Department of Chemistry , University of Victoria , Victoria , British Columbia V8W 3 V6 , Canada.
Department of Chemistry , University of Alberta , Edmonton , Alberta T6G 2G2 , Canada.
J Am Chem Soc. 2020 Jan 15;142(2):669-673. doi: 10.1021/jacs.9b11710. Epub 2020 Jan 7.
The structure of water adjacent to silica is sensitive to the degree of deprotonation of surface silanol groups. As a result, close inspection of signals originating from these water molecules can be used to reveal the surface charge density. We have used nonlinear vibrational spectroscopy of the water O-H stretching band over a temperature range of 10-75 °C to account for the increase in surface potential from deprotonation. We demonstrate that the behavior at the silica surface is a balance between increasing surface charge and a decreasing contribution of water molecules aligned by the surface charge. Together with a model that accounts for two different types of silanol sites, we use our data to report the changes in enthalpy and entropy for deprotonation at each site. This is the first experimental determination of these thermodynamic parameters for hydrated silanol groups at the silica surface, critical to a wide range of geochemical and technological applications.
水在二氧化硅表面的结构对硅醇基离解程度很敏感。因此，对这些水分子的信号进行仔细检查可以用来揭示表面电荷密度。我们使用水的 O-H 伸缩带的非线性振动光谱，在 10-75°C 的温度范围内，解释了表面电荷增加引起的表面电势的增加。我们证明，在二氧化硅表面上的行为是表面电荷增加和表面电荷排列的水分子贡献减少之间的平衡。结合一个考虑两种不同类型硅醇基位点的模型，我们使用我们的数据报告每个位点的离解的焓和熵的变化。这是在二氧化硅表面上水合硅醇基的这些热力学参数的首次实验测定，对广泛的地球化学和技术应用至关重要。
