(149d) Computational and Experimental Study of the Interactions Between Ionic Liquids and Volatile Organic Compounds

Abstract
     
Computational chemistry calculations were performed to investigate the
interactions of ionic liquids with different classes of volatile organic
compounds (VOCs), including alcohols, aldehydes, ketones, alkanes, alkenes and
aromatic compounds. At least one VOC was studied to represent each class.  Initially,
1-butyl-3-methylimindazolium chloride (abbreviated as C₄minCl) was
used as the test ionic liquid compound. Calculated interaction lengths between
atoms in the ionic liquid and the VOC tested as well as thermodynamic data
suggest that C₄minCl preferentially interacts with alcohols as
compared to other classes of volatile organic compounds. Interactions of
methanol with different kinds of ionic liquids, specifically 1-butyl-3-methylimidazolium
bromine (C₄minBr) and 1-butyl-3-methylimidazolium tetrafluoroborate (C₄minBF₄)
were also studied. In comparing C₄minCl, C₄minBr, and
C₄minBF₄, the computational results suggest that C₄minCl
is more likely to interact with methanol. Laboratory experiments were performed
to provide further evidence for the interaction between C₄minCl and
different classes of VOCs. Fourier transform infrared spectroscopy was used to
probe the ionic liquid surface before and after exposure to the VOCs that were
tested. A new spectral feature was detected after the exposure of C₄minCl
to alcohols. The new feature is characteristic of alcohols. No new IR features
were detected after exposure of the C₄minCl to aldehydes, ketones,
alkanes, alkenes or aromatic compounds. In addition, after exposing the C₄minCl
to a multi-component mixture of various classes of compounds (including an
alcohol), only one new peak was detected, and this was characteristic of the
alcohol that was tested. These experimental results demonstrated that C₄minCl
is selective to alcohols, even in complex mixtures. The findings in this work
provide information for future gas-phase alcohol sensor design.