Synthesis And Application Of Inorganic Materials Through Alcothermal Process

The objective of this doctoral dissertation is to explore the synthesis of someinorganic materials, including: metal oxides, carbon microspheres and metaloxide/carbon composites by a low-temperature solvothermal method, employingethanol as solvent. Ethanol is the cheapest solvent except water. Thus it is widely usedas solvent in the synthetic chemistry, especially solvothermal method. Besides solvent,here it can also carbonize with the assistance of iodine to form carbon. The reactioncontainer is autoclave with Teflon inner inside. This kind of autoclave is usually usedbelow200°C. Thus the reactions performed belong to the low-or mid-temperaturesolvothermal synthesis. The solvothermal synthesis is simple and the reactants andtemperature are easily controlled. The obtained inorganic materials were characterizedby X-ray powder diffraction, transmission and scanning electron microscopy, energydispersive X-ray spectroscopy, Brunauer-Emmett-Teller surface area, pore sizedistribution, IR, UV-Vis, Raman, electrochemical workstation and X-ray photoelectronspectroscopy. Finally, according to the respective properties of the synthesized inorganicmaterials, preliminary studies of their applications were performed. Specific workincludes the following sections:1、Fe₂O₃homogeneous core/shell hierarchical nanostructures as well as other shapeswere synthesized via solvothermal treatment of different concentrations ofFeCl₃·6H₂O and ethanol. Ethanol acts as solvent. The shapes and structures ofsynthesized hematite were found to be influenced by several factors, such asreaction time, concentration of Fe³⁺and temperature. The forming mechanism ofhematite was concluded according to the time-dependent experiments. Fe₂O₃homogeneous core/shell hierarchical microshperes were used as catalyst forselective oxidation of benzyl alcohol to benzaldehyde. It was found that such ironoxide catalyst may improve both the selectivity and conversion of the reaction. Interms of Fe³⁺as a catalyst for the reaction, the conversion is high, but theselectivity is low. The primary product was benzoic acid. Using commercial iron oxide as a catalyst, the conversion is very low. The reason is that there aremesoporous structures inside the iron oxide.2、 Carbon microspheres （CMSs） were prepared by the iodine-catalyzed carbonizationof ethanol at low temperatures by a solvothermal synthesis. In the reactionanhydrous FeCl₃was used as oxidant. Without iodine, the carbonizationtemperature of ethanol is at least500°C. Iodine acted as a catalyst and reduced thecarbonization temperature to160°C. The characteristic of this reaction is thatethanol acts as both solvent and carbon resource. It was suggested that the shapeand structure of the as-obtained CMSs were influenced by the reaction time,concentration of FeCl₃, temperature and iodine amount. The forming mechanismof CMSs was concluded according to the time-dependent experiments as well asdifferent alcohols as carbon resource. In addition to ethanol, n-propanol,i-propanol, n-butanol, i-butanol, t-butanol, ethylene glycol may also carbonize insimilar conditions. But methanol is exceptional. The CMS-supported Pt catalystshowed enhanced specific activity during the room-temperature methanolelectrooxidation.3、 ZnO/C composite spheres were fabricated by one step solvothermal treatment ofethanol, Zn（Ac）₂·2H₂O and iodine. Once again, ethanol acts as both solvent andcarbon resource. The synthesized carbon content in the ZnO/C compositematerials is related to the iodine additions. Less iodine leads to less carbon contentand more to more. At last only carbon spheres of about100nm in diameter can beobtained. If iodine amount is further increased, no more precipitates can beobtained. The photocatalytic activities of the samples with different amounts ofcarbon are evaluated by the degradation degree of aqueous solutions of pollutionin visible-light irradiation. The photocatalytic activity of the sample with30%carbon content shows the best catalytic performance comparing with othersamples.4、 Mesoporous TiO₂/C composite microspheres were directly synthesized by asolvothermal method employing tetrabutyl titanate as solute, iodine as catalyst.During the solvothermal process, ethanol acted as both solvent and carbonprecursor. The attendance of iodine catalyst promotes the carbonization of ethanol.After burning carbon in air at500°C, mesoporous structure of TiO₂spheres were retained. However the specific surface area and pore size distribution werechanged from230.0m²/g and4.0nm to180.0m²/g and5.5nm, respectively. Theiodine-catalyzed reaction provides an opportunity to obtain crystalline mesoporousTiO₂without using surfactants or structure-directing agents. The synthesizedTiO₂/C composite spheres were used as anode of Li ion battery. The electrodepresented good performance: it delivers a capacity of222mAh·g^-1in the firstdischarge cycle at0.1C.The above experiments prove that ethanol is an excellent solvent in thesolvothermal synthesis and can be applied to the synthesis of metal oxides. It can alsocarbonize with the help of iodine, so it can be used for the fabrication of carbon or metaloxides/carbon composite materials. At the same time, the iodine is proved to be a verygood catalyst. Except iodine, the carbonization of ethanol is also related to the metalions. Only carbon can be obtained when Fe³⁺is in the solvothermal process. When Ti⁴⁺or Zn²⁺is in the solution, the carbonization and alcoholysis of the ions happensimultaneously.