# Ionic Liquids Hybridization for Carbon Dioxide Capture: A Review
## 4 Application of ILs Hybrid Material in Carbon Dioxide
### ILs/Cellulose  
Known as the most abundant natural occurring polymer, cellulose building blocks consist of series of glucose chains that are linked by \(\beta\)-glycosidic linkages. Cellulose has been seen as a potential alternative sorbent for CO\({}_{2}\) removal as it exhibits the excellent properties of being low-cost, renewable, non-toxic, biocompatible and biodegradable. Several strategies including cellulose chemical modification and incorporation of inorganic nanoparticle into nanocellulose were proposed to enhance their selectivity towards CO\({}_{2}\). [PERSON] and co-workers suggested a new approach on utilizing cellulose extracted from rice husk as a solid support for CO\({}_{2}\) capture in an effort to overcome the drawbacks posed by amines. It was discovered that the combination of extracted cellulose with JEFFAMIINE\({}^{\text{\textregistered}}\) D-400 Polyetheramine showed 1.091 and 0.409 mmol CO\({}_{2}\)/g of CO\({}_{2}\) uptake at 10 and 1 bar, respectively [111]. In another study, [PERSON] and co-workers employed cellulose aerogels constructed from old corrugated containers for CO\({}_{2}\) capture at ambient conditions [112]. This work indicates that the CO\({}_{2}\) adsorption capacity of cellulose aerogels was in the range of 1.96-11.78 mmol/g. Though cellulose showed great potential as a renewable adsorbent for CO\({}_{2}\) removal, there are several drawbacks that need to be considered. Up to this time, the structural strength and thermal stability of cellulose are still not meeting the requirement in CO\({}_{2}\) adsorption [113]. Meanwhile, the process for modifying cellulose pores involving various processes, such as silanization [114] and esterification [115], has a relatively high cost. [PERSON] and co-workers explored the use of cationic cellulosic poly(ILs) to improve CO\({}_{2}\) sorption [116]. For this study, imidazolium and ammonium cations coupled with different anions such as [Cl]\({}^{-}\), [Tf\({}_{2}\)N]\({}^{-}\), [BF\({}_{4}\)]\({}^{-}\) and [PF\({}_{6}\)]\({}^{-}\) were selected to be combined with extracted cellulose. Prior to synthesis of cellulose-based poly(ILs), cellulose was extracted from rice husk and underwent modification using SOCI\({}_{2}\) to produce chlorinated cellulose (CDC). The cellulose-based poly(ILs) was prepared by adding CDC into 1-methylimidazole or triethylamine to produce [Celmim][Cl] and [CelEt\({}_{3}\)N][Cl] precipitates. The ILs precipitate was purified with methanol before drying under vacuum at 60 \({}^{\circ}\)C. In the meantime, anion exchange was conducted at room temperature in designated solvent to produce [Celmim][Tf\({}_{2}\)N], [Celmim][BF\({}_{4}\)], [Celmim][PF\({}_{6}\)], [CelEt\({}_{3}\)N][Tf\({}_{2}\)N], [CelEt\({}_{3}\)N][BF\({}_{4}\)] and [CelEt\({}_{3}\)N][PF\({}_{6}\)]. Analysis on \({}^{13}\)C NMR confirmed the structures of cellulosic poly(ILs). On the other hand, XPS data revealed the presence of the atoms from all anions with traces of impurities came from SiO\({}_{2}\) of rice husk, and not all halogenated carbons were likely subjected to the reaction with cation. XRD pattern revealed drastic reduction in crystallinity of cellulosic poly(ILs) compared to cellulose. The result of CO\({}_{2}\) uptake capacity showed the cellulose functionalization promotes CO\({}_{2}\) affinity towards the adsorbent. For example, the CO\({}_{2}\) uptake capacity of [CelEt\({}_{3}\)N][PF\({}_{6}\)] and cellulose at 3.0 MPa and 0 \({}^{\circ}\)C were 88 and 168 mg/g, respectively. Moreover, it has been found that [CelEt\({}_{3}\)N][PF\({}_{6}\)] with [PF\({}_{6}\)]\({}^{-}\) anion displayed superior CO\({}_{2}\) uptake compared to other anion attributed by well distributed of fluorine atom in cellulose space. The evaluation on [CelEt\({}_{3}\)N][PF\({}_{6}\)] reusability at 0.1 MPa demonstrated the constant sorption value in all five cycles indicates the robustness of the material for CO\({}_{2}\) removal. In other work, [PERSON] and co-workers investigated the pressure swing CO\({}_{2}\) capture using cellulose-supported ILs [117].