| Environmental pollution is one of the major problems of the modern world. Organic chemicals which may be found as pollutants in waste water effluents from industrial or domestic sources, must be removed or destroyed before discharge to the environment. Such pollutants may also be found in ground and source waters that also require treatment to achieve acceptable drinking water quality. The increased public concern with these environmental pollutants has prompted the need to develop novel treatment methods with photocatalysis gaining a lot of attention in the field of pollutant degradation.The application of illuminated semiconductors for degrading undesirable organics dissolved in air or water is well documented and has been successful for a wide variety of compounds. Organic compounds such as alcohols, carboxylic acids, amines, herbicides and aldehydes, have been photocatalytically destroyed hi laboratory and field studies. The photocatalytic process can mineralize the hazardous organic chemicals to carbon dioxide, water and simple mineral acids. Thus, one of the major advantages of the photocatalytic process over existing technologies is that there is no further requirement for secondary disposal methods.Another advantage of this process is that when compared to other advanced oxidation technologies, especially those using oxidants such as hydrogen peroxide and ozone, expensive oxidizing chemicals are not required as ambient oxygen is the oxidant. Photocatalysts are also self-regenerated and can be reused or recycled.Finally, the solar photocatalytic process can also be applied to destroy some organic compounds which means the process can be operated in a low cost.An ideal photocatalyst should be stable, inexpensive, non-toxic, highly photoactive and, of course, good visible light absorptive.hi recent years, many researches have focused on the binary or ternary metal oxide to find a more effective photocatalyst by increasing the efficiency of charge separationand extending the photo-responsing range.In this dissertation, we are motivated to work in this direction and finally find some interesting and useful results.This dissertation mainly includes 4 parts as follows:1. The photocatalytic principle of semiconductors used in air and water treatment is introduced, and some recent developments in the modification for the photocatalysts, including metal ion doping, surface sensitization, clay cross-linked semiconductors and coupled oxide semiconductors, are also introduced. Additionally, the principle and some recent developments of nano-sized photocatalyst are also introduced.2. Nano-sized Zn2SnO4 materials have been synthesized using the coprecipitation method. The synthetic conditions and the calcination behaviors of nano-sized Zn2SnO4 materials have been studied. The nano-sized Zn2SnO4 materials have been characterized with X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetry and differential thermal analysis (TG-DTA) and specific surface area. As a result, the kinetic grain growth equation for nano-sized Zn2SnO4 can beexpressed as: Z)478 =9.12xl023fexp(-40.6xl03 IT), with an activation energy forgrain growth of Q=337.9 KJ/mol. The nano-sized Zn2SnO4 materials have been used as photocatalysts to decompose benzene in water solution. The results show that Zn2SnO4 can photocatalytically decompose benzene, and the photocatalytic capacity for Zn2SnO4 relates to the grain size, which is discussed in terms of the surface effect and the quantum size effect.3. The nano-sized coupled oxides ZnO/SnO2 in a molar ratio of 2:1 (Z2St) and ZnO/SnO2 in a molar ratio of 1:1 (ZjS,) were prepared using the coprecipitation method and characterized with X-ray diffraction (XRD), UV-Vis diffuse reflectance spectroscopy and specific surface area (BET). Their photocatalytic activities were also evaluated using methyl orange (MO) as a model organic compound. The isothermal adsorption behavior of MO on Z2S,, and the factors affecting the photocatalytic activity...
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