Density and dynamic viscosity data of binary mixtures of ionic liquids (ILs) were determined in this work, at temperatures from 283.15 to 363.15 K and at 0.1 MPa. The mixtures of two ILs comprise a common cation and different anions, combining 1-butyl-3-methylimidazolium bis­(trifluoromethylsulfonyl)­imide with eight other ionic liquids, namely, 1-butyl-3-methylimidazolium thiocyanate, 1-butyl-3-methylimidazolium dicyanamide, 1-butyl-3-methylimidazolium tricyanomethane, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium trifluoromethanesulfonate, and 1-butyl-3-methylimidazolium dimethylphosphate. Five mole fractions (0.00, 0.25, 0.50, 0.75, 1.00) of each mixture were prepared and characterized in terms of density and dynamic viscosity. The temperature dependence of density was described using a linear model, while the Vogel–Tammann–Fulcher equation was used to describe the temperature dependence of viscosity. Ideal mixing rules were used to predict the molar volume and viscosity and to infer on the mixtures ideal/nonideal behavior. For the mixtures of ILs investigated almost null or small deviations were observed in the molar volumes, meaning that their mixing is remarkably close to linear ideal behavior when molar volumes of mixtures are considered. For viscosity, larger deviations were observed for some particular systems; yet, and in general, mixtures of ILs do not deviate in a significant extent from ideal behavior. Therefore, ideal mixture models can be used to predict the physical properties of mixtures of ILs and to a priori design mixtures with specific features.

Ionic liquids (ILs) with improved hydrogen-bonding acceptor abilities, such as acetate-based compounds, have shown great potential for CO 2 capture and biomass dissolution. In this context, the knowledge of the thermophysical properties of acetate-based fluids is essential for the design and scale-up of related processes. However, at this stage, acetate-based ILs are still poorly characterized. In this work, four thermophysical properties, specifically, density, viscosity, refractive index, and surface tension, were determined for five acetate-based ILs. Both protic and aprotic ILs were investigated, namely, N,N-dimethyl-N-ethylammonium acetate, 1-ethylimidazolium acetate, 1-ethyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium acetate, and 1-butyl-1-methylpyrrolidinium acetate. From the temperature dependence of the measured properties, additional properties, such as the isobaric thermal expansion coefficient, the surface entropy and enthalpy, and the critical temperature, were further estimated. ■ INTRODUCTIONDuring the past decade research has emerged in various areas involving ionic liquids (ILs), and their potential applications are nowadays widespread. Ionic liquids are a group of molten salts normally composed of inorganic or organic anions, and relatively large organic cations, which do not easily form an ordered crystal and, therefore, they remain liquid at or near room temperature. 1−3 Recently, certain classes of ILs with improved hydrogenbonding acceptor capability, such as acetate-based fluids, have shown to be promising solvents for CO 2 capture 4−7 and cellulose and/or biomass dissolution. 8−11 Acetate-based fluids are able to strongly coordinate with CO 2 and hydrogen bond donator groups, such as −OH groups, and favorable results have thus been published. Moreover, acetate-based ILs present low toxicity, low corrosiveness, and favorable biodegradability. 12 Despite their undeniable interest, the thermophysical properties of acetate-based fluids are still poorly characterized. In a previous work we have determined the densities and viscosities of a series of imidazolium-based ILs which have shown potential for the dissolution of biomass. 13 Fendt et al. 14 presented the viscosities of acetate-based ILs and some of their mixtures with water and organic solvents. Qian et al. 15 explored the densities and viscosities of the protic IL 1-methylimidazolium acetate and its binary mixtures with alcohols. Additional scarce reports have addressed the measurements of densities, 16−18 viscosities, 19 refractive index, 16,20 and surface tension 18 of aprotic acetate-based ILs.In this work, the thermophysical properties of acetate-based ILs, specifically density, viscosity, refractive index, and surface tension, were measured as a function of temperature. The ILs are formed by the common anion acetate, combined either with protic (N,N-dimethyl-N-ethylammonium and 1-ethylimidazolium) or aprotic cations (1-ethyl-3-methylimidazolium, 1-butyl-3-methylimidazolium and 1-butyl-1-methylpyrrolydinium). Additio...

Aiming at providing a comprehensive study of the influence of the cation symmetry and alkyl side chain length on the surface tension and surface organization of ionic liquids (ILs), this work addresses the experimental measurements of the surface tension of two extended series of ILs, namely R,R'-dialkylimidazolium bis[(trifluoromethyl)sulfonyl]imide ([C(n)C(n)im][NTf2]) and R-alkyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide ([C(n)C(1)im][NTf2]), and their dependence with temperature (from 298 to 343 K). For both series of ILs the surface tension decreases with an increase in the cation side alkyl chain length up to aliphatic chains no longer than hexyl, here labeled as critical alkyl chain length (CACL). For ILs with aliphatic moieties longer than CACL the surface tension displays an almost constant value up to [C12C12im][NTf2] or [C16C1im][NTf2]. These constant values further converge to the surface tension of long chain n-alkanes, indicating that, for sufficiently long alkyl side chains, the surface ordering is strongly dominated by the aliphatic tails present in the IL. The enthalpies and entropies of surface were also derived and the critical temperatures were estimated from the experimental data. The trend of the derived thermodynamic properties highlights the effect of the structural organization of the IL at the surface with visible trend shifts occurring at a well-defined CACL in both symmetric and asymmetric series of ILs. Finally, the structure of a long-alkyl side chain IL at the vacuum-liquid interface was also explored using Molecular Dynamics simulations. In general, it was found that for the symmetric series of ILs, at the outermost polar layers, more cations point one of their aliphatic tails outward and the other inward, relative to the surface, than cations pointing both tails outward. The number of the former, while being the preferred conformation, exceeds the latter by around 75%.

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In the current era of human life, we have been facing an increased consumption of Non-Steroidal Anti-Inflammatory Drugs (NSAIDs). Nevertheless, NSAIDs are not completely metabolized by humans and are further excreted into domestical effluents. Several studies have been showing that a wide variety of pharmaceuticals are present in water effluents and are thus a matter of serious concern in the public health. Although treatment plants use sophisticated technologies for pollutants/contaminants removal, none of these processes was particularly designed for NSAIDs. In this perspective, this work addresses the use of a liquid-liquid extraction approach, employing ionic liquids (ILs), for the removal of NSAIDs from aqueous media. In particular, aqueous biphasic systems (ABS) composed of ILs and aluminium-based salts, which are already used in water treatment plants, were tested for the removal of diclofenac, ibuprofen, naproxen and ketoprofen. With these systems, extraction efficiencies of NSAIDs up to 100% were obtained in a single-step. The recovery of NSAIDs from the IL medium and the recyclability of the IL-rich phase were then ascertained to guarantee the development of a more sustainable and cost-effective strategy. Based on the remarkable increase in the solubility of NSAIDs in the IL-rich phase (from a 300- to a 4100-fold when compared with pure water), water was then studied as an effective anti-solvent, and where single-step recovery percentages of NSAIDs from the IL-rich phase up to 91% were obtained. After the “cleaning” of the IL-rich phase by the induced precipitation of NSAIDs, the phase-forming components were recovered and reused in four consecutive cycles, with no detected losses on both the extraction efficiency and recovery of NSAIDs by induced precipitation. Finally, an integrated process is here proposed, which comprises the (i) removal of NSAIDs from aqueous media, (ii) the cleaning of the IL-rich phase by the recovery of NSAIDs by induced precipitation, and (iii) the phase-forming components recycling and reuse, aiming at unlocking new doors for alternative treatment strategies of aqueous environments.

In the past few years, the improvement of advanced analytical tools allowed to confirm the presence of trace amounts of metabolized and unchanged active pharmaceutical ingredients (APIs) in wastewater treatment plants (WWTPs) as well as in freshwater surfaces. It is known that the continuous contact with APIs, even at very low concentrations (ng L −1 -μg L −1 ), leads to serious human health problems. In this context, this work shows the feasibility of using ionic-liquid-based aqueous biphasic systems (IL-based ABS) in the extraction of quinolones present in aqueous media. In particular, ABS composed of imidazolium-and phosphonium-based ILs and aluminiumbased salts (already used in water treatment plants) were evaluated in one-step extractions of six fluoroquinolones (FQs), namely ciprofloxacin, enrofloxacin, moxifloxacin, norfloxacin, ofloxacin and sarafloxacin, and extraction efficiencies up to 98% were obtained. Despite the large interest devoted to IL-based ABS as extractive systems of outstanding performance, their recyclability/ reusability has seldomly been studied. An efficient extraction/cleaning process of the IL-rich phase is here proposed by FQs induced precipitation. The recycling of the IL and its further reuse without losses in the ABS extractive performance for FQs were established, as confirmed by the four consecutive removal/extraction cycles evaluated. This novel recycling strategy supports ILbased ABS as sustainable and cost-efficient extraction platforms.

Fluoroquinolones (FQs) and Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) are two classes of Active Pharmaceutical Ingredients (APIs), widespreadly used in human healthcare and as veterinary drugs, and that have been found throughout the water cycle in the past years. These two classes of APIs are commonly present in aqueous streams in concentrations ranging from ng.L-1 to µg.L-1. Despite such low concentrations, these contaminants tend to bioaccumulate, leading to serious environmental and health issues after chronic exposure. The low concentrations of FQs and NSAIDs in aqueous media also render their difficult identification and quantification, wich may result in an unefficient evaluation of their environmental impact and persistence. Therefore, the development of alternative pre-treatment techniques for their extraction and concentration from aqueous samples is a crucial requirement. In this work, liquid-liquid systems, namely ionic-liquid-based aqueous biphasic systems (IL-based ABS), were tested as simultaneous extraction and concentration platforms of FQs and NSAIDs. ABS composed of imidazolium-, ammonium- and phosphonium-based ILs and a citrate-based salt (C6H5K3O7) were evaluated for the single-step extraction and concentration of three FQs (ciprofloxacin, enrofloxacin and norfloxacin) and three NSAIDs (diclofenac, naproxen and ketoprofen) from aqueous samples. Outstanding one-step extraction efficiencies of APIs close to 100% were obtained. Furthermore, concentration factors of both FQs and NSAIDs were optimized by an appropriate manipulation of the phase-forming components compositions to tailor the volumes of the coexisting phases. Concentration factors of 1000-fold of both FQS and NSAIDs were obtained in a single-step, without reaching the saturation of the IL-rich phase. The concentration of APIs up to the mg.L-1 allowed their easy and straightforward identification and quantification by High-Performance Liquid Chromatography (HPLC) coupled to an UV detector, as shown either with model aqueous samples or real wastewater effluent samples.