# Ionic Liquids Hybridization for Carbon Dioxide Capture: A Review
## 3 ILs Hybridization Strategy  
The preceding section summarizes the evolution in ILs development for CO2 capture. It is undeniable that ILs have shown excellent potential to be alternative sorbents for CO2 removal. However, the utilization of ILs in real application has been hampered due to several challenges. ILs demonstrate high viscosity property which will impede the mass transfer by inhibiting gas diffusion into liquid, thus reducing the efficiency in capturing CO2 [55]. Some functionalized ILs including AAILs, sulfone and acetate were reported to display a significant increase in viscosity after CO2 absorption [56]. This effect will be more pronounced at industrial level where the need of rapid CO2 removal is required. Besides that, several ILs utilize specific precursors which involve extensive purification during their synthesis procedure, and this is seen to be a major drawback [57]. For example, ILs with aprotic heterocyclic anion (AHA) have been recognized as a promising candidate for CO2 capture due to their capability to react stoichiometrically and reversibly with CO2 while avoiding the increase in viscosity as being observed in AAILs [58]. Nevertheless, the synthesis of AHA-ILs requires multiple steps including anion exchange and neutralization reaction to yield the desired ILs. In addition to the time-consuming anion exchange process, effective CO2 capture necessitates ILs to undergo thorough drying process, which typically takes about a week. In turn, these present economic challenges for industrial application due to high production cost. Other than that, the complexity in IL preparation is not only limited to the selection of cation and anion combination, but also involves the intricate nature of ILs synthesis as parameters that prove to be effective on a small scale may not directly applicable to larger-scale production. Factors such as mixing speed, reaction temperature and synthesis period need to be carefully considered due to their significant impact on the process.  
Therefore, to address the limitation of ILs in CO2 capture, ongoing research focuses on exploring new materials. One of the popular alternatives is to produce a hybrid material consists of IL with the goal to enhance properties or functionalities beyond what either component can achieve individually. According to [PERSON] and co-workers, \"hybridization\" is a biological term referring to artificial integrations of two distinction species [59]. In the context of ILs, the term \"ILs hybridization\" refers to the process of incorporating substances such as mesoporous silica, metal organic frameworks (MOFs), activated carbon (AC), carbon nanotube (CNT) and deep eutectic solvent (DES) with ILs to produce new materials with superior property [60; 61; 62]. For instance, [PERSON] et al. employed this term to describe the combination of their IL with carbon nanotube (CNT), while [PERSON] and co-workers used it in their work related to ILs encapsulation with shell of polyurea and alkylated graphene oxide [63; 64]. Hybridization of ILs allows the material to have more versatility and adaptability for specific application. ILs hybridization also minimizes the amount of ILs required, thereby effectively reducing the associated cost [59]. Furthermore, the hybridization of ILs with other materials, such as amine blending, has proven to be an effective approach in addressing the issue of viscosity [65].