Study of a Family of 40 Hydroxylated -Cristobalite Surfaces Using Empirical Potential Energy Functions

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• 作者：Shikha Nangia ; Nancy M. Washton ; Karl T. Mueller ; James D. Kubicki ; Barbara J. Garrison
• 刊名：Journal of Physical Chemistry C
• 出版年：2007
• 出版时间：April 5, 2007
• 年：2007
• 卷：111
• 期：13
• 页码：5169 - 5177
• 全文大小：707K
• 年卷期：v.111,no.13(April 5, 2007)
• ISSN：1932-7455

文摘

We present a study of a family of 40 unique hydroxylated mages/gifchars/beta2.gif" BORDER=0 ALIGN="middle">-cristobalite surfaces generated by cleaving themages/gifchars/beta2.gif" BORDER=0 ALIGN="middle">-cristobalite unit cell along crystallographic planes to include a combination of several low Miller indexsurfaces. The surface silicon atoms are quantified as percentages of Q² and Q³ centers based on their polymericstate. We find that Q³ centers are, on average, three times more abundant than Q² centers. To study thesurface properties, we use two different empirical potential energy functions: the multibody potential proposedby Fueston and Garofalini (J. Phys. Chem. 1990, 94, 5351) and the newly developed CHARMM potential byLopes et al. (J. Phys. Chem. B 2006, 110, 2782). Our results for the surface water interactions are in goodagreement with previous ab initio theoretical studies by Yang et al. (Phys. Rev. B 2006, 73, 146102) for the(100) surface. We find that the most commonly studied family of {100} surfaces is unique and is the onlysurface with 100% abundance of Q² centers, whereas there are nine examples of surfaces with 100% Q³centers. The predominantly pure Q³ surfaces show no hydrogen bonding with the neighboring surface hydroxylgroups and weakly adsorb water overlayers. This is markedly different from the {100} pure Q² surface thatshows strong hydrogen bonding within the surface groups and with water. As compared to all the surfacesstudied in this work, we find that the {100} surfaces are not true representations of the overall mages/gifchars/beta2.gif" BORDER=0 ALIGN="middle">-cristobalitesurfaces and their properties. We find that the two main factors that characterize the physical properties ofsilica surfaces are the polymeric state of the silicon atom and surface topography. Two types of pure Q³crystallographic planes have been identified and are labeled as Q^3A and Q^3B based on the differences in theirtopological features. Using the {111} and {011} surfaces as examples, we show that the Q^3A surface adsorbsH₂O that forms a stable monolayer, but the Q^3B surface fails to form a stable H₂O overlayer. Othercrystallographic planes with different ratios of Q² to Q³ centers are contrasted by the differences in the hydrogen-bonding network and their ability to form ordered H₂O overlayers.