Adsorption of Formamide on Kaolinite Surfaces: A Combined Infrared Experimental and Theoretical Study

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• 作者：M. Michele Dawley ; Andrea Michalkova Scott ; Frances C. Hill ; Jerzy Leszczynski ; Thomas M. Orlando
• 刊名：The Journal of Physical Chemistry C
• 出版年：2012
• 出版时间：November 15, 2012
• 年：2012
• 卷：116
• 期：45
• 页码：23981-23991
• 全文大小：518K
• 年卷期：v.116,no.45(November 15, 2012)
• ISSN：1932-7455

文摘

The interaction of formamide with kaolinite has been studied using transmission Fourier transform-infrared spectroscopy (FT-IR) and temperature programmed desorption (TPD) under ultra-high vacuum conditions. The theoretical harmonic infrared frequencies have been calculated using M05-2X/6-31G(d), 6-31G(d,p), and 6-31+G(d,p) levels of density functional theory, and general agreement with experiment has been found for condensed formamide and the formamide鈥搆aolinite surface complexes. The kaolinite OH band positions change as a function of temperature, which have been previously correlated with surface reconstructions and changes in interlayer bond distances in the kaolinite. The temperature dependence of the kaolinite鈥揙H and formamide vibrational frequencies can be sensitive probes of formamide interactions with the exposed and interlayer surfaces of kaolinite. Samples dosed directly with formamide show that the C鈺怬 stretching feature is broadened and shifts to lower frequency at low temperatures (67鈥?0 K). The NH and CH stretches of formamide are also very weak at these temperatures. We interpret these features as manifestations of hydrogen bonding between the Al鈥揙H octahedral kaolinite face (inner surface OH group) and formamide鈥檚 carbonyl group. Intercalation and subsequent bonding may be facilitated by the increased O鈥揌路路路O bond lengths between kaolinite lattices and increased availability of Al鈥揙H sites in the low-temperature regime. At 100鈥?10 K, the C鈺怬 feature sharpens and shifts to a higher frequency, while the NH and CH stretches become more distinct. With increasing temperature, formamide diffusion and formamide鈥揻ormamide interactions become more dominant. TPD analysis gives a mean binding energy of 11.7 卤 0.24 kcal/mol, which agrees well with the calculated values of adsorption energy and indicates strong physisorption.