Publication Details (including relevant citation information):
Golanoski, K.S.; Fang, S.; Del Vecchio, R.; Blough, N.V. Investigating the Mechanism of Phenol Photooxidation by Humic Substances. Environ. Sci. Technol. 2012, 46, 3912−3920.
To probe the mechanism of the photosensitized loss of phenols by humic substances (HS), the dependence of the initial rate of 2,4,6-trimethylphenol (TMP) loss (RTMP) on dioxygen concentration was examined both for a variety of untreated as well as borohydride-reduced HS and C18 extracts from the Delaware Bay and Mid-Atlantic Bight. RTMP was inversely proportional to dioxygen concentration at [O2] > 50 μM, a dependence consistent with reaction with triplet excited states, but not with 1O2 or RO2. Modeling the dependence of RTMP on [O2] provided rate constants for TMP reaction, O2
quenching, and lifetimes compatible with a triplet intermediate. Borohydride reduction significantly reduced TMP loss, supporting the role of aromatic ketone triplets in this process. However, for most samples, the incomplete loss of sensitization following borohydride reduction, as well as the inverse dependence of RTMP on [O2] for these samples, suggests that there remains another class of oxidizing triplet sensitizer, perhaps quinones.