Synthesis of a new ionic liquid for efficient liquid/liquid extraction of lead ions from neutral aqueous environment without the use of extractants

This work introduces a new air and moisture stable ionic liquid which is tested for the extraction of Pb2+from neutral aqueous solution. Here, no chelating agents were used. Grafting coordinating functional groups on the cation of the ionic liquid was not necessary. Very small ionic liquid to aqueous phase ratio was used. The ionic liquid used for this purpose was N-hexyl-4,4-bipyridinium bis(trifluoromethylsulfonyl)imide([C6byp][Tf2 N]). Its synthesis is characterized by spectrometry (1 H, 13 C, and 19 F NMR, ESI-MS, FTIR) as well as Carbon, Hydrogen and Nitrogen (CHN) elemental analysis. Differential scanning calorimetry (DSC) has been used to analyze in detail the thermal behavior in the temperature range of −20 to 200 °C. Interestingly, the ionic liquid demonstrated nearly complete removal of the metal ion from the aqueous phase (98.16%). Furthermore, the reusability (recyclability) investigation demonstrated that the ionic liquid can be used at least for four cycles with undiminished efficiency (98.16% for the second cycle, 97.64% for the third and fourth cycles). Its cycle ability reduces the concern arising from the high cost of ILs. This result indicates that the use of this ionic liquid for the extraction of heavy metals is very promising. The mechanism of removal of the Pb2+ ions is speculated to be by the formation of a complex with a formula of [Pb(C6bpy)n][(CF3SO2)2 N]n(NO3), where, n = 1–6.

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