Surface vs. Bulk Resolved Reaction Kinetics of Double Charged Anions in Aqueous Solutions

Researchers in the Condensed Phase and Interfacial Molecular Science (CPIMS) program
combined single droplet mass spectrometry, ambient pressure X-ray photoelectron spectroscopy and second harmonic generation has enabled an exquisitely detailed molecular view of the multiphase oxidation mechanism of thiosulfate by ozone at aqueous surfaces

Developed an entirely new mechanism for thiosulfate oxidation by ozone that resolves the importance of surface partitioning of doubled charged anions for the overall reaction mechanis
This work has implications for mining wastewater remediation, atmospheric chemistry, and understanding other complex reaction mechanisms in multiphase environments

Single droplet mass spectrometry quantifies multiphase reaction kinetics. To unravel the mechanism requires understanding the interface propensity of thiosulfate and its reaction products
Measured using deep UV second harmonic generation to obtain Gibb’s adsorption free energies
Ambient pressure X-ray photoemission is used to quantify the concentration of salt species at the interface
Information from these three techniques constrains a detailed and predictive kinetic model.
Primary reaction between thiosulfate and ozone occurs at the interface and in the bulk, with the contribution of the interface decreasing from ~65% at pH 5 to ~45% at pH 13.
Sulfate, the major product and an important species in atmospheric processes is produced by two different pathways at pH 5, one with a contribution from the interface of >70% and the other occurring predominantly in the bulk (>98%)

A. M. Deal, F. Bernal, A. Siebert, A. M. Prophet, M. Lopez Luna, M. Blum, R. J. Saykally and K. R. Wilson, Chemical Sciences (2025).