| It is a hot research in the field of water treatment with the degradation of phenolic compounds. Due to its green process, high efficiency and well controllability, electrochemical advanced oxidation progress(EAOPs) has been widely utilized towards various organic pollutants. Boron doped diamond thin electrode on three-dimensional porous titanium(3D-Ti/BDD), since it possesses wide electrochemical window, low background current and high oxygen evolution overpotential. 3D matrix provides larger specific surface area and more reactive sites for the electrochemical reaction while faster electron transfer rate could be realized on 3D-Ti/BDD.Electrochemical oxidation of phenolic organic compounds with different structures were showed on 3D-Ti/BDD electrode in this paper. The relationship among the location, type of substituent groups and electric electro-catalytic activity was also investigated systematically using cyclic voltammetry and UV visible spectrophotometric measurement. The synergistic effect of counter electrode(Ti/RuO2-TiO2-SnO2) was discussed during electrochemical oxidation degradation of chlorinated organic compounds on porous Ti/BDD anode in the same time.1) Cyclic voltammetry was conducted to investigate the oxidation behavior of different benzenediols on porous Ti/BDD electrode and the oxidation peak current, which corresponding to the electrochemical activity on BDD electrode, gave the order: catechol > hydroquinone > resorcinol. The removal rate of interproximal hydroquinone was consistent with electrocatalytic activity after electrolysis time of 12 h. The results further validated that the hydroxyl groups at ortho and para could active the benzene ring and meta-hydroxyl could passivate the benzene ring due to its electrophilic substitution reaction.2) Using electrochemical oxidation of different substituent at the para substituted phenols on porous Ti/BDD electrode, conversion rate of organic matter and COD removal rate were in the same trend, and the order was that-NH2>-OH > phenol >-Cl >-NO2 when the reaction was 8 h. It showed that the electrochemical reaction rate was related to the substituent groups and the essence was the difference of electronic effect, which further leading to the difference of electron density of benzene ring.3) Electrochemical oxidation of different organic dyes with different chromophores was studied on porous Ti/BDD electrode. The experimental results showed that removal rate of COD was in the following order: Safranine T > Methylene Blue > Xylenol Orange > Alizarin red S. The results obtained from UV visible spectroscopy further proved that the decrease rate of chromophore was faster than COD, which indicated that the breakage of chemical bond of chromophore was firstly conducted before the removel of COD during electrode degradation of organic dyes, then formed colorless intermediates, and finally the dyes were totally mineralized to carbon dioxide and water. On the other hand, the decolorization rate was consistent with the degradation rate of COD, indicating that the electro-catalytic oxidation of organic dyes was connected with the chromophore structure.4) The comparison of electrochemical degradation of 4-chlorophenol in single and double-cell electrolyzer were conducted and the results showed that the removal rate of COD in single cell system, anode and cathode chamber in double cell system were 87.8%, 71.5%, 0% after the electrolysis time of 12 h, corresponding conversion rate of 4-chlorophenol were 95.8%, 84.4%, 35.4%. The electrochemical oxidation behavior in anode chamber of single and double-cell was basically the same while reduction of 4-chlorophenol in cathode of double-cell system was carried to generate other organic compounds.5) The dechlorination process of 4-chlorophenol in single and double-cell electrolyzer were studied using UV-Vis spectroscopy and ion analysis technology. The results showed that dechlorination process in single compartment electrolytic cell was accordance with the anode surface of double-cell system, where oxidizing ClO- was generated in anode compartment and chlorine in the cathode chamber existing mainly in the form of Cl-. The intermediates in the anode and cathode chamber of double-cell system were identified using high performance liquid phase chromatography, where the products of the anode chamber were mainly catechol, hydroquinone, o-quinone, benzoquinone, fumaric acid, etc and one step reduction occurred to produce phenol in the cathode region. Meanwhile, the degradation pathway of 4-chlorophenol in anode and cathode region was also proposed according to the intermediates. |
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