| Most recently, metal oxides nanomaterials have become one of the most important research directions of chemistry, materials, and physics because of their excellent optical, electrical, thermal, and magnetic properties. Moreover, several researches indicated that the performance and application of the nanomaterials are decided by their phases, morphologies, sizes, and compositions. Thus, structure and shape controlled synthesis of nanoscale metal oxides will not only bring the theoretically progresses, but also extend the corresponding application field. Among them aluminum oxide, aluminum oxide hydroxide and zinc aluminate spinel compound are low cost materials widely used in industries, therefore have attracted interest. In this dissertation, a valuable research has been carried out to explore the new ionic liquid-assisted hydrothermal routes to y-aluminum oxide and ZnAl2O4 spinel nanostructures.Ionic liquids (ILs), which are liquid salts at room temperature, have attracted tremendous attention due to their unique properties. As a burgeoning field, ILs has been employed as solvents, reactants, or templates for the preparation of inorganic nanomaterials. In this paper, ILs was used to prepared y-aluminum oxide and ZnAl2O4 spinel nanostructures. The purposes are to develop new synthetic methods of y-aluminum oxide and ZnAl2O4 spinel and explore the new functions of ILs. The main points can be summarized as follows:(1) Morphology controllable synthesis of y-alumina nanostructures via two step ionic liquid-assisted hydrothermal route. Firstly, precursor aluminum acetate hydroxide (CH3COO)2A1(OH) crystals with different morphologies, including nanoleaves, nanofibers, flowerlike nanoarchtectures, polyhedrons, and nanorods, by using ionic liquid 1-buthyl-2,3-dimethyl imidazollium chloride [Bdmim][Cl)] as a template were successfully synthesized. The morphologies of the precursor aluminum acetate hydroxide (CH3COO)2A1(OH) crystal can be controlled by simply changing the amount of ionic liquid in the reaction system, the reactant concentrations and the reaction temperature. In particular, the ionic liquid [Bdmim][Cl] plays a key role on the morphology of the products as a soft template or a capping agent by the hydrogen bond-co-π-πstack mechanism. Secondly,γ-boehmite andγ-alumina nanostructures with the same morphologies were obtained by calcining at 300℃and 600℃, respectively. BET characterization of final productγ-alumina nanostructures display spesific area of 250-380m2/g and pore dimeter of 3.5nm, indicating their excellent surface property.(2) Noble direct synthesis of hierarchical flowerlikeγ-AlOOH nanostructures by addition of Zn salt in the same reaction system via ionic liquid-assisted hydrothermal method. We have demonstrated that Zn salt added in the reaction system plays an important role on the formation of AlOOH as a coupling agent. The ionic liquid [Bdmim][Cl] plays a key role on the morphology of the products as a soft template or a capping agent by the hydrogen bond-co-π-πstack mechanism. According to ionic liquid amount increased, the flowers of the product were decreased in size and the leaves of the flower were increased in length-to-width ratio. The hierarchical flowerlike y-Al2O3 nanostructures obtained by calcining at 600℃for 2 h display excellent surface and mesoporous properties. BET characterization of final product flowerlikeγ-alumina nanostructures display spesific area of 150m2/g and pore dimeter of 3.6nm, indicating their excellent surface property.(3) Ionic liquid-assisted hydrothermal synthesis of Dowsonite (denoted Na-Dw) nanorod and formation of nanotube by electron beam irradiation from Dowsonite-type nanorod precursor. Firstly, well-grown Na-Dw nano rod with length of about 200 nm and diameter of about 25nm was successfully synthesized by using NaHC03 and AICl3 as reactant, and ionic liquid [Bdmim][Cl] as a template, respectively. Secondly, uniform nanotubes whose surface consisted of AlOOH were obtained by high energy electron beam irradiation. The experimental results reveal that the decomposition of Na-Dw by electron beam irradiation is absolutely different with the thermal decomposition process. In general, Na-Dw is thermal-decomposed to form NaA102, however, in present case, Na-Dw is decomposed by high energy electron beam to form A100H surface membrane and NaCO3 internal wall. Moreover, inside formed gases, i.e, H2O and CO2 are difficult to leak out because of that membrane, leading to formation of more and more expanding nanorods. In the present reaction system, ionic liquid plays a key role on the formation of well-grown Na-Dw nanorod.(4) Preparation of ZnAl2O4 spinel nanoplate by Zn2+ ion exchange from Na-Dw parent in the ionic liquid-assisted system at low temperature. Firstly, mediate compound nanoplate consisted of Al2O3·H2O and Zn6Al2(OH)16·CO3·4H2O was successfully synthesized by ion exchange in the ionic liquid system. In this stage, ionic liquid [Bdmim][Cl] plays a key role on the formation of nanoplate. Secondly, ZnAl2O4 spinel nanoplate was obtained by clcined the mediate mixture crystal at 700℃for 2 h. TEM images exhibites that ZnAl2O4 spinel nanoplate composed of fine particles with diameter of about 20 nm. The product exhibites the specific area of about 245 m2/g, indicating its excellent surface property.(5) Ionic liquid-assisted hydrothermal synthsis of y-alumina nanostructures by using (NH4)2CO3 as a basic source. In the same reaction system, different products and different morphologies were obtained at different temperature. NH4Al(OH)2CO3 (NH4-DW) bamboo leavelike and fiberlike nanostructures were obtained at 75℃, they thereafter converted toγ-Al2O3 with the same morphologies by calcining 500℃for 2 h. However, bamboo leavelike and fiberlike y-AlOOH nanostructures were obtained at 120℃, hexagonalγ-AlOOH nanoplates was obtained at 150℃. In the every case, ionic liquid plays key role on the morphologies of the products.In summary, we presented some facile and environmentally friendly methods for the controllable hydrothermal synthesis ofγ-Al2O3 and ZnAl2O4 spinel nanostructures by using ionic liquid as a template in this dissertation. It has been proved that the ionic liquid possessing the extraordinary potential is favorable for the fabrication of nanomaterials with novel morphologies and improved properties; moreover, these ionic liquids-assisted routes may offer a novel pathway towards the controllable synthesis of other inorganic nanomaterials. |
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