Studies On Nano- Oxide And Its Application In Environmental Determination

Environmental problems are more and more concerned and both environmental protection and sustainable development are paid close attention to all over the world. Chemical oxygen demand(COD) and total phosphorus have preferentially been used as parameters to represent the degree of organic pollution of waste water. The traditional determination methods of chemical oxygen demand and total phosphorus are very time-consuming, and they demand high-quality personnel and expensive and toxic reagents. Compared to those methods, nano-semiconductor oxide photocatalysis is highly sensitive, simple to operate and reagents are cheap. Therefore, there is a great interest in the development of nano-semiconductor oxide photocatalysis for determination of COD and total phosphorus.This dissertation fell to two hierarchical and four sections. Firstly, the existence of OH, the active substance, was detected in the catalytical and oxidizing system of the nano-semiconductor by ESR, which provided a useful analytical and detective method for the detection of the OH .Then chemical oxygen demand and total phosphorus were determinated by nano-semiconductor oxide photocatalytic method. This method was applied in the real samples and the results were satisfactory. These works had a deep meaning in the environmental detection by nano-science.The first chapter In this part, three parts, that is the development of the nanomaterial and its application in the environmental analysis, the development and view of environment water analysis, the development of organic substance determination by nano-semiconductor oxide photocatalytic method.The second chapter In nano TiO2 photocatalytic oxidation system, adding inorganic oxidizing species can efficiently trap photogenerated electrons , increase the concentrations of hydroxyl radicals in the solution and enhance the photocatalytic oxidation rate of nano TiO2 to different organic matter. In this part, the correlation of the production of hydroxyl radicals and the photoinduced electron transfer of nano-TiO2 by inorganic species (K2S2O8) was verified by means of the free radicals measured by spin trapping-ESR methods in which DMPO was selected as the spin-trap reagent. The photocatalytic oxidation mechanism of glycine was studied.The third chapter The photocatalytic method is built on the reactive properties of electron-hole pairs generated in the semiconductor particles under illumination by light whose energy is greater than the semiconductor bandgap. Upon migration to the surface, the hole would react with water to produce hydroxyl radicals. These radicals play an important role in oxidizing organic pollutants. In contrast, when the electron reaches the surface, it would reduce any available species, or recombine with the hole. In this part, KMnO4 was used to serve as electron scavengers, which inhibit the recombination of electrons and holes, and enhance the rate of photocatalytic degradation of organic compounds.The forth chapter In this part, a new photocatalytic oxidation method using. nano TiO2 membrane for the rapid determination of total phosphorus in water is described. The optimized operation conditions were studied using HEDP as standard substance. Experiments indicated that this method has mild operation conditions, doesn't cause secondary pollution, and can achieve rapid and accurate determination of total phosphorus. This method was also applied to the determination of total phosphorus of real wastewater samples and the results were in good agreement with those from the conventional methods.