Removal of Rhodamine B from Water by Benzyl-Functionalized Ionic Liquids

The removal of rhodamine B by benzyl-functionalized ionic liquids (ILs) from water was carried out. Effects of aqueous pH value, concentration of rhodamine B, phase volume ratio, and the presence of salt on the extraction efficiency have been investigated. Experimental results showed that the extraction efficiency of rhodamine B decreased with the increase of pH value. Thermodynamic studies indicated that hydrophobic interaction is the main driving force, besides, pi-pi stacking, electrostatic interaction, and salting-out effect are also important for the extraction of rhodamine B. Notably, the quantitative extraction of rhodamine B into 1-butyl-3-benzylimidazolium bis(trifluoromethylsulfonyl) imide ([C(4)Bzim]NTf2) was achieved even at the phase volume ratio V-w/V-IL = 500: 1. After extraction, [C(4)Bzim]NTf2, could be directly reused at least five times. These results suggest that the [C(4)Bzim]NTf2 has potential application in the removal of rhodamine B from water.