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Studies of the Effects of Composited TiO2/SiO2 Catalyst for the Photocatalytic

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Tutor: XuZiLi
School: Jilin University
Course: Environmental Science
Keywords: TiO2/SiO2,photocatalysis,NO2,heptheptence,degradation
CLC: X132
Type: Master's thesis
Year:  2006
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The environmental pollution is getting worse day by daybecause of the rapid development of modern industry, especially theatmospheric pollution causing by NOx and VOCS, which has becomethe environmental protection question many countries urgent to solve.At present, people already have done some researches onphotocatalysis degradation of micro-noxious gas in the atmosphere.In 1972, Fujishima discovered the photocatalytic splitting of water onTiO2 electrodes. This event marked the beginning of a new era inheterogeneous photocatalysis. In recent years, applications toenvironmental cleanup have been one of the most active areas inheterogeneous photocatalysis. This is inspired by the potentialapplication of semiconductor metal oxides and sulfidesphotocatalysts for the entire destruction of organic compounds inpolluted air and wastewaters. TiO2, ZnO, Fe2O3, WO3, CdS, etc, aresemiconductors, Under illumination by photons of greater thanband-gap energies, the valence band electrons can be excited to theconduction band, creating highly reactive electron-hole pairs. Aftermigration to the solid surface, these may undergo electron-transferprocesses with adsorbates of suitable redox potentials. At present,there are some researches on photocatalytic degradation of volatilityorganics, and the products are CO2 and H2O. The organics aretransformed to N2 or NO3-when photocatalytic degradation of NOX.But studies involving heptheptence and NO2 photocatalysis arerelatively few. In this paper, the reaction between heptheptence andNO2 is studied.In this paper, firstly we prepare the TiO2-SiO2 catalyst by using asol-gel method. Firstly we studied the effect of SiO2 concentrationand TiO2-SiO2calcination temperature. The results showed that thecatalyst with little particle size, uniform distributing, and gooddispersing was gained after adding SiO2, all of this advantages willincrease the catalyzing activity. But the unformed catalyst that lack ofactivity will be made if adding too much SiO2. Hence through a seriesexperiments we conclude the highest catalyst activity would beachieved when about 9.1 % SiO2 was added. The heat stability wasimproved in evidence when SiO2 was added. The defect of bodyappearance will be eliminated effectively, the transformation ofcrystal type will be restrained and the surface area will be reducedobviously under the process of calcination. Hence through thedegradation experiment we achieved the best calcinationstemperature was 600¡æ.In this paper, the adsorption and photocatalytic degradation ofheptheptence over TiO2/SiO2 photocatalyst with the aid of UV lightwere investigated carefully in the presence of NO2. The experimentdata indicated that Mmax (the maximum adsorption amount ofTiO2/SiO2 towards heptheptence) is 3.10 mg, and is increased to3.80mg in the presence of NO2(44.64 ¦Ìmol/L). In the photocatalyticreaction process of heptheptence (40.76 ¦Ìmol/L and 163.04 ¦Ìmol/L),the degradation of heptheptence and creation of CO2 under differentNO2 concentrations, the results indicated that when initialconcentration of CO2 was equal to 3 times initial concentration ofheptheptence (3:1), the degradation of heptheptence was the best.Through GC-MS and FT-IR we respectively determined theintermediate products of three different reaction systems, such as theorganic matters C7H15NO2 ¡¢ C6H13ONO2 ¡¢ 1,2-C7H14(OH)2 ¡¢C7H15ONO2¡¢C9H19ONO2 et al., and accordingly deduced the possiblereaction mechanism.In this paper, we also studied the effects of different oxygen andvapor concentration on photocatalyst degradation heptheptence andNO2. The reaction speed increased along with the increase of oxygenconcentration. Especially when the oxygen concentration was 5%the speed was the most and close to steady. The best concentration ofvapor was 15% that influenced CH3-C6H6 reaction speed. Thereaction speed of CH3-C6H6 was increased along with the increase oflight strength. Finally the activity losing and regeneration wasinvestigated, and the results showed the synthetic catalyst possessoutstanding reaction enduring characteristic.
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