It is now well established that dissolved organic matter (DOM) can act, through its antioxidant moieties, as an inhibitor of the transformation of aromatic amines that is photoinitiated by DOM itself. This dual role of DOM complicates the classical picture of the indirect phototransformation of organic contaminants induced by a merely photosensitizing DOM. To clarify this topic, the photosensitizing and inhibitory effects of various types of DOM on the indirect phototransformation rates of 4-(dimethylamino)benzonitrile (DMABN) were investigated. Relationships describing the dependence of these rates on the DOM concentration were derived. The main transient species responsible for the observed inhibitory effect on DMABN was postulated to be its radical cation, DMABN●+. In a subsequent laser flash photolysis study, we were able to produce DMABN●+ and measure the kinetics of its reactions with DOM and model phenols. These reactions, leading to the reduction of DMABN●+ back to its parent compound (DMABN), are a mechanistic key to understand the inhibitory effect of DOM.

Use of 4-(dimethylamino)benzonitrile to probe the photosensitizing and inhibitory effects of dissolved organic matter

253rd National Meeting (2017)

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