Microporous zeolite-templated carbon as an adsorbent for the removal of long alkyl-chained imidazolium-based ionic liquid from aqueous media

Zeolite-templated carbon (ZTC) was synthesized for the adsorption of imidazolium-based ionic liquids (ILs), including [C(4)mim] [Cl], [C(8)mim][Cl] and [C(16)mim] [Cl]. To clarify the adsorption mechanism, three carbonaceous materials coconut-shell-based activated carbon (CSAC), coal-based activated carbon (F300) and ordered mesoporous carbon material (CMK-3) were also prepared as additional sorbents. The sorbents were characterized by X-ray diffraction, transmission electron microscopy, N-2 adsorption, X-ray photoelectron spectroscopy, Raman spectroscopy and zeta potential measurements in terms of structural and surface characteristics. Batch adsorption tests indicated that the CSAC exhibited a high adsorption capacity for short-alkyl-chain [C(4)mim] [Cl], originating from the micropore-filling effect. ZTC displayed a markedly higher adsorption capacity for long alkyl-chained [C(16)mim][Cl] compared with other tested sorbents due to its regular-shaped, open and interconnected channel structure, as well as the good matching between pore size and adsorbate dimension. The uniform pore structure also endowed ZTC and CMK-3 with considerably faster adsorption kinetics for [C(16)mim] [Cl] than the activated carbons. Thermodynamic studies revealed that the uptake of [C(16)mim] [Cl] on ZTC was spontaneous physical adsorption. [C(16)mim] [Cl] adsorption was enhanced by increasing the ionic strength of the aqueous solution and was slightly influenced by the solution pH. Additionally, ZTC was easily regenerated with ethyl alcohol for reuse for at least ten times. Thus, the findings demonstrated that ZTC is an ideal candidate for the adsorptive removal of long-alkyl-chain ILs from water and wastewater.