Preparation and Modification of Titanium Dioxide Photocatalyst Film and its Application on the Removal Efficiency of Aromatic Organics

• Main Authors: Po-Lin Lu, 盧伯麟
• Other Authors: Jerry
• Format: Others
• Language: zh-TW
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/99287754307966488565

碩士 === 逢甲大學 === 環境工程與科學所 === 93 === With the rapid development of industry, solvents used widely in manufacturing processes are wasted into our environment at excess quantities. Due to the difficulties using traditional treatment processes to treat refractory organics discharged from the industry, new treatment technology should be further developed and applied. Therefore, in this study photocatalyst was employed to decompose the recalcitrant organics and to evaluate the major controlling factors for the photodecomposition of organics. The photocatalysis using titanium dioxide film coated and immobilized on the supported materials and high-pressure ultraviolet lamp was expected to have enough oxidation power to mineralize the organics into water and carbon dioxide. This research is composed of four topics including preparation of titanium dioxide film by chemical vapor deposition technique, evaluation of photo-decomposition on benzenes with different substituted functional groups, changes of using different sorts of supporter materials to deposit photocatalyst film, and modification of photocatalyst through the addition of metal elements. It was found that titanium dioxide film deposited at 400 ℃ for ten hours and calcined at 600 ℃ would become a better photocatayst as it offers more complex surface array and owns compacted crystalline structure with anatase phase growing on. Since benzoic acid can be directly decomposed by UV light, the overall decomposition rate is ranked following the order of benzoic acid, phenol, then nitrobenzene. If solely considering the efficiency the photo-oxidation on the decomposition of organics, phenol would be ranked as the first due to its electron-donating functional group by which the hydroxyl radicals could accelerate its electrophilic attack. On the contrary, benzoic acid carrying an electron-withdrawal functional group could not be easily decomposed via photocatalysis process. Besides, the operational conditions of our photo-oxidation system were evaluated by changing detention time, pH and dissolved oxygen level. Longer retention time can increase the removal rate of organics. Since pH values might affect the adsorption affinity between the organics and photocatalyst, phenol and nitrobenzene are found to be decomposed optimally at neutral pH, but benzoic acid at acidic pH. Dissolved oxygen plays an important role as being an electron carrier during the course of photocatalysis. Excess dissolved oxygen, however, would scavenge hydroxyl radicals generated from the UV irradiation on the photocatalyst. Therefore, It was found that maintaining medium DO level would be better to decompose organics in aqueous phase. The only exception is for nitrobenzene by which the nitrite ions released by oxidation attack on its parent compound can represent another electron carrier even at rather lower DO level. Using 316 stainless steel to replace pyrex glass as the supporter materials coated with titanium dioxide photocatalyst could have better decomposition efficiency due to the full utilization of UV light inside the reactor. Finally, with the implantation of heavy metal, such as silver and copper ions, onto the titanium dioxide film by chemical vapor deposition, it was found that decomposition rate of the target organics had been enhanced, but not significantly. Therefore, the modification of photocatalyst by doped metal contents should be carried out not only to intensify the oxidation ability but also to utilize the visible light as the energy source.