| Boron doped diamond electrode is one of the best candidates used as anode in electrochemistry. Because it owns several excellent electrochemical performances, including wide electrochemical potential window, low background current and high stability et al. In this dissertation, hot filament chemical vapor deposition (HFCVD) method was employed to fabricate boron doped diamond (BDD) electrodes with different grain size, and the degradation of humidity condensate and human urine in the confined space using BDD anode was also studied.Microcrystalline diamond film and nanocrystalline diamond film were both fabricated by HFCVD method using methane and hydrogen as precursors. Effects of methane concentration, reaction pressure and substrate temperature on the quality of films and the growth rate of diamond films were studied, respectively, and the diamond film growth kinetics model was established. The results showed that methane concentration, reaction pressure and substrate temperature were the main factors on the influence of diamond film’s growing.Boron doped microcrystalline diamond (BDMCD) electrode and boron doped nanocrystalline diamond (BDNCD) electrode were prepared through adding diborane as boron source. Then electrochemical oxidation method was adopted to treat the artificial humidity condensate and artificial human urine, with BDMCD or BDNCD electrode used as anode and stainless steel used as cathode. Mineralization of artificial humidity condensate on both electrodes were over 95%, and mineralization of artificial human urine could reach over 99%. Results revealed that nano-scaled BDNCD electrode showed a slower degradation rate and an oxidation lag when compared with micro-scaled BDMCD electrode, which is mainly due to the large amount of sp2 carbon in the nano-scaled BDNCD electrode.During the electrochemical oxidation of artificial humidity condensate, organic compounds were oxidized to formic acid, acetic acid and oxalic acid first, and oxalic acid was the final product. When study the oxidation of inorganic compounds during the electrochemical oxidation of artificial human urine, it revealed that sulfur ions will not be oxidized, chloride compounds will eventually be oxidized to perchlorate ion and nitrogen compounds will be oxidized to nitrate ions finally. In order to achieve deep treatment, ion exchange resin was coupled after electrochemical oxidation, with 200ml artificial human urine as an example, after whole process the TOC of the solution reduced to 7mg/L and the conductivity was about 0.6μS/cm, the energy consumption was 0.096kWh, and the consumption of anion and cation exchange resin was 26.9g respectively. For real human urine, the consumption of both energy and ion exchange resins will increase. Also considering 200mL real human urine, the TOC of the solution reduced to 30mg/L and the conductivity was about 0.7μS/cm, the energy consumption was 0.166kWh, and the consumption of anion and cation exchange resin was 67.4g respectively, which meet the requirements of the reuse of wastewater in confined space.Although BDNCD electrode owned a slower degradation rate, the pseudo first order kinetic degradation rate constants for degradation of artificial humidity condensate and human urine were only 76.7% and 69.9% of BDMCD electrode, but it had a much longer lifetime. BDNCD electrode had an accelerated lifetime of 465h, which was 32.8% higher than that of BDMCD electrode. That was because the grain size in BDNCD electrode was much smaller, and its surface roughness was 20 times lower when compared with BDMCD electrode. Based on these results, the estimated lifetime for electrochemical oxidation of artificial humidity condensate and artificial human urine in confined space could be about 17 years and 1.6 years, respectively, which could totally meet the requirements of the electrode replacement in the confined space. |
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