**4.2. Ionic liquid applications**

Since the academic world began to become interested in ILs in the 1990s, the number of scientific articles and patents related to the topic has incredibly increased. For example, in 2000 about 100 patent applications had been reported, while in 2004 this number increased to 800 (Keskin et al., 2007). Nowadays, about 28200 patents related to ILs can be described.

<sup>1</sup> See apendix (section 7) for nomenclature abbreviations.

Some applications arise from the fact that many ILs are powerful solvents, able to dissolve salts, fats, proteins, amino acids, surfactants or sugars. For instance, [(MeOEt)MeIm][BF4] can dissolve glucose 100 times better than acetone (Park et al., 2001). They can even dissolve crude oil, inks, plastics or DNA. For this reason, they can be used as reaction media for electrochemical and chemical syntheses (Torimoto et al., 2010), giving rise to reaction rates similar or even better than those obtained when using aqueous or organic solvents. Another advantage of using them with this aim is the ease in recovering the resulting products from the reaction medium, especially in those cases in which distillation is not practical, for example, because the reaction products are thermally sensible (Keskin et al., 2007). In addition, it has been reported that ILs can be used as solvents for insoluble bio-related materials like cellulose, which is easily dissolved by strong hydrogen bond-acceptor ILs (like chloride anion-based ones) (Keskin et al., 2007; Torimoto et al., 2010).

Another typical application is their use in gas purification because many gases are soluble in ILs (for example CO2 is highly soluble in [BuMeIm][PF6]) (Anthony et al., 2002). This feature also makes them excellent candidates to be employed in gas absorption applications, together with the fact that gas separation from the IL stream would be very easy (i.e. by simple flash distillation) (Keskin et al., 2007).

Related to materials science, ILs have been widely used in chemical synthesis of nanoparticles, with self-evident advantages like the fact that almost no stabilizing agents that prevent from particle coalescence are needed (requisite almost indispensable in the case of aqueous or organic solvents) (Torimoto et al., 2010). For example, it is possible to synthesize particles for the preparation of MFs such as magnetite (Wang et al., 2009) or cobalt (Behrens et al., 2012) nanoparticles. This would allow an *in situ* synthesis of the dispersed particles.

As a final point, the preparation of IL-based MFs would allow the use of some of the devices mentioned in section 3 under extreme environmental conditions (ultra-high vacuum or high temperature applications). This would be particularly interesting in the case of space technology such as dampers, dynamic seals or hydrodynamic bearings in gyroscopes for mini-satellites. As a matter of fact, the first MF patent was aimed to prepare controlling fluids for space applications (Papell, 1965).
