The Preparation Of Ytterbium-doped PbO₂ Electrode And Research On The Application Of Electrochemical Degradation Of Perfluorooctanoic Acid

With a strong chemical stability, perfluorinated carboxylic acid compound （PFCAs） is a kind of typical refractory organic pollutants. This thesis started from the preparation and characterization of Yb-doped PbO₂ electrode. Then we did the research about the modification and application testing of PbO₂ electrode. Meanwhile, we explored the degradation conditions of perfluorooctanoic acid （PFOA） by the new type of ytterbium-doped PbO₂ electrode. Finally, we proposed the degradation mechanism of PFOA and verified the speculation by mass spectrometry.In this thesis, the three kind of PbO₂ electrode （Ti/SnO₂-Sb-Yb electrode, Ti/SnO₂-Sb/PbO₂ electrode and Ti/SnO₂-Sb/Yb-PbO₂ electrode） were prepared by the method of brushing and electrodeposition under the same conditions electrode. Then the electrodes were characterized by some physical methods like SEM, EDS and XRD. Then, we tested the electrochemical performance by CV test, LSV, Tafel curve tests and accelerated life testing. We evaluated the properties of electrodes by the degradation of PFOA and other indexs. We compared the rate of degradation of the three electrodes. The results indicate that the Yb-doped electrodes have a better performance of electrochemical. The surface of modified electrode was more dense and full. What’s more, the modification of electrode have a stronger conduction, a higher oxygen evolution potential and a longer lifetime. The Yb-doped PbO₂ electrode was determined a superior performance.Then the preferred Ti/SnO₂-Sb/Yb-PbO₂ electrode was worked as a anode, and the Ti sheet was treated as cathode. In the electrolytic cell without diaphragm. A systematic control variable experimental was designed as follows to analyze the influenceing factors:initial concentration of PFOA （Co,10 mg/L-200mg/L）, current density （J, 1mA/cm2-40mA/cm2）, initial pH value （3-11） and electrode distance （d, 5mm-20mm）. After a 150 min electrolysis（25℃）, the optimum reaction conditions were obtained, degradation and defluorination ratios of the PFOA were reached 95.11±3.9% and 76.7±2.8%, respectively.High Performance Liquid Chromatography （HPLC） was used to analyze the intermediate in electrolyte and Fluorine Ion Detection was used as detectors to measure the concentration of fluorine ion during the 150 minutes degradation. The kinetics and mechanism during the degradation were investigated at the meanwhile. Results show that the degradation process fits the first order reaction kinetics well, what’s more, hydroxyl radical （·OH） was generated on the surface of anode, the PFOA was oxidized constantly by delivering the CF2 groups. After that, the PFOA become a shorter chain PFCAs and eventually degradated as water and carbon dioxide.