Department of Chemistry, University of California, Berkeley, California 94720, United States.
Kavli Energy NanoScience Institute, Berkeley, California 94720, United States.
J Am Chem Soc. 2023 Mar 29;145(12):6648-6657. doi: 10.1021/jacs.2c07778. Epub 2023 Mar 20.
Graphene liquid cell transmission electron microscopy is a powerful technique to visualize nanoscale dynamics and transformations at atomic resolution. However, the solution in liquid cells is known to be affected by radiolysis, and the stochastic formation of graphene liquid cells raises questions about the solution chemistry in individual pockets. In this study, electron energy loss spectroscopy (EELS) was used to evaluate a model encapsulated solution, aqueous CeCl. First, the ratio between the O K-edge and Ce M-edge was used to approximate the concentration of cerium salt in the graphene liquid cell. It was determined that the ratio between oxygen and cerium was orders of magnitude lower than what is expected for a dilute solution, indicating that the encapsulated solution is highly concentrated. To probe how this affects the chemistry within graphene liquid cells, the oxidation of Ce was measured using time-resolved parallel EELS. It was determined that Ce oxidizes faster under high electron fluxes, but reaches the same steady-state Ce concentration regardless of flux. The time-resolved concentration profiles enabled direct comparison to radiolysis models, which indicate rate constants and -values of certain molecular species are substantially different in the highly concentrated environment. Finally, electron flux-dependent gold nanocrystal etching trajectories showed that gold nanocrystals etch faster at higher electron fluxes, correlating well with the Ce oxidation kinetics. Understanding the effects of the highly concentrated solution in graphene liquid cells will provide new insight on previous studies and may open up opportunities to systematically study systems in highly concentrated solutions at high resolution.
石墨烯液相电子显微镜透射技术是一种在原子分辨率下可视化纳米级动态和转变的强大技术。然而，已知液相中的溶液会受到辐射分解的影响，而石墨烯液相的随机形成引发了对各个口袋中溶液化学的质疑。在这项研究中，电子能量损失光谱（EELS）被用于评估封装模型溶液，水合 CeCl。首先，O K 边和 Ce M 边的比值被用来近似石墨烯液相中的铈盐浓度。结果表明，氧和铈的比值比稀溶液的预期值低几个数量级，这表明封装溶液的浓度非常高。为了探究这如何影响石墨烯液相中的化学，使用时间分辨平行 EELS 测量了 Ce 的氧化。结果表明，在高电子通量下 Ce 氧化更快，但无论通量如何，都达到相同的稳态 Ce 浓度。时间分辨的浓度分布使我们能够直接与辐射分解模型进行比较，这表明某些分子物种的速率常数和 - 值在高浓度环境中存在显著差异。最后，电子通量依赖性的金纳米晶体刻蚀轨迹表明，金纳米晶体在更高的电子通量下刻蚀更快，这与 Ce 氧化动力学很好地相关。了解高浓度溶液在石墨烯液相中的影响将为先前的研究提供新的见解，并可能为在高分辨率下系统研究高浓度溶液中的系统提供机会。
