Preparation, Properties Of Ti/BDD Electrodes And Their Applications In Wastewater Treatment

In recent years, the advanced electrochemical oxidation process for the treatmentof the wastewater have attracted ever-increasing attention due to their easyapplicability to automation, high efficiency and environmental compatibility.Thecurrent efficiency of an oxidation process depends strongly on the electrodeproperties, the anodes must have high O2evolution overpotential.The BDD has numerous unique properties, such as extremely wide potentialwindow, low background current, corrosion stability, so it has attracted extensiveattention recently, and it has been widely investigated and applied inelectrooxidation, electroanalysis, electrosynthesis, capacitor, biosensors. But in thosestudies, the BDD electrodes were mostly using flat Si, Ta, Nb, and W as substrates,their wide application in wastewater treatment is impossible because of the poormechanical strength and low conductivity of Si and the unacceptably high costs ofTa, Nb, and W. So it is necessary to search for new electrode substrates.In this study, we have used flat Ti and porous Ti as electrode substrates,prepared BDD electrodes in different experimental conditions, and we studied theproperties and their application to wastewater treatment. The main contributions ofthis research are as follows: (1) Preparation and properties of flat Ti/BDD electrodesThe high quality of BDD film was synthesized on flat Ti plate by MP-CVDmethod. The mixture of methane, hydrogen and B(OCH₃)₃/H₂was used as the gassource. The grain size of BDD is uniform and the distribution is dense withoutcracks or holes, the concentration of sp³-bonded carbon is high. The results of theCV showed that there was a wide electrochemical window, low current density andhigh oxidation stability of the BDD electrodes. The service life of Ti/BDD was longin an accelerated life test.(2) The study on wastewater treatment by flat Ti/BDDThe electrocatalytic oxidation activity of Ti/BDD was evaluated using lowconcentration phenol and ARS as model pollutants. The experiments of CV inphenol aqueous solution have confirmed that the current density of oxidation peak isproportional to phenol concentration and the electrode process is controlled by masstransfer. The electrochemical oxidation of ARS could leads to direct production ofcarbon dioxide at the Ti/BDD electrode. It is expected that Ti/BDD electrodes beextensively applied in industry and treatment of difficultly degradation wastewater.(3) Research on deposition conditions of BDD coatings on porous Ti substratesThe high quality of BDD film was synthesized on porous Ti substrate byHFCVD method. This work studied how far the deposition parameters (the biasvoltage, the flow ratio of B(OCH₃)₃/H₂) have an influence on growth and quality ofthe deposited diamond layers and their adhesion with the substrate. The resultsshowed that the best condition of the porous Ti/BDD preparation isV_CH4:V_B(OCH3)3/H2:V_H2=3:(9-3):300, the reaction pressure was4kPa, the proper biasvoltage is57V. The results showed that the electrodes had good crystalline quality,and the substrates can be completely covered, including the surfaces, bottoms andwalls in the pores, there were no fissures or delaminations in the diamond film.(4) Research on the properties of the porous Ti/BDD electrodesThe properties of porous Ti/BDD electrodes were investigated by means of SEM,Raman and XRD, The results showed the crystalline quality of porous Ti/BDD electrodes was better, the content of sp³diamond phase was high. The results of theCV showed the porous Ti/BDD electrodes have wide potential window. For the[Fe(CN)₆]^3-/4- redox couple, the electrode reaction process is quasi-reversible. Theporous Ti/BDD electrodes showed higher degradation rate to eliminate COD thanflat Ti/BDD electrodes in the process of hydroquinone degradation.