Key Laboratory of Mesoscopic Chemistry of MOE and Collaborative Innovation Center of Chemistry for Life Sciences, School of Chemistry and Chemical Engineering, Nanjing University, 163 Xianlin Road, Nanjing 210023, China.
Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, U.K.
J Am Chem Soc. 2020 Jun 24;142(25):11173-11182. doi: 10.1021/jacs.0c03760. Epub 2020 Jun 11.
Hydrous materials are ubiquitous in the natural environment and efforts have previously been made to investigate the structures and dynamics of hydrated surfaces for their key roles in various chemical and physical applications, with the help of theoretical modeling and microscopy techniques. However, an overall atomic-scale understanding of the water-solid interface, including the effect of water on surface ions, is still lacking. Herein, we employ ceria nanorods with different amounts of water as an example and demonstrate a new approach to explore the water-surface interactions by using solid-state NMR in combination with density functional theory. NMR shifts and relaxation time analysis provide detailed information on the local structure of oxygen ions and the nature of water motion on the surface: the amount of molecularly adsorbed water decreases rapidly with increasing temperature (from room temperature to 150 °C), whereas hydroxyl groups are stable up to 150 °C, and dynamic water molecules are found to instantaneously coordinate to the surface oxygen ions. The applicability of dynamic nuclear polarization for selective detection of surface oxygen species is also compared to conventional NMR with surface selective isotopic-labeling: the optimal method depends on the feasibility of enrichment and the concentration of protons in the sample. These results provide new insight into the interfacial structure of hydrated oxide nanostructures, which is important to improve performance for various applications.
水合材料在自然环境中无处不在，为了研究水合表面在各种化学和物理应用中的关键作用，人们以前曾利用理论建模和显微镜技术来研究水合表面的结构和动力学。然而，对于水-固界面的原子尺度的全面理解，包括水对表面离子的影响，仍然缺乏了解。在此，我们以不同含水量的氧化铈纳米棒为例，展示了一种新的方法，通过固态 NMR 与密度泛函理论相结合来探索水-表面相互作用。NMR 位移和弛豫时间分析提供了氧离子局部结构和表面水运动性质的详细信息：随着温度的升高（从室温到 150°C），分子吸附水的量迅速减少，而羟基在 150°C 下稳定存在，并且发现动态水分子会立即与表面氧离子配位。还将动态核极化用于选择性检测表面氧物种的适用性与具有表面选择性同位素标记的常规 NMR 进行了比较：最佳方法取决于富集的可行性和样品中质子的浓度。这些结果为水合氧化物纳米结构的界面结构提供了新的见解，这对于提高各种应用的性能很重要。
