| With the improvement of industrialization, together with the development of economy and society, the natural environment in China has been destroyed seriously. Recently, the fog haze weather appears frequently and PM2.5 becomes more and more serious, Chinese government pays high attention to the air pollution. As one of the most important pollutants in waste air, nitrous oxides(NOx) could directly or indirectly cause serious harm toward environment and human. Thus, the control and removal of NOx in air have become one of the hottest research topics. To date, several rechnologies have been developed and practically applied to remove NOx in the waste gas, such as selective catalytic reduction, selective non-catalytic reduction and so on. However, these technologies could only remove NOx at high temperature, high concentration and stationary source emissions. it displays poor efficiencies in removing NOx resulted from motor vehicle and trash burning etc. since the NOx in released from those processes generally shows relatively low concentration, long durability, and difficult purification. Therefore, it is an urgent requirement to develop new effective catalytic technologies to solve this problem.Photocatalytic oxidation removal of NOx displays good potential owing to the advantages of mild reaction conditions, energy saving and absence of secondary pollution. Meanwhile, the final oxidation product could be easily absorbed by plants and microorganisms etc. But the current photocatalytic oxidation technologies to remove NOx still show many disadvantages including low catalytic efficiency and rapid deactivation etc., which strongly limit their practical applications.Based on the problems in the photocatalytic oxidation removal of NOx, herein, we focus on the titanium-based photocatalysts as the research subject. Firstly, we prepare several new titanium-based photocatalysts through advanced microwave synthesis technology and examine their activities and stabilities in photocatalytic oxidation NO. According to the detailed characterizations, we investigate the influences of both photocatalyst composition and structure on the photocatalytic performance. We hope our research will supply useful experimental and theoretical supports for the practical application of photocatalytic oxidation removal of NOx in air cleaning.The principal contents and innovation points are summarized in the following three parts.1. A new porous Au/Ce O2-Ti O2 photocatalyst with layered structure and high stability was prepared by microwave assisted alcoholysis, which was then used in photocatalytic oxidation of NO. This photocatalyst exhibited both high activity, excellent stability and long lifetime during the photocatalytic reactions under irradiation with either the simulated sunlight or the ultraviolet light. Based on the characterizations including TEM, XPS and XRD etc., the influences of Au and Ce O2 doping contents on the activity were examined, which revealed that the Au and Ce O2 dopants not only promote the absorption and utilization of lights, but also effectively separated the photogenerated electrons from holes and thus retarded their recombination. Meanwhile, the Ce O2 could enhance the oxygen storage capacity, which favored the production of active species like superoxide radicals etc. essential for photocatalysis. Thus, the Au/Ce O2-Ti O2 photocatalyst displayed much higher activities than either the Ce O2-Ti O2 or the Au/Ti O2 or the pure Ti O2. At the same time, the synergistic effect between different components and the photocatalytic mechanism were also investigated and discussed, which seems useful for supplying new ideas in future design of efficient photocatalysts.2. A novel Au/Ce O2-Ti O2 photocatalyst was synthesized through the EISA process in the presence of surfactant self-assembly, followed by impregnation and hydrogen reduction of Au ions. The ordered mesoporous channels were confirmed by various characterizations. Meanwhile, we found that all the Au nanoparticles occupied in the mesopores with small size, which could strongly interact with the Ti O2 support. This photocatalyst still kept and even improved synergistic promoting effects of Au/Ce O2 on the photocatalytic performance of Ti O2. It also enhanced the crystallization degree of Ti O2 favoring the electron transfer and thus, could facilitate the separation of photoelectrons from holes to reduce their recombination. Meanwhile, the ordered mesoporous channels could also diminish the mass transfer resistance and promote the light harvesting and NO adsorption, which further improved the photocatalytic activities. Moreover, the high surface area resulted from the mesoporous structure could enhance the adsorption for the products from photocatalytic oxidation of NO, which could effectively reduce the poisoning deactivation.3. A novel Ag-supported organotitanium polymer with MOFs-like structure was in situ prepared with the help of microwave assisted synthesis technology. Based on the detailed characterizations, we found that the present sample exhibited high specific surface area and uniform dispersion of Ag nanoparticles etc. During photocatalytic reactions, the organic ligand could be excited under visible light owing to its narrow energy band gap. The photogenerated electrons could transfer to Ti atom or Ag nanoparticles active sites through the intramolecular pathways, which could start photocatalysis on one hand and also inhibit the photoelectron-hole recombination on the other hand. This photocatalyst exhibited both the high activity and the stong durability in visible lights induced photocatalytic oxidation removal of NO. Combining the examination of reaction kinetics and the detailed characterizations, we proposed a plausible activation mechanism of the present photocatalyst. Meanwhile, the correlation of the photocatalytic performance to the structural characteristics was also explored. Then, by improving microwave synthesis technology and the composition in mother solution, we successfully prepared a NH2-MIL-125(Ti) with well-defined MOFs structure and high crystallization degree, which showed enhanced activity in photocatalytic NO oxidation. According to the structural characterizations and kinetic studies, the promoting effects from crystallization degree and other parameters were briefly explored.4. The single-crystalline silicon with high purity and bulk structure was prepared silicon tetrachloride and metallic sodium by microwave assisted liquid phase synthesis under mild conditions. Its electrochemical behaviors and stability was briefly examined and the growth mechanism of single-crystalline silicon under microwave irradiation was simply analyzed, based on which, the single-crystalline silicon and silicon carbide composite was achieved by changing the reaction system and conditions.
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