Study On Preparation Of Pd-Fe/Graphene Catalytic Cathode And The Degradation Of4-Chlorophenols

The chlorophenols are one kind of persistent organic pollutants with high hazard, and the non-degradation makes it exist in water environment for a long time. They are accumulated in human and animal bodies to harm to human health. Recent years, electrochemical oxidation reduction technology has been widely applicated in the field of chlorophenols pollutant degradation. In this paper, the self-made Pd-Fe/graphene gas diffusion electrode was used as a cathode and Ti/RuO2/IrO2electrode was used as an anode. The result and mechanism of the degradation of chlorophenols (4-chlorophenol) were investigated by cooperation effect of the anode and cathode.In this study, the Pd-Fe/graphene catalyst has been prepared by the Hummers oxidation method and sodium borohydride reduction method. The different proportions of Pd and Fe catalysts were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electrode microcopy (TEM), X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry (CV) techniques. The results indicated that the catalyst which the proportion of Pd and Fe was1:1had optimal electrochemical performance. For the surface, Pd and Fe were well-dispersed with the Pd/C of0.8%and the Fe/C为0.86%. The average size was5.2±0.3nm, Pd-Fe/graphene catalyst can promote the H2O2generated efficiently and decrease the reduction and oxidation potential, which can reduce energy consumption of electrolytic reaction.The catalysis layer of gas diffused electrode was made by the mixture of Pd-Fe/graphene and polytetrafluoroethylene (PTFE). Then the catalysis layer, stainless steel net and the gas diffused layer were pressed together to obtain a gas diffused electrode which was used for degrading4-chlorophenol. The best electrolyse condition of the4-chlorophenol degradation was investigated by changing the current density, electrolyte concentration, initial pH and reaction time and was analysed by response surface methodology. The best condition was as follows:the initial pH was7.00, electrolyte (sodium sulfate) concentration was0.02mol/L, the current was27mA/cm-2, the reaction time was120minute, and the ventilation was hydrogen and air (former sixty min hydrogen, later60min air). The degradation rates of cathode and anode was more than98%and95%respectively, which were abviously higher than the degradation rates of Pd/grapheme,93%and91%.The result of degradation of the4-chlorophenol and the intermediates in the process were detect with total organic carbon (TOC), Ultraviolet Spectrum (UV), high performance liquid chromatography (HPLC) and ion chromatography (IR) analysis methods. The results showed that removal efficiency of4-chlorophenol in this electrolyse system was emarkable. In the anodic comparment,4-chlorophenol was decomposed into intermediates, such as phenol, hydroquinone and benzoquinone. In the cathodic compartment, with the hydrogen condition, hydrogen atoms occured electrophilic addition reaction so that the chlorine atoms were replaced, then the phenol was produced. Because of the further oxidation, anodic and cathodic compartment produced some molecule organic acid, including fumaric acid, succinic acid, formic acid and acetic acid, which were mineralized into CO2and H2O.