| With the rapid development of our society, the environmental pollution and energy shortage are getting more severe. Therefore, it is extremely urgent to seek effective methods for dealing with these problems. As a new and modern technology, photocatalysis can convert the low density solar energy to chemical energy, and then applied in photocatalytic splitting of water into H2, photodecomposition of pollutants, and CO2 photoreduction. Photocatalytic technology has considerable promise for solving environmental pollution and energy shortage.Semiconductor photocatalysts can absorb light energy which is higher than the band gap, and the electrons are excited to conductive band (CB) with equal holes leaving in the valance band (VB). Then the photogenerated electrons and holes will be transferred to the photocatalysts surface, and react with the related trapping agent, forming hydroxyl radical or superoxide radical to participate in redox reaction. So the photocatalysts are the key of photocatalysis. However, there are two main critical questions in developing photocatalysis technology, narrow light response and low quantum efficiency, resulting in poor photocatalytic activity and limiting their practical applications.With the aim to further extend the light absorption spectra of photocatalysis,we briefly reviewed some strategies such as ion doping、solid solution strategies、 plasmonic photocatalysis and exploration more new-type photocatalysis. So far, the absorption spectra of photocatalysis have been expanded to the visible portion and even near infrared portion. Therefore, it is more and more significant to improve the quantum efficiency of photocatalyst. Although semiconductor coupling and noble metal loading have been explored to enhance the quantum efficiency after considerable research, their limitations is obvious. Firstly, the interfacial electric field formed by semiconductor coupling and noble metal loading is too weak to have impact on total structure, which limits the separation of photo-induced carriers. Moreover, ions doping can modify band structure, it will also introduces recombination centers which will accelerate photo-induced carries recombination. The effect of ion doping is influenced by various factors such as the type of doping ions, the amount of doping and the doping position, which requires us to do a lot of experiments to explore the optimal conditions. Based on these, a new mechanism shall be proposed to enhance photocatalytic activity by improving photo-induced carries separation.Photo-induced separation are essentially countermovement of electrons and holes. The existence of electric field is conducive to the movement. A polarization electric field can be excited by external field in some piezoelectric and pyroelectric materials, which is powerful enough to separate photo-induced carries and then improve photocatalytic activity. In this thesis, we introduces the preparation, characterization, sono-photo synergistic catalytic and thermo-photo synergistic catalytic of zinc oxide and lead zirconium titanate material. We presented a mechanism that the ultrasonic field and thermal field influence photo-induced carriers generation efficiency by the piezoelectric effect and secondary pyroelectric effect respectively through the analysis of the crystal structure and properties. The following are the five chapters of this thesis:In the first chapter, a brief introduction to the research background n fundamental theory, primary application were presented firstly. Then problems in photocatalytic process were proposed and current solving methods to enhance photocatalytic properties were also discussed. Because of the potential limitation of traditional scheme, we put forward a model that the internal polarization electric field excited by external field could promote photo-induced carrier separation. Then we introduced piezoelectric material. After that the piezoelectric effect and pyroelectric effect were explained and a scheme which can convert external field to internal polarization field was proposed. Finaly we proposed the significance and content of our research.In the second chapter, we synthesized and characterized various nano zinc oxide with different aspect ratio. Firstly zinc oxide nanoplates was synthesized by a simple reflux method and zinc oxide nanorods with different aspect ratio were synthesized by a simple solvothermal method. A series of characterization had been carried out to determine the crystal structure and microstructure of zinc oxide. All catalytic reactions were conducted under 10 degrees temperature environment to degrade MO solvent.Through the comparison of photocatalytic degradation efficiency and sono-photocatalytic degradation efficiency for these zinc oxide, pointed out that the ultrasound has different impacts on different zinc oxide, so the piezoelectric polarization fields excited by ultrasound are different between them. Photo carrier separation efficiency are different due to the combined impact of piezoelectric polarization fields and spontaneous polarization field.In the third chapter, a series of lead zirconate titanate with different component were synthesized through one step hydrothermal method. The components of Pb(ZrxTi1-X)O3 samples were characterized by XRD and the microstructure was captured by SEM. The synergistic effect between piezoelectricity and photocatalysis was investigated in detail to prove that the piezoelectric polarization field could accelerate the separation of photo-carrier.In the forth chapter, PbZr0.44Ti0.56O3 and PbTiO3 were synthesized, and the influence of temperature on efficiency of photo-carriers separation was investigated. PbZr0.44Ti0.56O3 and PbTiO3 nanocrystalline were abtained through one step hydrothermal process. XRD and SEM were conducted to confirm the properties of samples. Then the photocatalytic degradation activities of samples were conducted in two different degree environment. Finally, the relationship between temperature and photocatalytic efficiency were discussed. And then, the secondary pyroelectric effect which could excite polarization field that can promote carriers separation was identified to be the crucial factor to enhance photocatalytic activity.In the last chapter, we summarized main work of the thesis. And then the innovative points and some issues were discussed. These provide us new directions for future work. |
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