Dual functional behaviour of dicationic ionic liquid as extractant and hydrophobic biphasic solvent for extraction of Pb(II) in water

Herein, it was aimed to investigate the extraction ability of hydrophobic di-cationic imidazolium-based ionic liquid with inbuilt carboxylic acid functionalities for one of the heavy metals, Pb(II) from aqueous solution. Two dicationic ionic liquids, IL-1 named 1,1′(butane-1,4-diyl)bis(3-(4carboxyphenyl)-2-methyl-1H-imidazol-3-ium) chloride and IL-2 named 1,1′(dodecane-1,12-diyl)bis(3-(4carboxyphenyl)-2-methyl-1H-imidazol-3-ium)chloride tailored with (CH2)n bridging spacer chains, n = 4 and n = 12 respectively were synthesized. The Pb(II) displayed extraction percentages greater than 90% with both the aqueous biphasic system of IL-1 and IL-2. An efficient back-stripping of the Pb(II) metal ion was done using with aqueous solution of oxalic acid. Calcination of lead oxalate salt obtained showed highest purity of PbO confirmed by PXRD and EDX data. The established experimental condition with the synthesized ionic liquids is a distinguished one as no salting out agent, no extra extracting agents other than the synthesized ionic liquids were used. Moreover, the regeneration of the ionic liquid (IL-2), and back stripping of Pb(II) as oxalate salt makes this system an efficient one with negligible loss of the ionic liquid (IL-2) into the aqueous medium thus obliging the standards of environment-friendly sustainable development.