Experimental Study On Photocatalytic De-gradation Of Plychlorobenzenes On Nano-TiO₂ Under UV Irradiation

The part of municipal solid wastes (MSW) dealing with incineration has been increasing in the last ten years. There are a lot of works to do in china for executing the Stockholm Convention on Persistent Organic Pollutants. The dioxins control technologies on incinerators become more and more important. The emission of dioxins of incinerators can be reduced to meet standards using activated carbon (AC) injection, but secondary pollution appears after this technology.Plychlorobenzenes are selected as substitutes of dioxins in this paper. The photocatalytic degradation mechanisms of chloroaromatic compounds both in oxidizing atmosphere and reducing atmosphere are studied, and so some important infectors during the photocatalytic degradation are. The major parts are following:(1) The review first describes the principles of photocatalytic destruction by semiconductors and then focuses on degradation rates and reaction mechanisms in a variety of photocatalytic uses of modified TiO2. Finally, these concepts are illustrated by selected examples relating to the photocatalytic degradation of organic persistent pollutants. And some approaches towards industrial application are analyzed.(2) Nano-TiO2 film was prepared in homogeneous, and adhered to the plate stoutly. The photocatalytic degradation experiments were carried out by doping HCB solvent on the TiO2 film under UV light irradiation in the air and nitrogen atmospheres. The photocatalytic degradation rates of HCB distinctly increase in both air and nitrogen atmospheres when the nano-TiO2 catalyst was added, while the trend of degradation in the two astrospheres is very different. It is found that the degradation efficiencies of HCB are 99.6% and 86.1% respectively in the air and nitrogen atmospheres. The photocatalytic degradation mechanism of HCB on nano-TiO2 was discussed.(3) Titania nanorod thin films and titania nanowire thin films were prepared by hydrogen peroxide. It is found that the degradation rate of hexachlorobenzene on titania nanorod film is two times as it on P25 film in nitrogen, and the rate on titania nanowire get a 50 percent increase compare with P25 film. After thermal treatment, titania nanorod film possessed higher activity to assist the degradation of hexachlorobenzene. Titania nanorod films and P25 films get a same degradation tendency when atmosphere is change from air to nitrogen.(4) Experimental study on photocatalytic degradation of 1,2-dichlorobenzene on P25 films were executed. It found that adsorption was more important during the degradation process. And photocatalytic degradation was more after adsorption saturation. The photocatalytic degradation mechanisms of 1,2-dichlorobenzene were different from hexachlorobenzen. When the carrier gas was air, 1,2-dichlorobenzene was decomposed by dechlornination followed by ring cleavage, and the chloride was discharged in the form of HCl. When the carrier gas was nitrogen,1,2-dichlorobenzene was decomposed by ring cleavage followed by dechlornation, and the chloride was discharged in the form of Cl-.