| With the increasingly severe environmental pollution, the department of environmental protection is attaching great importance on the environmental detection. The advance of the detective equipment is the indication of the modern detection. Water is the important media for the element circulation in the natural environment, therefore, research on water is one of the most important subject in environmental research and have attracted great attention of the world. Chemical oxygen demand (COD), which displays great significance on the evaluation of water environment, has preferentially been used as a parameter to represent the degree of organic pollution of wastewater. The conventional method for COD determination is manual and is based on titration of the samples with a toxic reagent such as potassium permanganate or potassium dichromate. This type of standard manual 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. Currently, extensive work on new mechanism, methods and instruments of COD determination has been accomplished in order to shorten the titration time. Most improvements focus on the digestion of the sample, chloride interference and detection method. In recent years, nano-materials has attracted great attention. With its special photoelectrical characteristics, nano-semiconductor oxides can produce strong oxidizing agents such as hydroxide radicals, which play an important role in degradation of organic compounds, by reacting with hydroxyl and/or water on their surface. Therefore, nano-semiconductor oxides have shown promising prospect inenvironmental detection.In this article the current theories , methods and instruments for COD determination are generalized, the photocatalytic mechanism of nano-semiconductor is studied and a method for COD determination using a system containing nano metal oxides and inorganic oxides is described and its operation conditions are optimized. Moreover, one kind of COD analytical instrument based on colorimetric detection method is developed. The established methods have good behaviors and their results are well correlated with those using conventional methods. Thus, they display a great potential in COD on-site monitoring.Chapter OneIn this part, two main parts were introduced. Firstly, an outline of the current theories, methods and instruments of fast COD determination was described. The second part included the development and the characteristics of the nano-materials, the photocatalytic mechanism of the nano-semiconductor and their application in the environmental area.Chapter TwoA new photocatalytic and oxidation system , nano TiO2-KBrO3 synergic system, using bromide selective electrode as detection method for COD determination was studied. The conditions of the reaction including the initial concentration, pH value, the dosage of TiO2 and temperature were optimized.Chapter ThreeA new photocatalytic system, nano-TiO2-Ce(SO4)2 coexisted system, which can be used to determine the low chemical oxygen demand (COD) is described. This measuring method is based on direct determination of the change of Ce(IV)concentration resulting from photocatalytic oxidation of organic compounds by using nano-TiO2 powders as photocatalyst. When determining the real samples, the results were in good agreement with those from the conventional methods.Chapter FourCe(IV), which could reduce the recombination of the photogenerated electrons and holes and thus accelerated the degradation of the organic compounds, was used as an electron scavenger. The T1O2 film, which made the operation easier and could be repeatedly used, was prepared and characterized in the article. The determinative COD value was calculated from the differential pulse voltammetry (DPV) peak current of Ce(III) at multiwall carbon nanotube(MWNT) modified electrode. The results obtained by the method for determination of COD were in excellent correspondence with th...
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