| The eutrophication of natural waters in Dianchi Lake has led to an increase in the incidence of cyanobacteria or blue-green algae, which subsequently causes the deterioration of water resources and seriously affects the scenery of Lake Dianchi. So far, Physical, chemical and biological approaches to curb cyanobacteria in Dianchi Lake there have been used, and some of them have made positive effects, however, these methods were also limited in practical use. Over the recent years, there has been an extensive literature on the application of TiO2 as photocatalyst in destroying bacteria, degrading or mineralizing organic compounds, such as aromatic and haloaromatic, to CO2 and H2O. Nano-TiO2 has been widely employed as photocatalyst due to its high activity of photocatalysis, its availability at a reasonable cost, in addition to its nontoxic nature, its chemical stability, and its capability of being used repeatedly without substantial loss of catalytic activity. Furthermore, TiO2 photo-catalyst does not produce hazardous waste byproducts in the process of photocatalysis. Up to now, the application of nano-TiO2 photocatalysts to curb cyanobacteria or blue bacteria from Dianchi Lake has not been reported.This thesis was aimed to study the possibility for the application of modified nano-TiO2 photocatalysts inhibiting the growth of cyanobacteria from Lake Dianchi under the irradiation of sunlight. Firstly, nano-TiO2 was prepared by Sol-Gel method with hydrolysis of Ti(OC4H9) 4．Secondly, Pd (or Pt) doped nano-TiO2 was prepared by means of using NaBH4 to reduce the mixture of PdCl2 (or H2PtCl6) and nano-TiO2 in the ethanol. Moreover, according to the requirements of experiment, different proportion of Fe2O3, ZnO, WO3, rare-earth element, active carbon, noble metal Ag and Ru doped respectively on nano-TiO2 were made, during the process of hydrolysis of Ti(OC4H9) 4, by treating Ti(OC4H9) 4 which served as precursor to prepare homogeneous and transparent solution, and the different content of compounds which were introduced from Fe(NO3) 3·6H2O, Zn(NO)3·9H2O, (NH4) 2WO4, Mn(NO3) 2·2H2O, Ce(NO3) 3·6H2O, actived carbon, AgNO3 and RuCl3 solution. The structure of modifi-ed nano-TiO2 were measured and determined by means of IR, UV-Vis , XRD, TEM, XPS, ICP and HPLC.Then, the experiments on nano-TiO2 inhibitory effect on the growth of cyanobacteria taken from Dianchi Lake were conducted under the irradiation of the high pressure mercury lamp,ultraviolet light lamp and the sunlight, respectively, which lay foundation for the preparation and application of modified nano-TiO2．In the experiments, different proportion of Fe2O3, ZnO, WO3, rare-earth element, and active carbon doped, respectively, on nano-TiO2 were used to curb the growth of cyanobacteria taken from Dianchi Lake under the irradiation of sunlight. And different proportion of Ru,Ag,Pd and Pt doped nano-TiO2 were used to study their inhibitory effects on growth of cyanobacteria from Dianchi Lake under the irradiation of sunlight and in dark room. The case in dark room eliminated the capability of noble metal ions to destroy cyanobacteria. Finally, the relatively high active of modified nano-TiO2 photocatalysts selected from different types of photocatalysts were used in the study on the inhibitory effect on the growth of cyanobacteria from Dianchi Lake under the irradiation of sunlight. 1%Pt doped on nano-TiO2 was used in small-scaled experiment in imitation of Dianchi Lake.From above experiments, we could come to the following conclusions:1．Using nano-TiO2 under the irradiation of sunlight exerted little effect on curbing the growth of cyanobacteria from Dianchi Lake. However, it has exhibited better inhibitory effects under irradiation of the high pressure mercury lamp and ultraviolet light lamp. In the experiments of differently modified nano-TiO2 photocatalysts, the noble metal doped nano-TiO2, 5%ZnO doped nano-TiO2, 40% actived carbon doped nano-TiO2 and rare-earth element 3．3%MnO2/6．7%CeO2 doped nano-TiO2 could effectively curb the growth of cyanobacteria from the Dianchi Lake exposed to the sunlight.2．After the experiments of the modified nano-TiO2 photocatalysts on the studies of inhibitory effects on the growth of cyanobacteria under the same condition, we got the activity sequence of the modified nano-TiO2, which was 1%Ag/TiO2 > 1% Pt/ TiO2 > 40%active carbon/TiO2 > 3．3%MnO2/6．7% CeO2 / TiO2 >5%ZnO/ TiO2．3．It was found that the amount of photocatalyst had effect on the growth of Cyanobacteria .If the amount was too small, the adsorption of Cyanobacteria would be incompleted, where as too high amount would result in high cost.The suitable amount was found to be 0．1g photocalyst when the chlorophyll is 4．2g·L-1 in 25mL liqual. 4．The mechanism how modified nano-TiO2 photocatalysts exert inhibitory effect on the growth of Cyanobacteria was studied.To summary in this thesis, it is for the first time to apply different proportion of Fe2O3, ZnO, WO3 doped respectively on nano-TiO2 complex semiconductor to the studies on inhibitory effects on growth of cyanobacteria taken from Dianchi Lake, to use modified nano-TiO2 by rare-earth element to the studies on inhibitory effects on growth of cyanobacteria taken from Dianchi Lake, to employ the noble metal Ru, Ag, Pd and Pt doped respectively on nano-TiO2 to the studies on inhibitory effects on growth of cyanobacteria from Dianchi Lake, and to use TiO2-mounted activated carbon to the studies on inhibitory effects on the growth of cyanobacteria. Finally, a new reagent, 4-(2-hydroxy-naphthalene-1-ylmefhylene)-thiazolidine-2, 5-dithione (HNMTD) was synthesized during the process of determination of the content and form of noble metal existing in the photocatalyst. A new method for the simultaneous determination of palladium, platinum and rutium ions as metal-HNMTD chelates was developed using high performance liquid chromatography equipped with an on-line enrichment technique, and the method was applied with good results to the determination of the content and form of Ru, Ag, Pd and Pt in the photocatalyst.
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