Preparation Of Pd/MWNTs Gas Diffusion Electrodes And The Degradation Of Chlorophenols

The chlorophenols are one kind of persistent organic pollutants with high hazard, and electrochemical oxidation reduction technology has been widely applicated in the field of chlorophenols pollutant degradation. In this paper, Ti/RuO2/IrO2electrode was used as an anode and Pd/multi-walled carbon nanotubes (Pd/MWNTs) gas diffusion electrode was used as a cathode. Degradation of four kinds of chlorophenols (2-chlorophenol,4-chlorophenol,3-chlorophenol and2,4-dichlorophenol) were investigated by the cooperation effect of the anode and cathode.Carbon nanotubes have been pretreated by HNO3, mixed acid and the mixture of HNO3and H2O2. The density of the organic functions regiment on the carbon nano-tubes by different pretreated methods has been measured, and the result showed that the organic functions reginment of the pretreated CNTs by mixed acid and HNO3are most and reached2mmol/g.Pd/MWNTs catalyst used for the Pd/MWNTs gas diffusion cathodes has been prepared by ethylene glycol reduction method and formaldehyde reduction method, and characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electrode microcopy (TEM), X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry (CV) techniques. And the results indicated that the nitric acid of preparation of catalyst pretreatment glycol reduction show the best performance, Pd average particle size is3.7nm, and the Pd average particle size of the catalyst pretreated by formaldehyde is4.5nm. Cyclic voltammogram for different catalysts at oxygen gas showed that the performance of the catalyst pretreated by ethylene glycol reduction method is better than formaldehyde.The catalysis layer of gas diffused electrode was made by the mixture of Pd/MWNTs and PTFE. Then the catalysis layer, stainless steel net and the gas diffused layer were pressed together to obtain a gas diffused electrode. The electrolyse conditions was investigated by changing the current density, electrolyte concentration, initial pH and ventilation solution. Response surface methodology (RSM) was used to analysed the best condition of the4-chlorophenol degradation. And the best condition was as fellows:the initial pH is7, electrolyte (sodium sulfate) concentration is0.05mol/L, the current is50mA/cm-2, hydrogen was fed in the0-80min and air was fed in the80-120min, the degradation rate is more than90%.High Performance Liquid Chromatography (HPLC), Ion Chromatography (IR) and Ultraviolet Spectrum (UV) analysis method were used to detect the degradation intermediates of the four chlorophenols. The results showed that degradation efficiency of the four kinds of chlorophenols in this electrolyse system is high, the chlorophenols removal is more than90%and the TOC degradation is more than75%. The degaradation result in the anode compartment are as follows,4-chlorophenol> 2,4-dichlorophenol>3-chlorophenol>2-chlorophenol. The degaradation result in the cathode compartment are as follows,2-chlorophenol>3-chlorophenol>2,4-dichlorophenol>4-chlorophenol. By HPLC and IR analysis, the four kinds of chlorophenols were proposed containing the intermediates, such as phenol, hydroquinone, benzoquinone, maleic acid, fumaric acid, succinic acid, malonic acid, oxalic acid, acetic acid, formic acid.