PEGylated Quasi-Ionic Liquid Electrolytes: Fundamental

Research Article pubs.acs.org/journal/ascecg

PEGylated Quasi-Ionic Liquid Electrolytes: Fundamental Physiochemical Properties and Electrodeposition of Aluminum Jingyun Jiang,† Wancheng Zhao,† Zhimin Xue,‡ Qingbo Li,† Chuanyu Yan,† and Tiancheng Mu*,† †

Department of Chemistry, Renmin University of China, Beijing 100872, China Beijing Key Laboratory of Lignocellulosic Chemistry, College of Materials Science and Technology, Beijing Forestry University, Beijing 100083, China

‡

S Supporting Information *

ABSTRACT: PEGylated quasi-ionic liquid electrolytes were obtained by simply mixing organic/inorganic salts and lowmolecular-weight poly(ethylene glycol) (PEG 200, 300, 400) at room temperature. There were 14 salts investigated in this paper, and most of them were soluble in PEGs. The different solubilities of salts in PEGs may be due to their interactions between the composed organic cations/anions and the PEG chains. The proposed quasi-ionic liquids were proven to have good physiochemical properties including negligible volatility, low viscosity (about 50 mPa s), intrinsic conductivity, and wide electrochemical window (>2.5 V). Moreover, the electrolytes can be used inter alia for electrochemical applications, such as the electrodeposition of aluminum. Homogeneous, high-purity, adherent aluminum layers were obtained at low potential (−0.2 V) and room temperature (303.15 K). The developed PEGylated quasi-ionic liquid electrolytes offer a new system to easily co-deposit the active metal, such as Zn, Mg with high performance at low potentials. KEYWORDS: Ionic liquid, Electrolyte, PEG, Thermodynamics, Physicochemical property, Electrodeposition

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INTRODUCTION The concept of green and sustainable chemistry has drawn tremendous attention during the past decade.1,2 One of the key points of green chemistry is the development and application of green solvents.3 Water, ionic liquids, deep eutectic solvents, and poly(ethylene glycol) (PEG, H(OCH2CH2)nOH) have been widely used as green solvents in extraction and separation,4,5 materials preparation,6−8 chemical reactions,9,10 pharmaceutical industry applications,11 and electrochemical applications.12−15 Nonaqueous solvents are essential in electrochemical applications due to the wider potential and higher energy capacity compared with water.16 Ionic liquids13,17 and deep eutectic solvents12 have been widely used in electrochemical processes owing to the high electrical conductivity and wide electrochemical window. However, the commonly used ionic liquids are generally expensive and viscous,18 and have uncertain influences on environments and ecosystems,19 and deep eutectic solvents usually have a high melting temperature (typically need additional heating even up to 373 K at the mixture process),20 which unfortunately hinders their applications in electrochemistry. Liquid PEGs with low molecular weight (3 g per 100 g) in PEGs and one-third of all determined solubilities are around or less than 1 (g salt per 100 g), which indicate that the PEGs do not have comparable dissolving abilities for salts with water (Table S1). For all of the investigated systems, the solubilities of salts in water are on average 16 times higher than that in PEG 200. However, the order of solubilities of salts in PEG 200 is apparently in accord with that in water. For example, for sodium salt in PEG 200 (Figure S1), the solubilities decrease in the following order: NaSCN > CH3COONa > NaClO4 > NaNO3 > NaNO2 > NaClO3 > NaBr > HCOONa > NaCl, which is in accord with that in water (NaClO4 > NaSCN > NaClO3 > HCOONa > NaBr > NaNO3 > NaNO2 > CH3COONa > NaCl). In particular, the PEGylated quasiionic liquid electrolyte, no matter whether it has higher or

lower solubility, stays in the primary state without any precipitation even after six months, which partly proved that the salt was dissolved but not dispersed in the PEGs (Figure S2). The distinct solubilities of different salts in PEGs due to their interactions between the composed organic cations/anions and PEG chains can be partly proved by the 1H nuclear magnetic resonance (NMR) chemical shifts of PEG 200 with different salts (Figure S3). 1H NMR measurements of pure PEG, and a series of salt-in-PEG electrolytes, were carried out at 298.15 K, and the changes in chemical shift of individual hydrogen atoms after the dissolution process were evaluated. As can be seen in Figure 2a, the chemical shift variations of the terminal alcoholic groups on PEG are positive which states that the chemical shifts of hydroxyl hydrogen atoms on PEG gradually move downfield with the addition of salts. Cations (NH4+, Na+, K+) are coordinated with the ether oxygen from PEG which results in the bend of the PEG chain24−26 and the formation of new cation containing species.27 The peak for the terminal alcoholic groups in salt-in-PEG electrolytes was shifted downfield, which is attributed to the hydrogen bonding between the anions and the terminal alcoholic groups from PEG.24,28 The IR spectra 5815

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systems are in the range 48−53 mPa s at 298.15 K, while the corresponding viscosities of the commonly used ionic liquids reach 273 mPa s for [BMIM][PF6]32 and 110.308 mPa s for [BMIM][BF4],33 which is much higher than that of PEGylated quasi-ionic liquid electrolytes. Because low viscosity is a significant advantage for an electrolyte in electrochemical applications, the very low viscosities of as-proposed conductive salt-in-PEG electrolytes should be sought as a priority. Figure 2b shows that the viscosities of salt-in-PEG electrolytes fit well to a variation of the chemical shifts. Since the viscosity is mainly determined by ion volume and the interaction between the ion and PEG chain, a variation of viscous behavior can be understood by the reciprocity of Coulomb and van der Waals interactions as well as hydrogenbond destruction.34 As mentioned previously, the intermolecular hydrogen bond of PEG was disturbed by the new hydrogen bond between the anions and the terminal alcoholic groups from PEG. The conductivity of an electrolyte is another crucial factor in electrochemical applications. The evolution of conductivity can be owed to several aspects, such as the geometrical and electronic structure of the cation and anion, hydrogen-bond interactions, diffusion coefficient of the proton, and viscosity.35 Molar conductivity, the degree of cation−anion aggregation, is defined as the measured conductivity of the electrolyte solution (κ) divided by the molar concentration of the electrolyte (c)

Λ m = κ /c

(1) −2

where Λm is molar conductivity in S mol m , κ is the measured conductivity in μS cm−1, and c is the molar concentration in mol dm−3. As Table 1 shows, the molar conductivities of salt in PEG were about 1/10th of that of salt in water, which may due to the lower mobility of ions in PEG compared with water. Salts consisting of weak acid radical (HCOO−, CH3COO−) or weak base radical (NH4+), as 1H NMR depicted, have larger interactions with PEG while also having lower molar conductivities. The electrochemical windows of PEG 200 combined with different salts (0.05 mol dm−3) were also measured, and the results are given in Table 1. The electrochemical window is defined as the potential range in which an electrolyte/solvent system does not get reduced or oxidized.13 Usually, the potentials at which specific current (cutoff current) densities (0.1 A cm−2) reached are identified as the electrochemical limits. Table 1 shows that PEG 200 associated with NaClO3 holds the widest window (4.93 V) while PEG 200 associated with NaNO2 has the narrowest window (2.94 V), which is wider than the PEGylated imidazolium ionic liquids.23 This order may contribute to the reductive ability of cations and the oxidation ability of anions involved in the sample.13 The wide electrochemical windows of salt-in-PEG electrolytes is an advantage compared with water because PEG is more electrochemically stable than water. Both the coordination ability of the anion with the ethyl oxygen group and the hydrogen-bonding ability of the cation with terminal hydroxyl groups influence the electrochemical windows. Electrodeposition of Aluminum. Since the PEGylated quasi-ionic liquid electrolytes have low viscosity, wide electrochemical window, and certain conductivity, they might be used as an excellent electrolyte in electrochemical applications directly. KCl solution was widely used as electrolyte due to the relatively high conductivity and the small hydration sphere of K+ ion.36 So, to verify this hypothesis, the mixture of PEG

1

Figure 2. H NMR spectra (a) and chemical shift (δ, ppm) dependence on the viscosity (η, mPa s) (b) of PEGylated quasiionic liquid electrolytes.

experiments (Figure S4) of the PEGylated quasi-ionic liquid electrolyte were studied, and the results showed that both the ν(C−O−C) and ν(C−O−H) of PEG 200 had a slight blue shift which proved the weak interaction between the PEG and salts.29 Thermal gravimetric analysis experiments of the salt-inPEG electrolytes were also carried out, and the results (Figure S5) showed the decomposition pattern of these salt-in-PEG electrolytes is similar to that of the individual salt and PEG, which means that the systems are thermally stable and no strong interactions exist between salts and PEGs. Apart from the type of salt, the length of the PEG chain also plays an important role in the solubility. For most of the salts investigated here, the solubility decreased dramatically with the increase of the molecular weight of PEGs (Table S1). The solubilities of salt in PEG 400 can only reach on average 19% of that in PEG 200. This is because hydrogen-bonding activity is inversely related to the chain length at a fixed concentration of the OH groups in the blend.30 Thus, with the increase of the molecular weight of PEG, which possesses longer molecular chains, the dissolution ability for salts decreases. Transport Properties and Electrochemical Windows of the PEGylated Quasi-Ionic Liquid. The transport properties (viscosity and conductivity) and electrochemical window of an electrolyte are very important for electrochemical applications. Therefore, viscosities and conductivities of salt-inPEG systems were measured, and the results are presented in Table 1. The viscosity of pure PEG 200 is 48.012 mPa s which is in accordance with the literature.31 The slight difference could be caused by the origin of the PEGs. The viscosities of 5816

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ACS Sustainable Chemistry & Engineering 200 and KCl was selected as the solvent to dissolve aluminum(III) chloride and achieve the electrodeposition of Al. Al metal is industrially important because of its light weight, workability, and corrosion resistance. Al plating is not feasible from aqueous solutions because water is reduced and hydrogen is evolved prior to Al deposition. Electrodeposition of Al had been carried out in many kinds of nonaqueous systems including organic solvents37 and ionic liquids.38−41 However, those systems have some common drawbacks, such as the high electrodeposited temperature and the impurities in the Al coating. In addition, the toxicity and volatility of organic solvents, with the high viscosity and cost of ionic liquids, hinder the industrial use of Al coating. Therefore, cheap, green, conductive, and low-viscosity salt-in-PEG electrolytes are desirable candidates. We dissolve aluminum(III) chloride into the mixture of PEG 200 and KCl to form a new homogeneous system, which not only makes the electrodeposition of Al at room temperature but also decreases the cost. The concentration of aluminum(III) chloride played an important role in the electrodeposition of Al. For dipropyl sulfide-based IL, no deposition occurred when the concentration of aluminum(III) chloride was lower than 51.2 mol %,39 while for 1,3-dimethyl-2-imidazolidinone-based ILs, the limit concentration of aluminum(III) chloride was 50 mol %.41 However, a typical cyclic voltammetry (CV) records onto the Pt working electrode with the Al wire working as the reference and counter electrode in our system where the concentration of aluminum(III) chloride was 25 mol % (Figure 3a). Well-defined Al deposition/stripping peaks were obtained during the initial CV scan. The current loop observed in the CV (Figure 3a) which is characteristic of Al deposition indicated that the rate of Al deposition is mostly nucleation controlled.39

The increasing anodic current density was corresponding to the Al stripping at 400 mV, and the peak current density reached 50 mA cm−2 which was about 10 times higher than that of the dipropyl sulfide-based IL39 (5.1 mA cm−2) and 5 times higher than that in 4-propylpyridine-based IL38 (9 mA cm−2). Then, the as-proposed salt-in-PEG electrolytes were used for electroplating Al at 303.15 K, which was much lower than that for electrolytes alone (323.15 K for dipropyl sulfide-based IL;39 383.15 K for organic solvent−dimenthylsulfone37). A constant voltage of −0.2 V was applied on the copper sheet (the working electrode) with Al wire as both counter and reference electrodes. Homogeneous, bright, adherent Al layers were obtained after plating for only 1 h. The deposition potential may influence the morphology of Al (Figure 3b,d) and the thickness of the Al layers (Figure S6). As Figure 3b shows (the electrodeposition potential was −0.5 V), Al is apt to tetrahedron-type crystal growth, and the thickness of the Al layer is 4.5 μm (Figure S6a); at lower deposition potential (−0.2 V), Al trends to dendritic growth which was similar to what was described in previous reports,38,39 and the thickness is 4 μm (Figure S6b). The detailed nucleation mechanism needs further research. The 1 h electrodeposited film was further analyzed with EDX to confirm the composition. As shown in Figure 3c, the signals correspond to the substrate copper and the deposited Al without any impurities. In contrast, we performed electrodeposition of Al in commonly used ILs (1ethly-3-methylimidazolium chloride) under the same conditions. From the EDX image (Figure S7), an obvious Cl signal was observed which was in accordance with literature reports.40 In addition, trace amounts of impurities were observed in organic-solvent-based electrolyte.37 The ability to electrodeposit Al from this PEGylated quasi-ionic liquid electrolytes shows that the low-viscosity, conductive KCl in PEG/aluminum(III) chloride is a good candidate for the electrodeposition of aluminum.

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CONCLUSIONS In conclusion, we developed a class of green PEGylated quasiionic liquid electrolytes through the simple mixing of lowmolecular-weight PEG (200, 300, 400 g mol−1) and organic or inorganic salts at room temperature. Most of the studied salts are soluble in PEG, and both the type of the salts and the length of PEG chain influence the solubility. The 1H NMR data reflecting the terminal alcoholic groups in salt-in-PEG electrolytes were shifted downfield, partly proving the interaction between the PEG and salts. Transport characterization showed that all investigated systems with low viscosity, certain conductivity, and wide electrochemical windows could be further used in electrochemical applications. The KCl-in-PEG system was selected as an example electrolyte for the electrodeposition of Al. Homogeneous, bright, adherent Al layers were obtained after plating only 1 h at low potential. The demonstrated salt-in-PEG electrolytes offer a new system to easily co-deposit the active metal, such as Zn, Mg with high performance at low potentials.

Figure 3. Electrodeposition of Al. (a) Cyclic voltammogram of aluminum(III) chloride:KCl-in-PEG solvent at a molar ratio of 1:3 on a platinum working electrode with Al wire as both counter and reference electrode at 100 mV s−1. (b, d) Scanning electron microscopy (SEM) images of Al deposition on copper substrate. Electrodeposition was performed by the potentiostatic method [−0.2 V vs Al3+/Al (b); −0.5 V vs Al3+/Al (d)] in aluminum(III) chloride:KCl in PEG electrolyte at a molar ratio of 1:3 at 298.15 K. Inset is magnification of part b. (c) Energy dispersive X-ray spectroscopy (EDX) analysis of Al deposition on copper substrate.

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EXPERIMENTAL SECTION

Materials. PEGs (PEG 200, PEG 300, and PEG 400, all in A.R. grade) were obtained from Sinopharm Chemical Reagent Co., Ltd.. The PEGs were bubbled with high-purity N2 (99.999%) for 24 h to exclude the residue water before use. All of the inorganic salts with purities higher than 98% were obtained from J&K Scientific Ltd. and 5817

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ACS Sustainable Chemistry & Engineering were put in the vacuum oven for 4 h at 333.15 K to exclude the trace of water absorbed on the surface of salts. Characterization Methods. PEGylated quasi-ionic liquids were synthesized by the simple mixing of low-molecular-weight PEG (200, 300, and 400) with organic or inorganic salts (CH3COONH4, HCOONH4, CH3COONa, HCOONa, NH4Cl, NaClO4, NaClO3, NaNO3, NaNO2, NaSCN, NaBr, NaCl, KBr, KCl). The PEGs were bubbled with N2 for 48 h at room temperature to remove water before use. The measurement of solubility was similar to that for our previous experiments.5 Since PEGs are very hygroscopic, the solubility determination experiments were carried out in a glovebox. The dissolution of inorganic salts was carried out in a 3-neck round-bottom flask (100 mL), which was immersed in an oil bath (DF-101S, Henan Yuhua Instrument Factory) with magnetic stirring. In a typical trial, 0.05 g of inorganic salt powder was added to 5 g of PEG under the continuous and mild mechanical stirring at a preset temperature. Then, additional inorganic salt (0.1 wt % of the PEGs) was added until the solution became clear. The dissolution was viewed as saturated when inorganic salts could not be dissolved within 2 h. Each reported datum was the average value of three independent measurements. Solution 1H NMR measurements were conducted on a Bruker DMX 300 NMR spectrometer (300 MHz) with D2O as the external standard. An internal reference was not used because deuterated reagents can change the concentration of salts and may intact with PEG, which was unfavorable in this study. In this paper, the NMR experiments of samples electing an external reference (D2O loaded in an inserted capillary tube) were performed.42 The data of chemical shifts were later processed by the MestReNova Program. The IR spectra were obtained by the coupling of the attenuated total reflection (ATR-IR) equipment with the FTIR spectrometer (Prestige 21, Shimadzu, Japan, DTGS detector) in the range 600−1500 cm−1. The viscosities (η) of the PEGylated quasi-ionic liquid electrolytes were measured at 298.15 K using an Anton Paar DMA 5000M. The viscosity of each sample was measured four times, and the average value was reported. The conductivities of the mixtures of PEGs and salts were measured by using a conductivity meter (DDS-307A, Shanghai INESA Scientific Instrument Co., Ltd., China). In each experiment, 5 mL of PEGylated quasi-ionic liquid electrolytes and the electrode were sealed in a glass tube to avoid exposure to moisture in the atmosphere, with the tube immersed in an oil bath (DF-101S, Henan Yuhua Instrument Factory) at a constant temperature of 298.15 K. The deviation of the equipment was less than ±0.5%. The electrochemical experiments were performed on a CHI 660D (Shanghai, China) electrochemical analyzer. The electrochemical windows of the samples were investigated by utilizing the cyclic voltammetry (CV) technique at 298.15 K. The CV consists of a three electrode system: glassy carbon (GC, d = 3 mm), platinum (Pt) wire, and Ag+/Ag performed as the working, the counter, and the reference electrodes. The electrodeposition of metal Al was performed by utilizing a potentiostatic method at 298.15 K. The platinum (3 mm) electrode and Cu substrate, Al wire, and spiral Al wire worked as the working, reference, and counter electrodes. The thermal stability of the PEGylated quasi-ionic liquid electrolytes was studied by utilizing a thermal gravimetric analysis (TGA) instrument (Q 50, TA Instrument Company, America). The 14 salts were dissolved in PEG 200 to form homogeneous PEGylated quasiionic liquid electrolytes at room temperature. Then, the salt, the PEG, and PEGylated quasi-ionic liquid electrolytes were placed in the platinum pan of the TGA instrument, respectively.

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PEGylated quasi-ionic liquid electrolytes and salt-inwater electrolytes; and energy dispersive X-ray spectroscopy (EDX) data of Al plate electrodeposited in 1-ethyl3-methylimidazolium (PDF)

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Phone: +86-10-62514925. Fax: +86-10-62516444. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors thank the National Natural Science Foundation of China (21473252) for financial support. REFERENCES

(1) Irimia-Vladu, M. ″Green″ electronics: biodegradable and biocompatible materials and devices for sustainable future. Chem. Soc. Rev. 2014, 43, 588−610. (2) Anastas, P. T.; Warner, J. C. Green Chemistry: Theory and Practice; Oxford University Press, 2000. (3) Jessop, P. G. Searching for green solvents. Green Chem. 2011, 13, 1391−1398. (4) Duan, L.; Dou, L.-L.; Guo, L.; Li, P.; Liu, E.-H. Comprehensive evaluation of deep eutectic solvents in extraction of bioactive natural products. ACS Sustainable Chem. Eng. 2016, 4, 2405−2411. (5) Sun, X.; Xue, Z.; Mu, T. Precipitation of chitosan from ionic liquid solution by the compressed CO2 anti-solvent method. Green Chem. 2014, 16, 2102−2106. (6) Duan, H.; Wang, D.; Li, Y. Green chemistry for nanoparticle synthesis. Chem. Soc. Rev. 2015, 44, 5778−5792. (7) Estager, J.; Nockemann, P.; Seddon, K. R.; Srinivasan, G.; Swadźba-Kwaśny, M. Electrochemical Synthesis of Indium (0) Nanoparticles in Haloindate (III) Ionic Liquids. ChemSusChem 2012, 5, 117−124. (8) Li, Z.; Li, R.; Mu, T.; Luan, Y. Ionic liquid assisted synthesis of Au−Pd bimetallic particles with enhanced electrocatalytic activity. Chem. - Eur. J. 2013, 19, 6005−6013. (9) Farrán, A.; Cai, C.; Sandoval, M.; Xu, Y.; Liu, J.; Hernáiz, M. J.; Linhardt, R. J. Green Solvents in Carbohydrate Chemistry: From Raw Materials to Fine Chemicals. Chem. Rev. 2015, 115, 6811−6853. (10) Heldebrant, D. J.; Jessop, P. G. Liquid Poly(ethylene glycol) and Supercritical Carbon Dioxide: A Benign Biphasic Solvent System for Use and Recycling of Homogeneous Catalysts. J. Am. Chem. Soc. 2003, 125, 5600−5601. (11) Knop, K.; Hoogenboom, R.; Fischer, D.; Schubert, U. S. Poly(ethylene glycol) in Drug Delivery: Pros and Cons as Well as Potential Alternatives. Angew. Chem., Int. Ed. 2010, 49, 6288−6308. (12) Smith, E. L.; Abbott, A. P.; Ryder, K. S. Deep Eutectic Solvents (DESs) and Their Applications. Chem. Rev. 2014, 114, 11060−11082. (13) Armand, M.; Endres, F.; MacFarlane, D. R.; Ohno, H.; Scrosati, B. Ionic-liquid materials for the electrochemical challenges of the future. Nat. Mater. 2009, 8, 621−629. (14) Obadia, M. M.; Drockenmuller, E. Poly (1, 2, 3-triazolium) s: a new class of functional polymer electrolytes. Chem. Commun. 2016, 52, 2433−2450. (15) Sasi, R.; Devaki, S. J.; Sarojam, S. High performing Bio-based ionic liquid crystal electrolytes for supercapacitors. ACS Sustainable Chem. Eng. 2016, 4, 3535−3543. (16) Lee, G.; Kim, D.; Kim, D.; Oh, S.; Yun, J.; Kim, J.; Lee, S.-S.; Ha, J. S. Fabrication of a stretchable and patchable array of high performance micro-supercapacitors using a non-aqueous solvent based gel electrolyte. Energy Environ. Sci. 2015, 8, 1764−1774. (17) Kathiresan, M.; Velayutham, D. Ionic liquids as an electrolyte for the electro synthesis of organic compounds. Chem. Commun. 2015, 51, 17499−17516.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.6b01860. Additional solubilities, photographs, origin 1H NMR spectrogram, TGA data, and molar conductivities of the 5818

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electrolytes with trimethylamine hydrochloride. Surf. Coat. Technol. 2012, 206, 4225−4229. (38) Fang, Y.; Yoshii, K.; Jiang, X.; Sun, X.-G.; Tsuda, T.; Mehio, N.; Dai, S. An AlCl3 based ionic liquid with a neutral substituted pyridine ligand for electrochemical deposition of aluminum. Electrochim. Acta 2015, 160, 82−88. (39) Fang, Y.; Jiang, X.; Sun, X.-G.; Dai, S. New ionic liquids based on the complexation of dipropyl sulfide and AlCl3 for electrodeposition of aluminum. Chem. Commun. 2015, 51, 13286−13289. (40) Bakkar, A.; Neubert, V. A new method for practical electrodeposition of aluminium from ionic liquids. Electrochem. Commun. 2015, 51, 113−116. (41) Endo, A.; Miyake, M.; Hirato, T. Electrodeposition of Aluminum from 1,3-Dimethyl-2-Imidazolidinone/AlCl3 baths. Electrochim. Acta 2014, 137, 470−475. (42) Yan, C.; Mu, T. Molecular understanding of ion specificity at the peptide bond. Phys. Chem. Chem. Phys. 2015, 17, 3241−3249.

(18) Jacquemin, J.; Husson, P.; Padua, A. A. H.; Majer, V. Density and viscosity of several pure and water-saturated ionic liquids. Green Chem. 2006, 8, 172−180. (19) Coleman, D.; Gathergood, N. Biodegradation studies of ionic liquids. Chem. Soc. Rev. 2010, 39, 600−637. (20) Li, G.; Yan, C.; Cao, B.; Jiang, J.; Zhao, W.; Wang, J.; Mu, T. Highly efficient I2 capture by simple and low-cost deep eutectic solvents. Green Chem. 2016, 18, 2522−2527. (21) Xue, Z.; Zhang, J.; Peng, L.; Li, J.; Mu, T.; Han, B.; Yang, G. Nanosized Poly(ethylene glycol) Domains within Reverse Micelles Formed in CO2. Angew. Chem., Int. Ed. 2012, 51, 12325−12329. (22) Chen, J.; Spear, S. K.; Huddleston, J. G.; Rogers, R. D. Polyethylene glycol and solutions of polyethylene glycol as green reaction media. Green Chem. 2005, 7, 64−82. (23) Ganapatibhotla, L. V.; Zheng, J.; Roy, D.; Krishnan, S. PEGylated imidazolium ionic liquid electrolytes: thermophysical and electrochemical properties. Chem. Mater. 2010, 22, 6347−6360. (24) Di Noto, V.; Longo, D.; Münchow, V. Ion-oligomer interactions in poly (ethylene glycol) 400/(LiCl)x electrolyte complexes. J. Phys. Chem. B 1999, 103, 2636−2646. (25) de A. A. Soler-Illia, G. J.; Sanchez, C. Interactions between poly (ethylene oxide)-based surfactants and transition metal alkoxides: their role in the templated construction of mesostructured hybrid organic− inorganic composites. New J. Chem. 2000, 24, 493−499. (26) Lee, J.-W.; Oliveira, M. T.; Jang, H. B.; Lee, S.; Chi, D. Y.; Kim, D. W.; Song, C. E. Hydrogen-bond promoted nucleophilic fluorination: concept, mechanism and applications in positron emission tomography. Chem. Soc. Rev. 2016, 45, 4638. (27) Bortolini, O.; Chiappe, C.; Ghilardi, T.; Massi, A.; Pomelli, C. S. Dissolution of metal salts in bis (trifluoromethylsulfonyl) imide-based ionic liquids: studying the affinity of metal cations toward a “weakly coordinating” anion. J. Phys. Chem. A 2015, 119, 5078−5087. (28) Kozlowska, M.; Goclon, J.; Rodziewicz, P. Intramolecular Hydrogen Bonds in Low-Molecular-Weight Polyethylene Glycol. ChemPhysChem 2016, 17, 1143−1153. (29) Rozenberg, M.; Loewenschuss, A.; Marcus, Y. IR spectra and hydration of short-chain polyethyleneglycols. Spectrochim. Acta, Part A 1998, 54, 1819−1826. (30) Feldstein, M.; Kuptsov, S.; Shandryuk, G.; Platé, N. Relation of glass transition temperature to the hydrogen-bonding degree and energy in poly (N-vinyl pyrrolidone) blends with hydroxyl-containing plasticizers. Part 2. Effects of poly (ethylene glycol) chain length. Polymer 2001, 42, 981−990. (31) Ottani, S.; Vitalini, D.; Comelli, F.; Castellari, C. Densities, viscosities, and refractive indices of poly (ethylene glycol) 200 and 400+ cyclic ethers at 303.15 K. J. Chem. Eng. Data 2002, 47, 1197− 1204. (32) Harris, K. R.; Woolf, L. A.; Kanakubo, M. Temperature and pressure dependence of the viscosity of the ionic liquid 1-butyl-3methylimidazolium hexafluorophosphate. J. Chem. Eng. Data 2005, 50, 1777−1782. (33) Wang, J.; Tian, Y.; Zhao, Y.; Zhuo, K. A volumetric and viscosity study for the mixtures of 1-n-butyl-3-methylimidazolium tetrafluoroborate ionic liquid with acetonitrile, dichloromethane, 2-butanone and N, N−dimethylformamide. Green Chem. 2003, 5, 618−622. (34) MacFarlane, D. R.; Forsyth, S. A.; Golding, J.; Deacon, G. B. Ionic liquids based on imidazolium, ammonium and pyrrolidinium salts of the dicyanamide anion. Green Chem. 2002, 4, 444−448. (35) Zhao, C.; Burrell, G.; Torriero, A. A.; Separovic, F.; Dunlop, N. F.; MacFarlane, D. R.; Bond, A. M. Electrochemistry of room temperature protic ionic liquids. J. Phys. Chem. B 2008, 112, 6923− 6936. (36) Jamnik, B.; Vlachy, V. Ion partitioning between charged micropores and bulk electrolyte solution. Mixtures of mono-and divalent counterions and monovalent co-ions. J. Am. Chem. Soc. 1995, 117, 8010−8016. (37) Miyake, M.; Motonami, H.; Shiomi, S.; Hirato, T. Electrodeposition of purified aluminum coatings from dimethylsulfone−AlCl3 5819

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