Enhanced Gas Separation through Nanoconfined Ionic Liquid in

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Enhanced Gas Separation through Nanoconfined Ionic Liquid in Laminated MoS2 Membrane Danke Chen, Wen Ying, Yi Guo, Yulong Ying, and Xinsheng Peng ACS Appl. Mater. Interfaces, Just Accepted Manuscript • Publication Date (Web): 30 Nov 2017 Downloaded from http://pubs.acs.org on December 1, 2017

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ACS Applied Materials & Interfaces

Enhanced Gas Separation through Nanoconfined Ionic Liquid in Laminated MoS2 Membrane Danke Chen,1† Wen Ying,1† Yi Guo,1 Yulong Ying,1 Xinsheng Peng1* 1

State Key Laboratory of Silicon Materials, School of Materials Science and Engineering,

Zhejiang University, Hangzhou, China, 310027. Corresponding author: X. Peng (email: [email protected])

ACS Paragon Plus Environment

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ABSTRACT：：Two-dimensional (2D) materials based membranes show great potential for gas separation. Herein, ionic liquid, 1-butyl-3-methyl imidazolium tetrafluoroborate ([BMIM][BF4]), confined in 2D channels of MoS2 laminated membranes were fabricated via an infiltration process. Compared with the corresponding bulk [BMIM][BF4], nanoconfined [BMIM][BF4] shows an obvious increment of freezing point and shift of their vibration bands. The resulted MoS2 supported ionic liquid membrane (MoS2 SILM) exhibits excellent CO2 separation performance with high CO2 permeance (47.88 GPU) and fantastic selectivity of CO2/N2 (131.42), CO2/CH4 (43.52) and CO2/H2 (14.95), which is much better than neat [BMIM][BF4] and [BMIM][BF4]-based membranes. The outstanding performance of MoS2 SILMs is attributed to the nanoconfined [BMIM][BF4], which composes a fast transportation path for CO2. Longterm operation also reveals the durability and stability of the prepared MoS2 SILMs. The method of confining ILs in 2D nanochannels of 2D materials may pave a new way for CO2 capture and separation.

KEYWORDS Nanoconfinement, ionic liquid, MoS2 membrane, CO2 separation, two-dimensional channels


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1. INTRODUCTION Two-dimensional (2D) materials with unique physical and chemical properties,1 have been extensively studied for decades. Except for the representative 2D materials graphene and graphene oxide (GO), other 2D materials such as hexagonal boron nitride (hBN), black phosphorus, molybdenum disulphide (MoS2), other dichalcogenides and layered oxides have gained more attention in recent years2-4 for electronic devices,5-7 energy storage,8-10 photonic applications,11-12 sensors,13-14 mass transport applications,15-17 and catalysis.18-20 Recently, 2D materials constructed membranes have shown promising potential for separation processes.1, 15-16, 21-26 These membranes function as a barrier between different phases, allowing some molecules pass through while others are restricted for liquid separation.22-27 Except for the separation of molecules and ions from liquid, membranes based on 2D materials have also developed for gas separation. Park et al. prepared GO membranes with well-interlocked GO stacking structure possessing high CO2/N2 selectivity in high relative humidity.28-29 They found that the incorporation of water into the GO membranes significantly enhance the permeation of CO2 over other light gases. However, the water could transport quickly through GO membrane.22 It’s also quite volatile and easily lost, and thus keeping the long-term durability of the water-wetted GO membranes for CO2 separation is a great challenge. Except for GO membranes, very recently, single-layered MoS2-based ultrathin membrane (17 nm in thickness) was reported and exhibited a H2/CO2 selectivity of 3.4,30 much lower than 4.69 of Knudsen selectivity. MoS2 nanosheets with 1T crystal phase were constructed to membranes, which presented a H2/CO2 selectivity of ~10.31 The lower selectivity of MoS2 membrane


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than those of GO membrane28-29 may result from large defects in the MoS2 nanosheets assembled membranes. In order to improve the gas separation performance of MoS2based membrane, filling another material with good gas separation performance into the 2D channels of MoS2 membrane is a promising way. Since ionic liquids (ILs) have negligible vapor pressure and excellent solubility of CO2,32-35 it could overcome the volatility of water based separation membrane. Many ILs have been utilized as separation agents in supported ionic liquid membranes (SILM) for CO2 separation.35-40 However, the liquid state of ILs greatly limits their applications. To overcome this drawback, fixing ILs into nanoporous hosts is a simple and practicable strategy.38 The confinement effect and the interactions between ILs and the pore walls endow the ILs with significantly uncommon physicochemical properties compared with the corresponding bulk ILs, such as melting temperature,42-48 thermal stability,44,

49-53

diffusion of ions,54-55 vibration bands,56-60 which will significantly influence the separation performance of nanoconfined SILMs. In present work, as a proof of concept, we chose 1-butyl-3-methyl imidazolium tetrafluoroborate ([BMIM][BF4]) as separation agent and confined it into the 2D channels of MoS2 laminated membranes for gas separation, since [BMIM][BF4] is an economical IL and has high solubility of CO2.34 As a result, the freezing point of the nanconfined [BMIM][BF4] increased from -75.4 °C of bulk [BMIM][BF4] to -69.9 °C of the confined [BMIM][BF4]. The corresponding shifted Fourier Transform infrared spectroscopy (FTIR) vibration bands indicate the strong interaction of the nanoconfined [BMIM][BF4] and MoS2. Furthermore, the Synchronous Radiation results demonstrate the ordered stacking MoS2 nanosheets become more randomly after infiltrating with [BMIM][BF4].


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As expected, the nanoconfinement of ILs in the 2D channels of MoS2 membrane significantly facilitates the CO2 permeance and the selectivity of CO2/N2, CO2/CH4 and CO2/H2 pairs, respectively, under dry state, which surpass far beyond neat [BMIM][BF4] and [BMIM][BF4]-based membranes. Contrary to pure MoS2 membrane, the larger molecule CO2 (0.330 nm) transports much quicker than H2 (0.289 nm) in MoS2 SILMs. Confining ILs into 2D channels of 2D materials via infiltration process may open a new avenue for highly efficient and novel membranes for separating CO2 from other light gases. 2. RESULTS AND DISCUSSION 2.1 Synthesis and characterization of MoS2 SILMs. The MoS2 nanosheets were prepared by chemical exfoliation (see details in Experimental Section).24 The zeta potential of the MoS2 nanosheets aqueous dispersion is -44.2 mV, which shows the negatively charged surfaces of MoS2 nanosheets. The transmission electron microscopy (TEM) and selected area electron diffraction (SAED) (Fig. S1) results demonstrate the exfoliated sheets show a hexagonal crystalline structure with lattice spacing of 2.6 Å assigned to (100) planes (Supporting Information, Fig S1b). Fig. S2 shows the size of prepared MoS2 nanosheets is in micrometer scale. The average topographic height of a single MoS2 sheet is about 1.2 nm, which is in agreement with the thickness of monolayer MoS2.24


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Scheme 1. Schematic diagram of the synthesis process of MoS2 SILM, demonstrating ionic liquid is confined in the MoS2 two-dimensional channels via infiltration.

MoS2 membranes were prepared on porous anodic alumina oxide (AAO) membranes with pore size of 200 nm from the aqueous dispersion of MoS2 nanosheets by vacuum filtration (Scheme 1). The morphologies and structures of a MoS2 membrane are shown in the scanning electronic microscopy (SEM) images (Fig. 1a-b). Fig. 1a shows many wrinkles on the surface of the prepared MoS2 membrane, which are formed during the filtration process due to the quick assembling process, flexibility of MoS2 nanoshheets, and relative rough AAO surface. Fig. 1b shows the cross section of MoS2 membrane with a uniform thickness of around 0.74 µm. It demonstrates the laminated assembly style of the MoS2 nanosheets. Furthermore, the contact angle (θc) of [BMIM][BF4] on the MoS2 membrane is ~34.1° (Fig. S3), which shows a good wettability between [BMIM][BF4] and MoS2. It means that the [BMIM][BF4] can be trapped into the channels of MoS2 by a positive capillary force. Based on the Young-Laplace equation, the capillary force for trapping


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[BMIM][BF4] into MoS2 nanochannels is calculated to be 60.42 MPa (see details in Experimental Section). This means that [BMIM][BF4] can be easily filled into the nanochannels of MoS2 by capillary force. Therefore, a series of MoS2 SILMs were fabricated by dropping certain volume of [BMIM][BF4] on the surface of the as-prepared MoS2 membranes (see details in Experimental Section). The MoS2 SILMs with 26.50 wt%, 32.23 wt%, 59.31 wt% [BMIM][BF4], respectively, are referred as MoS2 SILM-1, MoS2 SILM-2 and MoS2 SILM-3 in this work. The weight percent of ILs was measured by weight balance. Remarkably, the surface and crosssectional SEM images of them (Fig. 1c-d; Fig. 2) clearly demonstrate continuous membranes that are formed after ionic liquid infiltration. The thickness is increased from 0.74 µm of MoS2 (Fig 1b) to 1.20 µm MoS2 SILM-1 (Fig. 2b), 1.46 µm of MoS2 SILM-2 (Fig. 2d) and 1.94 µm (Fig 1d) of MoS2 SILM-3, respectively.

Figure 1. The morphology and membrane structure characterizations of MoS2 and MoS2SILM-3. a) Surface and b) cross-section SEM images of MoS2 membrane; c) Surface, d) cross-section SEM images of MoS2 SILM-3; e)-j) elements mapping images of Mo, S, C, N, B and F recorded from the marked zone in d), respectively.


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Figure 2. The surface and cross-section SEM images. (a) and (b) of MoS2 SILMs-1; and (c) and (d) of MoS2 SILMs-2.

In addition, the apparent layered structures of MoS2 membrane (Fig. 1b) are not observed in the MoS2 SILMs. These indicate the ILs occupy the space between MoS2 nanosheets and expand the thickness of the membrane up to 1.94 µm after fully filled the MoS2 channels with 59.31 wt% ILs. Energy-dispersive X-ray analysis spectroscope (EDS) mapping images recorded from the marked area of the cross section of MoS2 SILM-3 in Fig. 1d are shown in Fig. 1e-j, respectively. It demonstrates that Mo, S, C, N, B and F are distributed uniformly in the MoS2 SILM-3, which indicates that [BMIM][BF4] is uniformly filled between the MoS2 layers without conspicuous voids. Fig. 1 and 2 also shows that no obvious ILs is trapped into the AAO pores as confirmed by EDS (Fig. S4).


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Figure 3. FTIR spectra and DSC curves. (a) FTIR spectra of MoS2 membrane, MoS2 SILMs and pure [BMIM][BF4]; (b) DSC curves of [BMIM][BF4] and MoS2 SILM-3.

Synchronous Radiation X-ray diffraction results (Fig. S5a-d)) of the samples show that, comparing to the pure MoS2 membrane, some peaks clearly decline in MoS2 SILM-3, which refers to the addition of ILs leading to the reduction of the order of the membrane. Most peaks in the curve of MoS2 membrane are indexed to 2H-MoS2 (PDF #65-7025), similar to the starting MoS2 powers (Fig. S5e), except some weak impure peaks. The peak at 1.61° demonstrates the spacing between layers which is about 24.5 Å. The corresponding peak of MoS2 SILM-3 membrane remains as that of the MoS2 membrane, but the peak intensity decreases distinctly, which indicates that the ILs molecules are filled into the interlayer of MoS2 sheets, making the membrane more disorder. The FTIR spectra of MoS2 membrane and MoS2 SILMs are shown in Fig. 3a. Peaks at 1245.81 cm-1 in the FTIR spectra of MoS2 SILM-1, MoS2 SILM-2 and MoS2 SILM-3 can be assigned to [BMIM][BF4] but show a 5.79 cm-1 red shift from those of bulk [BMIM][BF4] (1251.60 cm-1), which relate to rocking of C2-H of imidazolium ring and twisting of CH2.61 What’s more, peaks at 1168.67 cm-1 of bulk [BMIM][BF4]


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corresponding to stretch of N-Bu, N-Me and rocking of CH, show 3.86 cm-1, 3.86 cm-1, 2.89 cm-1 red shift, respectively in MoS2 SILM-1, MoS2 SILM-2 and MoS2 SILM-3. The apparent vibrations shift (Supporting Information, Table S1) is due to the interactions between ILs and the channel walls, which partly reveals the uncommon physicochemical properties of nanoconfined [BMIM][BF4]. The thermal behavior of the ILs confined in the nanospace of MoS2 membrane was investigated by differential scanning calorimetry (DSC). As shown in Fig 3b, an obvious difference of the freezing point of the confined [BMIM][BF4] between bulk [BMIM][BF4] can be seen. Confining ILs in the channels of MoS2 leads to an increment of 5.5 °C in freezing point, which ensures the stability of [BMIM][BF4] in MoS2 SILMs, and promise for gas separation. 2.2 Gas separation: The gas permeations of different gas molecules (H2, CO2, CH4 and N2) were conducted to evaluate the gas separation performance of MoS2 SILMs with different content of ILs. Fig. 4a shows H2 has the highest permeance among H2, CH4, N2 and CO2 through pure MoS2 membrane, while its selectivity is pretty low. The selectivity of H2/CO2, CH4/CO2, and N2/CO2 pairs is 3.79, 1.71 and 2.12, respectively. It can be seen the variation of gas performance is proportional to the gas molecular weight and its kinetic diameters. In contrast to pure MoS2 membrane, MoS2 SILMs present highest CO2 permeance and superior selectivity for CO2/N2, CO2/CH4 and CO2/H2 pairs (Fig. 4b-c). The permeance of N2, CH4 and H2 is immensely reduced, respectively, as compared to CO2. Besides, the content of ILs plays an important role. Among them, MoS2 SILM-3 exhibits the best gas separation performance that the permeance of CO2 is up to 47.88 GPU and ideal selectivity of CO2/N2, CO2/CH4 and CO2/H2 are 131.42, 43.52 and 14.95.


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It also implies that the selectivity increases along with the increment of the content of ILs in MoS2 SILMs. Furthermore, as for MoS2 SILM-3, the selectivity of CO2/N2, CO2/CH4 and CO2/H2 in the mixtures is 53.41, 19.98 and 6.66, respectively. The apparent decrease of selectivity may attribute to the crowding-out effect, which has been extensively observed in other membranes.69

Figure 4. Gas separation performance. a) permeance and selectivity of MoS2 membrane. Gas permeation behaviors through MoS2 SILMs: b) permeance, c) selectivity. The error bars are between 5%-10%. d) Permeance of CO2 and CH4 through MoS2 SILM-3 at pressure of 0.06 MPa at room temperature for 7 days. The separation performances of MoS2 SILMs compared with other supported [Bmim][BF4] membranes62-68 (black squares): e) CO2/N2, f) CO2/CH4.respectively.

Besides, the as-prepared MoS2 SILM shows nice durability for seven days (Fig. 4d), which is due to the nonvolatility of ILs and strong confinement of ILs in the 2D nanochannels of MoS2 membrane. After operated 7 days, no ILs is leached out from the


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MoS2 SILM to the AAO support (Fig. S6, EDS), showing the promise for real gas separation. The excellent performance of the prepared MoS2 SILMs mainly results from the effects of nanoconfined ILs. The backbone of MoS2 SILMs is based on stacking structure of MoS2 nanosheets, while the ILs are confined in the 2D nanochannels of MoS2. Therefore, the gas could only transport through nanoconfined ILs that occupy the nanospace between the MoS2 nanosheets entirely (Scheme S1). Furthermore, the gas permeation through MoS2 SILM is based on solution-diffusion mechanism, as SILMs reported previously.70 Compared with the neat [BMIM][BF4],63 MoS2 SILMs show splendid selectivity of gases. We attribute it to nanoconfined [BMIM][BF4] in the nanochannels. As zeta potential reveals, MoS2 nanosheets contain negative charges. On this occasion, positively charged [BMIM]+ would interact with negatively charged MoS2 nanosheets via electrostatic interaction, leading to the [BF4]– anion without strong bondage behaving more freely. Generally, the interaction between CO2 and [BF4]– plays a crucial role in transportation of CO2 in [BMIM][BF4].71 And thus, the relatively free [BF4]– anions of nanoconfined ILs compose a fast transportation networks for CO2, leading to the high permeance of CO2 and superior selectivity of CO2/N2, CO2/CH4 and CO2/H2 pairs. In addition, as IL content increases, more remaining voids between the MoS2 layers can be filled with added IL, resulting in the increase of selectivity. However, the gas transportation path becomes relatively longer at the same time, making the gas permeance slightly decreases (Fig. 4b-c).


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Comparing with neat [BMIM][BF4] and other [BMIM][BF4]-based membranes (Fig. 4e-f, and see details in Supporting Information), MoS2 SILMs show both significantly enhanced CO2 permeance and selectivity of CO2/N2, CO2/CH4. Since there is almost no report about the separation performance of [BMIM][BF4]-based membranes for CO2/H2, the comparison of MoS2 SILM is not given. Notably, the separation performance of MoS2 SILM-3 for CO2/N2 and CO2/H2 surpass the Robeson upper bound63 and the predicted upper bound established by Paul64, repectively. As for the separation of CO2/CH4, it is also very colse to the Robesen upper bound63. All of these performances are very competive with those of the state-of-the-art membranes (Fig. S7, Table S2 and Table S3). 3. CONCLUSION In summary, MoS2 SILMs with high CO2 permeability and selectivity are fabricated by confining [BMIM][BF4] into the 2D channels of MoS2 laminated membranes. The nanoconfinement of ILs results in high CO2 permeance and superior selectivity for CO2/N2, CO2/CH4 and CO2/H2 pairs of MoS2 SILMs with nice durability far more than pure MoS2 membrane, neat [BMIM][BF4] and other [BMIM][BF4]-based membranes. Confining ILs into 2D channels of 2D materials via infiltration process may open a new avenue for highly efficient CO2 separation membrane. EXPERIMENTAL SECTION Materials: Molybdenum disulfide (MoS2) powder and n-butyl lithium were purchased from Aladdin. 1-butyl-3-methyl imidazolium tetrafluoroborate ([BMIM][BF4]) was purchased from Macklin. Hexane was purchased from Sinopharm Chemical Reagent. The supports were anodic alumina oxide (AAO) membranes (Whatman Anopore) with an average pore size of ca. 200 nm, porosity of 50% and diameter of 25 mm.


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Polytetrafluoroethylene filter membrane (PTFE) with an average pore size of ca. 0.45 µm and diameter of 47 mm. The ultrapure water (18.2 MΩ) used throughout the whole experiment was produced by a Millipore direct-Q system (Millipore). Synthesis of MoS2 nanosheets aqueous dispersion: MoS2 nanosheets were exfoliated in an Ar-filled glove box, according to the method reported elsewhere.24 200 mg MoS2 powder was dispersed in 2 ml of 1.6 M n-butyl lithium in hexane at room temperature under stirring for 48 hours. The black resultant was filtered through a PTFE filter membrane with repeated washing by sufficient hexane. Then the obtained powder was redispersed in 100 ml ultrapure water by mild ultrasonication for 1 h. Excess lithium hydroxyl was removed by centrifuging. Synthesis of MoS2 membrane and MoS2 SILMs: MoS2 membrane was prepared by vacuum filtrating 3~5 ml diluted MoS2 nanosheets dispersion (0.29 mg/ml) on an AAO substrate. 0.2~1 ml [BMIM][BF4] was dropped on the obtained MoS2 membrane. After 12~72 h, [BMIM][BF4] would enter into MoS2 two-dimensional channels via capillary force and finally confined in the channels to form MoS2 SILM. The excess ionic liquid was wiped off with filter paper. Characterization: TEM (JEM-2100F, JEOL) and Atomic Force Microscope (AFM, Bruker Dimension Edge) were performed to get information about morphologies, thickness and structures of MoS2 nanosheets. The morphologies and structures of membrane were characterized by SEM (S-4800, Hitachi) with Energy Dispersive Spectrometer. SEM observations were conducted after coating a thin platinum layer with a Hitachi e-1030 ion sputter at a pressure of 10 Pa and current density of 10 mA. The crystal information of the as-prepared membrane was obtained by Shanghai Synchrotron


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Radiation Facility with an 18 KeV energy of light source. FTIR was recorded by Nicolet5700, ThermoFisher Co. DSC was carried out by TA, Q200. Contact angle and surface tension of [BMIM][BF4] were respectively measured by OCA 20, Dataphysics. Zeta potential of MoS2 nanosheets dispersion was tested by Zetasizer Nano-ZS, Malwern. Gas chromatography was measured by GC9790, Fuli. Gas permeation: The gas permeation measurement of MoS2 membrane and MoS2 SILMs was determined by a constant-pressure variable volume method.25 The upstream pressure was 0.16 MPa, while the downstream pressure was 0.10 MPa (atmosphere pressure). The gas measurements for gas molecules of different kinetic diameters (e.g., H2 (0.289 nm), N2 (0.364 nm), CH4 (0.384 nm) and CO2 (0.330 nm)) were tested at room temperature. Gas flow rate was detected with a bubble flow-meter with effective membrane area being 2.99 cm2. Gas permeance (Q) was determined using the following equation:28 Qi =

P 1 dV 1 273.15 ⋅ ⋅ MPa ⋅ ⋅ ( ) P2 − P1 273.15 + T 0.1 A dt

(1)

Where P2 is the upstream pressure, P1 is the downstream pressure, PMPa is the atmospheric pressure (0.1 MPa), A is the membrane effective area, T is the temperature (Celsius), and dV/dt is the volumetric displacement rate in the bubble flow meter. The ideal selectivity of two kinds of gas (i, j) is defined as the ratio of the measured gas permeance value: α =

Qi Qj

(2)

Where Qi and Qj refer to the permeance of each gas, respectively. Gas chromatography is carried out to measure the selectivity of CO2/N2 (49.7%:50.3%),


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CO2/CH4 (50.1%:49.9%) and CO2/H2 (49.6%:50.4%) mixtures, respectively, at room temperature. The upstream pressure was also 0.16 MPa, while the downstream pressure was 0.10 MPa (atmosphere pressure). Capillary force estimation: The contact angle (θc) of [BMIM][BF4] on the MoS2 membrane is ~34.1° (Fig. S3). Based on the Young-Laplace equation, the capillary pressure difference of filling [BMIM] [BF4] into MoS2 nanochannels is calculated. In a sufficiently narrow tube of circular cross-section (radius α), the pressure jump is described as follows:74

P = 2γ cos θc / α

(3)

Where △P is the pressure difference across the fluid interface, γ is the surface tension, θc is the contact angle of the fluids and the solids in which they are contacted. The surface tension of [Bmim][BF4] is measured to be 46.19 mN/m, while the lamellar space of MoS2 nanosheets is 24.51 Å. And thus, the capillary force is estimated to be 60.42 MPa from Young-Laplace equation. ACKNOWLEDGEMENT This research was supported by the National Natural Science Foundations of China (NSFC 21671171), National Basic Research Program of China 973 Program (2015CB655302),

and

National

Key

Research

and

Development

Program

(2016YFA0200200). Supporting Information Available The contents of Supporting Information may include the following: (1) TEM images of MoS2 sheets and corresponding Typical electron diffraction pattern, (2) AFM image of MoS2 sheet, (3) [BMIM][BF4] contact angle image of MoS2 membrane surface, (4) cross-section SEM images of


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MoS2 SILM-3 with the AAO support and corresponding EDS of AAO, (5) SAXS curve of MoS2 and MoS2 SILM-3, (6) cross-section SEM images of MoS2 SILM-3 with the AAO support after 7 days operation and corresponding EDS of AAO, (7) the separation performances of MoS2 SILMs compared with other membranes, (8) MoS2 SILMs’ obvious FTIR Shift compared with pure [BMIM][BF4], (9) Gas separation performance of [BMIM][BF4]-based membranes. AUTHOR INFORMATION Corresponding author: X. Peng (email: [email protected]). Author Contributions Danke Chen and Wen Ying contributed equally to this work. Notes The authors declare no competing financial interest. REFERENCES 1. Liu, G.; Jin, W.; Xu, N., Two-Dimensional-Material Membranes: A New Family of HighPerformance Separation Membranes. Angew. Chem. Int. Ed. 2016, 55, 13384-13397. 2. Geim, A. K.; Grigorieva, I. V., Van der Waals Heterostructures. Nature 2013, 499, 419-425. 3. Liu, G.; Jin, W.; Xu, N., Graphene-Based Membranes. Chem. Soc. Rev. 2015, 44, 5016-5030. 4. Chua, C. K.; Sofer, Z.; Pumera, M., Functionalization of Hydrogenated Graphene: TransitionMetal-Catalyzed Cross-Coupling Reactions of Allylic C-H Bonds. Angew. Chem. Int. Ed. 2016, 55, 10751-10754. 5. Sun, D. M.; Liu, C.; Ren, W. C.; Cheng, H. M., A Review of Carbon Nanotube- and Graphene-Based Flexible Thin-Film Transistors. Small 2013, 9, 1188-1205.


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Enhanced Gas Separation through Nanoconfined Ionic Liquid in

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