Ionic Liquids As Tunable Toxicity Storage Media ... - ACS Publications

Research Article pubs.acs.org/journal/ascecg

Ionic Liquids As Tunable Toxicity Storage Media for Sustainable Chemical Waste Management Marina M. Seitkalieva, Alexey S. Kashin, Ksenia S. Egorova, and Valentine P. Ananikov* N.D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Leninsky prospect, 47, Moscow 119991, Russia S Supporting Information *

ABSTRACT: Storage and handling of toxic wastes is a toppriority challenge for sustainable development and public health. In recent years, the risk of irreversible environmental pollution has been increasing gradually, necessitating the development of new concepts in this highly demanding area. Here, we report a flexible approach to address the problem using tunable ionic liquids as a carrier and storage medium for chemicals. Encapsulation in microscale tunable media surrounded by an inert ionic liquid facilitates the efficient capture of chemicals. The adaptive character of the designed microscale compartments opens new possibilities for the waste management of chemicals of a diverse nature. Real-time field-emission scanning electron microscopy was used to visualize the formation of microscale compartments upon the sequestration of chemicals in ionic liquids. Ionic liquids captured the chemicals better than traditional organic solvents or water; moreover, the chemicals subsequently could be effectively extracted for destruction or utilization. Our work presents a new model for the sustainable management of chemical wastes; the concept was evaluated for a number of multiton chemicals currently affecting our environment. KEYWORDS: Waste management, Chemical waste, Waste storage, Pollution, Ionic liquids, Electron microscopy

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complexation, and inclusion in a stable medium.1,15−17 Biodegradation is considered as one of the most promising strategies for the treatment of contaminants.18,19 However, a crucial point for hazardous waste management is safe storage in dedicated containers with suitable toxicity carriers, which are necessary for transportation and subsequent destruction (Figure 1a).1,20,21 It should be emphasized that suitable toxicity

INTRODUCTION Numerous chemicals are routinely released into the air, water, and soil, thereby influencing the environment and, directly or indirectly, human life. These chemicals can penetrate into gaseous, liquid, and solid media and can exhibit profound harmful effects. Even if present at trace levels, their adverse effects on aquatic and terrestrial life cause significant alarm. Pesticides1,2 and active pharmaceutical ingredients (APIs)3,4 have been attracting much attention lately due to a constant increase of their usage all around the world. Metabolized and dissolved APIs are found in sewage waters, as well as in freshwater sources.5,6 Of great concern is the accumulation of large quantities of hazardous metabolized chemicals in the farmlands of many rapidly developing countries, where a significant part of the land is contaminated with pesticides and herbicides.7,8 If a chemical dissolves in water, it can rapidly penetrate biosystems and can end up very far from the site of the initial pollution. Even chemicals with low water solubility can permeate various ecological systems, albeit slowly, and can accumulate in significant amounts over time.9−12 Compounds with negligible water solubility can impose harmful impacts on the environment due to different mechanisms, some of which occur at the nanotoxicological level and are yet to be studied in detail.13,14 In recent decades, several methods of waste removal have been developed, including extraction, adsorption, precipitation, © 2017 American Chemical Society

Figure 1. Traditional hazardous waste storage in containers (a), supplemented with microscale compartments in an ionic liquid medium used as a carrier (b). Received: August 31, 2017 Revised: October 19, 2017 Published: November 21, 2017 719

DOI: 10.1021/acssuschemeng.7b03036 ACS Sustainable Chem. Eng. 2018, 6, 719−726

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ACS Sustainable Chemistry & Engineering

performed with PFTBA (MS-grade, Synquest Laboratories) in the automatic mode. Measurements were performed in the full-scan mode (scan range from m/z 35 to m/z 500) with the ionization energy set at 70 eV, source temperature set at 230 °C, and transfer capillary temperature set at 300 °C. Separation was carried out in an Agilent HP-5 ms fused silica capillary column (30 m length; 250 μm I.D.; 0.25 μm film thicknesses, (5% phenyl)-methylpolysiloxane) using He (6.0 grade, NII KM) as a carrier gas with the flow set at 1 mL/min. The temperature program was started at 60 °C and fixed for 2 min and then was increased at a rate of 20 °C/min to 300 °C and held for 5 min. The injection port temperature was set at 300 °C and operated in the split mode at a 10:1 ratio with a sample injection volume of 1 μL. The spectra were processed using the Agilent MassHunter B.06.00 software package. Sample Preparation for FE-SEM Observation. For reproducing the data with a model ionic liquid−water system, [C4MIM][BF4] (0.09 or 0.08 mL) and water (0.01 or 0.02 mL for 10 vol % or 20 vol % solutions, respectively) were stirred vigorously for 5 min in a standard 1.5 mL plastic tube. For FE-SEM investigations of model compounds (sodium hydroxide, naphthalene, glycine and casein), 0.001 g of a target compound was mixed with 0.1 g of [C4MIM][BF4]/H2O (9:1) or [C4MIM][OAc] in a 2.5 mL glass tube; in the case of sulfuric acid, 0.001 mL was mixed with 0.1 mL of [C4MIM][BF4]/H2O (9:1) or [C4MIM][OAc]). The mixture was stirred for 1 h at room temperature (r.t.). For experiments with toxic compounds, washing powder (0.01 g), amoxicillin (0.02 g), dichlorodiphenyltrichloroethane (DDT; 0.02 g), glyphosate (0.02 g), malathion (0.05 g), or a mixture of chlorobenzene, bromobenzene, and 1,3-dichlorobenzene (volume ratio 1:1:1, 0.021 mL) was mixed with the [C4MIM][BF4]/water system (9:1; 0.5 mL) and was stirred for 1 h at r.t. In the case of [C4MIM][OAc], washing powder, amoxicillin, DDT, malathion, or glyphosate (0.02 g) or a mixture of chlorobenzene, bromobenzene, and 1,3-dichlorobenzene (1:1:1, 0.021 mL) was mixed with 0.5 mL of the ionic liquid and was stirred for 1 h at r.t. If the compound did not completely dissolve in the ionic liquid system, the final mixture was centrifuged until a clear solution was obtained. The resulting solution was applied to a copper TEM grid (200 or 300 mesh) using a micropipette, and an excess of the solution was removed from the grid surface. Permeability Test. For each experiment, specially designed glass U-tubes were used (see Figures S1 and S2 in the Supporting Information). The tubes were preliminarily blown by argon and then were filled with 0.4 g of water or ionic liquid. Then, a toxic compound (0.004 g, 1 wt %) was placed into the left shoulder of the tube, and both ends were sealed with plastic film. The system was kept at r.t. Samples were taken from the right shoulder of the tube at specified time points (every 2 h), and NMR spectra were recorded for the water medium and ionic liquid (in deuterated water with the suppression of the water signal, using 3-(trimethylsilyl)-1-propanesulfonic acid sodium salt ((CH3)3Si(CH2)3SO3Na) as an internal standard). For the ionic liquid medium, the first 24 h of monitoring did not reveal traces of the compounds in any sample. We continued to register spectra every 24 h for a week, but still no traces were registered. Additionally, the gas phase from the right shoulder was checked by gas chromatography−mass spectrometry (GC-MS), and no traces of the compounds were found in the samples with [C4MIM][BF4]/water. Extraction. A mixture of 0.01 g of a compound of interest and 1 mL of [C4MIM][BF4]/H2O (9:1) was stirred vigorously for 1 h at r.t. in a 2.5 mL glass tube equipped with a magnetic stir bar. All the compounds demonstrated good solubility in the media applied. Then, an organic solvent (diethyl ether) was added to the mixture, and the system was stirred for 1 min. After that, the stirring was stopped, and the top organic layer was removed. This procedure was repeated at least five times. The extracts were combined, and the solvent was evaporated. The overall mass of the extracted compound was measured, and the purity was checked by 1H NMR. The additional optimization of the conditions is described in the Supporting Information.

carriers must meet a number of challenging requirements, such as an inert nature, stability, retention capability, universal/ tunable solvation properties, and an inability to penetrate into the atmosphere. Not surprisingly, universal and versatile toxicity carriers for efficient waste storage are very difficult to design. Moreover, the possibility of subsequent recovery of a stored toxic substance can present considerable advantages, though it is extremely difficult to achieve. Due to their fascinating solvating properties,22−24 ionic liquids have been suggested to be used for the processing of spent organic solvents,25 mercury,26 radioactive substances,27−29 pharmaceuticals,30 and other toxic chemicals.31 In a recent work, a dynamic phenomenon in aqueous ionic liquid systems was described for controlling the solvent behavior.32 Dynamic microscale processes occur in ionic liquid-water systems during extraction.33 Water tends to form various structures, depending on its concentration in the ionic liquid, and these structures possess high levels of micro- and nanoscale organization in ionic liquid/water mixtures.34−40 High efficiency of ionic liquid-water mixtures for processing plant biomass was demonstrated.32 Moreover, production costs of ionic liquids are decreasing rapidly,41 and the possibility of their recycling also can significantly alleviate the expenses.42,43 In the current work, we report microscale-optimized ionic liquid systems for dealing with waste storage. We have found that self-organized microstructures are involved in solvent− solute interactions and provide an amazing opportunity for trapping of chemical compounds. Thus, ionic liquids that do not exhibit significant environmental toxicity can be used as excellent toxicity carriers (Figure 1b) compatible with modern hazardous waste storage containers (Figure 1a). Here, we also describe the controllable nature of the microscale compartments formed in the ionic liquid. Therefore, ionic liquid toxicity carriers allow not only the storage of a potentially harmful substance within a restricted microscopic volume but also its subsequent extraction for destruction or utilization.

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EXPERIMENTAL SECTION

Materials and Measurements. Ionic liquids were purchased from Sigma-Aldrich (1-butyl-3-methyl imidazolium acetate, [C4MIM][OAc]) and ABCR, Germany (1-butyl-3-methyl imidazolium tetrafluoroborate, [C4MIM][BF4]). Reagents from commercial sources were checked by NMR and chromatography before use. The stability of the ionic liquids under the conditions used in the study (at r.t.), as well as at higher temperatures (heating for 1 h at 60 °C), was verified by 1H, 13C, and 19F NMR and ESI-MS. 1 H and 13C NMR data were collected on Bruker AV 600 and Bruker Avance III 400 spectrometers operating at 600.1 and 400.1 MHz for 1 H and 150.9 and 100 MHz for 13C nuclei, respectively. The NMR chemical shifts are reported relative to the corresponding deuterated solvent signals. The spectra were processed using the Bruker Topspin 2.1 software package (Bruker). Scanning electron microscopy (SEM) measurements were performed on a Hitachi SU8000 field-emission scanning electron microscope. Images were acquired in the secondary electron mode at a 2 kV accelerating voltage. Field-emission scanning electron microscopy (FE-SEM) video recording was conducted using an Epiphan DVI2USB3.0 video capture device. The video stream from a built-in HP workstation was redirected to a video capture device and recorded with the Epiphan Frame Grabber software (version 3.29.1.0) installed on a laptop. The videos were acquired in the secondary electron mode at a 2 kV accelerating voltage using the fast scanning mode (12.5 frames/s). Mass spectra were measured on an Agilent 5977A quadrupole instrument using an electron ionization source with sample injection via an Agilent 7890 gas chromatograph. External calibration was 720


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Figure 2. Schematic 3D representation (top) and experimental FE-SEM images (bottom) of [C4MIM][BF4]/water system without added water (a), with 10 vol % of added water (b), and with 20 vol % of added water (c).

Figure 3. Structures of selected compounds used in the study.

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RESULTS AND DISCUSSION From the viewpoint of the microscale optimized waste storage proposed in the present work, three models can be realized in the ionic liquid/water system: (a) molecular storage, (b) encapsulation in microvesicles, and (c) retention in microchannels (Figure 2). The morphology of the microscale compartments can be controlled by the nature of the ionic liquid and by the amount of the added water. A series of dedicated field-emission scanning electron microscopy (FESEM)32 experiments was performed here for the characterization of these possibilities using a model system with the [C4MIM][BF4] ionic liquid. A dry ionic liquid without added water has a uniform surface (without detectable particles) and can be considered as a medium for molecular storage (Figure 2a). The addition of 10 vol % water leads to the formation of small droplets of approximately 0.5−15 μm in diameter, which are suitable for the encapsulation of various compounds (Figure 2b). An

increase of the water content to 20 vol % promotes microchannel formation and creates meshwork-like storage compartments (Figure 2c). It should be mentioned that both the droplets and channels have microheterogeneous inclusions, which provide an additional level of structural organization (see also Figure S3). Droplets and microchannels observed in the [C4MIM][BF4]/water system present spatially suitable compartments for the storage of toxic substances. First, in order to assess the applicability of the developed approach, we used a set of 1 wt % solutions of model compounds in the mixed [C4MIM][BF4]/ water system with a microvesicle-type intrinsic structure. Inorganic (sodium hydroxide, sulfuric acid), organic (naphthalene, glycine), and biomolecular (casein) substances were investigated to cover a broad range of molecules (Figure 3). Samples were prepared simply by stirring the compound of interest with the [C4MIM][BF4]/water system for 1 h at r.t. 721


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Figure 4. FE-SEM images of 1 wt % (1% vol. for sulfuric acid) solutions of various compounds in the mixture of [C4MIM][BF4] and 10 vol % water.

Figure 5. Snapshots taken from FE-SEM videos reflecting dynamic processes in the NaOH−[C4MIM][BF4]/H2O system under electron beam irradiation (see Supporting Information for video).

SEM video in a direct microscopic study of the samples (see Figure 5 and Figures S7 and S8 for snapshots and the Supporting Information for video). The study of the dynamics demonstrated that the droplets and inclusions moved synchronously and behaved integrally. Therefore, we observed that the addition of a model waste compound to a preformed two-component ionic liquid−water system initiated solvent−solute interactions reflected at the microscale level. A variety of different types of morphologies (such as droplets with inclusions and solid-phase and liquidphase meshworks) were accessible, suggesting a promising tunable potential for the studied system. At the next step, we examined solutions of toxic compounds in the [C4MIM][BF4]/water mixture and in pure [C4MIM][OAc]. As shown above, [C4MIM][BF4] in the mixture with water represented an excellent tunable medium for storage in microcompartments. However, the achievement of a real waterfree or water-independent morphology for this ionic liquid was a complicated task since even trace amounts of water had a significant impact on the morphology of this ionic liquid. To resolve this problem, [C4MIM][OAc] was chosen as a reference homogeneous medium instead of “pure” [C4MIM][BF4], because water traces did not create any additional morphology in [C 4 MIM][OAc] (see Figure S9). Six representative compounds potentially dangerous to the environment were chosen: amoxicillin (antibiotic); washing powder (detergent); a 1:1:1 mixture of chlorobenzene, bromobenzene, and 1,3-dichlorobenzene (halogenated aromatic compounds); the isopropylamine salt of glyphosate (herbicide and crop desiccant); malathion (insecticide, also known as carbophos); and DDT (illicit insecticide) (Figure 3). Our experimental study showed that all the compounds were held tightly in the ionic liquid system. The morphology and dynamic nature of these compounds in the ionic liquid medium

After mixing with the [C4MIM][BF4]/water system, sulfuric acid and naphthalene gave clear, colorless solutions. A mixture of sodium hydroxide with the ionic liquid system changed color from colorless to yellow and turned colorless again after longer stirring. Glycine and casein formed suspensions in the studied ionic liquid system. Samples were taken from each solution and were subjected to electron microscopy study (see Experimental Section for details). Initially, dissolution of model compounds in one or several phases of the [C4MIM][BF4]/water system was proposed, but the FE-SEM study of the solutions revealed the amazing tunability of the storage mode (Figure 4). The major observed changes were an increase in the amount of solid phase (sodium hydroxide, naphthalene, casein), growth of meshwork (sulfuric acid), and complete homogenization (glycine). The typical microstructures observed were microsized droplets with inclusions (Figure 4, initial ionic liquid/water mixture and solution of casein), web-like aggregates (Figure 4, solutions of sodium hydroxide and naphthalene), and a perforated liquid film (Figure 4, solution of sulfuric acid; see also Figures S4− S6). The obtained microscopy results clearly showed that for the microheterogeneous IL/water system, an addition of the third component led to the shift of equilibrium and redistribution of water, most likely in a thermodynamically favorable manner. Presumably, during the establishment of equilibrium, water microcompartments acted as a source of water for newly formed phases with independent morphology: microsized structures with a solid/liquid interface, liquid films, or undetectable submicrosized (possibly, molecular) species. The microdroplets and microchannels in the ionic liquid medium demonstrated dynamic behavior, which retained the ability for tuning these systems for different types of solvent− solute capture. Such dynamic behavior was detected by a FE722


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Figure 6. FE-SEM images of solutions of various toxic chemical compounds (amoxicillin, glyphosate, washing powder, malathion, aromatic compounds, and DDT) in the mixture of [C4MIM][BF4] and 10 vol % water (a) and in [C4MIM][OAc] (b).

morphologies were obtained for [C4MIM][OAc] without added water. In this case, washing powder and the aromatic compounds formed predominantly homogeneous mixtures (Figure 6b and Figures S13 and S15). Amoxicillin, glyphosate, and malathion dissolved to form microdroplets from 1 μm to several dozens of micrometers in diameter. Big droplets more than 10 μm in diameter (along with the smaller ones) were observed for amoxicillin and glyphosate, whereas small droplets of approximately 1−5 μm in diameter were detected in the case of malathion (Figure 6b and Figures S13−S14). As in the previous case, the DDT-containing system consisted of microchannels (Figure 6b and Figure S15). Some systems were highly flexible under electron beam irradiation and allowed the observation of dynamic processes in the video mode (see Figure S16 and video in the Supporting Information). On the basis of the microcopy data, the following conclusions can be made. For the water-soluble compounds (amoxicillin, glyphosate, and washing powder), the difference in morphology in the hydrated and dry media was quite obvious. An addition of water led to an increase of dispersity of the toxic compounds: a uniform solution was formed instead of microdroplets; liquid microdroplets were formed instead of solid particles. For the poorly water-soluble compounds (malathion, aromatic compounds, and DDT), an addition of

were investigated, and the micro- and nano-organized structures were characterized. The washing powder, amoxicillin, and malathion produced suspensions in hydrated [C4MIM][BF4] or neat [C4MIM][OAc]; the resulting solutions contained small amounts of a dispersed solid phase, assumedly inorganic species present in the commercial specimens. A suspension was also observed in the case of DDT in the [C4MIM][BF4]/water mixture, while a visually homogeneous solution was observed in the pure [C4MIM][OAc]. The aromatic compounds and glyphosate formed homogeneous clear solutions in both cases. Electron microscopy reaffirmed the structural variations in the morphology of the resulting solutions (Figure 6). A microheterogeneous [C4MIM][BF4]/water mixture turned homogeneous upon the addition of amoxicillin or glyphosate (Figure 6a and Figure S10). Washing powder and malathion resulted in the formation of a microdroplet morphology from 1 μm to several dozens of micrometers in diameter (Figure 6a and Figure S11). The dissolution of the aromatic compounds resulted in the formation of small agglomerated particles less than 100 nm in diameter, whereas microdroplets were not detected. Microchannels were observed in the case of the DDT[C4MIM][BF4]/water system (Figure 6a and Figure S12). The amount of added water could be an efficient tool for controlling the nature of the system. Different solution 723


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ACS Sustainable Chemistry & Engineering water did not change the morphology of the resulting solution considerably. Thus, for the hydrophilic substances, water played a crucial role in the formation of microcompartments; however, the preformation of microdroplets and microchannels did not have a significant impact on the final morphology of the threecomponent system, because in the complex mixture an addition of a new component led to a subsequent shift of equilibrium and formation of a new stable morphology. The issue of stability of IL and IL/water mixtures was also addressed. Under the studied conditions (at r.t.), [C4MIM][BF4]/water and [C4MIM][OAc] mixtures were found stable, as evidenced by 1H, 13C, and 19F NMR and ESI-MS. To demonstrate the remarkable ability of ionic liquids to decelerate the penetration of toxic substances, a set of experiments was carried out in comparison with water. The permeability of potentially dangerous model compounds was evaluated in an ionic liquid system and pure water (Table 1). All experiments were performed in a glass U-shaped tube, into which test substances were introduced via one shoulder (see Figure S2 in the Supporting Information for detail).

Table 2. Extraction of Dissolved Compounds from [C4MIM][BF4]/H2O by Diethyl Ether

entry

compound

1 2 3 4 5 6

diisopropylphosphite pyridine SDS butylamine glyphosate metribuzin

6 8 22 27 27 102

time of penetration through [C4MIM] [BF4]/water, h ND ND ND ND ND ND

compound

efficiency of extraction, %a

1 2 3 4

aromatic compounds malathion (carbophos) metribuzin DDT

99 99 99 99

a

Structures of the studied compounds are shown in Figure 3; efficiency of extraction = m(extracted) × m(loaded)−1 × 100%; see Supporting Information for details.

lipophilic molecules and lipid membranes and to influence their morphology, whereas ionic liquids with short alkyl chains do not exhibit such an effect.44−48 The water in ionic liquid can be a crucial determinant of the formation of microstructures in a three-component system (ionic liquid−water−solute).32,33,44 Water molecules form hydrogen-bond networks at charged interfaces and also interact with ionic liquids, thus changing the possible arrangement between the ionic liquid and dissolved compounds. This observation can also apply to bulky charged solutes, such as proteins, for which the presence of some amounts of water is often necessary for retaining the native structure.44,49−51 In this case, the water shell encloses the protein molecule protecting it (to some degree) from the ionic liquid environment. Thus, intrinsic flexibility and tunability of ionic liquids, combined with the extra degree of controlled structuring achieved by the addition of water, gives an impressive opportunity for the design of 3D microcompartments.

Table 1. Time of Diffusion of Toxic Compounds through the Layer of Water or [C4MIM][BF4]/Watera time of penetration through water, h

entry

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CONCLUSIONS A microscopic FE-SEM study demonstrated that various microscale compartments were accessible in the ionic liquid/ water systems: (1) capsules and micelles, (2) channels and networks, and (3) hybrid systems, which combined different structures. The dynamic and tunable nature of these soft microsized compartments provides an excellent possibility for the controlled storage of toxic wastes. High chemical stability,52 excellent thermal stability,53−55 low vapor pressure,24,53,54 radiation stability,56−58 easy recycling and reuse,42,54 inability to penetrate into the gas phase (atmosphere),24,54 compatibility with biomolecules,49,59 and flexibility in tuning of physical and chemical properties44,60 are well-known characteristics of ionic liquids. A combination of these properties renders ionic liquid systems a practical carrier for waste management with an outstanding potential. The present study confirmed the ability of ionic liquid-based carriers to hold toxic compounds within their volume, apparently due to the tunable interactions between the cations and anions of the ionic liquid and the solute molecules. The excellent retention properties of the ionic liquids were confirmed experimentally, and the possibility of the recovery of dissolved chemicals from the ionic liquid carriers was demonstrated. The storage of chemical compounds in the microscale tunable environment surrounded by an inert ionic liquid adds an additional level of safety to standard waste containers (Figure 1). The morphology of the microscale environment can be controlled simply by varying the amount of added water. The diverse molecular scope (Figure 3) suggests a plausible application of ionic liquids for handling of a broad range of

a

See Figures S17−S19 in the Supporting Information for details; ND, not detected in 1 week.

Diisopropylphosphite passed through the water layer faster than the other studied compounds: its traces were detected in 6 h (entry 1, Table 1). The appearance of pyridine was detected in 8 h (entry 2, Table 1), sodium dodecyl sulfate (SDS) in 22 h (entry 3, Table 1), butylamine and glyphosate in 27 h (entries 4 and 5, Table 1), and metribuzin in 102 h (entry 6, Table 1). However, none of the studied compounds penetrated through the [C4MIM][BF4]/water layer of the same thickness (Table 1). Even after 1 week of storage, none of the compounds had penetrated through the ionic liquid system, as detected by NMR and GC-MS. The possibility of recovering a chemical of interest after storage is attractive from the economic and sustainability points of view. To corroborate this idea, the recovery of chemicals stored in the ionic liquid/water system was addressed using a simple and practically convenient extraction process. The dissolved compounds were easily recovered by extraction to the organic phase. Remarkably, a complete recovery was observed for the aromatic compounds, malathion, metribuzin, and DDT (Table 2). An analytic study showed that the structure of the ionic liquid did not change during the storage or extraction process. Thus, ionic liquids could be reused again to ensure the cost-efficiency and sustainability of the process. Overall, it should be noted that the nature of the ionic liquid and the solute do have a significant impact on the interactions between them. It is known that ionic liquids with cations carrying long alkyl chains are prone to interacting strongly with 724


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(5) Jones, O. A.; Lester, J. N.; Voulvoulis, N. Pharmaceuticals: a threat to drinking water? Trends Biotechnol. 2005, 23 (4), 163−167. (6) Mutiyar, P. K.; Mittal, A. K. Risk assessment of antibiotic residues in different water matrices in India: key issues and challenges. Environ. Sci. Pollut. Res. 2014, 21 (12), 7723−7736. (7) Lu, Y.; Song, S.; Wang, R.; Liu, Z.; Meng, J.; Sweetman, A. J.; Jenkins, A.; Ferrier, R. C.; Li, H.; Luo, W.; Wang, T. Impacts of soil and water pollution on food safety and health risks in China. Environ. Int. 2015, 77, 5−15. (8) Strokal, M.; Ma, L.; Bai, Z.; Luan, S.; Kroeze, C.; Oenema, O.; Velthof, G.; Zhang, F. Alarming nutrient pollution of Chinese rivers as a result of agricultural transitions. Environ. Res. Lett. 2016, 11 (2), 024014. (9) Craig, P. J. Organometallic Compounds in the Environment; WileyVCH Verlag GmbH & Co. KGaA: Great Britain, 2003. (10) Merian, E.; Anke, M.; Ihnat, M.; Stoeppler, M. Elements and Their Compounds in the Environment, 2nd ed.; Wiley-VCH Verlag GmbH & Co. KGaA: Weinheim, 2004. (11) Nordberg, G. F.; Fowler, B. A.; Nordberg, M. Handbook on the Toxicology of Metals, 4th ed.; Elsevier: London, 2015. (12) Barra Caracciolo, A.; Topp, E.; Grenni, P. Pharmaceuticals in the environment: biodegradation and effects on natural microbial communities. A review. J. Pharm. Biomed. Anal. 2015, 106, 25−36. (13) Egorova, K. S.; Ananikov, V. P. Which metals are green for catalysis? Comparison of the toxicities of Ni, Cu, Fe, Pd, Pt, Rh, and Au salts. Angew. Chem., Int. Ed. 2016, 55 (40), 12150−12162. (14) Nel, A.; Xia, T.; Mädler, L.; Li, N. Toxic potential of materials at the nanolevel. Science 2006, 311 (5761), 622−627. (15) Albelda, M. T.; Frias, J. C.; García-España, E.; Schneider, H. J. Supramolecular complexation for environmental control. Chem. Soc. Rev. 2012, 41 (10), 3859−3877. (16) Shah, A.; Shahzad, S.; Munir, A.; Nadagouda, M. N.; Khan, G. S.; Shams, D. F.; Dionysiou, D. D.; Rana, U. A. Micelles as soil and water decontamination agents. Chem. Rev. 2016, 116 (10), 6042− 6074. (17) Clarke, D. R. Ceramic materials for the immobilization of nuclear waste. Annu. Rev. Mater. Sci. 1983, 13 (1), 191−218. (18) Fuchs, G.; Boll, M.; Heider, J. Microbial degradation of aromatic compounds - from one strategy to four. Nat. Rev. Microbiol. 2011, 9 (11), 803−816. (19) Harms, H.; Schlosser, D.; Wick, L. Y. Untapped potential: exploiting fungi in bioremediation of hazardous chemicals. Nat. Rev. Microbiol. 2011, 9 (3), 177−192. (20) Tarr, M. A. Chemical Degradation Methods for Wastes and Pollutants; Marcel Dekker, Inc.: New York, 2003. (21) Blackman, W. C., Jr. Basic Hazardous Waste Management, 3rd ed.; Lewis Publishers: Boca Raton, FL, 2001. (22) Welton, T. Room-temperature ionic liquids. Solvents for synthesis and catalysis. Chem. Rev. 1999, 99 (8), 2071−2084. (23) Plechkova, N. V.; Seddon, K. R. Applications of ionic liquids in the chemical industry. Chem. Soc. Rev. 2008, 37 (1), 123−150. (24) Hallett, J. P.; Welton, T. Room-temperature ionic liquids: solvents for synthesis and catalysis. 2. Chem. Rev. 2011, 111 (5), 3508−3576. (25) Moodley, K.; Mabaso, M.; Bahadur, I.; Redhi, G. G. Industrial application of ionic liquids for the recoveries of spent paint solvent. J. Mol. Liq. 2016, 219, 206−210. (26) Abai, M.; Atkins, M. P.; Hassan, A.; Holbrey, J. D.; Kuah, Y.; Nockemann, P.; Oliferenko, A. A.; Plechkova, N. V.; Rafeen, S.; Rahman, A. A.; Ramli, R.; Shariff, S. M.; Seddon, K. R.; Srinivasan, G.; Zou, Y. An ionic liquid process for mercury removal from natural gas. Dalton Trans. 2015, 44 (18), 8617−8624. (27) Wang, Y.; Tong, J.; Wu, W.; Lu, Y. Halogen bonds between I2 and ion pairs: Interpreting the ability of ionic liquids in efficient capture of radioactive iodine. Comput. Theor. Chem. 2014, 1049, 97− 101. (28) Yan, C.; Mu, T. Investigation of ionic liquids for efficient removal and reliable storage of radioactive iodine: a halogen-bonding case. Phys. Chem. Chem. Phys. 2014, 16 (11), 5071−5075.

chemicals, which are expected to distribute within the environment according to their nature.33 Here, we demonstrate the applicability of ionic liquid-water systems for tunable storage of chemicals with the possibility of adjusting the property of the media and back recovery of stored chemicals. The findings strongly support the excellent potential of ionic liquids in the field of waste storage. Of course, one should not overestimate the results reported in the present mechanistic study. It should be noted that this work presents only the first step toward the development of sustainable waste management in tunable media. The development of a practical solution would require addressing various aspects of this concept, and more detailed studies are needed in connection with the particular waste treatment technology. It should be pointed out that similar processes may also occur in the systems dealing with extraction and separation processes in ionic liquids, which represent important practical applications. Formation of microscale compartments and redistribution of solute molecules between different domains in ionic liquids (polar domains, nonpolar domains, water droplets, etc.) may have a significant impact on the extraction/ separation processes.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.7b03036. Electron microscopy images, NMR spectroscopy data, details on permeability and extraction experiments (PDF) Dynamic processes in NaOH-[C4MIM][BF4]/H2O system under electron microscopy detection (AVI) Dynamic processes in glyphosate-[C4MIM][BF4]/H2O system under electron microscopy detection (AVI)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Valentine P. Ananikov: 0000-0002-6447-557X Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Mechanistic studies were supported by the Russian Science Foundation (RSF grant 14-50-00126). The part of the work related to synthesis and application was supported by the Russian Foundation for Basic Research (grant 16-29-10804).

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REFERENCES

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