Jhang Jin-Hao, Boscoboinik J Anibal, Altman Eric I
Department of Chemical and Environmental Engineering, Yale University, New Haven, Connecticut 06520, USA.
Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York 11973, USA.
J Chem Phys. 2020 Feb 28;152(8):084705. doi: 10.1063/1.5142621.
Ambient pressure x-ray photoelectron spectroscopy (AP-XPS) supported by density functional theory (DFT) calculations was used to characterize the interaction of water with two-dimensional (2D) silica and aluminosilicate bilayers on Pd(111). Starting with oxygen adsorbed at the SiO/Pd interface, exposure to water caused the SiO-derived XPS peaks to shift to higher binding energy and the removal of an O 1s feature associated with interfacial adsorbed oxygen. These observations were attributed to the formation of a mixed water-hydroxyl interface, which eliminates the interfacial dipolar layer, and its associated electrostatic potential, created by adsorbed oxygen. Interfacial oxygen also reacted with H to produce adsorbed water which also caused an upward binding energy shift of the SiO peaks. Spectra recorded under 0.5 Torr water revealed additional water adsorption and a further shift of the overlayer peaks to higher binding energy. Incorporating Al into the 2D material caused the bilayer peaks to shift to lower binding energy which could be explained by electron donation from the metal to the bilayer. Although the stronger interaction between the bilayer and Pd substrate should restrict interfacial adsorption and reaction, similar trends were observed for water and hydrogen exposure to interfacial adsorbed oxygen. Less water adsorption was observed at the aluminosilicate interface which is a consequence of Al strengthening the bond to the metal substrate. The results reveal how the sensitivity of XPS to interfacial dipoles can be exploited to distinguish reactions taking place in confined spaces under 2D layers and how tuning the composition of the 2D layer can impact such reactions.
在密度泛函理论（DFT）计算的支持下，利用环境压力X射线光电子能谱（AP-XPS）来表征水与Pd(111)上的二维（2D）二氧化硅和铝硅酸盐双层膜之间的相互作用。从吸附在SiO/Pd界面的氧开始，暴露于水会导致源自SiO的XPS峰向更高结合能移动，并消除与界面吸附氧相关的O 1s特征峰。这些观察结果归因于形成了混合的水-羟基界面，该界面消除了由吸附氧产生的界面偶极层及其相关的静电势。界面氧也与H反应生成吸附水，这也导致SiO峰的结合能向上移动。在0.5托水的条件下记录的光谱显示有额外的水吸附，并且覆盖层峰进一步向更高结合能移动。将Al掺入二维材料中会导致双层峰向更低结合能移动，这可以用金属向双层的电子给予来解释。尽管双层与Pd衬底之间更强的相互作用应该会限制界面吸附和反应，但在水和氢暴露于界面吸附氧的情况下也观察到了类似的趋势。在铝硅酸盐界面观察到较少的水吸附，这是Al加强与金属衬底键合的结果。结果揭示了如何利用XPS对界面偶极的敏感性来区分二维层下受限空间中发生的反应，以及如何调整二维层的组成会影响此类反应。
