Theoretical model for moisture adsorption on ionic liquids: A modified Brunauer–Emmet–Teller isotherm approach

The adsorption of atmospheric water on the air–liquid interface of ionic liquids is analyzed by means of a modified version of the Brunauer–Emmet–Teller (BET) multilayer adsorption isotherm including lateral interactions between adsorbed molecules, treated in a mean-field fashion. Recently reported experimental results of water adsorption on hydrophobic ionic liquids of the 1-alkyl-3-methyl imidazolium tetrafluoroborate (CnMIM-BF4) family are analyzed in the present theoretical framework. The calculated values of the lateral interaction are seen to be compatible with the Keesom dipole–dipole interaction in water, confirming the validity of the multilayer assumption hypothesis. A somehow surprisingly ordered hydrophilic-like adsorption of atmospheric water is suggested to take place in the free surface of hydrophobic ILs of the imidazolium family.