduction and oxidation. In the cathodic compartment, the chlorine atoms of chlorophenol pollutants are removed from the aromatic structure and chlorophenol pollutants are reduced to non-chlorinated intermediates. Then, the non-chlorinated intermediates are oxidized and degraded in the anodic compartment and the cathodic compartment.Pd/C catalyst used for the Pd/C gas diffusion cathodes is prepared by hydrogen reduction method and formaldehyde reduction method, and characterized by X-ray diffraction (XRD), transmission electrode microcopy (TEM), X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry (CV) techniques. The electrochemical degradation of chlorophenol pollutants (4-chlorophenol, 2,4-dichlorophenol, and sodium pentachlorophate) is investigated in the diaphragm electrolysis system through three kinds of gas types, using three different kinds of gas diffusion cathode. The results indicated that the self-made Pd/C gas diffusion cathode can not only reductively dechlorinate chlorophenol pollutants by aerating hydrogen gas, but also accelerate the two-electron reduction of O2 to hydrogen peroxide (H2O2) by aerating air. Furthermore, the type of aeration, that is, first air, then hydrogen, is in favor of improving chlorophenol pollutants removal efficiency. Therefore, both the removal efficiency and the dechlorination degree of chlorophenol pollutants reach about 100% after 100 min.By high-performance liquid chromatography (HPLC), the main intermediates of 2,4-dichlorophenol dechlorination in the cathodic compartment are determined as 4-chlorophenol and 2-chlorophenol, which further dechlorinate to phenol. Benzoquinone is the first product formed from the oxidation of phenol. The further oxidation of benzoquinone, after ring opening, leads to the formation of aliphatic carboxylic acids such as maleic acid, fumaric acid and oxalic acid. A reaction scheme involving all these intermediates is proposed.Therefore, it is feasible to degrade chlorophenol pollutants by electrochemical reduction to phenol, which is further degraded on the cathode and anode by electrochemical oxidation in the diaphragm electrolysis.
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