Hydroxylation structure of quartz surface and its molecular hydrophobicity

Abstract

The hydroxylation behavior of water on the quartz surface plays an important role in many fields. In this paper, the surface hydroxylation behavior of quartz and the molecular hydrophobicity of the hydroxylated surface were systematically studied by means of thermogravimetric analysis & differential scanning calorimetry (TGA-DSC), FTIR spectroscopy, and DFT calculations. TGA-DSC analysis showed that the complete desorption of structural water on the quartz surface needs to be carried out at 180.5 °C. FTIR spectra showed that the dehydrated sample had an obvious blue shift compared with the hydrated sample, suggesting that the hydrogen bonds on the surface of the dehydrated sample were weakened. The weakened hydrogen bonds are largely attributed to the partial desorption of water molecules in the hydroxyl hydration layer on quartz surface under vacuum at 130 °C, which is confirmed by DFT calculations. An interesting scientific discovery is that although quartz is highly hydrophilic and water molecules can be adsorbed on and hydroxylate the quartz surface, the hydroxylated surface is hydrophobic, and the secondary adsorption of water molecules on the hydroxylated surface is thermodynamically unfavorable.