Ionothermal synthesis of magnetically-retrievable mesoporous carbons from alkyne-appended ionic liquids and demonstration of their use in selective dye removal

Abstract

We have devised a simple, convenient, and template-free synthetic strategy to make inherently functional (magnetically-responsive) mesoporous carbons by single-step ionothermal cyclotrimerization of alkyne-functionalized ionic liquids (AFILs) comprising paramagnetic anions. During the carbonization process, bromotrichloroferrate(III) [FeBrCl₃]⁻ or tetrabromoferrate(III) [FeBr₄]⁻ anions act as catalysts in controlling the textural properties of carbon, whereas the cation acts as a carbon source. The resulting mesoporous carbons were probed using a host of tools, including X-ray diffraction, thermogravimetric analysis, nitrogen porosimetry (BET analysis), and transmission electron microscopy. Depending on the nature of the parent anion, magnetically-responsive mesoporous carbons (Fe-AFILs@C) with specific surface areas as high as 544 m² g⁻¹ and good structural stability were obtained from the ionothermal synthesis. The current AFILs are shown to be viable precursors to mesoporous carbons with interesting potential applications. For instance, we demonstrate the sorption of the cationic dye methylene blue (MB) and the anionic dye thiazine red R (TRR) from a contaminated aqueous stream using Fe-AFILs@C as well as their subsequent degradation via Fenton chemistry. The detailed sorption kinetics and the isotherm model for the equilibrium process were investigated and are in accordance with pseudo-second-order kinetics for a Langmuir-type adsorption isotherm. Interestingly, the mesoporous carbons were also successfully applied as selective sorbents to separate a binary mixture of the MB and TRR dyes. Significantly, the Fe-AFILs@C can be easily separated from the aqueous solution following the sorption process and can be easily regenerated using a simple ethanol washing step which releases the dye.