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Study of TiO2 and ZnO Nanomaterials Prepared Via Ultrasonic Irradiation

Author: WangHaiYan
Tutor: YangYueTao
School: Nanjing University
Course: Acoustics
Keywords: Nanomaterials Zinc oxide Nanorods Sol - gel method . Titanium dioxide Photoacoustic spectroscopy Nanocrystalline particles Ultrasonic irradiation Quantum size effect Ionic liquids -Ray diffraction analysis Nanoparticles Dispersion Ultrasound Preparation The intensity of the diffraction peaks Sound probe Preparation Growth Mechanism Preparation and Application Size
CLC: TB383.1
Type: Master's thesis
Year: 2011
Downloads: 27
Quote: 1
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Abstract


The preparation and application of nanomaterials have been studied intensively in recent years due to their excellent performances different from the bulk materlals. Many methods have been developed to prepare nano-sized materials, among which sonochemical process has been proved to be a useful technical for preparing nanomaterials. In this study, the nanocrystalline TiO2 powders doped the rare earth ions with good dispersibility and stability have prepared by the sol-gel process via the ultrasonic irradiation. The structural variation of the as prepared TiO2 gel powders is studied according to the rare earth ions (Er3+) combined with the PAS technique as a probe. The nanocrystalline ZnO powders have prepared in room temperature ionic liquid via ultrasonic irradiation. The photoacoustic spectroscopy (PAS) has been used to study the optical properties and quantum size effect of the samples. The morphology and properties of ZnO products have been characterized using XRD and TEM. A possible mechanism is discussed to explain the formation of ZnO nanostructures, and a reaction model is also established.There are five parts in the thesis as follows:In the first chapter, a series of especial properties and leading preparation methods of nanomaterials are summarized briefly. According to the basic theories of sonochemical preparation of nanomaterials, the preparation methods and application of sonochemisty are introduced. Meanwhile, the principles, characteristics and influencing factors of sonication are outlined. The primary coverage and the meaning of this thesis are put forward at the end of this chapter.In the second chapter, with the primary analysis methods of XRD TEM and PAS, the prepared nanomaterials under ultrasonic irradiation are introduced. The backgrounds and developments of the PA techcique are reviewed. We describe the basic concepts of the PAS including the R-G theory. After a review of the common applications of the PAS technique, we introduce the recent advance of the PA theories and instruments.In the third chapter, we study the mechanism of the sol-gel process and the influence of the ultrasonic irradiation. The nanocrystalline TiO2 particles with good dispersibility and stability are prepared. And the agglomeration of the particles is well controlled. The process flows of the sol-gel method coupled with ultrasonic irradiation are introduced. The XRD is used to determine the identity of any phase present and their crystallite size. Appearance, sizes and micromechanism of products are represented by TEM. We introduce how to use the PA probe to study the structural variation of the prepared TiO2 samples. The PAS of the samples are recorded in the region 340-700 nm by a PA spectrometer which was built in our lab. The study shows:(1) At 70℃, the "degree of covalency" of the bond is the lowest. TiO2 gel heated at 70℃still contained abundant trapped water and ethanol, and the environment around Er3+ was similar to the one in the aqueous ion. (2) The "degree of covalency" for Er3+ bonding increased continuously during the gel-to-anatase transition. (3) For the sample calcined at 1100℃, however, the f-f transitions of Er3+ showed blue shifts and the intensity of the hypersensitive transition decreased, indicating the "degree of covalency" for Er3+ bonding decreased again. This can be attributed to the segregation of Er3+ ions to the external surface, forming Er2Ti2O7 during the anatase-to-rutile transition the sample.In the fourth chapter, ionic liquids are promising green replacement for tradition volatile organic solvents. In this work, a simple, fast and green approach for preparation of zinc oxide nanorods has been achieved in an ionic liquid, 1-butyl-3-meyhylimidazolium tetrafluoroborate via ultrasonic irradiation. Probe ultrasonic and trench type ultrasonic are prepared the samples of ZnO nanomatials, in which ionic liquid as a reaction solvent. For comparison, ZnO nanomatials have been prepared under probe ultrasonic in triethylene glycol, a conventional organ solvent with low vapor pressure and high boiling point 288℃. The as-prepared products which was isolated by centrifugation and dried are characterized by the X-ray diffraction, the transmission electron microscope. Photoacoustic spectroscop (PAS) has been used to study the optical properties and quantum size effect of the samples. It is found that the different appearance of ZnO nanorods have been obtained in ionic liquid with ultrasound, in contrast to spherical ZnO nanoparticles obtained under the same experimental condition in triethylene glycol, which shows that ZnO nanostructures of different morphology are associated with different intensity ultrasonic irradiation and reactive solvents. The mechanism study of nanomaterials preparation in ionic liquids via ultrasonic irradiation has been rarely exploited. Therefore, a possible mechanism is discussed to explain the formation of ZnO nanostructures, and a reaction model is also established. It is discussed ionic liquids and ultrasonic have influenced to the formation of ZnO nanostructure.In the fifth chapter, the work of this thesis is summarized.

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