| Hydrothermal solvent and solvent thermal synthesis means:in a closed container with water or other substances as a solvent, a common method of preparing the material. With this method, we can get different morphologies size and structures of nanomaterials by regulating temperature, reaction time, precursors and other conditions. It has become a major method of synthesis and design nanomaterials. With hydrothermal solvothermal development to study the effects of experimental parameter, on the system of people’s reaction system temperature, reaction time, concentration, PH value, etc. have been deeply investigated. But due to the influence of experimental conditions and other factors, which is an important factor in the influence of solvethermal reaction-the pressure is very few experiments reported. Normal pressure hydrothermal reaction mostly around 4 MPa-10 MPa, in recent years, the use of diamond anvil cell (DAC) methods can be subjected to the reaction system 1 GPa-100 GPa pressure, and by the pressure of the reaction between the two documents of the line of research rarely reported. Therefore, high pressure solvent thermal reaction apparatus combined with laboratory independent research and development, this thesis, the pressure range 10MPa-300MPa under pressure hot water thermal solvent system nanocrystals Aggregation, and directional growth and other baking and theoretical the method of calculation to study the characteristics of crystal growth under high pressure, high-pressure solvothermal synthesis method is applied to common oxide and sulfide synthesis, and synthetic products related properties were studied. The result are as follow:1. Synthesis SnO2 nanoparticles by high pressure solvent thermal method and their gas sensor performance.With high-pressure hot solvent experimental apparatus under pressure 200MPa, olive SnO2 nanoparticles was synthesized, and by comparison with the product of common solvent thermal synthesis method, and the morphology of the product at different times, we make a preliminary understanding the influence of the pressure on growth of nanoparticles. In addition, with the reaction concentration of tetramethylammonium hydroxide (TMAH) from 0.6M to 2.0M, we get a further dodecahedron, octahedron, eggs and other type of SnO2 particles with different morphologies. And we further study of the different morphology of gas sensing properties of SnO2 nanoparticles, found that the olive like SnO2 nanoparticles show a very high response to N(CH3)3.2.Pressure-Induced Oriented Attachment Growth of Large-Size Crystals for Constructing 3D Ordered Superstructures.Mixture of water and ethanol 85:15 were used as solvent, N (CH3)3 as a protective agent, by control the concentration of reactants through the system, we successfully obtained SnO2 ordered self-assembled three-dimensional superstructures build up by dodecahedron SnO2 nanopaticles with eight{111} planes and four{110} planes through (oriented Attachment) mechanism. Adjacent nanoparticles attached together by disappearance of the crystal planes, and to reduce the energy of the system. Molecular dynamics simulation (MD) was used to get further understanding of the formation mechanism, we found the pressure has trimethylamine influence of trimethylamine adsorption on SnO2 different crystal planes, as well as impact on the grain pressure on aggregate growth. To learn more about the effect of pressure on the system, a series of orthogonal experimental about temperature and pressure, the pressure on further research and found that pressure and temperature on the formation of the architecture has a complementary role. The use of high-resolution HRTEM, our large size (100nm or more) OA mechanism of growth between particles by the line-depth study found that OA never fully grown to perfection OA growth process, and found a large radius of curvature will place priority growth. In addition, we have discussed the system of van der Waals forces between the particles, the Coulomb force, electrostatic interactions and diffusion depletion effects were analyzed and found that the pressure impress on the system, van der Waals interactions and diffusion depletion significantly affected, thus affecting the system aggregate growth behavior in grains. In addition, we have gas-sensing properties of the resulting structure and conductivity through the line, and found that by reducing the crystal surface, reducing the grain boundary barrier electron transfer in different planes, making it gas sensing compared with the dispersed nature of the monomer has been significantly improved.Ethanol as a solvent, FeCl3.6H2O as raw materials, by high pressure solvent thermal method, we successfully synthesis 1D self-assembly Fe2O3 nanocolumn, as ordered along the [100] direction of the orientation of a one-dimensional array structure. And by adjusting the pressure in the range of 50-200MPa, we get one-dimensional array of different lengths, and found that the system pressure is proportional to the length of the array by TEM and SEM. Further deepen the understanding of the influence of pressure on the system.3.Growth of Large-Size SnS Ultrathin Crystals Driven by Oriented Attachment and Applications to Gas Sensors and Photodetectors.Olyamine as solvent and surface modifier, anhydrous SnCl2 as raw material, we synthesized SnS nanosheets with the length is about 10-20um, width of 2 um, and a thickness of 30 nm. And assisted by XRD, HRTEM, and an optical microscope, we analysis of the structure, explored the mechanism of their formation te. By photolithography, thermal evaporation techniquewas used to prepare monolithic SnS sensors devise, found that the use of high pressure solvent thermal synthesis sensors has a very good response and selectivity for NO2 at room temperature, and the wavelength of 532 nm also showed relatively good response. In addition, we also added the elements Cu doping, and Cu elements found by maping well in SnS surface distribution, in order to further improve the performance of the device provides a strong premise.4.High pressure solvent thermal method for the synthesis of other metal-sulfide.Using the above method, we have successfully synthesized SnS2 with special structure, β-In2S3nanobelts, as well as C doped MoS2. By XRD, HRTEM, mapping and other tests we talk about their structures. The synthesis of SnS2 has a similar structure to SnS and MoS2was2 nm single layer nanosheets, and through the replacement of molybdenum we synthesis successfully of the carbon doped MoS2 and In2S3 structure length is 50 um nanobelts. Compared with common solvent thermal reaction, we find that the pressure is introduced to not only make the crystallinity of the product changed better and the size of the product significantly increased; the oriented attachment mechanism is still the dominant mechanism of crystal growth. |
PDF Full Text Request