| Titanium dioxide as a n-type semiconductor material has been widely concerned because of its chemical stability, cheapness, non-toxicity, high catalytic efficiency, and has good prospect in photocatalytic degradation of environmental pollutants. However, titanium dioxide as photocatalyst has two disadvantages of easy recombination of photoinduced electron-hole pairs and weak visible light absorption ability. Therefore, the research topics on the visible light enhancement and improvement of the quantum yield of titanium dioxide become a hotspot research. In this thesis, the preparation and photocatalytic activity of silver/silver halide and AgBr/TiO2 composite photocatalysts were studied and the modified TiO2 exhibited higher photocatalytic activity under visible light illumination. The thesis also did some preliminary researches and explorations on other new photocatalysts, including titanium dioxide doped with nitrogen by shock wave and free-metal g-C3N4 photocatalyst treated by shock wave.We prepared a series of Ag/AgCl,Ag/AgBr,Ag/AgI photocatalysts and compared their photocatalytic activity by degradation of methyl orange. The characterization results of XRD, SEM showed that Ag/AgBr prepared by titration method has the best photocatalytic activity due to good particle distribution and stability. By comparing the three reductants including hydrazine hydrate, ascorbic acid and visible light we found that Ag/AgBr photocatalyst reduced by visible irradiation has the best photocatalytic degradation activity of methyl orange due to formation of the homogeneous silver loading on AgBr. And the relative content of Ag in the Ag/AgBr photocatalyst nearly has no change before and after the process of photocatalytic degradation due to its better light irradiation stability.A serial of AgBr/TiO2 photocatalysts were synthesized using Ti(OC4H9)4, KBr and AgNO3 as precursors. The phase composition, particle morphology, size, microstructure and absorbance of these samples were characterized by XRD, TEM, HRTEM and UV-vis spectra. The results of photocatalytic degradation to methylene blue showed that the activity order of these samples is of AgBr/TiO2> AgBr> AgBr/P25> P25> TiO2. The complex and mono-component photocatalysts with AgBr have exhibited higher activity because of the strong absorption in visible light region. The photocatalytic activities of AgBr/TiO2 increase first and then decrease with increasing mass ratio of mAgNO3/mTiO2 in which the mass ratio of 3.35 has the highest photocatalytic activity. Analysis revealed that the particle size of this complex photocataylst is about 15 nm and homogeneous dispersion and has formed an intimate contact heterojunction microstructure and the strongest absorption in whole UV-vis light region (250-800 nm). The structure of AgBr/TiO2 is stable before and after photocatalytic reaction, but its photocatalytic activity decreased in five-circle runs originated from the pollution of adsorbed carbon on the surface of photosensitizer AgBr in the reaction system by evaluating the cycling life of the photocatalysts and characterization of XPS and EDX.The new free-metal photocatalysts of carbon nitride were synthesized under solvothermal condition or by thermolysis, which are identified as graphitic C3N4 (g-C3N4) and have some absorptions in the visible region. The g-C3N4 synthesized by solvothermal method has good photocatalytic activity, while the g-C3N4 prepared by thermolysis has no photocatalytic activity; however, its photocatalytic activity was significantly enhanced after loading by a flyer at volecity of 2.52 km·s-1. The redshift of adsorption edge of the doped TiO2 by shock wave occurred, but it has little photocatalytic activity. The nanosized anatase TiO2 transforms partially into srilankite phase of high pressure after shock treatment and has a worse photocatalytic activity indicating srilankite phase of high pressure could deteriorate the photocatalytic activity.
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