Synthesis And Characterization Of Nanomaterials By Hydrothermal/Solvothermal Methods

The present thesis is focused on the first step of nanostructured materials research --the synthesis and characterization of nanomaterials. By the adoption of new hydrothermal/solvothermal methods and varying the experimental parameters such as reaction temperature and time, source species and amounts, solvents, etc., the shape-controlled synthesis of different manganese oxides nanocrytallites, and semiconducting metal sulfides (CuS, PbS) nano/microcrystallites has been achieved. Meanwhile, many techniques including XRD, FTIR, XPS, TEM, HRTEM and SAED, etc. were used to characterize the as-synthesized products.The main work completed in this thesis can be summarized as the following:1. Without the use of any extra surfactant or template, y-MnOOH single crystalline nanowires with the diameters of 10-12 nm and lengths of 1.6-2.4 μrn were synthesized directly through the hydrothennal reaction between KMnO₄ and toluene in distilled water at a relatively low temperature of 180 ℃. Then, β-MnO₂ single crystalline nanowires with the diameters of 14-17 nm and lengths of 0.3-1.8 μrn could be obtained just by low temperature thermal oxidization of the y-MnOOH nanowires in air at 280 ℃, and Mn₃O₄ nanocrystallites had been prepared by solvothermal treatment of the y-MnOOH nanowires in ethylenediamine (EDA) and ethylene glycol (EG) at 150 ℃ for 24 h. The as-prepared γ-MnOOH and β-MnO₂ nanowires and Mn₃O₄ nanocrystallites were characterized by XRD, FTIR, XPS, TEM, HRTEM and SAED, etc. The possible reaction mechanisms leading to γ-MnOOH, β-MnO₂ and Mn₃O₄ were also proposed.2. Without the use of any surfactant, template or other additives, shape-controlledsynthesis of grain-like, quadrate, plate-like, spherical, urchin-like and tubular CuS nanocrystallites had been achieved just via hydrothermal reactions of Na₂S₂O₃·5H₂O and different copper sources (including CuO, CuSO_·5H₂O and CuCl₂·2H₂O) in water at 130-170 ℃ for 6-24 h. The morphologies of the obtained products could be well controlled simply by adjusting the copper source species, the amount of the source materials, reaction temperature and reaction time. The as-prepared CuS nanocrystallites were characterized by XRD, XPS, SEM and TEM, etc. The possible formation mechanisms of the nanocrystalline CuS powders during the hydrothermal processing were also proposed.3. The shape-controlled synthesis of PbS microcrystallites from an air-stable single-source molecular precursor (lead diethyldithiocarbamate: Pb-DDTC) under mild conditions had been achieved by two simple steps: firstly, the Pb-DDTC was prepared directly through the precipitation reaction of lead acetate and sodium diethyldithiocarbamate in distilled water at room temperature; secondly, without the use of any extra surfactant/template, pure PbS microcrystallites with irregular polyhedral, cubic, and dendrite-, star-, and flower-like morphologies could be obtained just via solvothermal decomposition of the Pb-DDTC in four different solvents (including ethanol, ethylene glycol, ethylenediamine and tetrahydrofuran) at 150-180 ℃ for 12 h. The as-obtained PbS microcrystallites were characterized by XRD, XPS, SEM and TEM, etc. To our knowledge, the suitability of these single-source molecular precursors in the preparation of PbS microcrystallites under high-pressure solvothermal environment has not yet been investigated.The above synthesis routes proposed by us are simple, mild, low cost, low pollution, high yield and high purity; and more important, they are capable of preparing the target products with different morphologies and sizes in a controllable manner, which provides us a good chance for study of the relationship between the structure and property of the nanomaterials with different morphology and size.