Silvio Canonica, Tamar Kohn, Marek Mac, Francisco J. Real, Jakob Wirz, and Urs von Gunten, "Photosensitizer Method to Determine Rate Constants for the Reaction of Carbonate Radical with Organic Compounds", Environmental Science and Technology, 2005, 39, 9182-9188.


Abstract: Carbonate radical (CO3.-) is a powerful oxidant that is present in sunlit surface waters and in natural waters treated by advanced oxidation processes. To better assess its impact on the oxidative transformation of organic contaminants, methods for its production and for the determination of second-order rate constants for its reaction with organic compounds were developed. The main production method consisted in oxidizing carbonate anion by excited triplet states of aromatic ketones, in particular 4-carboxybenzophenone and duroquinone, using laser flash photolysis or steady-state irradiation. For these two sensitizers, triplet quenching rate constants in aqueous solution were 1.3E5 and 3.0E7 M-1 s-1, respectively, and yields of CO3.- approached unity. Rate constants for reaction of CO3.- with various anilines and phenoxide ions were measured and agreed well with published data obtained by other methods. Moreover, bimolecular rate constants in the range of 4E5 to 1E8 M-1 s-1 were determined for the reaction of CO3.- with several s-triazine and phenylurea herbicides. Dissolved natural organic matter (DOM) was shown to reduce the lifetime of CO3.-, and a second-order rate constant of (280+-90) (mg of C/L)-1 s-1 was obtained for the reaction of CO3.- with Suwannee River fulvic acid. The use of anilines as probes for CO3.- in natural waters is discouraged, since their oxidative transformation is hampered by DOM.