Vibrational spectroscopic evaluation of hydrophilic or hydrophobic properties of oxide surfaces

Herein, we evaluated the hydrophilic or hydrophobic surface properties of various oxides using vibrational spectroscopy, such as FT‐IR (mid‐IR) and near‐IR spectroscopy. Pristine SiO2 showed hydrophobic properties because H2O molecules weakly interacted with the hydroxyl groups via hydrogen bonding....

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Bibliographic Details
Published inJournal of Raman spectroscopy Vol. 53; no. 10; pp. 1793 - 1804
Main Authors Takeuchi, Masato, Kurosawa, Ryo, Ryu, Junichi
Format Journal Article
LanguageEnglish
Published Bognor Regis Wiley Subscription Services, Inc 01.10.2022
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Summary:Herein, we evaluated the hydrophilic or hydrophobic surface properties of various oxides using vibrational spectroscopy, such as FT‐IR (mid‐IR) and near‐IR spectroscopy. Pristine SiO2 showed hydrophobic properties because H2O molecules weakly interacted with the hydroxyl groups via hydrogen bonding. Furthermore, the hydrophobic SiO2 adsorbed less toluene, as a hydrophobic probe molecule. In case of the alkyl‐groups‐modified SiO2, H2O molecules were barely adsorbed on the surface even in air, confirming the water‐repellent property. The TiO2 and Al2O3 surfaces adsorbed larger amounts of H2O than did pristine SiO2, indicating hydrophilic properties, because the Ti4+ and Al3+ sites play an essential role in strong interactions with H2O molecules via coordinative adsorption. Furthermore, the hydrophilic TiO2 and Al2O3 showed a high affinity to toluene, indicating oleophilic (affinity to oil or non‐polar compounds) properties, because the aromatic compounds were adsorbed on the cation sites by cation‐π interaction. Moreover, MgO reacted with H2O molecules to yield Mg(OH)2, indicating a greater hydrophilicity than TiO2 or Al2O3. Based on the considerations, when evaluating the hydrophilic or hydrophobic properties of oxide surfaces, the hydroxyl groups and the cation sites on the surface must be considered. Silica surfaces are accepted as “hydrophilic.” However, the silica surface weakly interacts H2O molecules, indicating its “hydrophobic” property. In contrast, TiO2 and Al2O3 surfaces adsorbed larger amounts of H2O as compared with the SiO2, confirming the hydrophilic property, because the Ti4+ and Al3+ sites work as a strong adsorption site for H2O molecules. Further, MgO showed higher affinity to H2O molecules to yield Mg(OH)2, indicating a more hydrophilic property compared to the TiO2 or Al2O3.
ISSN:0377-0486
1097-4555
DOI:10.1002/jrs.6380