## 1 Introduction  
Room-temperature ionic liquids (RTILs), or more simply, ionic liquids (ILs), have attracted a great deal of attention from the mid-1970s as environmentally friendly alternatives to volatile organic compounds. As it is well known, ILs are molten salts with a very low vapor pressure composed of an organic cation and an organic/inorganic anion, which remain in the liquid state for temperatures below 100 \({}^{\circ}\)C. Moreover, other significant properties of ILs such as their high solubility, thermal stability, water sensitivity and eco-friendly character, as well as their elevated ionic mobility and viscosity, are nowadays characteristics of great interest in diverse research and industrial areas [1]. In fact, the particular properties of ILs allow for their use in a large number of different applications, such as solvents for organic reactions and catalysis, electrodeposition, extraction, energy, membranes for separation processes, electrochemical devices (capacitors, fuel cells, batteries or solar cells) or optical sensors [2; 3; 4; 5; 6; 7; 8; 9; 10; 11; 12]. Imidazolium-based ILs (1-methyl-3-butylimidazolium tetrafluoroborate, 1-methyl-3-butylimidazolium bromide, 1-allyl-3-methylimidazolium tetrafluoroborate, 1-methyl-3-butylimidazolium hexafluorophosphate,... ) are commonly used in such applications, but trioctylmethylammonium chloride (or AliquatCI) and its derivatives (AliquatNO\({}_{3}\) or AliquatSCN), n-dodecyltriethylammonium chloride (or DTACI) and many others ILs are also usually considered [13; 14; 15]. In fact, a significant aspect of ILs is the possibility of tailoring their physicochemical properties via the selection of the cation/anion, which enables researchers to obtain ILs with the most adequate characteristics for a specific application. Additionally, since the liquid state of ILs is not associated with solvent presence, they are considered green products, and different hybrid IL/biopolymer materials are being studied for biomedical applications [16]. In this context, the modification of polymeric membranes by different ILs for applications in many separation processes (fuel and microbial cells, CO\({}_{2}\) separation,... ) has already been reported [17; 18; 19; 20; 21]. In particular, the surface modification/incorporation of various ILs in Nafion membranes by immersion in solutions with different percentages of IL via the proton/cation exchange process has been performed to improve the thermal stability of membranes, which might favor their possible application as polymer electrolyte membranes at high temperatures or for methanol and gas crossover reduction in the case of direct methanol fuel cells [22; 23; 24; 25]. Moreover, ILs are also used in the fabrication of polymer inclusion membranes (PIMs), with applications in the separation of different kinds of compounds (anions, metallic species or small organic molecules), as a way to improve their mechanical stability when cellulose triacetate or polyvinyl chloride is used as the polymeric matrix [26; 27; 28; 29; 30]. Another polymeric but biocompatible material widely used for membranes or thin films manufacturing is regenerated cellulose (RC), and different cellulose-ILs hybrid materials for drug delivery, biosensing or tissue engineering applications have already been reported [16; 31]. On the other hand, the modification of regenerated cellulose (RC) films with lipids or ILs layers and/or the incorporation of different nano-structures (nanoparticles, dendrimers or different kinds of quantum dots) by simple dip coating in aqueous solutions of the modifying agents (without any chemical reaction) has also been reported, with the simplicity of this modification process being associated with the high hydrophilic character and swelling degree of the RC-support [32; 33; 34; 35; 36].