Cellulose based poly(ionic liquids): Tuning cation-anion interaction to improve carbon dioxide sorption

Abstract

Mitigation of climate change is an urgent agenda. Development of materials from agroindustrial residue to be used as sorbents for CO2 capture is a significant goal to be achieved both for environmental protection and resource utilization. In this work, cationic cellulosic poly(ionic liquids) PILs using cellulose extracted from rice husk were synthesized. Imidazolium and ammonium were evaluated as cations combined with different counter-anions (chloride [Cl]−, tetrafluoroborate [BF4]−, hexafluorophosphate [PF6]− or bis(trifluoromethanesulfonyl)imide [TF2N]−). Synthesized PILs were characterized by nuclear magnetic resonance (NMR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), universal attenuated total reflectance sensor (UATR-FTIR), thermogravimetric analysis (TGA) and field emission scanning electron microscopy (FESEM). Reusability and CO2 sorption capacity were performed by pressure decay-technique. Competitive atom-atom coordination was investigated by semi-empirical molecular dynamics simulations, PM7-MD simulations. PILs showed a high CO2 sorption capacity directly influenced by anion. At 3MPa of CO2 pressure the sorption capacity increases in the following order for both cations [Cl]−<[BF4]−<[TF2N]−<[PF6]−. Computational modeling suggests that TF2N blocks important CO2 binding sites. The best sorption value was found for PIL [CelEt3N][PF6] of 38mg/g at 0.1MPa and 168mg/g at 3MPa at 25°C. The recycling experiments of CO2 sorption demonstrated a good reusability of synthesized PILs for CO2 sorption.