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模板法制备介孔材料及其表征
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摘要
有序介孔材料(如命名为MCM-41的介孔材料)因其较大且连续可调的孔径、大的比表面积和孔体积而在大分子的吸附、催化和分离,纳米组装技术以及光、电、磁等领域具有广泛的潜在应用价值而受到人们的关注,正成为众多领域的研究热点之一。本文主要做了以下几个方面的工作:
     1.利用一种阳离子模板剂—十八烷基三甲基溴化铵(STAB)为模板在强酸性条件下合成出了具有MCM-41结构的介孔氧化硅材料,并分别利用煅烧和热乙醇萃取的方法除去模板剂。采用FT-IR、SAXRD、HRTEM和N_2的吸附—脱附等温线对介孔材料进行了表征。结果表明萃取的样品具有比煅烧样品更大的比表面积和更有序的介孔结构,在煅烧升温过程中适当提高升温速率可以使介孔孔壁有序化。SAXRD和HRTEM的结果进一步表明制备的介孔材料具有六方有序的结构,孔径大小在2-3nm且分布很窄,材料的N_2的吸附—脱附等温线呈现第Ⅳ型吸附曲线类型,表明合成的材料确为介孔结构,比表面积和孔体积分别高达1400 m~2/g和1.04cm~3/g。
     2.尝试利用STAB作为模板剂来合成介孔氧化钛材料,并且利用FT-IR,SAXRD,HRTEM和N_2的吸附—脱附等温线对样品进行了表征。结果表明合成的介孔结构为短程有序的蠕虫状孔,孔径达8nm。N_2的吸附—脱附等温线呈现第Ⅳ型吸附曲线的特征,说明材料确为介孔结构,但比表面积和孔体积均只有86 m~2/g和0.23cm~3/g。
     3.在常温常压下利用聚苯乙烯微乳液为模板制备出了有序介孔氧化硅,并分别利用热乙醇萃取和煅烧的方法除去模板剂。利用FT-IR,SAXRD,HRTEM和N_2的吸附—脱附等温线对介孔材料进行了表征。FT-IR的结果表明经过二次萃取可以有效的除去模板剂。SAXRD和HRTEM的结果则显示样品为具有六方有序结构的MCM-41氧化硅材料,孔径大小为4-5nm且分布较窄,材料的N_2吸附—脱附等温线的分析表明了样品确为呈现第Ⅳ型吸附曲线的介孔材料,而进一步的表征则表明样品的比表面积和孔体积高达1300 m~2/g和1.27cm~3/g。
Up to now, mesoporous materials with ordered pore structures, large and regulablepore diameter, BET surface area and pore volume were rapidly developed because oftheir potential applications in many fields such as adsorption, catalysis, separation ofmacromolecules, optics, nano-assembly technologies, electronics, magnetisms andchemical sensors.
     1. In this thesis, the MCM-41 mesoporous silica was synthesized by using cationicsurfactant stearictrimethyl ammonium bromide (STAB) as template under strong acidconditions, and STAB was removed by calcination and hot ethanol-extraction. Thethree-dimension MCM-41 mesopores was characterized by FT-IR, SAXRD, nitrogenadsorption-desorption isotherm and HRTEM. The results showed that samples byextraction had bigger BET surface area and more ordered pore structure than those bycalcination, but pore structure could be more ordered under more rapid calefactiverate when calcining. SAXRD and TEM results indicated that all samples had ahexagon pore structures with narrow pore diameter distribution(2-3nm) and allnitrogen adsorption-desorption isotherm exhibited a LangmuirⅣcategory which isrelated to mesoporous materials with large BET surface area (more than 1400m~2/g)and pore volume (1.04cm~3/g).
     2. In this part, a mesoporous titania materials was synthesized by using STAB astemplate, and FT-IR, SAXRD, HRTEM and nitrogen adsorption-desorption was takento the sample. The results showed that a worm-like pore structure with larger porediameter (8nm) was synthesized. Nitrogen adsorption-desorption isotherm showed aLangmuirⅣcategory which is related to mesoporous materials, and the BET surfacearea and pore volume was 86m~2/g and 0.23cm~3/g respective.
     3. On the base of chapter 1 and 2, we synthesized ordered mesoporous silica bypolystyrene microemulsion as template under normal temperature and pressure, andtemplate was removed by calcination and hot ethanol-extraction, respectively.Similarly, the three-dimension MCM-41 mesopores was characterized by FT-IR, SAXRD, nitrogen adsorption-desorption isotherm and HRTEM. FT-IR results showedthat template could be thoroughly removed by two-time extraction. SAXRD andHRTEM results showed that the synthesized mesoporous materials had a hexagonpore structure same to MCM-41 with a pore diameter at 4-5nm. It was also analyzedthat all nitrogen adsorption-desorption isotherm exhibited a LangmuirⅣcategorywhich is related to mesoporous materials. And the samples had a uniform porediameter distribution, high surface area and pore volume (more than 1300m~2/g and1.27cm~3/g).
引文
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