Probing Hydrogen Bonding and the Local Environment of Silanols on Silica Surfaces via Nuclear Spin Cross Polarization Dynamics

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• 作者：I-Ssuer Chuang and Gary E. Maciel
• 刊名：Journal of the American Chemical Society
• 出版年：1996
• 出版时间：January 17, 1996
• 年：1996
• 卷：118
• 期：2
• 页码：401 - 406
• 全文大小：141K
• 年卷期：v.118,no.2(January 17, 1996)
• ISSN：1520-5126

文摘

By studying ¹Hs/entities/rarr.gif">²⁹Sicross-polarization dynamics of two untreated and two "dry" silicagel samples (oneevacuated at 25 s/entities/deg.gif">C and one evacuated at 200 s/entities/deg.gif">C), we find that allthe surface silanols on the two untreated silicasare hydrogen bonded, either to the hydroxyl groups of adjacentsilanol(s) or to water molecule(s). About 46%and47% of the geminal silanols and 53% and 58% of the single silanolsthat were hydrogen bonded only to water in thetwo untreated silicas become non-hydrogen bonded on the two "dry"silica surfaces, but the remainder of the silanolsof the untreated silicas (i.e., those hydrogen bonded to othersilanols) remain hydrogen bonded to other silanolsupon drying. The ratio of the number of hydrogen-bonding singlesilanols to the number of hydrogen-bondinggeminal silanols is 17-to-1 for a Fisher silica surface evacuated at 25s/entities/deg.gif">C and 16-to-1 for a Baker silica surfaceevacuated at 200 s/entities/deg.gif">C. These results can be explained in terms ofa generalized silica surface model based on thes/gifchars/beta2.gif" BORDER=0 ALIGN="middle">-cristobalite crystal structure.