Structure of water at hydrophilic and hydrophobic interfaces: raman spectroscopy of water confined in periodic mesoporous (organo)silicas

Journal
The journal of physical chemistry C  
Volume
126
Issue
7
Start Page
3520 - 3531
End Page
3520 - 3531
Citation
Journal of Physical Chemistry C 126 (7): 3520-3531 (2022)
Publisher DOI
10.1021/acs.jpcc.1c09801
Scopus ID
2-s2.0-85124883253
Publisher
Soc.
The temperature dependence of the structure of water confined in hydrophilic mesostructured porous silica (MCM-41) and hydrophobic benzene-bridged periodic mesoporous organosilicas (PMOs) is studied by Raman vibrational spectroscopy. For capillary filled pores (75% relative humidity, RH), the OH stretching region is dominated by the contribution from liquid water situated in the core part of the pore. It adopts a bulklike structure that is modestly disrupted by confinement and surface hydrophobicity. For partially filled pores (33% RH), the structure of the nonfreezable adsorbed film radically differs from that found in capillary filled pores. A first remarkable feature is the absence of the Raman spectral fingerprint of low-density amorphous ice, even at a low temperature (-120 °C). Second, additional bands reveal water hydroxyl groups pointing toward the different water/solid and water/vapor interfaces. For MCM-41, they correspond to water molecules acting as weak H-bond donors with silica and dangling hydroxyl groups oriented toward the empty center of the pore. For benzene-bridged PMO, we found an additional type of dangling hydroxyl groups, which we attribute to water at the hydrophobic solid interface.
DDC Class
530: Physik
Funding(s)
Veränderung der Eigenschaften mehrphasiger Flüssigkeiten durch geometrische Beschränkung in modernen mesoporösen Materialien  
Funding Organisations
Deutsche Forschungsgemeinschaft (DFG)  
More Funding Information
This work was conducted in the frame of the DFG-ANR collaborative project (Project NanoLiquids No. ANR-18-CE92-0011-01, DFG Grant No. Fr 1372/25-1-Project number 407319385, and DFG Grant No. Hu850/11-1-Project number 407319385), which is acknowledged.