| Summary: | 碩士 === 國立臺南大學 === 環境生態研究所碩士班 === 95 === The electrochemical behavior of environmental organic compounds, ca. methanol, formaldehyde, and benzyl alcohol at the boron-doped diamond electrode (BDD) is examined by cyclic voltammetry (CV), linear scanning voltammetry, and electrochemical impedance spectroscopy (EIS). Organic oxidation on the BDD electrode surface is influenced by the indirect oxidation which is caused by other oxidants, for example hydroxyl radical. The reaction kinetics in alkaline solution is studied at various concentrations of the organic compounds, various pHs and temperatures. According to the kinetic analysis, it indicates that the adsorptions of organic molecules on the BDD electrodes are the rate-determining steps at low potential range. In addition, EIS results also show the evidence for the adsorption behavior of organic molecules on the BDD electrode.
In order to study the effect of pH, formaldehyde is employed as the model compound. There is no significant oxidation peak of formaldehyde in acidic solution because the oxidation of formaldehyde is at the potential range of water discharge. In neutral solution, there is a well-defined oxidation peak at about +2.2 V versus Ag/AgCl. However, in neutral solution, the oxidation of formaldehyde is dominated by indirect oxidation at lower formaldehyde concentration, and it is dominated by direct oxidation at higher concentration. Finally, in alkaline solution, the oxidation of formaldehyde is dominated by indirect oxidation caused by powerful oxidant and is related to the ratio of the amounts of formaldehyde and OH- ions at the BDD electrode surface.
The response current for benzyl alcohol oxidation is declined with time due to the deposition of polymeric film at the BDD electrode surface, while it is not for methanol. Prolonged (24 hours) polarization of the BDD electrode at +2.0 V in benzyl alcohol generated enough fouling film for investigation by AFM, SEM, Raman, and FTIR techniques. AFM and SEM microscopy images confirm a fouling film confined to the low-lying regions of the poly-crystallite BDD surface, indicating the active sites of benzyl alcohol oxidation are located within these low-lying regions. The fouling material was identified from Raman and FTIR spectroscopy as poly-ester. Experiments confirm the fouling film can be removed and the electrode surface reactivated by brief polarization at +3.0 V.
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