The interaction of liquid water with gases or surfaces plays a major role in many processes of heterogeneous catalysis, electrochemistry, and environmental chemistry. Near Ambient Pressure X-ray Photoelectron Spectroscopy (NAP-XPS) is an excellent method for the investigation of the interfacial chemistry. In newly developed NAP-XPS setups, the work pressure in the analysis chamber is raised up to 20 mbar. In those conditions, not only solid/gas interfaces are investigable by NAP-XPS, but also liquid water/solid and vapor/ liquid interfaces.
I will present two illustrative examples relevant to environmental molecular chemistry. First, I will demonstrate that core-level XPS can monitor the hydration process of the interlayer counterions of swelling clays. Second, I will show how XPS reveals the ion segregation at the vapor/ liquid water interface of sodium halide solutions.
LCPMR, Université Pierre-et-Marie-Curie, Paris et Ligne TEMPO, Synchrotron SOLEIL