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Catalytic Ozonation by Metal Doped-TiO2 for Degradation of Organic Pollutants in Water

Author: ZhangJing
Tutor: MaJun
School: Harbin Institute of Technology
Course: Municipal Engineering
Keywords: Ozone Titanium dioxide Nitrobenzene Oxalic acid Doping modification Hydroxyl radicals
CLC: X52
Type: PhD thesis
Year: 2010
Downloads: 615
Quote: 0
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Abstract


With the rapid development of industry, more and more serious water crisis facing humanity, difficult for conventional water treatment processes to remove harmful toxic organics in water. Advanced oxidation process has a rapid response, for a wide range of high stability of refractory organics removal efficiency advantages, extensive research by researchers. TiO2 addition as the photocatalyst, in the field of ozone catalytic oxidation also exhibit excellent catalytic activity. This paper, the use of sol-gel method rutile TiO2 and TiO2 nanoscale metal doping modification. Nitrobenzene and oxalic acid as the target, respectively, to filter out the best catalyst, and to optimize the preparation conditions of the doping effect. In this study, the characterization of the surface properties of the catalyst, and speculated that the ozone catalytic oxidation mechanism. In this paper, the sol-gel method nano-TiO2, nitrobenzene target ozone catalytic oxidation test. The results showed that different crystal forms of TiO2 with different catalytic properties, almost no catalytic ozone anatase TiO2, rutile TiO2 has excellent catalytic performance. In rutile TiO2 catalytic ozone reaction, with the catalyst dosage, ozone concentration, reaction temperature was raised, nitrobenzene removal rate increases; solution pH increases, the removal rate of nitrobenzene with elevated in the pH value of the solution 10 is to have the highest removal efficiency, subsequently reduces; different water background nitrophenyl substantially no effect on the removal rate. The rutile TiO2 catalytic ozonation process in the formation of hydroxyl radicals is the dominant reaction mechanism, the process of organic matter degradation intermediates generated ozone alone process is basically the same: carboxylic acids, aldehydes and ketones, phenols. Choose cobalt, iron, nickel, manganese, and zinc five kinds of transition state metal ion doping modification of TiO2. The prepared the Mn/TiO2 was the Ni/TiO2 Co/TiO2 Fe/TiO2 Zn/TiO2 these five catalysts relatively separate ozone oxidation process are significantly improved nitrobenzene removal, but with pure TiO2 rutile The difference is not large catalytic effect, doping does not improve the effect of ozone catalytic decomposition of nitrobenzene. Monitoring results show that the trace metal ion dissolution in the ozone catalytic oxidation process, but were far below the national standard. The both doped catalyst Mn/TiO2 and Co/TiO2 can greatly improve TOC removal system, intermediate, Mn/TiO2 and Co/TiO2 is able to further catalytic ozonation of nitrobenzene in the middle product, for example, is difficult to be oxidized directly to the ozone molecule oxalate. Oxalic acid, as the target object, respectively, of each of the catalyst activity of the ozone catalytic oxidation. Found that, Mn/TiO2, and Co/TiO2 have good catalytic ability, can significantly improve the efficiency of ozone removal of oxalic acid, TiO2, the Ni/TiO2 Fe/TiO2, Zn/TiO2 catalytic ozonation process of oxalate removal rate is not high. Preparation of the proportion of the catalyst calcination temperature and the metal ion-doped, respectively conditions optimized changing the calcination temperature and the ion doping ratio Ni/TiO2, Fe/TiO2, Zn/TiO2 catalytic efficiency of ozone decomposition oxalic improved basically no effect; Mn / of TiO2 optimum calcination temperature of 500 ° C, manganese and titanium molar doping ratio of 1/20, the mixed crystal phase of anatase and rutile phase; Co/TiO2 optimal calcination temperature of 500 ° C, cobalt doped and titanium optimum molar ratio of 1/30, anatase and rutile mixed crystal phase. Study the process of decomposition of oxalic acid Mn/TiO2 and Co/TiO2 catalytic ozone factors: ozone flow range examined in the present experiment, the changes in the ozone dosage had no effect on oxalic acid removal rate; initial concentrations with oxalic acid increases, the removal rate of the oxalic acid is reduced; removal rate also will increase with the amount of catalyst, the elevated temperature of the water body, oxalic, but under different reaction conditions in the reaction after 30min oxalate have substantially been removed; in the reaction temperature to the oxalate removal under the conditions of 10 ° C is much lower than at 20 ° C, 30 ° C, 40 ° C reaction temperature removal efficiency; pH ??values ??affect Mn/TiO2 surface charge carried by positive and negative, and oxalic acid ionization removal rate significantly affected the degree of solution pH on oxalic acid, ozone catalytic oxidation of oxalic acid has better removal of lower initial pH conditions. Was found by XRD characterization, manganese, and cobalt-doped TiO2 anatase elevated to the phase transition temperature of the rutile structure, and the particle size of the powder is increased. Right the experimentally prepared Mn/TiO2 Co/TiO2 XRF XPS characterization, manganese and cobalt elements in the proportion of the surface of the catalyst is higher than the internal proportional, respectively in MnO2 and TiCoO3, form exists. Manganese and cobalt doped appear positive trivalent titanium makes the surface of the catalyst, resulting in oxygen vacancies appears, causing TiO2 lattice defects in the surface of the catalyst Ti exists mainly in the form of positive tetravalent, about 70%. Carbon dioxide and water in to utilize Mn/TiO2 and Co/TiO2 catalytic ozone decomposition of oxalic acid process oxalic direct mineralization intermediate generation. By adding t-butanol, and by ESR tests proved the hydroxyl radicals generated in these two reaction system and involved in the oxidation reaction of the oxalic acid, the hydroxyl radical is not the sole oxidizer. Speculated oxalic first be adsorbed or complexed on the catalyst surface, and then oxidized by hydroxyl radicals and ozone molecules, the adsorption of the oxalic acid is the constraints of the entire reaction step.

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CLC: > Environmental science, safety science > Environmental pollution and its prevention > Water pollution and its control
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