The characterization of molecular water on silica surfaces

K.Robert Lange
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引用次数: 70

Abstract

The existence of two types of molecular, adsorbed water on the surface of precipitated silica has been confirmed. It has been shown that the physically adsorbed water gives a Type II isotherm and requires an activation energy of 6.6, 7.4, and 8.2 kcal./mole for its removal, on three different precipitated silica samples studied. The second type of water is probably H-bonded to SiOH groups and conforms to a Langmuir isotherm, requiring about 10 kcal. activation energy for its removal. The data are consistent with a bridged structure involving one water and two SiOH groups. The data suggest that past reports of water adsorption on silica surfaces have shown monolayer coverage to be complete at spurious partial pressures because the two types of water adsorption have not been clearly separated.

二氧化硅表面分子水的表征
证实了沉淀二氧化硅表面吸附水的两类分子的存在。研究表明,在三种不同的沉淀二氧化硅样品上,物理吸附的水呈现II型等温线,需要6.6、7.4和8.2千卡/摩尔的活化能才能去除。第二类水可能与SiOH基团成氢键,符合Langmuir等温线,需要大约10千卡的活化能才能去除。数据与一个水和两个SiOH基团的桥式结构相一致。数据表明,过去关于水吸附在二氧化硅表面的报道表明,在虚假的分压下,单层覆盖是完全的,因为两种类型的水吸附没有被清楚地分开。
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