Energy Landscape of Water and Ethanol on Silica Surfaces
- Univ. of California, Davis, CA (United States)
- Univ. of California, Davis, CA (United States); Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
- East China Univ. of Science and Technology, Shanghai (China)
Fundamental understanding of small molecule–silica surface interactions at their interfaces is essential for the scientific, technological, and medical communities. We report direct enthalpy of adsorption (Δhads) measurements for ethanol and water vapor on porous silica glass (CPG-10), in both hydroxylated and dehydroxylated (hydrophobic) forms. Results suggest a spectrum of energetics as a function of coverage, stepwise for ethanol but continuous for water. The zero-coverage enthalpy of adsorption for hydroxylated silica shows the most exothermic enthalpies for both water (-72.7 ± 3.1 kJ/mol water) and ethanol (-78.0 ± 1.9 kJ/mol ethanol). The water adsorption enthalpy becomes less exothermic gradually until reaching its only plateau (-20.7 ± 2.2 kJ/mol water) reflecting water clustering on a largely hydrophobic surface, while the enthalpy of ethanol adsorption profile presents two well separated plateaus, corresponding to strong chemisorption of ethanol on adsorbate-free silica surface (-66.4 ± 4.8 kJ/mol ethanol), and weak physisorption of ethanol on ethanol covered silica (-4.0 ± 1.6 kJ/mol ethanol). On the other hand, dehydroxylation leads to missing water–silica interactions, whereas the number of ethanol binding sites is not impacted. The isotherms and partial molar properties of adsorption suggest that water may only bind strongly onto the silanols (which are a minor species on silica glass), whereas ethanol can interact strongly with both silanols and the hydrophobic areas of the silica surface.
- Research Organization:
- Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES)
- Grant/Contract Number:
- FG02-97ER14749; AC52-06NA25396
- OSTI ID:
- 1221610
- Report Number(s):
- LA-UR-15-24271
- Journal Information:
- Journal of Physical Chemistry. C, Vol. 119, Issue 27; ISSN 1932-7447
- Publisher:
- American Chemical SocietyCopyright Statement
- Country of Publication:
- United States
- Language:
- English
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