The Controlled Synthesis Of Multilevel Structural Functional Metal-Oxide Materials Driven By Non-Covalent Interactions

Multilevel micro/nano structural materials combine the properties of both nano and micron structural materials. Compared with the same-sized solid counterparts, these fantastic multilevel micro/nanomaterials exhibit a number of outstanding properties that enable them extensive applications in sensors, microreactors, Li-ion batteries, biomedicines, catalysis, and many others. Our group devoted to studying the non-covalent interaction between the host and guest in supramolecular inclusion and adduct systems over years. Recently, we found that this interaction plays an important role in the controlled synthesis of nanomaterials. Controlled synthesis of multi-level micro/nano materials driven by non-covalent interactions has a broad application prospect because it does not require harsh reaction conditions, toxic solvents and templates, and is suitable for large-scale synthesis. In this work, gallium (a main-group metal) and iron, cobalt (two transition metals) were chosen to explore the controlled synthesis method driven by non-covalent interactions for constructing multilevel micro/nano structural metal oxide materials, as well as the relationship between structures and properties:The first chapter describes the research background, preparation methods and application prospects of multi-level micro/nanomaterials. Our research results about the non-covalent interactions are introduced, including the interaction behavior in supramolecules and some instances of controlled synthesis of inorganic materials. The current status of the researches on gallium oxide materials and iron, cobalt oxide materials are also briefly described.In Chapter 2, the first part is devoted to the comparison between the doping effect of urea (a small molecule) and polyethylene glycol (PEG, a long-chain polymer) on the physical property of metallic gallium (Ga). The physical properties of the Ga adducted in the two materials:Ga/urea and Ga/PEG were investigated by scanning electron microscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy, differential scanning calorimetry, super-conducting quantum interference device and surface-enhanced Raman scattering spectra, and compared with our previous results for the effect of macrocyclic hosts (e.g., cyclodextrins, calixarenes) on the physical modification of metallic Ga. Our data provide new direct evidence that the modification of physical properties of Ga is highly dependent on the nature of dopants used. For example, the addition of a small amount of urea causes a fundamental change in the crystallization behavior of Ga, and the presence of PEG results in the occurrence of a weak paramagnetism of Ga at high fields, both of which are completely different from the effect of other dopants.The other part of Chapter 2 is devoted to demonstrating whether there is a significant difference in the oxidation process of metallic Ga and its adducts. Our result gives a strong positive answer to the question. (3-and y-gallium oxide nanocrystals were obtained by sintering the Ga/urea adduct at different temperatures, and exhibited distinctive photoluminescence and photocatalysis properties. These results gave a strong impression that the introduction of different dopants leads metallic Ga to generate different features in microstructure, physical property, and especially chemical reactivity. We believe that the findings of this study have important implications for the development of inorganic materials.In Chapter 3, the metastable γ-Ga2O3 nanoflowers with hexagonal nanopetals were obtained by the oxidation of metallic Ga in Ga/urea adduct in solution. The as-prepared γ-Ga2O3 materials show well crystallization and exhibit strong broad emission bands in the blue-violet region. Also, the γ-Ga2O3 nanoflowers show excellent solar-blind detection performance compared with the γ-Ga2O3 microspheres, eg, short response time and large light current-dark current ratios.In Chapter 4, we successfully synthesized the ZnGa2O4 microflowers self-assembled by hexagonal single-crystalline nanopetals in a water/ethanol solution through a novel solvothermal route. The self-assembled ZnGa2O4 microflower crystal exhibits improved solar-blind deep ultraviolet detection performance such as short response time, large light to dark current ratio, high photocurrent stability, and good wavelength selectivity under zero bias voltage, with the aid of the formation of heterojunctions with polyvinyl butyral. Our result is not only the best for self-powered solar-blind photodetect devices to date, but also the first report describing the effect of polymer concentrations on photoresponses.In Chapter 5, face-raised Co3O4 octahedral crystals were successfully constructed through a carbon-assisted method using cellulose as carbon resource and used for a catalyst for selective oxidation of alcohols. The face-raised Co3O4 octahedra are about 200 nm in edge length and assembled to microtubes with a length of ca.10 μm and a width of 2-3 μm. Our analysis showed that the thermal decomposition and carbonization of cellulose has contributed to the generation of the octahedral structure and the assembled process. Moreover, compared with normal Co3O4 octahedra, the face-raised Co3O4 octahedral crystals have higher remanence and saturation magnetization, which is attributed to their more uniform small grain sizes. In particular, the face-raised Co3O4 octahedra gave both higher activity and higher selectivity than the normal Co3O4 octahedra in the catalytic oxidation reactions of alcohols. More importantly, after eight cycles, the face-raised Co3O4 octahedral crystals still exhibited considerably high catalytic activity, suggesting promising applications in heterocatalysis.In Chapter 6, a novel metallo-supramolecular micelle PF-SDS-SM was formed at room temperature through the self-assembly of potassium ferrioxalate and sodium dodecyl sulphate. This leads to a new reaction pattern which is not yet fully understood, accompanying with the creation of hollow elongated square microtubular iron oxalate dihydrate during hydrothermal process.In Chapter 7, two ternary Fe/Fe3O4/Fe2O3 nanocomposites (TF-1 and TF-2) were constructed through a sintering process using Fc/β-CD/FeCl3 adduct as a precursor. Our results reveal that the structural and physical properties of the ternary nanocomposites can be mediated by the initial amount of Fc in the precursor. Importantly, (3-CD plays a key role in protecting metallic Fe and reducing Fe2O3 during the sintering process by generating carbon. Further, the TF-2 nanorods exhibit an excellent photocatalytic activity for methylene blue and a very high photocatalytic selectivity for the organic dyes:methylene blue> rhodamine B.In Chaper 8, the researches presented in the thesis are concluded and future study on construction of multilevel micro/nano structural metal oxide materials and their applications research are proposed.