Interplay between Ethanol Adsorption to High-Energy Sites and Clustering on Graphene and Graphite Alters the Measured Isosteric Adsorption Enthalpies

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• 作者：Franti拧ek Karlick媒 ; Eva Otyepkov谩 ; Pavel Ban谩拧 ; Petr Lazar ; Mikul谩拧 Kocman ; Michal Otyepka
• 刊名：Journal of Physical Chemistry C
• 出版年：2015
• 出版时间：September 3, 2015
• 年：2015
• 卷：119
• 期：35
• 页码：20535-20543
• 全文大小：591K
• ISSN：1932-7455

文摘

We present a combined experimental and theoretical study aimed at understanding the behavior of polar probe ethanol on graphene and graphite hydrophobic surfaces. We measured isosteric adsorption enthalpies and entropies by inverse gas chromatography for coverages ranging from 0.1 to 20%. The adsorption enthalpies were found to vary with surface coverage and differed considerably between the materials at low coverage. However, they approached the same adsorption enthalpy value of 鈭?2.0 卤 0.4 kcal/mol for T centered at 303鈥?93 K and coverages above 5%. We explained the observed behavior using molecular dynamics simulations by employing empirical force-field and density functional theory calculations on two graphene models: circumcoronene and infinite graphene. The simulations showed that various hydrogen-bonded ethanol clusters formed spontaneously from isolated ethanol molecules on graphene and provided a distribution of cluster sizes. Nonlocal density functional theory was used to calculate adsorption enthalpies for various sizes of ethanol clusters. A theoretical adsorption enthalpy of 鈭?1.6 kcal/mol at 340 K was obtained from the weighted average of the cluster size distribution, while the adsorption enthalpy of single ethanol molecule to graphene was 鈭?.3 kcal/mol at 323 K.