Photochemical Transformation of Four Ionic Liquid Cation Structures in Aqueous Solution

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 su...

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Bibliographic Details
Published in:Environmental science & technology 2017-10, Vol.51 (20), p.11780-11787
Main Authors: Pati, Sarah G, Arnold, William A
Format: Article
Language:English
Subjects:
Aquatic environment
Biodegradation
Cations
Chemical industry
Contaminants
Dissolved organic matter
Free radicals
Hydroxyl radicals
Ionic Liquids
Ions
Organic contaminants
Photochemical Processes
Photochemicals
Photodegradation
Photolysis
Pyridinium
Rate constants
Solvents
Surface water
Water
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Summary: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.
ISSN:0013-936X
1520-5851
DOI:10.1021/acs.est.7b04016