Synthesis Of Inorganic Micro-And Nanomaterials Using Ionic Liquids As Medium And Their Optical Properties

Green chemistry has been the hot topic and academic frontier of current chemical research.It is also the important direction of the chemical research of the 21^st century. The traditional solvents are high on the list of damaging chemicals for two simple reasons:(â…°) they are usually volatile liquids that are difficult to contain and(â…±) they are used in huge amounts.So,the search for alternatives to the most damaging solvents has become a high priority.Ionic liquids(ILs) developed latterly,are satisfied with green chemistry absolutely.Because,ionic liquids composed of organic cations and organic/inorganic anions are liquid salts with melting points at or below room temperature.Furthermore, they are a set of environmentally benign solvents with nonvolatilities or neligible vapor pressure,a broad range of room temperature liquid compositions,good electrical and thermal conductivity,excellent chemical and thermal stabilities,and selective solvency and design.Additionally,ionic liquids diversities and their special properties combination make them possible to be various functional materials and reaction mediums with diverse properties and extensive applications.Up to now,they have been widely applied in electrochemistry,organic chemistry,catalysis,analysis, and so on.In contrast,the use of ILs in inorganic synthesis is still in its infancy.In this dissertation,we synthesized three common ionic liquids at first,and then we used the ionic liquids to prepare of various micro/nanomaterials,including tricobalt tetraoxide(Co₃O₄) nanocubes,cadmium molybdate(CdMoO₄) microtubes and manganese sulfide(MnS) hollow microspheres.X-ray diffraction(XRD), scanning electron microscopy(SEM),transmission electron microscopy(TEM), UV-vis absorption spectroscopy and photoluminescence(PL) emission spectroscopy were used to investigate the phase structures,morphologies and optical properties of as-prepared materials.(1) Tricobalt tetraoxide(Co₃O₄) nauocubes were successfully synthesized through a facile solution oxidation route at room temperature and normal pressure for 6 h at first time,using an ionic liquid 1-n-butyl-3-methylimidazolium hydroxide ([BMIM]OH) as an assisted agent and cobalt nitrate(Co(NO₃)₂) and hydrogen peroxide(H₂O₂) as raw materials.The contrast experiments verified that the ionic liquid acted as a catalyst during the formation of Co₃O₄ nanocrystals.The possible formation mechanism of Co₃O₄ nanoparticles was simply proposed as well. Pronounced quantum confinement effects had been observed with the prepared Co₃O₄ nanocubes,and the optical band gap energies determined were 3.28 eV and 1.32 eV, respectively,for O^2--Co²⁺ and O^2--Co³⁺ charge-transfer processes.(2) Cadmium molybdate(CdMoO₄) microtubes consisted of microspheres were successfully prepared at 60℃using the rod-like precursors as self-sacrificial templates and sodium molybdate(Na₂MoO₄) as molybdenum source.The precursor was fabricated in large scale through the reaction of ionic liquid 1-n-butyl-3-methylimidazolium chloride([BMIM]CI) and cadmium chloride(CdCl₂) under ambient conditions.In addition,the influence of the ionic liquid adding amounts,reaction time and temperature on the structure,textural properties and morphologies of the final products were also detailedly investigated.Based on the results,the growth mechanism of the CdMoO₄ microtubes was proposed.It was found that the as prepared samples had original optical properties.(3) Metastable manganese sulfide(γ-MnS) hollow mierospheres assembled by nanorods and stable manganese sulfide(α-MnS) hollow spheres constructed by polyhedrons were successfully prepared by ionic liquid-assisted process at 180℃and 200℃,respectively,using an ordinary small biomolecure L-cysteine(HSCH₂CH (NH₂)COOH) as sulfide source and manganese acetate(Mn(CH₃COO)₂) as manganese source.Through varying the experimental parameters such as reaction temperature and time,we demonstrated that the formationg ofα-MnS hollow microspheres underwent two stages:first,theα-MnS solid microspheres assembled from polyhedrons were formed in situ using theγ-MnS hollow microspheres as self-generated sacrificial templates;second,on the base of Ostwald ripening process, the particles in the iner core of the solid spheres dissolved and resulted in the formation of hollow interior structures.Additionally,the ionic liquid-assisted phase and shape controllable growth mechanism of the MnS microstructured spheres was proposed.The optical properties of as-prepared MnS samples wvere also investigated.