Ionic liquids (ILs) are expected to be used increasingly in the coming years for industrial chemical applications as replacements for volatile organic solvents. The organic cations used in ILs typically contain quaternary ammonium groups and may reach aquatic environments due to their high water solubility and limited biodegradability. Given the persistence of IL cations in aquatic environments and the potential of quaternary ammonium compounds to form nitrosamines, the potential of advanced oxidation processes with UV irradiation (UV/AOP) to remove IL cations from drinking water sources was assessed. We found that IL cations react readily with hydroxyl and sulfate radicals with bimolecular reactions rate constants ranging from (1.2 ± 0.6) × 109 to (8.5 ± 1.0) × 109 M-1 s-1 and from (0.08 ± 0.06) × 109 to (1.7 ± 0.2) × 109 M-1 s-1, respectively. Consequently, half-lives in the order of minutes are expected for all IL cations in UV/AOP applications with hydrogen peroxide, persulfate, or free chlorine. In addition to efficient removal of the parent compounds, most transformation products of IL cations are formed through sequential hydroxylation reactions, which could ultimately lead to small, benign end-products. While we did not find evidence supporting the direct reaction of IL cations with reactive halogen species, a series of chlorinated transformation products were identified in UV/chlorine experiments. We hypothesize that these compounds are formed through the reactions of radical intermediates with free chlorine.
|Original language||English (US)|
|Number of pages||11|
|Journal||Environmental Science: Water Research and Technology|
|State||Published - Sep 2018|
Bibliographical noteFunding Information:
SGP would like to acknowledge the Swiss National Science Foundation for an Early Postdoc.Mobility fellowship. Additional support for this work was provided by the Minnesota Environment and Natural Resources Trust Fund as recommended by the Legislative-Citizen Commission on Minnesota Resources (LCCMR). Xun Ming, Makenzie Pillsbury, and Michael McCarty are thanked for support with LC-MS and LC/HRAM-MS/MS analysis and method development.
© The Royal Society of Chemistry 2018.