Influence of Organic Coatings on Pyrene Ozonolysis at the Air-Aqueous Interface

Glancing angle laser-induced fluorescence was used to investigate the effects of organic monolayer coatings on the ozonation kinetics of pyrene at the air-aqueous interface. Fluorescence spectra show that both 1-octanol and octanoic acid coatings give rise to similar decreased polarity at the interface relative to the uncoated surface and show a similar propensity of pyrene to partition to the interface. Ozonation kinetics follow a Langmuir-Hinshelwood mechanism, indicating a surface reaction. At high ozone concentrations, a monolayer coating of 1-octanol enhances the rate relative to the uncoated surface and a coating of octanoic acid decreases the rate. Pyrene fluorescence is most efficiently quenched by ozone in the presence Of a 1-octanol coating, followed by the uncoated surface, and least efficiently quenched by ozone in the presence of octanoic acid. In agreement with earlier work, a significant photoenhancement of the ozonation is observed at the uncoated surface; however, no enhancement is observed with monolayer coatings of either organic. Quantum chemical calculations indicate a reasonable binding of ozone by the carboxylic acid group (in both its dissociated and undissociated forms). We suggest that the inhibition of the water surface reaction by a monolayer of octanoic acid is due to the sequestration of ozone by the carboxylic acid group.