Controlled Synthesis And Self-assembly Of AlOOH And Low-cost Preparation Of Al₂O₃ Nanopowders And Nanomembranes

Nanomaterials have drawn continuous research attention because of their unique electrical, optical and magnetic properties different from that of bulk materials. But the main challenge in this area is how to precisely control the sizes, dimensionalities, compositions and crystal structures in nanoscale, which may serve as a powerful tool for the tailoring of physical/chemical properties of materials in a controllable way. In this dissertation, based on the comprehensive and thorough investigation of a lot of literatures, I gave a concise review on the structures, properties, applications and preparation methods. Following that, solution-based routes were developed to realize the chemical synthesis of special and novel nanomaterials. Furthermore, valuable explorations have been carried out on the research on their growth mechanism and properties and attempts have been made on low-cost preparation of alumina nanopowders and the possibilities of large scale production. The research conclusions provide some original and innovative results, and the main points are summarized as follows:1. A new and feasible emulsion route was established to control the synthesis of Al₂O₃ hollow spheres. The reaction was accomplished at the organic/aqueous biphasic boundary. Based on a series of comparative experiments under different reaction conditions, the probable formation mechanism of Al₂O₃ hollow spheres was proposed to be emulsion-morphology controlled growth process. The Al₂O₃ hollow spheres could be tailored by using different concentration of surfactant. In addition, Cu(OH)2 bamboo-leaf-like single crystals were successfully synthesized by increasing the surfactant amounts to 1.5g. It could be converted to a porous structure (CuO) after removing the Span80 molecules via calcination. The optical properties of these CuO nanostructures were studied with UV-vis spectra measurements and found to exhibit blue shifts in UV-vis spectra and possess larger band gaps compared with those of bulk crystals. 2. The AlOOH core/shell microspheres were successfully synthesized in large-scale via a one-step template-free solvothermal route. Most shells of the spheres composed of loosely stacked nanoplatelets and nanotubes as second order structure. Based on the evolution process of the products at various stages of the reaction, a possible mechanism was proposed to the formation of core-shell structures, which involved a surface reaction-dissolution-recrystallization process. Citrtate anion, as a coordination agent and shape modifier, plays a key role in determining the morphology of the final products. The as-prepared AlOOH core-shell superstructures are powerful in the removal of Congo red pollutant from waste water. Taking into account the high BET surface area and excellent porous properties, this novel structure is expected to be useful in many other applications, such as catalysts, sorbents, ceramics, and optical nanodevices.3. A solvothermal method using the mixed solvent of water and acetone was developed to prepare AlOOH hollow spheres. The structure and morphology of the products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), Brunauer-Emmett-Teller (BET) and room-temperature photoluminescence (PL) spectra, etc. The effect of the important experiment parameters on the morphology of the final products was deeply investigated. And we also investigated the dependent relationship between morphologies and PL. And this work may provide new insights into preparing other inorganic core/shell spheres with complicated structure.4. A new synthetic strategy has been established to prepare nano-alumina of high purity with exhausted aluminum scraps as the raw material. Aluminium ammonium sulphate (AA) with high purity was obtained via the reaction of aluminum scrap reacted with ammonium bisulfate and recrystallization several times. And aluminium ammonium carbonate hydroxide (AACH) was synthesized via the reaction of AA reacted with ammonium bicarbonate. The precursor was calcined to getα-Al₂O₃ nanometer powders with average grain size of 49nm. Inductive Coupled Plasma Emission Spectrometer (ICP) analysis result shows that the purity of Al₂O₃ is beyond 99.99%. Support vector machine, a new computational method which can avoid over-fitting and has powerful prediction ability, has been used for optimizing process parameters of AACH and establishing the models between process parameters and the mass ratio of AACH. By this way, the costs of the preparation of nanometer alumina can be reduced while the industrial waste is disposed at the same time.5. Alumina nanofiltration membrane has been prepared by sol-gel dip-coating method. The effects of preparation parameters during the preparation process on the quality of the final membrane were studied. These parameters included pore size of the substrate, alumina content, selection and dosage of the drying control chemical additives, times of dipping, drying process and heating conditions of the gel membrane. The problem of the desquamation between the selective layer and the substrate was solved; large area membrane without pinholes and cracks was prepared successfully. Orthogonality experiments were designed to examine the effects of different preparation parameters. Semi-empirical mathematical model of preparing crack free membrane was built based on the data mining of the preparation data.