Synthesis, Post-Treatments And Performances Of Visible Light Responding Nano-Photocatalysts

Environmental and energy issues were important challenges that human beings must go beyond at present and the future for a long time, which related to human survival and development. To accomplish this historical mission imminent, people developed a number of ways and means to deal with it. Photocatalytic technology become a research focus in the field of environmental management and renewable energy, by right of its advantages, such as low energy consumption, environmental management, renewable energy, moderate reaction conditions, no secondary pollution and simple operations. In the sunlight incident on the Earth, UV contented of only 3 to 5%, if you want to take full use of this energy, it was necessary to synthesize a photocatalytic material having high visible light response properties. Therefore, material synthesis method and the corresponding modification and enhancement technology became hot spots of extensive researchs. In view of this background, this thesis was related to the synthesis of nano photocatalyst responsive to visible light, focusing on TiO₂ mesoporous nanospheres and nonmetal compound g-C₃N₄. The modification techniques and their synthesis and photocatalytic mechanism were also subjected to a more thorough discussion.In the second chapter, we demonstrated a one-step hydrothermal process, which not only converted Gd-doped titanium glycolate precursor nanospheres into TiO₂:Gd mesoporous nanospheres via Ostwald ripening but also caused in-situ Mo- and Sdoping for TiO₂. By prolonging the hydrothermal reaction time, the resulting products demonstrated progressively larger mesoporous sizes, and the small particles on the surfaces of the nanospheres also grew into large particles and even into nanorods along a certain direction. Raman spectra illustrated that those Mo and S dopants were present in the crystal lattice instead of deposited on the surface. Importantly, the Mo,S-doped TiO₂:Gd mesoporous nanospheres exhibited superior photocatalytic properties, 3.8 times only S-doped samples, and better than MoS₂ sub-microspheres with visible light irradiation.Moreover, we expanded the range of vacuum level to low and easily achievable degree of vacuum, and a three-day moderate vacuum-treatment process（50 ± 5 mTorr, 150 °C） was adopted to reinforce the photocatalytic properties of TiO₂ mesoporous nanospheres, up to triple upgrade among all samples. A 2 to 3 nm thick of amorphous layer appeared in the surface of the well crystalline nanocrystals originally so that the color of vacuum-treated products become deeper and yellower macroscopically.Next, we demonstrated, for the first time, two physical strategies, vacuum heating and electron beam irradiation, to reinforce nonmetallic photocatalyst, g-C₃N₄. These two post-treatments also improved the visible light absorption properties of gC₃N₄, nevertheless, electron beam irradiation was more destructive, which caused a decided change for its chemical bonds and band structure. According to the postprocessing parameters of this chapter, vacuum heating（38 ± 2 mTorr for 4 days at 200 °C） could enhance the photocatalytic efficiency of original g-C₃N₄ 2.5 times, and electron beam irradiation（760 kGy at 1.8 MeV and 8 mA·s-1） could ameliorate that 4.5 times. Finally, the post-treated photocatalysts were stable during the photocatalytic oxidation and ensured those applications.