Hydrothermal Synthesis Of Nano-inorganic Materials And Characterization

The present thesis is aimed at exploring novel hydrothermal methods to synthesize inorganic nanomaterials that can be used to assemble nanomaterials and electrocatalysis analysis, and studing the corresponding formation mechanisms of the products under the hydrothermal conditions. The as-obtained products were characterized by means of X-ray diffraction (XRD), X-ray photoelectronic spectroscopy (XPS), transmission electron microscopy (TEM), scan electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetric and differential scanning calorimetry (TG-DSC), etc. The main works achieved are summed up as following:1. A new completely "green" hydrothermal method has been developed to synthesize nano/submicrometer-sized copper powders, based on the reduction of different copper sources (CuO, CuCl₂-2H₂O and CuSO₄· 5H₂O) by a green reducing agent (a-D-glucose) in aquous solutions at temperatures no higher than 180 ℃ in an autoclave. The effects of the copper source, reaction temperature and during time, additive (NaOH) concentration on the properties of the products (such as phase, morphologies and size, etc) were investigated. The as-obtained products were characterized by means of XRD, XPS, SEM, TEM, etc. The results indicated that nano/submicrometer-sized copper powders with different morphologies (such as sphere, rod and wire-like, etc.) can be obtained by this green hydrothermal route. Finally, the coordination-reduction reaction mechanism involved in the formation of metal Cu during this hydrothermal process was discussed.2. LiMn₂O₄ and Mn₃O₄ nanocrystallites were synthesized through the hydrothermal reactions of KMnO₄ and cyclohexanone in LiOH aqueous solutions under different conditions (such as amounts of the starting materials, the reaction tempareture and reaction time), and the corresponding reaction mechanisms leading to LiMn₂O₄ and Mn₃O₄ were investigated. To our knowledge, the hydrothermal synthesis of Mn₃O₄ nanocrystallites in a pure aqueous solution has not been reported so far. The as-obtained products were characterized by means of XRD, wet chemical analysis, FTIR, TEM and TG-DSC. The results showed that the as-synthesized LiMn₂O₄ consisted of uniform, square nanocrystallites with the sizes ranging from 11.5 to 23 nm, while theas-synthesized Mn₃O₄ comprise uniform, equiaxial-shaped nanocrystallites with the sizes in the range of 22 to 55 run.3. Ultrafine CaCO₃ powders were synthesized through the reactions of CaCl₂, Ca(OH)₂ or CaO and Na₂CO₃, NaHCO₃ or urea under low temperature hydrothermal conditions. The effects of the reaction temperature and during time, the kinds of reactants on the formed phase(s), morphology and size of the hydrothermally-synthesized CaCO₃ powders were also investigated. The products were characterized by means of XRD, FTIR, TEM and TG-DSC.4. Fe₃O₄ nanocrystallites were synthesized by a hydrothermal method using iron powders and water, and characterized by means of XRD, FTIR, TEM and TG-DSC. The results showed that the Fe₃O₄ obtained at 150 ℃ for 24 h or at 180 ℃ for 10 h consisted of nanoplates with an average thickness of about 82 nm or 96 nm, respectively, while that obtained at 180 ℃ for 24 h comprises nanodentries with the diameter in the range of 35-47 nm and length of 190-714 nm. The use of any extra surfactant or template during the synthesis is avoided. The possible formation mechanism of Fe3O4 in this hydrothermal system was discussed.5. γ-AlOOH nanocrystallites were synthesized by a mild and environmental benign hydrothermal method from Al₂O₃ powders and water, and characterized by means of XRD, FTIR, TEM and TG-DSC. The characterization results showed that the obtained y-AlOOH at 180 ℃ varied from cubic to lamellar shape, when the reaction time was prolonged from 10 h to 24 h, while that obtained at 200 ℃ for 24 h consists of lamellar-shaped nanocrystallites. Also, the possible formation mechanism of γ-AlOOH in the hydrothermal system was discussed.