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Preparation Of LDH And LDO In A Controllable Fashion For Specific Applications

Posted on:2003-08-06Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y ZhaoFull Text:PDF
GTID:1101360125470236Subject:Applied Chemistry
Abstract/Summary:PDF Full Text Request
In this Thesis, several controllable preparative methods and applications of Layered Double Hydroxide (LDH) and Layered Double Oxide (LDO) are reported. The influence of different synthetic methods and preparative conditions on the structure and crystallite size and its distribution of LDH has been investigated systematically. Various new methods for synthesizing LDH and modifying LDH have been developed. The crystal structure, crystallite size and its distribution, surface properties of LDH can be controlled under appropriate conditions using these different methods. Applications of LDH as flame retardants and thermal stabilizers in the polymer materials have also been investigated. The range of applications of LDH has thus been expanded. Mesoporous Layered Double Oxides (LDO) with narrow pore size distribution and high surface area have been prepared for the first time by calcination of an LDH precursor with a narrow particle size distribution. The catalytic properties of LDO as a solid catalyst in the reaction of propylene oxide with ethanol have been investigated.1. Preparation of LDH in a controllable fashion and the application of the resulting materials in polymer materials1) Preparation of LDH in a controllable fashionLDH have been synthesized using a new method developed in our laboratory involving separate nucleation and aging steps. The influence of nucleation and agingconditions on the crystal structure and crystallite size and its distribution has been investigated. LDH nanomaterials with well-formed crystal structures and uniform particle size have been prepared under reflux conditions. LDH crystals with larger size have been synthesized using hydrothermal aging conditions.The crystallites of LDH do not continue to grow with increasing aging time once the thermodynamic equilibrium has been reached. A new method of preparing LDH under non-equilibrium aging conditions has been developed which involves adding additional salt and base solutions after a period of aging in order to increase the crystallite size. LDH with well-formed crystal structures and controllable size in the range of 60 to 350nm can be prepared using this method. In addition, a new method using urea and sodium hydroxide as precipitating agents and a new method using gelatin to restrict the growth of LDH crystallites have been developed. LDH with small crystallite size and narrow crystallite size distribution have been synthesized using these methods. Finally, another new method, which uses ethanol and water as mixed solvent to prepare LDH crystallite with different sizes, is reported.The influence of aging conditions, charge density of the sheet and degree of supersaturation on the selectivity of crystal growth in different directions have been investigated. The size of the crystallites in the a direction was found to be larger than that in the c direction under all experimental conditions. The crystal growth rate in the c direction increases greatly with increasing charge density of the sheet and decreasing supersaturation of the preparative system so that LDH crystallites with lower aspect ratio are produce under these conditions.The surface of LDH has been modified by reaction with conventional organic coupling agents. To avoid the agglomeration of the nanoscale LDH, a dispersant of sodium polyacrylate and a coupling agent are used together during the course of the synthesis or before drying. In addition, ultrasound is used in the course of the modification. As a result, surface-modified LDH materials with small crystallite sizes are obtained.2) Application of LDH in polymer materialsComposite nanomaterials of EP/LDH are prepared by the addition of LDH to the epoxy resins (EP). The flame retardancy properties of EP/LDH composite materials have been investigated. Addition of LDH increases the oxygen index slightly but gives a greatly enhanced smoke inhibition effect. Composite nanomaterials of PMMA/LDH have been prepared using LDH as a thermal stabilizer. The relation between the degree of dispersion of LDH in PMM...
Keywords/Search Tags:Layered Double Hydroxide (LDH), hydrotalcite, preparation in a controllable fashion, application, crystallite size and distribution, Layered Double Oxide (LDO), mesoporous structure, catalyst, glycol ethers
PDF Full Text Request
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