Theoretical study on the interactions between dibenzothiophene/dibenzothiophene sulfone and ionic liquids

The interactions between sulfur-containing compounds of dibenzothiophene (DBT) and dibenzothiophene sulfone (DBTO2) and ionic liquids of 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]+[PF6]−) and 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]+[BF4]−) were comparatively studied by using density functional theory. The most stable structures of [BMIM]+[PF6]−, [BMIM]+[PF6]−-DBT, [BMIM]+[PF6]−-DBTO2, [BMIM]+[BF4]−, [BMIM]+[BF4]−-DBT, and [BMIM]+[BF4]−-DBTO2 systems were obtained by natural bond orbitals (NBO) and atoms in molecules (AIM) analyses. The results indicated that DBT and [BMIM] rings of [BMIM]+[PF6]−/[BMIM]+[BF4]− are parallel to each other. There is a strong π-π interaction between them in terms of NBO and AIM analyses. The H1′ and H9′ involved F…H hydrogen bonding interactions may favor the formation of π-π stacking interactions. The DBTO2 preferentially locates near the C2-H2 and methyl group of [BMIM]+ to form O…H interactions. The predicted geometries and interaction energies imply the preferential adsorption of DBTO2 on [BMIM]+[PF6]−/[BMIM]+[BF4]−. The [BMIM]+[PF6]−/[BF4]− have better extracting ability to remove DBTO2 than DBT, possibly due to the larger polarity of DBTO2 and stronger interactions between [BMIM]+[PF6]−/[BF4]− and DBTO2.