Vibrational spectroscopic evaluation of hydrophilic or hydrophobic properties of oxide surfaces

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  • Masato Takeuchi
    Department of Applied Chemistry, Graduate School of Engineering Osaka Prefecture University Sakai Osaka Japan
  • Ryo Kurosawa
    Graduate School of Engineering Chiba University Chiba Japan
  • Junichi Ryu
    Graduate School of Engineering Chiba University Chiba Japan

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<jats:title>Abstract</jats:title><jats:p>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 SiO<jats:sub>2</jats:sub> showed hydrophobic properties because H<jats:sub>2</jats:sub>O molecules weakly interacted with the hydroxyl groups via hydrogen bonding. Furthermore, the hydrophobic SiO<jats:sub>2</jats:sub> adsorbed less toluene, as a hydrophobic probe molecule. In case of the alkyl‐groups‐modified SiO<jats:sub>2</jats:sub>, H<jats:sub>2</jats:sub>O molecules were barely adsorbed on the surface even in air, confirming the water‐repellent property. The TiO<jats:sub>2</jats:sub> and Al<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub> surfaces adsorbed larger amounts of H<jats:sub>2</jats:sub>O than did pristine SiO<jats:sub>2</jats:sub>, indicating hydrophilic properties, because the Ti<jats:sup>4+</jats:sup> and Al<jats:sup>3+</jats:sup> sites play an essential role in strong interactions with H<jats:sub>2</jats:sub>O molecules via coordinative adsorption. Furthermore, the hydrophilic TiO<jats:sub>2</jats:sub> and Al<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub> 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 H<jats:sub>2</jats:sub>O molecules to yield Mg(OH)<jats:sub>2</jats:sub>, indicating a greater hydrophilicity than TiO<jats:sub>2</jats:sub> or Al<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub>. 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.</jats:p>

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