Langmuir. 2015 May 19;31(19):5432-9. doi: 10.1021/acs.langmuir.5b01354. Epub 2015 May 5.
Despite long-standing efforts, there is no agreed upon structural model for electrolyte solutions at air-liquid interfaces. We report the simultaneous detection of the near-surface and bulk coordination environments of a trivalent metal cation (europium) in an aqueous solution by use of X-ray absorption spectroscopy. Within the first few nanometers of the liquid surface, the cations exhibit oxygen coordination typical of inner-sphere hydration of an aquated Eu(3+) cation. Beyond that, outer-sphere ion-ion correlations are observed that are otherwise not present in the bulk electrolyte. The combination of near-surface and bulk sensitivities to probe metal ion speciation in electrolyte solutions is achieved by detecting electron-yield and X-ray fluorescence signals from an inverted pendant drop. The results provide new knowledge about the near-surface chemistry of aqueous solutions of relevance to aerosols and ion transport processes in chemical separations and biological systems.
尽管已经进行了长期的努力，但对于气液界面处的电解质溶液，目前还没有一个公认的结构模型。我们通过 X 射线吸收光谱法报告了在水溶液中同时检测三价金属阳离子（铕）的近表面和体相配位环境。在液体表面的最初几纳米范围内，阳离子表现出与水合 Eu(3+)阳离子的内球水合作用典型的氧配位。除此之外，还观察到了在体相电解质中不存在的外球离子-离子相关。通过从倒置悬挂液滴中检测电子产额和 X 射线荧光信号，实现了对电解质溶液中金属离子形态的近表面和体相灵敏度的组合探测。这些结果提供了有关气溶胶以及化学分离和生物系统中离子输运过程中水溶液近表面化学的新知识。
