Photochemical Transformation of Four Ionic Liquid Cation Structures in Aqueous Solution

Sarah G. Pati, William A. Arnold

Research output: Contribution to journalArticlepeer-review

10 Scopus citations

Abstract

Ionic liquids (ILs) are a new class of solvents expected to be used increasingly by the chemical industry in the coming years. Given their slow biodegradation and limited sorption affinities, IL cations have a high potential to reach aquatic environments. We investigated the fate of ILs in sunlit surface water by determining direct and indirect photochemical transformation rates of imidazolium, pyridinium, pyrrolidinium, and piperidinium cations. The photodegradation of all investigated IL cations was faster in solutions containing dissolved organic matter (DOM) than in ultrapure water, illustrating the importance of indirect photochemical processes. Experiments with model sensitizers and DOM isolates revealed that reactions with hydroxyl radicals dominated the transformation of tested IL cations. Bimolecular reaction rate constants with hydroxyl radicals ranged from (2.04 ± 0.37) × 109 to (8.47 ± 0.97) × 109 M-1 s-1 and showed an increase in rate constants with increasing carbon side-chain length. Consequently, average estimated half-lives of IL cations in sunlit surface water ranged from 32 ± 4 to 135 ± 25 days, highlighting the potential of IL cations to become persistent aquatic contaminants.

Original languageEnglish (US)
Pages (from-to)11780-11787
Number of pages8
JournalEnvironmental Science and Technology
Volume51
Issue number20
DOIs
StatePublished - Oct 17 2017

Bibliographical note

Funding Information:
This work was supported by the Swiss National Science Foundation (Early Postdoc.Mobility fellowship 168888 to S.G.P.) and the Joseph T. and Rose S. Ling Professorship (to W.A.A.). Thanks to Yousof Aly and Michael McCarty for their support with LC/MS analysis and Meghan O’Connor for providing the wastewater effluent sample.

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