Effect of Surface Characteristics of Graphene Aerogels and Hydrophilicity of Ionic Liquids on the CO<sub>2</sub>/CH<sub>4</sub> Separation Performance of Ionic Liquid/Reduced Graphene Aerogel Composites
Hatice Pelin Çağlayan, Uğur Ünal, Seda Keskın, Alper Uzun
Abstract
High Resolution Image Download MS PowerPoint Slide Two ionic liquids (ILs) having the same cation with different anions offering opposite hydrophilic/hydrophobic characters, 1- n -butyl-1-methylpyrrolidinium dicyanamide ([BMPyr][DCA]) and 1- n -butyl-1-methylpyrrolidinium hexafluorophosphate ([BMPyr][PF 6 ]), were impregnated onto two different reduced graphene aerogels (rGAs) prepared by the thermal treatment of GAs at 300 and 500 °C to investigate the consequences of the changes in the hydrophilic character of ILs and the reduction temperature of the GAs on the corresponding gas sorption and separation performance of the IL/rGAs. The structural analyses of nanoporous rGAs and IL/rGAs pointed to a change in the quantity of oxygenated functional groups upon thermal treatment and a change in the direct interactions between IL molecules and the host rGA surface upon IL deposition. Single-component CO 2 and CH 4 sorption measurements were performed for each rGA and IL/rGA composite, and both ideal and mixture CO 2 /CH 4 selectivities were calculated. The samples prepared by reducing the GA at 300 and 500 °C yielded ideal CO 2 /CH 4 selectivities of 3.6 and 18 at 1 mbar and 25 °C, respectively. Among IL/rGA composites, the one prepared at 300 °C displayed a remarkable CO 2 /CH 4 separation performance when combined with the hydrophobic [BMPyr][PF 6 ], offering an ideal selectivity of 450.9 at 1 mbar and 25 °C, whereas the composite prepared with rGA500 yielded a substantially high CO 2 /CH 4 selectivity of 173.5 after the incorporation of the hydrophilic [BMPyr][DCA] at 1 mbar and 25 °C. The ideal CO 2 /CH 4 selectivities of [BMPyr][PF 6 ]/rGA300 and [BMPyr][DCA]/rGA500 surpassed most of the previously reported selectivities of carbon-based materials in the literature. These results demonstrate the broad potential of IL/rGAs in sorption-based gas separations owing to the highly tunable nature of both the structure of IL and the surface characteristics of rGA.