## 1 Introduction  
The growth of industrial activities, as well as the increase in population, has boosted the consumption of natural resources and the concentration of pollutant substances both in the air and in water. Over the last years, the concern about the pollution problem has increased, and many countries and organizations, including the European Union, have established new laws to protect the environment, decreasing the limit concentration of different kind of pollutant substances. In this context, the European Commission directive 2001/81/EC established emission thresholds for acidifying, eutrophying, and other pollutant substances, with the aim of protecting the environment and the human health from the harmful effects of the poor quality of air that we breathe and water that we drink [1]. Water is a natural resource that is essential for life, and due to the industrial growth previously mentioned, many pollutant substances can be found in water, and they have to be eliminated in order to get water that can be used in farming and domestic activities. In addition to the pollution problem, the scarcity that part of the planet suffers as a result of the climate change makes it necessary to develop techniques that allow removing toxic substances from water [2]. In the 2008/105/CE directive, the European Parliament set the normativity to the quality of waters, establishing that the \"chemical contamination of surface waters is a threat for aquatic life which effects are the acute and chronic toxicity, as well as, the danger to human health\", and they created a list of priority pollutants where some phenolic compounds are included as very harmful and toxic substances [3]. Phenolic compounds are substances that are presented in the wastewaters of industries such as pharmaceutical, coal, or petrochemical, and the threshold quantities for these compounds are fixed by the Environmental Protection Agency (EPA) in 5 mg:L\({}^{-1}\) if these waters are to be discharged into the public sewage system, and 1 mg:L\({}^{-1}\) if they are to be discharged into inland waters. Due to this legal limitation, it is necessary to remove phenolic compounds from water before it was discharged [4; 5]. Distillation, chemical oxidation, adsorption, or biodegradation techniques have been used to remove phenols from water. Nevertheless, these techniques have some drawbacks, such as high-energy consumption, inefficient treatment at low concentration of phenols, or the difficulty to control the process. Another and common separation technique is the liquid-liquid extraction (LLE), which is a simple and effective technique to remove or recover phenolic compounds from aqueous systems [6]. In spite of the high extraction efficiencies obtained with conventional solvents, the consumption of harmful substances, volatile organic compounds (VOCs), is the most important drawback, so it is necessary to replace them with other safer and more environmental friendly substances [7; 8; 9]. Ionic liquids (ILs) are considered as good replacement substances for traditional organic compounds due to their negligible vapor pressure, high thermal and chemical stability, and their capability to dissolve a huge variety of materials [7; 10]. They are defined as salts that have a melting point lower than 373 K, most of them are liquids at room temperature, and they keep in this state in a wide range of temperatures [11]. Over the last few decades, the interest in the ILs has grown due to their versatility, and in recent works, it is possible to find studies with functionalized ionic liquids, incorporating hydroxyl, alkyl, and benzyl groups into the structures, improving phenolic extraction efficiencies [12]. On the other hand, [PERSON] et al. [13] investigated hydrophobic magnetic ILs and their applicability to remove phenolic compounds from water. Another advantage of the ILs is the possibility to recover and reuse them without loss of their properties. [PERSON] et al.