Title: Pore Size-Dependent Structure of Confined Water in Mesoporous Silica Films from Water Adsorption-Desorption using ATR-FTIR Spectroscopy
Language: English
Authors: Baumgartner, Bettina  
Hayden, Jakob 
Loizillon, Jérôme 
Steinbacher, Sophia 
Grosso, David 
Lendl, Bernhard  
Category: Research Article
Issue Date: 2019
Journal: Langmuir
ISSN: 1520-5827
The local structure of water on chemically and structurally different surfaces is a subject of ongoing research. In particular, confined spaces as found in mesoporous silica have a pronounced effect on the interplay between the adsorbate–adsorbate and adsorbate–surface interactions. Mid-infrared spectroscopy is ideally suited to quantitatively and qualitatively study such systems as the probed molecular vibrations are highly sensitive to intermolecular interactions. Here, the quantity and structure of water adsorbed from the gas phase into silica mesopores at different water vapor pressures was monitored using mid-infrared attenuated total reflection (ATR) spectroscopy. Germanium ATR crystals were coated with different mesoporous silica films prepared by evaporation-induced self-assembly. Quantitative analysis of the water bending vibration at 1640 cm–1 at varying vapor pressure allows for retrieving porosity and pore size distribution of the mesoporous films. The results were in excellent agreement with those obtained from ellipsometric porosimetry. In addition, different degrees of hydrogen bonding of water as reflected in the band position and shape of the stretching vibrations (3000–3800 cm–1) were analyzed and attributed to high-density, unordered bulk, low-density, and surface-induced ordered water. Thereby, the progression of surface-induced ordered water and bulk water as a function of water vapor pressure was studied for different pore sizes. Small pores of 5 nm diameter showed a number of two-ordered monolayers, whereas for pores >12 nm diameter, the number of ordered monolayers is significantly larger and agrees with the number observed on planar SiO2 surfaces.
DOI: 10.1021/acs.langmuir.9b01435
Library ID: AC15543800
URN: urn:nbn:at:at-ubtuw:3-8147
Organisation: E164 - Institut für Chemische Technologien und Analytik 
Publication Type: Article
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