Department of Chemical and Petroleum Engineering , University of Kansas , Lawrence , Kansas 66045 , United States.
Elettra-Sincrotrone Trieste ScPA , Trieste 34012 , Italy.
Langmuir. 2018 Aug 21;34(33):9606-9616. doi: 10.1021/acs.langmuir.8b00806. Epub 2018 Aug 9.
For nanoparticles active for chemical and energy transformations in static liquid environment, chemistries of surface or near-surface regions of these catalyst nanoparticles in liquid are crucial for fundamentally understanding their catalytic performances at a molecular level. Compared to catalysis at a solid-gas interface, there is very limited information on the surface of these catalyst nanoparticles under a working condition or during catalysis in liquid. Photoelectron spectroscopy is a surface-sensitive technique; however, it is challenging to study the surfaces of catalyst nanoparticles dispersed in static liquid because of the short inelastic mean free path of photoelectrons traveling in liquid. Here, we report a method for tracking the surface of nanoparticles dispersed in static liquid by employing graphene layers as an electron-transparent membrane to separate the static liquid containing a solvent, catalyst nanoparticles, and reactants from the high-vacuum environment of photoelectron spectrometers. The surfaces of Ag nanoparticles dispersed in static liquid sealed in such a graphene membrane liquid cell were successfully characterized using a photoelectron spectrometer equipped with a high vacuum energy analyzer. With this method, the surface of catalyst nanoparticles dispersed in liquid during catalysis at a relatively high temperature up to 150 °C can be tracked with photoelectron spectroscopy.
对于在静态液体环境中进行化学和能量转化的纳米粒子，这些催化剂纳米粒子表面或近表面区域的化学性质对于从分子水平上理解其催化性能至关重要。与固-气界面上的催化相比，对于这些催化剂纳米粒子在工作条件下或在液体中催化时的表面，信息非常有限。光电子能谱是一种表面敏感的技术；然而，由于在液体中传播的光电子的非弹性平均自由程很短，因此研究分散在静态液体中的催化剂纳米粒子的表面具有挑战性。在这里，我们报告了一种通过使用石墨烯层作为电子透明膜来跟踪分散在静态液体中的纳米粒子表面的方法，该石墨烯层将含有溶剂、催化剂纳米粒子和反应物的静态液体与光电子能谱仪的高真空环境隔开。使用配备有高真空能分析仪的光电子能谱仪，成功地对密封在这种石墨烯膜液池中分散在静态液体中的 Ag 纳米粒子的表面进行了表征。通过这种方法，可以用光电子能谱跟踪在高达 150°C 的相对高温下进行的液体中催化过程中催化剂纳米粒子的表面。
