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Preparation of Ldh Nanolayers from Brij97Lyotropic Liquid Crystal and Nanosphere Assembly

Author: YuanWenJie
Tutor: HouWanGuo
School: Qingdao University of Science and Technology
Course: Physical and chemical
Keywords: lyotropic liquid crystal layered double hydroxides micoreactor hollow nanosphere rare earth element
CLC: O753.2
Type: Master's thesis
Year: 2013
Downloads: 5
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Abstract


Layered double hydroxides (LDHs) are important layered materials composed of two or more types of metal ions. The host hydroxide layers are positive with the exchanged an ions and water intercalated in the galleries. LDHs have a wide range of applications in areas such as flame retardant catalysis, adsorption, drug release, and so on. Lyotropic liquid crystal (LLC) consisted of amphiphiles and solvent is of long-range structure, which is able to flow as liquid and isotropic as crystal. LLC has been widely used as micro-reactor or template for the preparation of nanomaterials. In this thesis, hexagonal and lamellar lyotropic liquid crystals composed of Brij97and C12EO4were used as micro-reactors to regulate and control the morphology and structure of LDHs. This study will offer scientific basis and raw materials for constructing LDHs functional materials.In this paper, non-ionic surfactant and magnesium and aluminum salt mixture were used to constuct hexagonal lyotropic liquid crystal and used as micro-reactor to prepare LDHs nanolayers. Effects of the following factors on the morph and structure of LDHs product were studied, including surfactant concentration, inorganic salt concentration, precipitation agent dosage and reaction time. Then, the prepared LDHs nanolayers were employed as building blocks for the assembling of nanospheres using layer-by-layer method on the polystyrene (PS) nanoparticles surface. After calcination or organic solvents solution of the PS core, LDHs or its oxide hollow spheres was obtained. In addition, rare earth element containing LDHs, magnesium-aluminum-europium ternary LDHs, was also prepared using the LLC as microreactor. Morph and fluorescence study of the product were also carried out. After assembling and calcination, fluorescent hollow nanospheres of LDH oxides were obtained.The main contents of this paper are as follows.(1) Preparation of Mg-AI LDHs from hexagonal lyotropic liquid crystal. According to the polarized optical micrograph and small angle x-ray scattering analysis, compositions of the stable hexagonal lyotropic liquid crystal were selected. Using dilute ammonia as precipitating agent. Mg-AI LDHs was prepared in liquid crystal phase by coprecipitation reaction. XRD, TEM, SEM, AFM, ICP, FT-IR, N2adsorption-desorption, TG technologies were used to characterize the structure, morph and composition of LDHs nanolayers. Experimental results showed that, under the circumstances of the following, the molar ratio of magnesium and aluminum was fixed at2, total cation concentration of0.45mol/L. surfactant concentration was selected as56wt%, the applied dosage of precipitation agent was8times of the theoretical amount, when the reaction time reached24h, LDHs nanolayers with lateral size of110nm, thickness of2-5nm and specific surface area of128.81m2/g could be prepared. These results indicated that the restriction effects of LLC microreactor had great effect on the morph, size and structure of the LDHs product.(2)Using the prepared LDHs as building blocks and polystyrene spheres as the sacrificial templates, PS@LDHs composites were prepared by layer-by-layer method. After calcination or dissolution of the PS core, hollow nanospheres of LDHs oxide were prepared. The soap-free emulsion polymerization method was used to prepare polystyrene spheres with diametor of250nm and820nm. The surface of polystyrene spheres were modificated with polystyrene sulfonic acid sodium salt. Effects of dispersion medium, the quality ratio of polystyrene and LDHs, polystyrene sulfonic acid sodium concentration, polystyrene spheres particle size, coating way and calcination condition on the structure of PS@LDHs composites and hollow nanospheres wre studied. Experimental results showed that, when the mass ratio of polystyrene and LDHs was fixed at5, the diametor of polystyrene spheres was820nm, PS@LDHs complexes were esily to be prepared. When the heating rate was controlled as20℃/h, after5h of calcination time at450℃, the hollow nanosphere of LDHs oxides were obtained.(3)Preparation of magnesium-aluminum-europium ternary LDHs. Non-ionic surfactant C12EO4or Brij97was mixed with salt solutions of magnesium, aluminum and europium. Then, dilute ammonia was added to the samples and the magnesium-aluminum-europium ternary LDHs were prepared after a certain reaction time. Experimental results showed that, when C12EO4concentration was selected as50wt%. cation total concentration as0.45mol/L, the molar ratio of Mg-Al-Eu as2/0.8/0.2, the applied dosage of the precipitation agent dosage was3times of the theoretical amount. upon the reaction time of48h, the ternary LDHs with fluorescence character was obtained. In addition, such ternary LDHs product could also be prepared from hexagonal LLC microreactor. These results indicated that the novel method of preparing LDHs from the LLC microreactor is general and versatile. On this basis, hollow nanospheres of LDHs oxide containing rare-earth element were obtained after assembly and calcination.

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CLC: > Mathematical sciences and chemical > Crystallography > Amorphous and class crystalline > Class crystalline > Liquid crystal
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