Amine-rich ionic liquid grafted graphene for sub-ambient carbon dioxide adsorption

Abstract

The present study describes the synthesis of the adsorptivity based amine-rich ionic liquid (ARIL), namely, 3,5-diamino-1-methyl-1,2,4-triazolium tetrafluoroborate grafted graphene (HEG/ARIL), and its application in carbon dioxide adsorption. This ionic liquid occurs in the solid form at standard atmospheric temperature and pressure, and forms solid-like short range ordering on a graphitic substrate. Molecular vibrational spectroscopy suggests that the ARIL molecules are physically adsorbed on the graphene surface with no detectable chemical interactions. The CO₂ adsorption on ARIL is not significantly accompanied by chemical interaction with the amine groups under sub-ambient conditions. The adsorption capacity of ARIL attained a significant improvement when it was grafted onto graphene. The favourability and energy of adsorption suggest that the cumulative interaction of CO₂ with ARIL moieties is weaker than that with residual oxygen-containing functional groups in graphene. The adsorbate retention of graphene is largely increased upon grafting ARIL. The isosteric heat and entropy of CO₂ adsorption on the HEG/ARIL is lower than that found on pristine HEG. Conclusively, ARIL functionalization improved the CO₂ adsorption capacity and decreased the interaction energy between CO₂ and graphene, because it enhances the density of the low affinity adsorption sites.