Preparation Of Palladium Modified Electrode And Its Electrochemical Degradation For Chlorinated Organics

Chlorophenols aromatic compounds was one of the typical refractory and toxic organic pollutants in wastewater treatment process.Due to the stable co njugated system formed by the aromatic ring and chlorine atoms of chlorophenols aromatic compounds,they were highly toxic and nonbiodegradable.More seriously,the more the chlorine atoms in the molecular,the more toxic and stable in the environment.Therefore,chlorphenols are defined as priority control pollutants in both Europe and China.The Electrochemical treatment technology has been paid attention for its advantages of the high efficiency,simple operation,the environmentally friendly electrode materials.In this thesis,four kinds of composite electrodes,including Pd/GO/Ni,Pd/Ti,Pd/GO/Ti and Pd/PAIN/Ti electrodes prepared by constant current electrode position,was investigated in the aspects of the surface structures,crystal structures,surface functional groups,suface element valence and composition of the surface electrodes by scanning tunnel electron microscopy,X-ray diffraction,Xray photoelectron spectroscopy and Fourier transform infrared spectroscopy.The electrochemical degradation characteristics of the elextrodes were mainly focus on the electrochemical degradation of 2,4-dichlorophenol,and the electrochemical degradation of 2,4,6-trichlorophenol,2,4-dichlorophenoxyacetic acid was also included in study.The degradation mechanism of 2,4-dichlorophenol by Pd/PAIN/ Ti electrodes was essentially elaborated.The oxidized graphene in this study was prepared by the conventional methods of Hummers.The Pd/GO/Ni electrode was made by using constant current electrodeposition method.The performances of electrodes were greatly effected by the manufacture conditions.The optimized manufacture parameters were obtained with the PdCl₂ concentration of 0.02 mmol/L,the reaction temperature of 40 °C,the GO concentration of 10 mg/L,the pH value of 3,and the Na₂SO₄ electrolyte concentration 0.05 mol/L.Great performance stablity was observed.After continuous using of 20 times,the removal of 2,4-chlorophenol by electrochemical degradation decreased by only 1.2%.The electrochemical degr adation of 2,4-chlorophenol,2,4,6-trichlorophenol and 2,4-dichlorophenoxyacetic acid was followed the Langmuir-Hinshelwood equation of pseudo-first order reaction kinetics,the reaction rate constants were 0.00961 min-1,0.00989 min-1 and 0.01040 min-1,respectivelyRoughened surface was formed on the titanium elecrode substrate by applying electrochemically etched.The nano Pd particles loaded on this kind of surface showed a spatial network structure,firm adhere degree with titanium elecrode substrate and high performance stability of the Pd/Ti electrodes.After continuous degradation of 20 times,the 2,4-chlorophenol removal rate was stable at around 82.1%.Extending the duration time of electrochemical etching,nanotubes were formed on the electrode surface.The electorde was first loaded with GO and then loaded with nano Pd particles to prepare Pd/GO/Ti electrode.The Pd particles was mainly observed in the nanotubes.The GO was riched of oxygen based active functional groups.These functional groups could transfer charge effectivly and improve the electrode performances.The exsiting of GO promoted the degradation of 2,4-dichlorophenol by Pd/GO/Ti electrodes.The PANI/Ti support electrodes were prepared by constant voltage method to produce polyaniline on Ti substrate.The nano palladium particles were then deposited using constant current electrodeposition method.The adding of polyaniline promoted the electrode catalysis.The 2,4-dichlorophenol degradation rate of Pd/PANI/Ti electrode in Na Cl electrolyte was ten times greater than that of other electrodes.The adding of polyaniline improve the adhere degree between Pd particals and Ti surface.The promoted catalytic effect of polyaniline was observed during the degradation 2,4-dichlorophenol of the Pd/PANI/Ti electrode.The good performance of Pd/PANI/Ti electrode about the degradation 2,4-dichlorophenol was due to the promoted catalytic effect of polyaniline and the coordination effect of catalysis of Pd particals.The electrochemical degradation of 2,4-chlorophenol,2,4,6-trichlorophenol,2,4-dichlorophenoxyacetic acid by the three kinds of titanium base electrodes were all followed the Langmuir-Hinshelwood equation of of pseudo-first order reaction kinetics.The degradation mechanisms and kinetics of 2,4-chlorophenol by using Pd/PANI/Ti electrodes were intensivly investigated.The possible electrochemical degradation pathway and mechanism of 2,4-dichlorophenol was put forward.The electrochemical degradation of 2,4-dichlorophenol on electrodes had two pathways.1.The 2,4-dichlorophenol open its benzene ring to produce a fatty acid containing two chlorine by hydroxyl radical attacks.2.The 2,4-dichlorophenol first lose a chlorine atom to form a chlorophenol.Then,the chlorophenol generate inferior intermediate products such as hydroquinone or benzoquinone etc.by hydroxyl radical attacks.The intermediate products were continuously oxidized to small molecules and eventually mineralized into CO₂ and water.