Insight into the behavior at the hygroscopicity and interface of the hydrophobic imidazolium-based ionic liquids

doi:10.1016/j.cjche.2020.09.047

Abstract

Abstract: How to completely remove the water from ionic liquids (ILs) is difficult for researchers because of the hygroscopicity of ILs. In order to study the hygroscopicity of ILs, two kinds of ILs, 1-Butyl-3-methylimidazolium hexafluorophosphate ([Bmim][PF₆]) and 1-Butyl-3-methylimidazolium Bis(trifluoromethanesulfonyl) ([Bmim][NTf₂]) were investigated by molecular dynamics simulations. Although [Bmim][PF₆] and [Bmim][NTf₂] are hydrophobic, both of the ILs could absorb water molecules from the vapor. In this work, the process of absorbing water from the vapor phase was studied, and the water molecules could disperse into the IL. Aggregation was observed with increasing the water concentration. Although the absorbed water increases obviously, the amount of free water and small cluster in the ILs does not change significantly and always stays at a certain level. The amount of free water and small cluster in [Bmim][PF₆] is more than that in [Bmim][NTf₂], which is consistent with their hydrophobicity. In addition, the liquid-vacuum and liquid–liquid interfaces of the ILs were simulated and analyzed in detail. The number density distribution and angle distribution indicated that [Bmim]⁺ cations arrangement regularly at the IL-vacuum interface. The butyl chain point to the vacuum, while the imidazlium ring is close to the IL phase region and perpendicular to the interface. While at the IL-water interface, the cations and anions are disordered.

Key words: Ionic liquid, Molecular simulation, Interface, Hygroscopicity, Cluster

摘要： How to completely remove the water from ionic liquids (ILs) is difficult for researchers because of the hygroscopicity of ILs. In order to study the hygroscopicity of ILs, two kinds of ILs, 1-Butyl-3-methylimidazolium hexafluorophosphate ([Bmim][PF₆]) and 1-Butyl-3-methylimidazolium Bis(trifluoromethanesulfonyl) ([Bmim][NTf₂]) were investigated by molecular dynamics simulations. Although [Bmim][PF₆] and [Bmim][NTf₂] are hydrophobic, both of the ILs could absorb water molecules from the vapor. In this work, the process of absorbing water from the vapor phase was studied, and the water molecules could disperse into the IL. Aggregation was observed with increasing the water concentration. Although the absorbed water increases obviously, the amount of free water and small cluster in the ILs does not change significantly and always stays at a certain level. The amount of free water and small cluster in [Bmim][PF₆] is more than that in [Bmim][NTf₂], which is consistent with their hydrophobicity. In addition, the liquid-vacuum and liquid–liquid interfaces of the ILs were simulated and analyzed in detail. The number density distribution and angle distribution indicated that [Bmim]⁺ cations arrangement regularly at the IL-vacuum interface. The butyl chain point to the vacuum, while the imidazlium ring is close to the IL phase region and perpendicular to the interface. While at the IL-water interface, the cations and anions are disordered.

关键词: Ionic liquid, Molecular simulation, Interface, Hygroscopicity, Cluster

Guohui Zhou, Kun Jiang, Zhenlei Wang, Xiaomin Liu. Insight into the behavior at the hygroscopicity and interface of the hydrophobic imidazolium-based ionic liquids[J]. Chinese Journal of Chemical Engineering, 2021, 29(3): 42-55.

Guohui Zhou, Kun Jiang, Zhenlei Wang, Xiaomin Liu. Insight into the behavior at the hygroscopicity and interface of the hydrophobic imidazolium-based ionic liquids[J]. 中国化学工程学报, 2021, 29(3): 42-55.

References

[1] J.P. Hallett, T. Welton, Room-temperature ionic liquids: Solvents for synthesis and catalysis. 2, Chem. Rev. 111 (5) (2011) 3508-3576.
[2] K.R. Seddon, A taste of the future, Nat. Mater 2 (6) (2003) 363-365.
[3] E. Markevich, V. Baranchugov, D. Aurbach, On the possibility of using ionic liquids as electrolyte solutions for rechargeable 5V Li ion batteries, Electrochem. Commun. 8 (8) (2006) 1331-1334.
[4] A. Lewandowski, A. Świderska-Mocek, Ionic liquids as electrolytes for Li-ion batteries—an overview of electrochemical studies, J. Power Sources 194 (2) (2009) 601-609.
[5] M.-C. Lin, M. Gong, B. Lu, Y. Wu, D.-Y. Wang, M. Guan, M. Angell, C. Chen, J. Yang, B.-J. Hwang, H. Dai, An ultrafast rechargeable aluminium-ion battery, Nature 520 (7547) (2015) 324-328.
[6] Y. Zhou, S. Gong, X. Xu, Z. Yu, J. Kiefer, Z. Wang, The interactions between polar solvents (methanol, acetonitrile, dimethylsulfoxide) and the ionic liquid 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide, J. Mol. Liq. 299 (2020) 112159.
[7] H. Abe, A. Takeshita, H. Sudo, K. Akiyama, CO₂ capture and surface structures of ionic liquid-propanol solutions, J. Mol. Liq. 301 (2020) 112445.
[8] C. Herrera, G. García, R. Alcalde, M. Atilhan, S. Aparicio, Interfacial properties of 1-ethyl-3-methylimidazolium glycinate ionic liquid regarding CO₂, SO₂ and water from molecular dynamics, J. Mol. Liq. 220 (2016) 910-917.
[9] M.G. Freire, L.M.N.B.F. Santos, A.M. Fernandes, J.A.P. Coutinho, I.M. Marrucho, An overview of the mutual solubilities of water-imidazolium-based ionic liquids systems, Fluid Phase Equilib. 261 (1-2) (2007) 449-454.
[10] A.E. Visser, M.P. Jensen, I. Laszak, K.L. Nash, G.R. Choppin, R.D. Rogers, Uranyl coordination environment in hydrophobic ionic liquids: An in situ investigation, Inorg. Chem. 42 (7) (2003) 2197-2199.
[11] M.G. Freire, C.M.S.S. Neves, P.J. Carvalho, R.L. Gardas, A.M. Fernandes, I.M. Marrucho, L.M.N.B.F. Santos, J.A.P. Coutinho, Mutual solubilities of water and hydrophobic ionic liquids, J. Phys. Chem. B 111 (45) (2007) 13082-13089.
[12] P. Tshibangu, S. Ndwandwe, E. Dikio, Density, viscosity and conductivity study of 1-butyl-3-methylimidazolium bromide, Int. J. Electrochem. Sci. 6 (6) (2011) 2201-2213.
[13] J. Widegren, E. Saurer, K. Marsh, J. Magee, Electrolytic conductivity of four imidazolium-based room-temperature ionic liquids and the effect of a water impurity, J. Chem. Thermodyn. 37 (2005) 569-575.
[14] B. McAuley, K. Seddon, A. Stark, M. Torres, Influence of chloride, water, and organic solvents on the physical properties of ionic liquids, Abstr. Pap. -Am. Chem. Soc. 221st (2001), IEC-277.
[15] L. Tomé, F. Varanda, M. Freire, I. Marrucho, Towards an understanding of the mutual solubilities of water and hydrophobic ionic liquids in the presence of salts: The anion effect, J. Phys. Chem. B 113 (2009) 2815-2825.
[16] M.G. Freire, P.J. Carvalho, R.L. Gardas, I.M. Marrucho, L.M.N.B.F. Santos, J.A.P. Coutinho, Mutual solubilities of water and the [C_nmim][Tf₂N] hydrophobic ionic liquids, J. Phys. Chem. B 112 (6) (2008) 1604-1610.
[17] K. Jiang, X.M. Liu, H.Y. He, J.J. Wang, S.J. Zhang, Insight into the formation and permeability of ionic liquid unilamellar vesicles by molecular dynamics simulation, Soft Matter 16 (10) (2020) 2605-2610.
[18] X.M. Liu, X.Q. Yao, Y.L. Wang, S.J. Zhang, Mesoscale structures and mechanisms in ionic liquids, Particuology 48 (2020) 55-64.
[19] J.K. Konieczny, B. Szefczyk, Structure of alkylimidazolium-based ionic liquids at the interface with vacuum and water—a molecular dynamics study, J. Phys. Chem. B 119 (9) (2015) 3795-3807.
[20] S.S. Sarangi, S.G. Raju, S. Balasubramanian, Molecular dynamics simulations of ionic liquid-vapour interfaces: effect of cation symmetry on structure at the interface, PCCP 13 (7) (2011) 2714-2722.
[21] M.E. Perez-Blanco, E.J. Maginn, Molecular dynamics simulations of carbon dioxide and water at an ionic liquid interface, J. Phys. Chem. B 115 (35) (2011) 10488-10499.
[22] N. Sieffert, G. Wipff, The [BMI][Tf₂N] ionic liquid/water binary system: A molecular dynamics study of phase separation and of the liquid liquid interface, J. Phys. Chem. B 110 (26) (2006) 13076-13085.
[23] T. Koishi, Molecular dynamics study of the effect of water on hydrophilic and hydrophobic ionic liquids, J. Phys. Chem. B 122 (51) (2018) 12342-12350.
[24] G. Hantal, M. Sega, S. Kantorovich, C. Schröder, M. Jorge, Intrinsic structure of the interface of partially miscible fluids: an application to ionic liquids, J. Phys. Chem. C 119 (51) (2015) 28448-28461.
[25] T.Y. Li, Z.C. Zhao, X.D. Zhang, X.C. Sun, Molecular dynamics studies on liquid/vapor interface properties and structures of 1-ethyl-3-methylimidazolium dimethylphosphate-water, J. Phys. Chem. B 121 (14) (2017) 3087-3098.
[26] J.G. McDaniel, A. Verma, On the miscibility and immiscibility of ionic liquids and water, J. Phys. Chem. B 123 (25) (2019) 5343-5356.
[27] R. Lynden-Bell, J. Kohanoff, M. Popolo, Simulation of interfaces between room temperature ionic liquids and other liquids, Faraday Discuss. 129 (2005) 57-67.
[28] K.R. Ramya, P. Kumar, A. Kumar, A. Venkatnathan, Interplay of phase separation, tail aggregation, and micelle formation in the nanostructured organization of hydrated imidazolium ionic liquid, J. Phys. Chem. B 118 (29) (2014) 8839-8847.
[29] G. Hantal, I. Voroshylova, M.N.D.S. Cordeiro, M. Jorge, A systematic molecular simulation study of ionic liquid surfaces using intrinsic analysis methods, PCCP 14 (15) (2012) 5200-5213.
[30] M. Lísal, Z. Posel, P. Izák, Air-liquid interfaces of imidazolium-based [TF2N^-] ionic liquids: insight from molecular dynamics simulations, PCCP 14 (15) (2012) 5164-5177.
[31] R. Biswas, P. Ghosh, T. Banerjee, S. Ali, K.T. Shenoy, Extractive insights in the cesium ion partitioning with bis(2-propyloxy)-calix [4]crown-6 and dicyclohexano-18-crown-6 in ionic liquid-water biphasic systems, J. Mol. Liq. 241 (2017) 279-291.
[32] Z. Pouramini, A. Mohebbi, M.H. Kowsari, The possibility of cadmium extraction to the ionic liquid 1-hexyl-3-methylimidazolium hexafluorophosphate in the presence of hydrochloric acid: a molecular dynamics study of the water-IL interface, Theor. Chem. Acc. 138 (8) (2019) 99.
[33] T. Iwahashi, Y. Sakai, D. Kim, T. Ishiyama, A. Morita, Y. Ouchi, Nonlinear vibrational spectroscopic studies on water/ionic liquid([C_nmim]TFSA: _n = 4, 8) interfaces, Faraday Discuss. 154 (2012) 289-301.
[34] W.L. Jorgensen, D.S. Maxwell, J. TiradoRives, Development and testing of the OPLS all-atom force field on conformational energetics and properties of organic liquids, J. Am. Chem. Soc. 118 (45) (1996) 11225-11236.
[35] J.N.C. Lopes, J. Deschamps, A.A.H. Padua, Modeling ionic liquids using a systematic all-atom force field, J. Phys. Chem. B 108 (30) (2004) 11250.
[36] Toukan and Rahman, Molecular-dynamics study of atomic motions in water, Phys. Rev. B: Condens. Matter 31 (5) (1985) 2643-2648.
[37] J. Wang, C. Yuan, Y. Han, Y. Wang, X. Liu, S. Zhang, X. Yan, Trace water as prominent factor to induce peptide self-assembly: dynamic evolution and governing interactions in ionic liquids, Small 13 (44) (2017) 1702175.
[38] J. Zhou, X. Liu, S. Zhang, X. Zhang, G. Yu, Effect of small amount of water on the dynamics properties and microstructures of ionic liquids, AIChE J. 63 (6) (2017) 2248-2256.
[39] J. Qian, X. Liu, R. Yan, C. Li, X. Zhang, S. Zhang, Effect of ion cluster on concentration of long-alkyl-chain ionic liquids aqueous solution by nanofiltration, Ind. Eng. Chem. Res. 57 (22) (2018) 7633-7642.
[40] M.J. Abraham, T. Murtola, R. Schulz, S. Pall, J.C. Smith, B. Hess, E. Lindahl, GROMACS: high performance molecular simulations through multi-level parallelism from laptops to supercomputers, SoftwareX 1 (2015) 19-25.
[41] L. Martinez, R. Andrade, E.G. Birgin, J.M. Martinez, PACKMOL: a package for building initial configurations for molecular dynamics simulations, J. Comput. Chem. 30 (13) (2009) 2157-2164.
[42] S. Nose, A molecular dynamics method for simulations in the canonical ensemble (Reprinted from Molecular Physics, vol 52, pg 255, 1984), Mol. Phys. 100 (1) (2002) 191-198.
[43] M. Parrinello, A. Rahman, Polymorphic transitions in single crystals: A new molecular dynamics method, J. Appl. Phys. 52 (1981) 7182-7190.
[44] R.G. Seoane, E.J. Gonzalez, B. Gonzalez, 1-Alkyl-3-methylimidazolium bis (trifluoromethylsulfonyl)imide ionic liquids as solvents in the separation of azeotropic mixtures, J. Chem. Thermodyn. 53 (2012) 152-157.
[45] J.E. Kim, J.S. Lim, J.W. Kang, Measurement and correlation of solubility of carbon dioxide in 1-alkyl-3-methylimidazolium hexafluorophosphate ionic liquids, Fluid Phase Equilib. 306 (2) (2011) 251-255.
[46] M. Hakala, K. Nygard, S. Manninen, S. Huotari, T. Buslaps, A. Nilsson, L.G.M. Pettersson, K. Hamalainen, Correlation of hydrogen bond lengths and angles in liquid water based on Compton scattering, J. Chem. Phys. 125 (8) (2006).
[47] W. Zheng, P. Cao, Y. Yuan, C. Huang, Z. Wang, W. Sun, L. Zhao, Experimental and modeling study of isobutane alkylation with C4 olefin catalyzed by Bronsted acidic ionic liquid/sulfuric acid, Chem. Eng. J. 377 (2019) 119578.
[48] Q. Huang, Y. Huang, Y. Luo, L. Li, G. Zhou, X. Chen, Z. Yang, Molecular-level insights into the structures, dynamics, and hydrogen bonds of ethylammonium nitrate protic ionic liquid at the liquid-vacuum interface, PCCP 22 (24) (2020) 13780-13789.
[49] D. Yang, F. Fu, L. Li, Z. Yang, Z. Wan, Y. Luo, N. Hu, X. Chen, G. Zeng, Unique orientations and rotational dynamics of a 1-butyl-3-methyl-imidazolium hexafluorophosphate ionic liquid at the gas-liquid interface: the effects of the hydrogen bond and hydrophobic interactions, PCCP 20 (17) (2018) 12043-12052.