Near the surface of an electrolyte solution
Senior Chemist Mark Antonio (CSE) and Postdoctoral Researcher Mrinal K. Bera (CSE) are exploring the simultaneous detection of the near-surface and bulk coordination environments of a trivalent metal cation (europium) in an aqueous solution by use of the bending magnet station at the XSD 12-BM-B beamline at the APS.
The results have provided new knowledge about the near-surface chemistry of aqueous solutions of relevance to aerosols and ion transport processes in chemical separations and biological systems.
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 Eu3+ 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.
Mark Antonio and Mrinal Bera, “Polynuclear Speciation of Trivalent Cations Near the Surface of an Electrolyte Solution,” Langmuir, Just Accepted Manuscript. DOI: 10.1021/acs.langmuir.5b01354, Published April 24, 2015.