The Study On The Preparation Of New Highly Effect Semiconductor Photocatalytic Materials And Their Photocatalytic Mechanism

Due to the lower utilization of visible light of semiconductor catalysts, we prepared Si-doped TiO2) Sn-doped TiO2, N/Zr-codoped TiO2and TiO2-N/ZrO2-N samples by using the methods of doping and coupling. We inveatigated the doping and coupling mechanism in the preparation of photocatalysts, as well as the photocatalytic of the catalysts under visible light irradiation. Besides, we paid attention to the quantum dots which was introduced to the photocatalysis filed at the recently years. The energy band and absorption spectures of quantum dots were calculated. We analysis the factors which leads the changing of the energyband of quantum dots. Our key words and results are shown as follows:1. Pure TiO2and Sn4+doped TiO2(TiO2-Sn x%) photocatalysts were prepared by a sol-gel method, where x%represents the nominal molar percentage of Sn4+ions in the TiO2structure. The crystal structure and energy band structure of the resultant catalysts were characterized by X-ray diffraction, X-ray photoelectron spectroscopy and surface photovoltage spectroscopy. The results show that for a low content of Sn4+ions, the Sn4+ions are doped into the TiO2lattice and replace lattice Ti4+ions in a substitute mode (Ti1-xSnxO2). The energy levels of these Sn4+ions are located0.38eV below the conduction band. Moreover, the rutile SnO2crystal structure evolves with increasing content of Sn4+ions, i.e., a TiO2/SnO2structure is formed. The conduction band of SnO2is located0.33eV lower than that of TiO2. The separation and recombination mechanism of the photo-generated carriers was characterized by photoluminescence and transient photovoltage techniques. The results showed that the formation of the energy levels of Sn4+ions and the conduction band of rutile SnO2can enhance’the separation of the photo-generated carriers, and suppress the recombination of photo-generated carriers. However, the energy levels of Sn4+can lead to a much longer lifetime and higher separation efficiency of the photo-generated carriers. For different content of Sn4+in Sn4+ion doped TiO2(TiO2-Snx%), the abovementioned aspects improve the photocatalytic activity. 2. TiO2photocatalysts (TiO2-XSi) doped by different contents of silicon were prepared by a sol-gel method. The catalysts exhibited a better photocatalytic ability than the pure TiO2and N-doped TiO2(TiO2-N). The samples were characterized by XRD, XPS, FT-IR. and UV-Vis diffuse reflectance absorption spectra. It was revealed that the doped silicon ions formed Si-O-Ti bonds on the surface of TiO2particles. And thus, surface state energy attributed to the silicon dopant was located at0.2-0.6eV below the conduction band of TiO2, which enhanced the response to the visible light and photocatalytic ability. It was discussed the suppression to the formation of rutile phase and the growth of titanium dioxide crystals because of the doped silica in TiO2particles and the effect of catalysts’surface area and surface species such as hydroxyl to the photocatalytic activity.3. A series of nitrogen and zirconium co-doped TiO2(TiO2-N-x%Zr) photocatalysts have been synthesized by a sol-gel method. They show higher activities than both nitrogen doped TiO2(TiO2-N) and zirconium doped TiO2(TiO2-x%Zr) for degradation of4-chlorophenol (4-CP) under visible-light irradiation. The samples were characterized by XRD, Raman, BET, XPS, UV-vis DRS and PL techniques. For TiO2-N-x%Zr samples, the introduced nitrogen is present as surface species (NOx) whose energy levels locate at0.3eV above the valence band of TiO2. Zirconium irons can incorporate into TiO2lattice and substitute the lattice Ti to form substitutional Zr4+irons, whose energy levels located below the conduction band of TiO2. Besides, on the surface of TiO2-x%Zr samples, a small amount of ZrTiO4species was formed, leading to the formation of TiO2/ZrTiO4heterostructures. As a result, the electronic excitations from energy level of NOx species to the conduction band of TiO2together with the electronic excitations from valance band of ZrTiO4to the conduction band of TiO2lead to significant absorption in the visible-light region. In addition, the separation of photogenerated electrons and holes was enhanced by the introduction of surface nitrogen specials and substitutional Zr4+irons. Therefore, TiO2-N-x%Zr samples exhibit higher activity than both TiO2-N and TiO2-x%Zr under visible-light irradiation.4. A new type of photocatalyst was prepared by coupling nitrogen-modified TiO2(TiO2-N) and nitrogen-modified ZrO2(ZrO2-N)[TiO2-N/ZrO2-N] with using a simple sol-gel method. Under visible and UV light irradiation, the TiO2-N/ZrO2-N photocatalyst exhibits a higher photocatalytic activity for HCHO photodegradation than that of TiO2-N as well as pure TiO2, which is due to the introducing of surface nitrogen species (such as N-O species), the formation of energy band structure at heterointerface and the increase of the total number of photogenerated charge carriers (electrons and holes). Besides, the surface oxygen vacancies on the surface of ZrO2-N plays an important role for promoting the separation of photogenerated electrons and holes at the heterointerface in TiO2-N/ZrO2-N and leads to further improvement of the photocatalytic activity of TiO2-N/ZrO2-N photocatalyst. Moreover, for TiO2-N/ZrO2-N, the energy levels of surface nitrogen species and the energy band structure are ascertained by the experiment results and the DFT calculation. The photocatalytic mechanism is discussed by using the energy band structure of TiO2-N/ZrO2-N under visible and UV irradiation.5. Building on the effective-mass envelope function theory, we focuses on the study of the energy band and absorption coefficient in InAs/InxGal-xAs quantum dots in a wells (DWELL) structures. The enegy band structure can be controlled through changing the size of the resultant quantum dots as well as changing the depth of the InxGa1-xAs layer. Hence, the InAs/InxGa1-xAs quantum dot may be can applied in the photocatalysis fileds.