Covalent Grafting to μ-Hydroxy-Capped Surfaces? A Kaolinite Case Study
Covalent Grafting to μ-Hydroxy-Capped Surfaces? A Kaolinite Case Study
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DOI：
10.1021/cm200235x
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发表时间：
2011-07-12
影响因子：
8.6
通讯作者：
Senker, Juergen
中科院分区：
文献类型：
--
作者：
Hirsemann, Dunja;Koester, Thomas K-J;Senker, Juergen
所有的多羟基都是在各种矿物的外表面经常遇到的盖基，这些矿物通常用作复合材料的填料。因此，共价接枝到这个官能团将提供一种通用的和有吸引力的表面改性途径。高岭石的八面体层由多桥铝醇基团组成。特别是，高岭石的插层化合物，其所有基面都暴露出来并且可以被修饰，是研究这种共价接枝的可行性的理想选择。巨大的（内）比表面积大大提高了分析的灵敏度，使高岭石成为理想的模型化合物。本文采用固体核磁共振技术分析了嵌入高岭石（EG高岭石）的乙二醇（EG）的键合模式。Al-27 MQMAS允许区分插入和接枝EG分子，因为层中八面体配位铝核的化学环境通过形成共价键而显着改变。此外，通过宽线固态H-1核磁共振测量，研究了EG分子在层间空间中的温度依赖动力学。EG分子在层间空间中围绕共价键的羟基进行圆周运动。结合EG动力学分析C-13-Al-27 REAPDOR测量，可以确定八面体铝与EG成键碳原子之间的C-13中心点中心点Al-27距离。这个距离是3.1埃。对EG分子的键合模式进行了详尽的描述，并毫无疑问地证明了共价接枝。这表明，一般来说，它-羟基的反应性足以实现各种矿物的共价表面改性。
All mu-hydroxyl groups are frequently encountered capping groups found on the external surfaces of various minerals that are often used as fillers in composite materials. Covalent grafting to this functional group would therefore offer a versatile and attractive route to surface modification. The octahedral layer of kaolinite is composed of mu-bridged aluminol groups. In particular, intercalation compounds of kaolinite, where all basal planes are exposed and may be modified, are ideally suited to study the feasibility of such covalent graftings. The huge (internal) specific surface area greatly improves the sensitivity of the analytics and renders kaolinite an ideal model compound. Herein we analyze the mode of bonding of ethylene glycol (EG), intercalated into kaolinite (EG kaolinite), by solid-state NMR techniques. Al-27 MQMAS allows for distinction between intercalated and grafted EG molecules because the chemical surroundings of octahedrally coordinated aluminum nuclei in the layer are significantly changed by the formation of a covalent bond. Moreover, the temperature-dependent dynamics of the EG molecules in the interlamellar space are examined by wide-line solid-state H-1 NMR measurements. The EG molecules perform a circular motion around the covalently bonded hydroxyl group in the interlamellar space. Analysis of the C-13-Al-27 REAPDOR measurement in conjunction with the EG dynamics allows for determination of the C-13 center dot center dot center dot Al-27 distance between octahedral aluminum and the bonded carbon atom of EG. This distance is 3.1 angstrom. A thorough description of the bonding mode of the EG molecules is provided and proves beyond any doubt the covalent grafting. This suggests that the reactivity of it-hydroxyl groups, in general, is sufficient to realize a covalent surface modification of a wide range of minerals.