| Ionic liquids (ILs), which are liquid salts at room temperature, have attracted tremendous attention due to their unique properties. Compared the widespread application in organic chemistry and organometallic catalysis, their use in inorganic synthesis is just about to begin. It is worth mentioning that the ionothermal synthesis is quite different from hydro-or solvothermal conditions, which may lead to new materials with interesting morphologies and that are not accessible by using conventional organic solvents or water due to the unique physicochemical properties of ionic liquids. Despite great efforts have been made on controlling crystal phase and morphology of inorganic materials using ionic liquid, a consensus of the effect type between the ionic liquids and the substrate has still not been achieved. As the consequences of this situation, most of the synthesis are not be predicted and simply use an IL or a mixture of IL with conventional solvent just like common surfactant, not sufficiently exploits the main advantage of ILs. In this paper, we systematically study the effect of ILs on the formation of inorganic nanomaterials. The purposes are to explore the new functions of ILs and develop new synthetic methods of nanomaterials with desired phase and morphology. The main points can be summarized as follows:1. Well-dispersed NH4-DW and y-A100H nanostructures with controlled morphologies have been synthesized employing an ionic liquid-assisted hydrothermal process. The basic strategies used in this work are (i) controllable phase transition from NH4-DW to y-A100H can be realized with increasing the reaction temperature, and (ii) morphological evolution of NH4-DW and γ-AlOOH nanostructures could be affected by ionic liquid concentration. Based on the experimental results, the main objective of this work is to clarify the ionic liquid effect models on the synthesis of NH4-DW and γ-AlOOH nanostructures, which can be divided into cationic or anionic dominant effect model determined by the different surface structure of the targets. Specifically, under the cationic dominant regime, ionic liquids mainly show dispersion effect for NH4-DW nanostructures meanwhile the anionic dominant model can induce y-AlOOH particles self-assembly to form hierarchical structures. Under the guidance of the models proposed, the effect of ionic liquids would be optimized by the appropriate choice of cations or anions considering different effect model with substrate surface. It is highly expected that such effect models between ionic liquids and target products are helpful to understand and design rational ionic liquids consisting of specific functional groups, thus open up new opportunities for synthesis of inorganic nanomaterials with novel morphology and improved property. In addition, the as-prepared NH4-Dw and y-AlOOH nanostructures can then be converted to porous γ-Al2O3nanostructures by thermal decomposition while preserving the same morphology. By HRTEM and nitrogen adsorption analysis, the obtained γ-Al2O3samples have excellent porous properties and might be useful in catalysis and adsorption.2. Well-dispersed ferric giniite microcrystals with controlled sizes and shapes are solvothermally synthesized from ionic liquid precursors using1-n-butyl-3-methy-limidazolium dihydrogenphosphate ([Bmim][H2PO4]) as phosphate source. The success of this synthesis relies on the concentration and composition of the ionic liquid precursors. By adjusting the molar ratios of Fe(NO3)3·9H2O to [Bmim][H2PO4] as well as the composition of ionic liquid precursors, we obtained uniform microstructures such as bipyramids exposing{111} facets, plates exposing{001} facets, hollow sphere, tetragonal hexadecahedron exposing{441} and{111} facets, truncated bipyamids with carved{001} facets. The crystalline structure of the ferric giniite microcrystals is disclosed by various characterization techniques. It was revealed that [Bmim][H2PC>4] played an important role in stabilizing the{111} facets of ferric giniite crystals, leading to the different morphologies in the presence of ionic liquid precursors with different composition. Furthermore, since these ferric giniite crystals were characterized by different facets, they could serve as model Fenton-like catalysts to uncover the correlation between the surface and the catalytic performance for photodegradation of organic dyes under visible-light irradiation. Our measurements indicate that the photocatalytic activity of as-prepared Fenton-like catalysts is highly depended on the exposed facets, and the surface area has essentially no obvious effect on the photocatalytic degradation of organic dyes in the present study. It is highly expected that these findings are useful in understanding the photocatalytic activity of Fenton-like catalysts with different morphologies, and suggest a promising new strategy for crystal facet engineering of photocatalysts for wastewater treatment based on heterogeneous Fenton-like process.3. Four well-defined morphologies, including nanorod, nanowire, nanoflower and nanowall, of MnO2nanostructures with different crystal phases (α-, β-, and8-MnO2) have been synthesized employing a simple hydrothermal process. Our experimental results demonstrate that the concentration of KMnO4plays a key role of forming different shapes and phases of MnO2nanostructures. Specifically, the K+concentration can affect the crystal phase of MnO2seeds in the nucleation processes and the decomposition rate of MnO4can influence the number of MnO2nucleus at the initial nucleating stage and also can affect the subsequent crystal growth process. Moreover, the effects of reaction temperature on the morphology of8-MnO2nanowall are systematically studied. The electrochemical performances of the as-prepared MnO2as the positive material of rechargeable Li-ion batteries have also been researched. It is found that8-MnO2nanowall possess largely enhanced electrochemical activity compared to a-MnO2nanowires and β-MnO2nanorods. The vast difference in electrochemical activity is discussed in terms of the morphology, crystal phase and specific surface area of MnO2nanostructures. It is highly expected that these findings are useful in understanding the formation of MnO2nanocrystals with different morphologies, which are also applicable to other metal oxides nanocrystals.4. High-stability hematite mesocrystals were prepared by a facile route using N,N-dimethylformamide (DMF) and methanol as the mixed solvent without polymer additives. The success of this synthesis relies on (i) carefully analzed the time-resolved structure formation process of pesudocubic hematite single-crystal, and (ii) tuned the crystallograpically aligned orientations of primary particle units by crystal facet engineering to prevent the crystallographic fusion to single-crystal. To the best our knowledge, this is the first attempt to investigate the role of crystal facet engineering on the formation of stable mesocrystals. In particular, the rhombic hematite mesocrystals exhibit excellent lithium insertion behavior compared to the hematite single-crystals.5. A novel PbS hierarchical superstructure, denoted as octapodal dendrites with a cubic center, has been synthesized employing a simple single-source precursor route. Our experimental results demonstrate that the novel hierarchical superstructure was generated through the delicate balance between the kinetic growth and thermodynamic growth regimes. Moreover, the morphology of PbS crystals can be controlled by adjusting the solvent under thermodynamically or kinetically controlled growth regime. It is highly expected that these findings are useful in understanding the formation of PbS nanocrystals with different morphologies, which are also applicable to other fcc nanocrystals.In summary, we presented some facile and environmentally friendly methods for the controllable synthesis of inorganic nanomaterials 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. We believe the understanding that we develop of effect model of ILs on the formation of nanostructures is of fundamental importance. Furthermore, it is hoped that this findings will aid in the design of new synthetic methodologies for preparation of inorganic materials using ILs. |
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