Vibrational spectroscopic evaluation of hydrophilic or hydrophobic properties of oxide surfaces

Abstract

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

Nanofibrous Dressing with Nanocomposite Monoporous Microspheres for Chemodynamic Antibacterial Therapy and Wound Healing

“…As shown in Figure e, PCL, MgO/Ag-PCL, and MgO/Cu-PCL were hydrophobic, with water contact angles (WCAs) of 139°, 129°, and 130°, respectively. The WCA of the nanocomposite dressing decreased by approximately 10°, possibly due to the hydrophilic nature of the NPs . Overall, the hydrophobic wound dressing developed here was expected to have the advantage of not adhering to the wound .…”

“…The WCA of the nanocomposite dressing decreased by approximately 10°, possibly due to the hydrophilic nature of the NPs. 51 Overall, the hydrophobic wound dressing developed here was expected to have the advantage of not adhering to the wound. 52 In addition, the mechanical properties of the nanofibrous dressings were evaluated.…”

Near-Infrared Spectroscopic Analysis─Formation of Ca(OH)2 and Ca(OD)2 by Hydration of CaO with H2O and D2O

“…NIR spectroscopy was first utilized in the 1960s for the analysis of grain water content. , The absorption resulting from combination bands and overtones observed in the NIR region has 10 3 to 10 2 times smaller absorption coefficients compared to fundamental vibrations observed in the MIR region. − Moreover, NIR spectroscopy has several advantages that have enabled its widespread use in various fields, including mineralogy, food chemistry, pharmacology, agriculture, and medical sciences. Recently, the NIR analysis on the surface of the asteroid “Ryugu” by Hayabusa2 has been a notable report in the field of astronomy .…”

“…Recently, the NIR analysis on the surface of the asteroid “Ryugu” by Hayabusa2 has been a notable report in the field of astronomy . In addition, this technique has been utilized in surface science to analyze the adsorption states of H 2 O, ,,− NH 3 , , and hydrazine, among others. Some notable findings include the description of hydrogen bond networks in H 2 O clusters adsorbed on catalyst surfaces under ambient conditions and the adsorption states of NH 3 and NH 4 + on hydrated zeolite surfaces.…”

Editorial on the special issue of JRS on vibrational spectroscopy of water

“…Water at interfaces exhibits properties distinct from bulk water. In this special issue, Takeuchi et al [ 15 ] applied IR and NIR spectroscopy to water at oxide surfaces to obtain molecular‐level understanding of hydrophobicity and hydrophilicity. Azam and Hore [ 16 ] reviewed novel two‐dimensional Raman‐SFG correlation spectroscopy that allows for reliable interpretation of surface‐selective vibrational spectra.…”