Effect of alkyl chain length on adsorption properties of alkyl imidazolium ionic liquids surface imprinting polymers

Abstract

An ionic liquid (IL) surface molecularly imprinted polymer (MIP) was prepared using 1-octyl-3-methylimidazolium chloride ([C8mim]Cl) as the template and acylated ethylenediamine-poly(styrene-divinylbenzene) particle as the supported material. The obtained MIP material was characterized by scanning electron microscopy, Brunauer–Emmett–Teller surface area analysis, and FT-IR spectroscopy. The adsorption property and selective recognition performance of [C8mim]ClMIP were studied by static adsorption and solid-phase extraction coupled with high-performance liquid chromatography. Next, the effect of alkyl chain length of imidazolium cations on the adsorption characteristics of [C2mim]ClMIP, [C4mim]ClMIP, and [C8mim]ClMIP was examined in detail. It was shown that the adsorption selectivity of the three IL MIPs was significantly affected by the alkyl chain length. [C8mim]ClMIP exhibited broad recognition characteristics for all the imidazolium chloride ILs studied ([C n mim]Cl, n = 2, 4, 6, 8, 12, 16), and the adsorption equilibrium was achieved within 40 min. [C4mim]ClMIP could enrich [Cnmim]Cl (n = 2, 4, 6, 8), but [C2mim]ClMIP could only recognize [C2mim]Cl and [C4mim]Cl selectively. It is obvious that the adsorption selectivity of the IL MIPs increased with the decrease of alkyl chain length of the template molecules. Furthermore, the possible recognition mechanism was suggested.