| The energy problem and shortage of resources are restricting the progress and development of human society, as a result, how to solve these problems are the top tasks in21th century. Meanwhile, the usage of all kinds of fossil fuel and vehicles are releasing CO2, SO2, NO2to our environment, which would damage our living system and cause greenhouse effect. Therefore, it is urgent to find a kind of environment friendly and effective renewable substitute energy. Solar energy is an inexhaustible and free energy, which is an ideal energy supply to solve the problems mentioned above. Semiconductor photocatalyst is a new branch of science. It can not only convert solar energy to H2, but also purify the nocuous substances in water and reduce the CO2in the air to relieve the greenhouse effect, which make photocatalyst the most promising solution to deal with energy and environment crisis. Thus, semiconductor photocatalyst has become the hot topic in the field of energy conversion and environment treatment.In the past forty years, the research of semiconductor photocatalyst has made a great step. Many effective photocatalysts have been reported and put into use. Due to their safety, good stability and high reactivity, titanium oxides and copper oxides are becoming the emphasis of photocatalysis research. However, both titanium oxides and copper oxides have vital drawbacks such as little response to visible-light, low quantum efficiency and hard to recycle that will deter their application in real world.In this thesis, we mainly show several strategies to improve semiconductor’s photocatalytic reactivity. We firstly synthesized N, H co-doped TiO2with enhanced visible-light absorption by a CVD method; then we used the method of self-doping and heterojuction to synthesized Ti3+:Ti02/TiF3hybrid photocatalyst, the TiF3heterojuction not only enhanced the hybrid’s visible-light absorption, but also stimulated the light-induced charge separation; we synthesized a SrTiO3/TiO2heterojuction with different ratios by a template method and explored a new way to synthesize MTiO3(M=Ba, Ca, Sr, Zn) using TiO2microsphere as template under hydrothermal condition; finally, we synthesized a kind of nano Cu2O with hollow structure and studied the impact of different synthesis conditions on products’ microstructure.The main contents of this thesis are shown as follows:In chapter one, we firstly introduced the fundamental mechanism of semiconductor photocatalysis, as well as the present research status concerning photcatalysis. And then present the main three applications of photocatalyst, including photocatalytic hydrogen production, photocatalytic reduction of carbon dioxide and photocatalytic degradation of harmful pollutants. Later we discussed the two key problems in photocatalysis technology:low quantum efficiency and little response to visible light. Based on the former information, we introduced the physical properties of TiO2and Cu2O such their electrical structure, energy band structure and crystal structure. After that, we specifically discussed about existing solution to the application of photocatalyst including element doping (metal/non-metal doping, self-doping), morphology modulation, semiconductor compositing. The contents and outlines of the whole thesis were also summarized in this section.In chapter two, we used CVD method to synthesize N, H co-doped TiO2visible-corresponding photcatalyst with hierarchical structure. We studied the effect of different annealing atmosphere on products. The TiO2hierarchical structure was synthesized by TiO2-H2TiO3-TiO2procedure. In photocatalytic performance comparison, the N, H co-doped TiO2show enhanced photocatalytic reactivity under visible light irradiation. We also discussed the photocatalytic mechanism induced by energy band doping.In chapter three, Ti3+:Ti02/TiF3hybrid photocatalyst was prepared by a one-step solvothermal method using Zn, TiF4and TiCl4as starting materials. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Due to the existence of TiF3, TiO2contained high concentration of Ti3+species and Ti3+was stabilized. Ti3+:TiO2/TiF3hybrid showed significant absorption in visible-light region in UV-Vis diffuse reflectance spectra (DRS). Furthermore, the hybrid prevented the recombination of light-induced charge, which was further confirmed by photoluminescent spectra (PL). Ti3+:TiO2/TiF3hybrid exhibited excellent photocatalytic reactivity during the degradation of MO under visible light irradiation. In addition, the electron structure of TiF3was studied by DFT calculation, and the mechanism of the enhanced photocatalytic properties was also proposed on the basis of theoretical calculations and experimental results.In chapter four, we synthesized SrTiO3/TiO2heterojuction microspheres by a template method. We studied the effect of different amount of SrCl2on the crystal growth of the products. Meanwhile, we proposed the crystal growth mechanism based on experimental data. Due to the heterojuction structure, SrTiO3/TiO2showed enhanced photocatalytic reactivity during degrading Cr6+. What’s more, we also applied this synthesis procedure to synthesized MTiO3(M=Ba, Sr, Ca, Zn), which turned out that only SrTiO3and CaTiO3can be produced by this method.In chapter five, we prepared Cu2O hollow structure by a facile procedure under room temperature. We studied different TEM images of different synthesis condition. Furthermore, a crystal growth mechanism based on Ostwald ripening was proposed. Since our Cu2O samples have strong electronegativity, they can electrically adsorb MO molecules in a massive way. What’s more, we also studied the influence of PVP during synthesis. Then we successfully prepared a uniform sized Cu2O nanosphere.In chapter six, we summarized the experimental results and calculation data, as well as the remaining problems. Future plans of those works were also proposed.In summary, the electrical structure, energy band structure and crystal structure of semiconductor play an important role in its photocatalytic reactivity. The thesis applied multiple measures such as ions doping, composite heteroj unction, microstructure modification to solve the two main problems that photocatalysis faces, which are of vital importance for lab research and industrial application. |
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