"中性"層状ケイ酸塩粘土鉱物の表面ルイス酸性 : 酸性部位と酸性発現機構

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The nature of the surface acidity of layer silicates with no layer charge is not well understood compared to that of the silicates with the charge. The objectives of this study were to characterize the surface acidity of four minerals (pyrophyllite, talc, kaolinite, and lizardite), and to elucidate the origin of the acidity of such 'neutral' minerals. The Hammett acid function (Ho) values and surface acid strength of the four minerals did not change with their exchangeble cation species. The degrees of the reduction in their acid strengths due to increase in relative humidity were smaller than the case of montmorillonite. In any conditions, acid strengths of dioctahedral minerals were greater than those of trioctahedral minerals. More than 70% of the external surfaces of the minerals were covered by methyl red, indicating that the acid sites distributed mostly in the external surfaces of the minerals. Both of pre-treatments by 1% sodium hexametaphosphate and by 1mM NaOH reduced the methyl red adsorption, but the acid strengths did not change after the NaOH treatment. From above results, we concluded that the acid sites of the 'neutral' minerals were the Lewis type, and derived from their ability to accept electrons due to the neutral layer compositions. We also concluded that the ability was related to enlargement of octahedral sheet in planer direction and elongations of some chemical bondings. The enlargement and elongations occur as a result of adjustment of misfit between tetrahedral and octahedral sheets, especially for dioctahedral minerals.
日本粘土学会の論文
1993-12-30

"中性"層状ケイ酸塩粘土鉱物の表面ルイス酸性 : 酸性部位と酸性発現機構

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