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.