Speaker
Description
The air-water interface is omnipresent in nature, e.g. in marine and freshwater environments, atmospheric aqueous aerosols and fog/cloud droplets.[1] This interface governs numerous heterogeneous chemical reactions, such as the sequestration of CO$_2$ by the oceans and the uptake and release of trace gases by aqueous aerosols. The reactivity of the air-water interface can vary widely depending on its chemical composition, e.g. the concentration of inorganic ions and organic molecules at the interface. Especially organic pollutants at air-water interfaces can engage in complex heterogeneous reactions by modifying the rate of gas transport across the interface and/or being directly involved in the heterogeneous reaction.
A reoccurring structure motif in organic matter is the aromatic phenyl group (C$_6$H$_5$), often in conjunction with different functional groups. One of the simplest examples of phenyl compounds is phenol (C$_6$H$_5$OH), which is a natural and anthropogenic pollutant. It is an amphiphilic molecule with the phenyl group being hydrophobic and the functional groups (–OH) being hydrophilic. The interplay between these two moieties determines its surfactant behavior. It has been shown for the structurally related benzoic acid (C$_6$H$_5$COOH) that this behavior can be drastically altered for different charge states, i.e. pH values. While benzoic acid shows a pronounced surface enrichment, the deprotonated benzoate (C$_6$H$_5$COO$^-$) is found deeper in the bulk.
The bulk-surface partitioning of organic pollutants is an important parameter to understand their heterogeneous chemistry at the air-water interface. Here, we present photoelectron spectroscopy and surface tension investigations to characterize the surfactant behavior of phenol. While surface tension measurements allow for an indirect determination of the surface excess concentration of phenol, photoelectron spectroscopy of liquid microjets enable the direct study of the composition of the liquid-vapor interface. The combination of the two methods allows for a comprehensive investigation of phenol solutions over a wide range of bulk concentrations and pH values. These experiments represent the fundament for further in situ investigations of the heterogeneous reaction of phenol with ozone at the liquid-vapor interface on liquid and frozen aqueous solutions using ambient pressure X-ray photoelectron spectroscopy (APXPS).
References
[1] B.J. Finlayson-Pitts, Phys. Chem. Chem. Phys. 11, 7760 (2009).
| Abstract Number (department-wise) | AC 5.2 |
|---|---|
| Department | AC (Schlögl) |
