Photochemical formation of carbonate radical and its reaction with dissolved organic matters

The carbonate radical (CO3 center dot-) is a strong oxidative radical that is generated via the reactions of HCO3-/ CO32- with hydroxyl radical (HO center dot) or triplet states of dissolved organic matter ((DOM)-D- 3*) in sunlit surface water. The bimolecular reaction rate constants of CO3 center dot- with various DOM isolates (k(CO3)(center dot-), DOM) were calculated as 15-239 (mg of C/L) (-1)s(-1) and were correlate to the bulk DOM properties, such as the content of phenolic moieties, the specific UV absorbance (SUVA), the E2/E3 value, and the fluorescence index (FI). The spectroscopic E2/E3 values was found to strongly correlated (R-2 = 0.93) with k CO3(center dot-), DOM , and an empirical equation was established. Our results also demonstrate that CO(3)(center dot-)is involved in the photobleaching of dissolved organic matter (DOM) and in particular reacts with electron-donor moieties, leading to faster decay rates at long wavelengths of UV-vis absorption. Furthermore, a model was developed to calculate the steady-state concentrations of CO3 center dot- during DOM photobleaching. These results allow us to estimate the reactivity of DOM with CO3 center dot- and to evaluate the role of CO3 center dot- in sunlit surface water. It will also allow a better assessment of the concentration and utilization of CO3 center dot- during the application of advanced oxidation processes. (C) 2019 Elsevier Ltd. All rights reserved.