The Electrochemistry Degradation Of Chlorinated Organic Acids

In this thesis,two methods including electro-oxidation and electro-reduction were employed to investigate the degradation of chlorinated organic acid.On the one hand,the decomposition of aqueous chloroacetic acid(CAs)was investigated by means of anodic contact glow discharge electrolysis(CGDE).With the decay of CAs,the corresponding total organic carbon(TOC)also decreased smoothly.Meanwhile,it was found that chlorine atoms in the CAs were released as chloride ions(Cl-).As the main by-products,Formic Acid(FA)were detected.The decay of both CAs and TOC obeyed the first-order rate law,respectively.The apparent rate constant for the decay of CAs and TOC were bigger with the less number of chlorine on CAs.The reaction pathway involving the successive attack of hydroxyl radical(·OH)as well as the carbon chain cleavage were discussed basing on the products and kinetics.Decomposition of aqueous chloropropionic acids(CPAs)by means of CGDE was similar with those of CAs.With the decay of CPAs,the corresponding TOC also decreased smoothly.Meanwhile,it was found that chlorine atoms in the CPAs were released as Cl-.As the main by-products,oxalic acid(OA)and formic FA were detected.The acetic acid(AA),monochloroacetic acid(MCA)and propanedioic acid(PDA)were also detected as the primary intermediates for decomposition of the corresponding CPAs.The decay of both CPAs and TOC obeyed the first-order rate law,respectively.The apparent rate constant for the decay of CPAs increased with the increase in pKa values of CPAs,while that for the decay of TOC was substantially unaffected.The reaction pathway involving the successive attack of ·OH as well as the carbon chain cleavage were discussed basing on the products and kinetics.On the other hand,the electro-reduction of trichloroacetic acid(TCA)was investigated.The cathode was Pd-loaded Ni foam electrode,and the anode was platinum wire(diameter 0.6mm).The effects of electrolyte,the concentration of electrolyte,current density,temperature and the quantity of Pd-loading were investigated.The characteristics of the Pd-loaded Ni foam was also investigated by scanning electron microscope(SEM).The best removal rate of TCA is 99.76% and the dechlorination of TCA is 73.46% under the condition: 20 mM sodium sulfate as electrolyte,the temperature 20 ?,the quantity of Pd-loading 4.5mg/cm2,and the constant current 10 mA,reduction time 240 min.According to the three products detected: dichloroacetic acid(DCA),MCA and AA,the dechlorination of TCA should take place by losing chlorine atom one by one.The electro-reduction of TCA followed first order law and the reactive rate is 0.0258min-1(R2=0.9955)and the concentration of the residual chlorine atoms on TCA followed the pseudo-first order reaction.The reactive rate is 0.0072min-1(R2=0.9958).