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首页> 外文期刊>The journal of physical chemistry, C. Nanomaterials and interfaces >Pulsed Field Gradient NMR Investigations of Alkyltripropylammonium—Silica Mixtures
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Pulsed Field Gradient NMR Investigations of Alkyltripropylammonium—Silica Mixtures

机译：烷基三丙基铵-二氧化硅混合物的脉冲场梯度NMR研究

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摘要

Pulsed field gradient nuclear magnetic resonance (PFG NMR) spectroscopy has been used to study the organocation—silica interactions in silica—alkyltripropylammonium solutions. Mixtures containing silica and methyltripropyiammonium, ethyltripropylammonium, and tetrapropylammonium cations have been investigated to determine how the organocation structure and hydrophobicity affect organocation—silica interactions. PFG NMR results show that, in the presence of silica, the diffusion coefficients of the tetraalkylammonium organocations decreased compared with those of the cations in water alone. This decrease is attributed to a reduction in the cation mobility as the cations interact with the silica nanoparticles. The diffusion coefficients as a function of the organocation concentration were measured to determine the fraction of organocations bound to the silica through a model that considers the cation in either a free or a bound state. The resulting adsorption isotherms were fit with the Langmuir model, from which the free energy of binding was determined to be between 10 and 13 kJ/mol. This value appeared insensitive to the organocation identity and the silica content of the mixture, although the most hydrophilic cation had the highest binding energy. The results show that the organocation—silica interactions play an important role in zeolite formation and can help to develop a more general approach to making high-silica zeolites from optically transparent mixtures containing silica nanoparticles.
机译：脉冲场梯度核磁共振（PFG NMR）光谱已用于研究二氧化硅-烷基三丙基铵溶液中的有机阳离子-二氧化硅相互作用。已经研究了含有二氧化硅和甲基三丙铵，乙基三丙基铵和四丙基铵阳离子的混合物，以确定有机阳离子的结构和疏水性如何影响有机阳离子与二氧化硅的相互作用。 PFG NMR结果表明，在二氧化硅的存在下，四烷基铵有机阳离子的扩散系数比单独在水中的阳离子的扩散系数降低。该降低归因于当阳离子与二氧化硅纳米颗粒相互作用时阳离子迁移率降低。测量扩散系数作为有机阳离子浓度的函数，以通过考虑阳离子处于游离态或结合态的模型确定与二氧化硅结合的有机阳离子的比例。所得的吸附等温线与Langmuir模型拟合，由此确定结合自由能在10到13 kJ / mol之间。尽管最亲水的阳离子具有最高的结合能，该值似乎对混合物的有机阳离子身份和二氧化硅含量不敏感。结果表明，有机阳离子与二氧化硅的相互作用在沸石的形成中起着重要作用，并且可以帮助开发一种更通用的方法，从包含二氧化硅纳米粒子的光学透明混合物中制备高二氧化硅沸石。

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