# Ionic Liquids Hybridization for Carbon Dioxide Capture: A Review
## 2 ILs Utilization for CO\({}_{2}\) Capture
stated one of their azolate anion-functionalized ILs, [P\({}_{2228}\)][6 BrInda], which was also known as aprotic heterocyclic anion (AHA), demonstrated nearly equimolar CO\({}_{2}\)-ILs uptake at 0.833 bar, 332 K [31]. This value is higher than what was previously reported for the conventional [HMIM][Tf\({}_{2}\)N] and [BMIM][OAc]. It was found that the CO\({}_{2}\) absorption was affected by the electron density of reactive nitrogen. [PERSON] and co-workers showed that the CO\({}_{2}\) absorption increased from 0.91 for [P\({}_{2228}\)][4 BrInda] to 0.98 molCO\({}_{2}\)/mol ILs for [P\({}_{2228}\)][6 BrInda], and the reason was attributed to the fact that [6 BrInda]\({}^{-}\) owned more electron withdrawing group (EDW) than that of [4 BrInda]\({}^{-}\). Consequently, the electron density increased with the presence of EDW, thereby enhancing the CO\({}_{2}\) absorption capacity of the ILs. In the meantime, the design of ILs for highly efficient CO\({}_{2}\) chemisorption was conducted by introducing TSILs comprise of commercial phenol as the starting material. [PERSON] reported a series of low viscous diamino protic ILs couples with phenolic anion prepared via direct neutralizationfor CO\({}_{2}\) absorption. The CO\({}_{2}\) solubility significantly increased with rising pressure in the low-pressure region, indicating that CO\({}_{2}\) absorption occurred through both chemical and physical mechanisms [32]. Furthermore, their [DMAPAH][4F-PhO] exhibited a CO\({}_{2}\) absorption capacity of up to 3.99 mol CO\({}_{2}\)/kg ILs. The recyclability test that was conducted up to five times showed a slight decline in CO\({}_{2}\) absorption, indicating the promising potential of ILs. The research in CO\({}_{2}\) was broadened to the development of polymeric-ILs with the goal of enhancing the stability, durability and capability to control the macromolecular framework of sorbents. Apart from that, the copolymerization of polymeric ILs with other polymers allows for the attainment of a high surface area, which is favorable for gas capture applications. In one of the earliest examples, [PERSON] and colleagues synthesized polymeric-ILs using imidazolium-based IL as monomers [33]. A comparative study revealed that [PVBIM][BF\({}_{4}\)] exhibited a CO\({}_{2}\) absorption capacity of 0.305 wt%, while [BMIM][BF\({}_{4}\)] had a capacity of 0.256 wt%. Additionally, they observed that all the polymeric ILs, namely, [PVBIM][PF\({}_{6}\)], [PVBIM][BF\({}_{4}\)] and [PBIMT][BF\({}_{4}\)], demonstrated rapid CO\({}_{2}\) sorption compared to the conventional [BMIM][BF\({}_{4}\)]. While [BMIM][BF\({}_{4}\)] required 400 min to reach its full capacity, all other polymeric-ILs achieved maximum absorption within just 30 min. Generally, the formation of a porous structure within the polymer matrix could facilitate the diffusion of CO\({}_{2}\) molecules into the polymeric-ILs, which in turn leads to rapid absorption kinetics and efficient CO\({}_{2}\) capture. Subsequently, numerous polymeric ILs with various cations, including pyridinium, ammonium and phosphonium, have emerged as promising solutions for the improvement in CO\({}_{2}\) uptake capacity. Another study involves the synthesis of pyridinium-based polymeric-ILs in which the polymer ILs [MDAP][TF\({}_{2}\)N]-PDC exhibited 1.39 wt% of CO\({}_{2}\) absorption at 1.0 bar under temperature 25 \({}^{\circ}\)C [34]. On the other hand, the recent trend in the field of polymeric ILs involves the development of hyper-cross-linked poly (ILs), (HCL-PILs). [PERSON] and [PERSON] synthesized HCL-PILs by introducing benzimidazole as additional monomer via Friedel-Crafts alkylation [35]. The analysis conducted using BET indicated that HPIL-Cl (1) exhibited a CO\({}_{2}\) uptake of 5.3 wt%, which was higher than the 4.5 wt% observed for HCP-Cl. According to the authors, the enhancing in CO\({}_{2}\) capture in HPIL-Cl (1) was due to the presence of imidazoline and imidazolinium cations that exhibit strong electrostatic force as the main configurations for the polymers.