Investigation On Preparation And Efficiency Of Organic Degradation On Boron-doped Diamond Films Electrode

As the heart of electrochemical waste water treatment technology, electrode materials play a great part in the efficiency and cost. Among kinds of electrodes, BDD electrode was noticed by researchers since its excellent physical properties, electrochemical properties and high catalytic activity. This dissertation focused on the application of organic degradation on boron-doped diamond films, which made by hot cathode DC chemical vapor deposition system. The preparation and characterization as well as the electrochemical catalysis on organics degradation by taking phenol and bisphenol A as model pollutant were studied. Meantime, the factors which could have effect on the electro-catalytic activity of BDD anodes were analyzed, and the corresponding path of electro-degradation and the mechanism about electro-catalysis were discussed.In this paper, hot cathode DC chemical vapor deposition technology was chosen as the preparation method. Taking p-type monocrystalline silicon, H₂ and CH₄, B(OCH₃)₃ as the substrate, the reactant gas, and the dopant respectively, we got BDD electrode under the flow ratio of CH₄:H₂:B(OCH₃)₃ being 5:190:10, and the substrate temperature of 1000℃. According to the result of film characterize by scanning electron microscope (SEM), Raman spectroscope and X-ray diffraction (XRD), the anode surface under this preparation condition were compact and uniform, and have intact crystalline structure, high purity of diamond and no crack phenomenon.Taking phenol and endocrine disruptors bisphenol A as the target pollutant respectively, initial concentration of model organics, current density during reaction and initial pH of the electrolyte were selected to examine the electro-catalytic rate under different conditions. It demonstrated, the electrochemical oxidation for organic on BDD electrode conform to the first-order equation, and the current density have the greatest influence on degradation rate, following with the initial concentration and pH values of electrolyte. Meanwhile, it has different impact on the current efficiency for the electrolysis conditions mentioned above.The intermediate products of electro-degradation of phenol and bisphenol A on BDD anode were detected using high performance liquid chromatography (HPLC), gas chromatography coupled with mass spectrometry (GC-MS), so we can conclude the pathways of the two kind of model pollutant. Compared with straight-chain organic acids, BDD anodes performed higher catalytic activity for aromatic organic, during the electro-degradation, little kind of aromatic intermediate products were detected, and there on significant accumulation for them, on the contrary, acid organic degradated slower, so that the acid environment lasted for a long time during electrochemical reaction. Since persistent organic pollutant can be transformed rapidly on BDD electrode, it could be convenient to the following biological treatment.In phenol solution, electrochemical cyclic voltammetry (CV) was applied to analyze directly electro-catalytic oxidation on BDD electrode. The result showed that phenol was oxidized irreversibly, and the reaction was controlled by diffusion process. In practical application, the reaction effectiveness and efficiency can be enhanced by improving mass transfer.