| Both ozone and zero-valent metals have been widely applied in the degradation of organic pollutants. Ozone, due to its high oxidation potential, has been used for the disinfection of drinking water and oxidation degradation of organic compounds.Nevertheless, owing to limited oxidation capacity of ozone alone, only a partial organic contaminants could be degraded by ozone and its mineralization achieved is not satisfactory.Thus, how to improve the oxidation capacity of ozone has received considerable attention.Recently, the heterogeneous catalytic ozonation technology, in which metal oxide or other synthetic materials have been adopted as heterogeneous catalysts to promote the decomposition of ozone and the generation of active oxygen species with higher oxidation capacity, especially hydroxyl radical (HO ), has exhibited a high potential for enhancing the degradation efficiency of organics. So there are more and more reports related to this respect. Different from ozone, zero-valent metals, such as zero-valent iron (Fe(0)),zero-valent zinc (Zn(0)), pose high reduction capacity and usually are used to remove halogen organic compounds and azo dyes. Now, zero-valent metals have been combined with oxidation agents, including hydrogen peroxide, persulfate, ozone and oxygen, to generate active oxygen species with higher oxidation potential, which could degrade organics effectively. It has been reported that the introduction of Fe(0) in the ozonation process could significantly reduce chemical oxygen demand (COD) and the reaction pathway of HO· generation by the interaction of ozone with Fe(0) was clarified.In this study, the degradation efficiency of organic contaminants by ozone in the presence of Zn(0) with higher reduction capacity was investigated. Both aniline and p-chloronitrobenzene (pCNB) are important synthetic intermediates, but they also are recognized as the major environmental pollutants and hazardous for human healthy.Therefore, aniline and pCNB were chosen as targets to explore their degradation efficiency by ozone combined with Zn(0). In addition, a possible synergistic effect mechanism of ozone with Zn(0) was investigated and the influence of variables on aniline and pCNB degradation by ozone assisted with Zn(0) were examined. Subsequently, we compared the enhancing role of zero-valent iron, cobalt, aluminum, copper in aniline ozonation degradation and investigated the reaction mechanism of aniline ozonation in the presence of zero-valent copper. Three parts were composed of this thesis.Part I: The degradation efficiency of aniline, one of the aromatic amine compounds,by ozone combined with zero-valent zinc (Zn(0)) was investigated, and the effect of Zn(0)dosage, ozone concentration, solution initial pH and temperature on aniline ozonation degradation in the presence of Zn(0) were explored through a series of batch experiments.The results demonstrated that Zn(0) had a significantly synergistic role with ozone for aniline degradation and mineralization. A complete decomposition of aniline (10 mg/L) was achieved by ozone together with Zn(0) within 25 min, and meanwhile nearly 70% of the total organic carbon (TOC) in the solution was removed. Zn(0) dosage had a markedly influence on aniline ozonation degradation. With an increase of Zn(0) dosage, the degradation rate and degree of aniline significantly increased. It is found that the reaction of aniline ozonation followed a pseudo-first-order reaction kinetics by the analysis of kinetic experimental data and the reaction rate constants had a linear relationship with Zn(0)dosage. The optimum degradation of aniline was realized at 25 ? and a higher temperature had a negative effect on aniline degradation. The effect of solution initial pH in the wide range of 2-12 on aniline degradation was also studied and it is found that aniline could be efficiently degraded at the all tested pH except for pH 12. At solution initial pH 12, Zn(0)had no promoting effect on aniline ozonation degradation. In order to investigate the potential mechanism on the synergistic role of Zn(0) with ozone for aniline degradation, we detected the variation of solution pH, Zn(?) concentration, generated H2O2 concentration with reaction time. The influence of scavengers, TBA and BQ, on aniline degradation was also investigated. Besides, the technology of electron paramagnetic resonance (EPR) was used to demonstrate whether the formation of HO· or not in ozone/Zn(0) system. The results indicated that superoxide anion radical (O2·-), instead of HO·, was the dominant active species responsible for aniline degradation. When ozone coexisted with Zn(0), the transformation of electrons occurred, resulting to decomposition of ozone into oxygen molecular and simultaneous the generation of Zn(II), following by the formation O2·- due to capture of electrons by oxygen. O2·- had the ability to make aniline degrade and simultaneously generate H2O2 due to its disproportionation reaction. The comparison of the reaction activity of micro-Zn(0) and nano-Zn(0) for aniline ozonation were made and it is found that nano-Zn(0) showed no obvious advantage for aniline ozonation degradation compared with micro-Zn(0), instead, the removal of TOC in the solution decreased in ozone/nano-Zn(0) system.Part ?: the degradation of p-chloronitrobenzene (pCNB) in different systems,including ozone alone, ozone together with zero-valent zinc (Zn(0)) and Zn(0) bubbled with air instead of ozone was investigated. The results suggested that the degradation of pCNB by ozone alone or Zn(0) bubbled with air was not satisfactory,however, the coexistence of ozone with Zn(0) exhibited a significantly synergistic role on pCNB degradation. The degradation efficiency of initial pCNB (10 mg/L) was reached to 98% within 18 min. Both Zn(0) dosage and ozone concentration had the positive effect on pCNB degradation. pCNB could be effectively degraded in a solution initial pH range of 4-10, but a higher or lower pH had no benefit for the removal of pCNB. The effect of accompanying anions on pCNB degradation was performed. Chloride and sulfate slightly improved pCNB degradation,whereas bicarbonate and phosphate considerably suppressed the degradation of pCNB. And nitrate had no effect on pCNB degradation. In order to reveal the mechanism of pCNB degradation by ozone catalyzed with Zn(0), the scavengers, TBA and BQ, were added into the system. No obvious effect was observed when TBA was added into the system.However, the introduction of BQ significantly inhibited pCNB degradation and the inhibiting effect increased with the increase of BQ concentration. This result suggested the major active species contributing to pCNB degradation was O2·- instead of HO·. The reuse of Zn(0) for pCNB ozonation implied that the reaction activity of Zn(0) maintained high and stable. Based on the result of Part ? and Part ?, it could be concluded that ozone catalyzed with Zn(O) is a potential and effective approach for the degradation of organic pollutants.Part ?: The degradation efficiency of aniline by ozone together with different zero-valent metals, including iron, cobalt, aluminum, copper was investigated, and the results demonstrated that zero-valent copper (Cu(0)) had highest reaction activity. 98%removal of initial aniline (10 mg/L) was achieved within 24 min when the solution initial pH was near-neutral and the Cu(0) dosage, ozone concentration were 2 g/L, 10.24 mg/min,respectively. The result obtained by EPR technology revealed that the interaction of ozone with Cu(0) leaded to the formation of HO·, which was the major active species responsible for aniline degradation. When ozone coexisted with Cu(0), ozone was decomposed into oxygen molecular,following by the transformation of oxygen to H2O2, meanwhile,Cu(O)was oxidized to form Cu(?) or Cu(?). The Fenton-like reaction between H2O2 and Cu(?)occurred, causing the formation of HO·. The aniline ozonation efficiency increased with the increase of Cu(O) dosage. However, solution pH did not exert obvious effect on aniline degradation when solution initial pH was in the range of 4-10. The presence of chloride in the system could retard the transformation rate of Cu(?) to Cu(?), therefore, chloride had a promoting effect on aniline degradation in system of ozone/Cu(O). |
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