Study On Photocatalytic Mechanism Of Nanostructured TiO₂ And Its Application In Novel Method And Instrument For COD Determination

With the increasingly severe environmental pollution, great attention has been paid to water pollution and its treatment in China. The water pollution is a large aspect of the environmental pollution. Whether the sewage can reach the discharge standard is determined by the pollution index of the sewage, among which the most important is the COD value of the sewage. Chemical oxygen demand (COD), which displays great significance on the evaluation of water environment, has been used as a parameter to represent the degree of organic pollution of wastewater. The conventional method for COD determination is based on titration of the samples with a strong oxidant such as potassium dichromate. This method is time consuming and its accuracy depends on operators' skill. Therefore, an alternative method for COD determination, if it is convenient, time-saving and low-cost, is most desirable.Over the past several decades, nano-semiconductor oxides such as TiO₂ is widely used as the photocatalyst. With its special photoelectrical characteristics, the TiO₂ can produce strong oxidizing agents such as hydroxide radicals, which play an important role in degradation of organic compounds. So the pollutant in the aqueous system will be reduced into harmless inorganic substances such as water and carbon dioxide, and would not bring with any serious secondary pollution. Therefore, nano-semiconductor oxides have shown promising prospect in environmental analysis.Unfortunately, the photocatalytic oxidation efficiency is greatly reduced by the high extent of hole-electron recombination and the utilizing efficiency of the sunlight is less than 10%, hindering their further manipulation and application. To improve these disadvantage, a lot of investigation has been devoted: Firstly, to avoided the aggregation and the difficulty of the catalyst recovery existing in the suspension system, the catalyst was immobilizated on the quartz tube; Secondly, photoelectrocatalytic technology has been employed to enhance the photocatalytic efficiency; Thirdly, titania nanotubes has been prepared and it has high photocatalytic efficiency because of its large surface area; Finaly, QD-CdS modified TiO₂ electrode has been prepared, shifting the absorbance toward the visible light region and improving the photocatalytic efficiency.