Mixed-Matrix Membranes Containing Carbon Nanotubes Composite

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Mixed Matrix Membranes Containing Carbon Nanotubes Composite with Hydrogel for Efficient CO2 Separation Haiyang Zhang, Ruili Guo, Jinpeng Hou, Zhong Wei, and Xueqin Li ACS Appl. Mater. Interfaces, Just Accepted Manuscript • Publication Date (Web): 10 Oct 2016 Downloaded from http://pubs.acs.org on October 10, 2016

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ACS Applied Materials & Interfaces

Mixed Carbon

Matrix

Membranes

Nanotubes

Containing

Composite

with

Hydrogel for Efficient CO2 Separation Haiyang Zhang, Ruili Guo, Jinpeng Hou, Zhong Wei, Xueqin Li∗ Key Laboratory for Green Process of Chemical Engineering of Xinjiang Bingtuan, School of Chemistry and Chemical Engineering, Shihezi University, Xinjiang, Shihezi 832003, China ABSTRACT: In this study, a carbon nanotubes composite coated with N-isopropylacrylamide hydrogel (NIPAM-CNTs) has been synthesized. Mixed matrix membranes (MMMs) were fabricated by incorporating NIPAM-CNTs composite filler into poly(ether-block-amide) (Pebax® MH 1657) matrix for efficient CO2 separation. The as-prepared NIPAM-CNTs composite filler mainly plays two roles: i) The extraordinary smooth one-dimensional nanochannels of CNTs act as the highways to accelerate CO2 transport through membranes, increasing CO2 permeability; ii) The NIPAM hydrogel layer coated on the outer walls of CNTs acts as the super water absorbent to increase water content of membranes, appealing both CO2 permeability and CO2/gas selectivity. MMM containing 5 wt% NIPAM-CNTs exhibited the highest CO2 permeability of 567 Barrer, CO2/CH4 selectivity of 35 and CO2/N2 selectivity of 70, transcending 2008 Robeson upper bound line. The improved CO2 separation performance of MMMs is mainly attributed to the construction of the efficient CO2 transport pathways by NIPAM-CNTs. Thus, MMMs incorporated with 1

ACS Paragon Plus Environment


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NIPAM-CNTs composite filler can be used as an excellent membrane material for efficient CO2 separation. KEYWORDS: Pebax®; Carbon nanotubes; N-isopropylacrylamide; Mixed matrix membrane; CO2 separation

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1. INTRODUCTION CO2 capture from natural gas (mainly CH4) and flue gas (mainly N2) is a critical issue that needs to be addressed promptly due to the global warming in recent years.1 Membrane-based gas separation technology has rapidly become a competitive alternative owing to its advantages of efficiency, low-energy consumption, and ease of operation compared with traditional gas separation methods such as chemical and physical adsorption, solvent absorption, and cryogenic distillation.2-4 According to the types of membrane materials, membrane can be classified by three types: polymeric membranes, inorganic membranes and mixed matrix membranes (MMMs).5 For polymeric membranes, they have the advantages of low-cost, flexibility, easy fabrication, etc., but their performance has been constrained to the “trade-off” between permeability and selectivity, the so-called Robeson upper bound.6-7 Inorganic membranes exhibit better thermal and chemical stabilities than polymeric membranes. However, the issues of such materials are difficult to process and expensive for large-scale production.8-9 MMMs are composed by a continuous polymer phase and a dispersed inorganic filler phase. They inherit the advantages of both polymer matrix and fillers and show superior gas separation performance, exhibiting a potential prospect to transcend the Robeson upper bound.1, 10 The major challenge of MMMs is to fabricate a defect-free polymer-filler interface with improved separation performance.11-12 For this purpose, various types of fillers had been utilized in MMMs, such as zeolite, mesoporous silica, carbon nanotubes (CNTs), montmorillonite (MMT), polyoctahedral oligomeric 3



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silsesquioxanes (POSS), graphene oxide (GO) and metal organic frameworks (MOFs), etc.13-21 Among these fillers, CNTs are regarded as a potential candidate to be used as fillers for gas separation due to their one-dimensional nanochannels. They have the unique structure with extraordinary smooth surfaces and high aspect ratios (>1000), remarkable mechanical and thermal properties. Especially, gas transport in CNTs is extremely fast, the transport rates of gases in CNTs are orders of magnitude faster than in the zeolites or in other porous fillers. The exceptionally high transport rates have been attributed to the inherent smoothness walls of CNTs.22-24 It indicated that CNTs-based MMMs exhibited some advantages in high gas transport rates.25 To improve gas separation performance, the functionalization of CNTs aiming towards target gas is considered as an efficient strategy. For example, Jiang et al.26 found that MMMs doped with 5 wt% polyzwitterion@CNTs composite fillers (SBMA@CNTs) showed the improved gas separation performance in both CO2 permeability and CO2/CH4 selectivity. Filiz et al.27 found that the CO2 solubility coefficient increased with increasing content of polyethylene glycol functionalized multi-walled carbon nanotubes (PEG-CNTs) in polymers of intrinsic microporosity (PIM) matrix for MMMs. These works indicated that the combination of CNTs with other functional material to fabricate composites filler can effectively improve the gas separation performance of MMMs to a large extent through the generated cooperative effect of different components on the composite filler.28 The composite filler can remedy the drawbacks of single CNTs and give some new possibilities that can never be reached through the single component. 4


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Recently, several studies have indicated that water played a pivotal role in the fast and selective transport of CO2 through a membrane.29-31 Therefore, designing a composite filler to tailor the water environment within a membrane is crucial to promote the efficient CO2 separation. Hydrogel is capable of improving water environment because it can absorb water and retain extremely high water content (>5000 g/g).32 In addition, hydrogel belongs to an organic polymer material, which is beneficial to improve the interface compatibility between polymer and filler. Herein, hydrogel is selected to prepare CNTs composite filler, and it is expected that the designed CNTs-hydrogel composite filler can achieve the purpose of efficient CO2 separation. In this study, a carbon nanotubes composite coated with N-isopropylacrylamide hydrogel (NIPAM-CNTs) has been synthesized. MMM were fabricated by incorporating NIPAM-CNTs composite filler into poly(ether-block-amide) (Pebax® MH 1657) matrix for efficient CO2 separation. The effect of different filler (CNTs or NIPAM-CNTs) loading on the structural properties of the membranes and CO2 separation performance is discussed. 2. EXPERIMENTAL SECTION 2.1. Materials. Pebax® MH 1657, which was abbreviated as Pebax® in the following text, was purchased from Shanghai Rongtian Chemical Co., Ltd. Hydroxyl modified multi-walled carbon nanotubes (CNTs) were purchased from Nanjing XFNANO Materials Tech Co., Ltd. N-isopropylacrylamide (NIPAM, 98.0 wt%), N,N,N',N'',N''-pentmethyldiethylenetriamine (PMDETA, 99%), cuprous bromide 5



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(CuBr, 99.99%), N,N-dimethylaminopyridine (DMAP, 99%) and triethylamine (TEA, 99.5%) were purchased from Aladdin Chemistry Co. Ltd. 2-bromo-2-methylpropionyl bromide (BMPB, 98%) was purchased from Sigma-Aldrich. Chloroform (CHCl3, 99%) was purchased from Tianjin Guangfu Technology Development Co. Ltd. Deionized water was used in all experiments. 2.2. Preparation of NIPAM-CNTs Composite Filler. NIPAM-CNTs composite filler were prepared by in situ atom transfer radical polymerization. CNTs (0.40 g) were placed into 10.00 mL of anhydrous CHCl3. DMAP (0.03 g) and TEA (0.30 g) were added, and then BMPB (0.38 g) was dissolved into 5 mL of anhydrous CHCl3 and was added dropwise to the resultant mixture at 0 °C in 60 min. The mixture was stirred for 3 h at 0 °C followed by stirring at 25 °C for 48 h. The solid was separated from the mixture by filtration and then washed with CHCl3 for 5 times. The resultant Br-CNTs were purified by three cycles of centrifugation followed by drying in a vacuum oven at 40 °C until constant weight was reached. In a typical experiment of modification, Br-CNTs (0.03 g) with a mixture of CuBr, and PMDETA were dissolved into 0.5 mL deionized water with stirring in dry flask. The flask was evacuated and filled with argon. 0.13 g of NIPAM dissolved in 0.5 mL of degassed water was injected into the flask. The mole ratio of NIPAM : CuBr : PMDETA was 1.1 : 0.05 : 0.05. The solution was kept at room temperature and stirred for 48 h. Then, the resulting mixture was diluted in water and filtered and purified with deionized water. The product of NIPAM-CNTs composite filler was dried in a vacuum oven until constant weight. 6


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2.3. Membrane Preparation. To prepare MMMs, a certain amount of Pebax® pellets were dissolved into a mixed solvent (ethanol/water = 70/30, wt%) under reflux at 80 °C for 2 h, leading to a 4 wt% Pebax® solution. The required amount of NIPAM-CNTs composite filler was dispersed into a 1.0 mL of mixed solvent (ethanol/water = 70/30, wt%) under sonication for 30 min. Then this suspension was added to Pebax® solution and stirred for 24 h. Subsequently, the homogeneous suspension was poured on a flat glass plate and then left overnight under ambient temperature, followed by further degassing in a vacuum oven at 40 °C overnight. For comparison, pure Pebax® membrane was prepared following an identical procedure, but without NIPAM-CNTs composite filler loading. The as-prepared MMMs containing NIPAM-CNTs composite filler were denoted as Pebax-NIPAM-CNTs-X, where X corresponds to NIPAM-CNTs loading. The thickness of the resulting membranes was 70–90 µm. 2.4. Characterization. The morphology of NIPAM-CNTs composite filler was investigated on a Tecnai G2 F20 Transmission electron microscope (TEM). The chemical structures of composite filler and membranes (Figure S1) were measured in the range of 400–4000 cm−1 on a Nicolet-560 Fourier transform infrared (FT-IR) spectrometer. The cross-sectional morphologies of all membranes were observed on JSM-6490LV scanning electron microscope (SEM). Glass transition temperatures (Tgs) of all membranes were conducted using DSC 200 F3 differential scanning calorimeter (DSC) in the range of 30-250 °C. Tensile tests of all membranes were conducted using an INSTRON 3366 machine. The physical structure of membranes (Figure S2) 7



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was measured by a D8 Advance X-ray diffractometer (XRD) at a scanning speed of 10 °/min. The d-spacing of membranes was calculated by the Bragg’s law.30 The measurement method of water uptake is in accordance with previous work.33 After gas permeation, the membranes were weighed to determine the “humidified” weight (Wh, mg). The membranes were weighed to determine “dried” weight (Wd, mg) after they were dried at 150 °C until a constant weight was reached. The weight of each membrane was repeatedly measured 3 times. In this way, water uptake was calculated by the following equation: Water uptake (%) =

W h -W d Wd

× 100

(1)

2.5. Gas Permeation Tests. Gas permeation was measured using a constant pressure/variable volume method. The measurements of gas transport properties of membranes were conducted by using a home-made gas permeation apparatus shown in Scheme 1. Membrane areas of 12.90 cm2 were cut from the as-prepared membranes and placed on a circular stainless-steel cell. This cell was placed inside an oven in a permeation setup with accurate temperature control. Pure gas of CO2, CH4 or N2 and mixture gas of CO2/CH4 (10 vol% : 90 vol%) or CO2/N2 (10 vol% : 90 vol%) were employed as feed gas. CH4 was used as the sweep gas when CO2, N2 or CO2/N2 permeabilites were measured. N2 was used as the sweep gas when CH4 or CO2/CH4 permeabilites were measured. The compositions of gases were analyzed by Agilent 6820 gas chromatography. No sweep gas was detected in the retentate, indicating no back-diffusion occurred. For humidified state test, both feed gas and sweep gas were

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saturated with water before contacting the membrane. All membranes were measured for 3 times at feed pressure of 2 bar and room temperature.

Scheme 1. Schematic of Gas Permeation Apparatus. Gas separation performance was defined by the separation selectivity and gas permeabilities of the individual components. The permeability for the i component (Pi, Barrer, and 1 Barrer = 10-10 cm3 (STP) cm/(cm2 s cmHg)) was calculated as shown in Eq. (2).

Pi =

Qi l ∆P i A

(2)

where Qi is the volumetric flow rate of gas [cm3(STP)/s], l is the thickness of membrane (cm), and ∆pi refers to the transmembrane partial pressure difference of gas i (cmHg) and A is permeation membrane area. The partial pressure of CO2, CH4 or N2 on the permeate side approaches to zero because the flow rate of sweep gas is much larger than permeate gas. The ideal selectivity (determined from pure gas permeation experiments) and separation factor (determined from mixed-gas permeation experiments) of gas i over j (αij) can be 9



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calculated as the ratio of the permeability of the more fast component (CO2) to the permeability of the less slow component (CH4 or N2) as given in Eq. (3).

α ij =

Pi Pj

(3)

The scientific investigations are required in order to examine the effect of the gas components on the stability of membranes. The life time of the synthesized membrane is assessed at 2 bar and room temperature. 3. RESULTS AND DISCUSSION 3.1. Characterization. The morphologies of pristine CNTs and NIPAM-CNTs composite filler were observed by TEM. As shown in Figure 1(b), it can be observed that NIPAM hydrogels were coated on the outer surfaces of CNTs with the layer thickness of ~3 nm. The as-prepared NIPAM-CNTs composite filler have a core of CNTs and a shell layer of NIPAM hydrogels.

Figure 1. TEM images of (a) pristine CNTs and (b) NIPAM-CNTs composite filler. The representative SEM images of membranes are displayed in Figure 2. The terminals of NIPAM-CNTs composite filler in membrane matrix are marked by the red circles in Figure 2(c) and (d). The void formed around pristine CNTs aggregates indicated the poor adhesion between pristine CNTs and Pebax® matrix (Figure 2(f)). 10


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In contrast, the cross-section morphologies of membranes showed that NIPAM hydrogels

functionalized

CNTs

(NIPAM-CNTs)

composite

filler

dispersed

homogeneously in Pebax® matrix. No voids formed and no filler agglomeration occurred in MMMs when the loading of NIPAM-CNTs was up to 5 wt% (Figure 2(c)). As the loading of NIPAM-CNTs was further increased to 10 wt%, the NIPAM-CNTs tended to agglomerate and were not well dispersed in Pebax® matrix (Figure 2(d)). This observation verified that the NIPAM hydrogel layer coated on the outer surface of CNTs improved the interface compatibility between CNTs and Pebax® matrix.

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Figure 2. SEM images of cross-section of (a) Pebax®-NIPAM-CNTs-1, (b) Pebax®-NIPAM-CNTs-3, (c) Pebax®-NIPAM-CNTs-5, (d) Pebax®-NIPAM-CNTs-10, (e) pure Pebax® and (f) Pebax®-CNTs-15 MMMs. Figure 3 displays the thermal properties of pure Pebax® membrane and Pebax-NIPAM-CNTs MMMs. Glass transition temperature (Tg) determined by DSC is used to estimate the flexibility of Pebax® polymer chains. Figure 3(a) shows a significant change in Tg values of MMMs, and Tg values increase with the increase of NIPAM-CNTs loading in Pebax® matrix. The increase in Tg results from the favorable 12


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interaction between polymer and fillers. The favorable interactions also result in a rigidified interfacial region between polymer and fillers in MMMs, which is

-49.6 oC

Heat flow (mw/mg) endo

beneficial to increase CO2/gas selectivity.

Heat flow (mw/mg) endo

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Pebax-NIPAM-CNTs-10 

-47.4 oC

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-48.5 oC

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-50.1 oC

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Figure 3. DSC curves of pure Pebax® membrane and Pebax®-NIPAM-CNTs MMMs. 3.2. Membrane Separation Performance. 3.2.1. Pure gas permeation performance. Pure gas permeation was measured to evaluate the gas separation performance of the as-prepared membranes. Figure 4 shows the CO2 permeability and ideal selectivity of pure Pebax® membrane and MMMs with the different content of NIPAM-CNTs. Both the CO2 permeability and ideal selectivity (CO2/CH4 and CO2/N2) increase with increasing NIPAM-CNTs loading in MMMs, indicating NIPAM-CNTs facilitates the permeation of CO2. On one hand, the CNTs are beneficial to enhance CO2 permeability because their extraordinary smooth one-dimensional nanochannels can act as the highways to accelerate CO2 transport through the MMMs. On the other hand, the NIPAM hydrogel layer coated on the outer walls of CNTs helps to increase water uptake of membranes (Figure S3), which allows highly soluble of CO2 to penetrate through the MMMs and restricts low 13



soluble of CH4 and N2 to penetrate through MMMs, obtaining considerable improvement in CO2/gas selectivity. Compared with pure Pebax® membrane, the Pebax®-NIPAM-CNTs-5 MMM displayed an increase in both CO2 permeability and CO2/gas selectivity. However, the high loading of NIPAM-CNTs beyond 10 wt% results in void structure in MMMs, decreasing CO2 separation performance.

CO2 permeability CO2/CH4

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Content of NIPAM-CNTs (wt%) Figure 4. The effect of NIPAM-CNTs content on gas separation performance. 3.2.2. Mixed-gas permeation performance. Mixed-gas permeation experiments were performed to examine the gas separation performance of MMMs. Figure 5 presents the separation results of different membranes with different NIPAM-CNTs loadings under mixed-gas (CO2/CH4 or CO2/N2). CO2 permeability and CO2/gas selectivity decreased when the loading of NIPAM-CNTs increased from 5 wt% to 10 wt% in MMMs. The decrease of CO2 permeability and CO2/gas selectivity was attributed to the filler agglomerations in MMMs. For a MMM doped with a specific 14


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filler loading, the separation factor is slightly lower than the corresponding ideal selectivity. This discrepancy can be ascribed to the competitive interaction between the two separating gases. They presented in the mixture and were competitive to adsorb on the membrane pores. The relative reduction in separation factor of MMMs was slightly reduced in contrast to that of pure Pebax® membrane. The introduction of NIPAM-CNTs was beneficial to construct CO2 efficient pathways in MMMs, improving CO2 separation performance. Thus, the CO2/CH4 and CO2/N2 separation


factors of MMMs were improved.

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0 12

Content of NIPAM-CNTs (wt%) Figure 5. The effect of filler content on gas separation performance of pure Pebax® membrane and Pebax®-NIPAM-CNTs MMMs: (a) CO2/CH4 separation performance and (b) CO2/N2 separation performance. 3.2.3. Effect of feed pressure on gas separation performance. The effects of feed pressures on gas separation performance were studied for pure Pebax® membrane and Pebax®-NIPAM-CNTs-5 MMM. The CO2/CH4 and CO2/N2 separation performance of the Pebax®-NIPAM-CNTs-5 MMM and pure Pebax® membrane at increasing feed pressure were compared in Figure 6. It can be seen from Figure 6 that CO2 permeability and CO2/gas separation factors decreased with increasing feed pressure. The decrease of CO2 separation performance is attributed to the dense polymeric chain packing at high feed pressure. The decreases in permeability and separation factor for MMM containing NIPAM-CNTs are less than that for pure Pebax® membrane. This observation demonstrates that the incorporation of NIPAM-CNTs 16


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improves the chain packing of Pebax® matrix in MMMs and helps to reduce the dependence of CO2 separation performance on the feed pressure.

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Feed pressure (bar) Figure 6. The effect of feed pressure on gas separation performance of pure Pebax® 17



membrane and Pebax®-NIPAM-CNTs-5 MMM: (a) CO2/CH4 separation performance and (b) CO2/N2 separation performance. 3.2.4. Effect of operating temperature on gas separation performance. The effects of operating temperatures on gas separation performance were assessed for pure Pebax® membrane and Pebax®-NIPAM-CNTs-5 MMM. As summarized in Figure 7(a), the decrease of the operating temperature from 348 K to 298 K results in up to twofold increment in CO2/CH4 separation factor for both pure Pebax® membrane and Pebax®-NIPAM-CNTs-5 MMM. This enhancement in separation factor, however, is at the expense of the decrease in the permeability of both gases. At 298 K, CH4 concentration in the permeation side is low. MMM containing NIPAM-CNTs filler shows an obvious decrease in CO2 permeability with the decreasing operating temperature. We attribute the stronger temperature sensitivity to the higher water content in the MMM than that in pure Pebax® membrane.

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Temperature (K) Figure 7. Effect of operating temperature on gas separation performance of pure Pebax® membrane and Pebax®-NIPAM-CNTs-5 MMM: (a) CO2/CH4 separation performance and (b) CO2/N2 separation performance. 3.2.5. The stability of membranes. The performance of the selected MMM containing 5 wt% NIPAM-CNTs has been evaluated by long-term gas permeation experiments. As shown in Figure 8, a stead state is maintained for long-terms running (> 120 h), and the gas separation performance does not change appreciably in the timescale studied.

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CO 2 permeability (Barrer)

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Time on stream (h) (b) Figure 8. The long-term stability test of the separation performance of Pebax®-NIPAM-CNTs-5 MMM: (a) CO2/CH4 separation performance and (b) CO2/N2 20


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separation performance. 3.3. Comparison of Results to Robeson’s Upper Bound Curve. The separation performance of the MMMs in this work was compared with a compilation of results from other CNT-based MMMs previously reported (Figure 9 and Table 1).26-27, 34-39 As expected, the performance of CNTs-based MMMs is located in the unattractive region because of the low permeability or selectivity. In contrast, MMMs containing NIPAM-CNTs clearly transcend the trade-off between permeability and selectivity. Pebax®-NIPAM-CNTs MMMs showed much higher CO2 permeability (>560 Barrer) than any other CNT-based MMMs with a CO2/CH4 selectivity of 35 and CO2/N2 selectivity of 70. This result indicates that the designed membranes exhibit excellent performance for CO2/CH4 separation and promising CO2/N2 separation performance. Table 1 Comparison of gas permeability and selectivity of other CNTs-based MMMs with that of the MMMs in this work. pCO2/ Temp. Polymer

Test

PCO2/

Filler atm

o

/C

condition Barrer

αCO2/CH4

αCO2/N2

Ref.

Matrimid®

CNTs

2.0

30

Dry state

103

36

-

26

PIM-1

CNTs

2.0

30

Dry state

15721

8.6

16.5

27

Polyimide

CNT

15.0

25

Dry state

37.31

16.5

-

34

PSF

CNTs

4.0

35

Dry state

5.19

18.5

22.6

35

BPPO

CNTs

~0.7

25

Dry state

123

-

29

36

PDMS41

CNTs

4.0

35

Dry state

191.3

5.21

10.7

37

Pebax®

CNTs

10.0

~30

Dry state

329.7

-

78.5

38

21



PIM-1

CNTs

2.0

27

Dry state

8250

9.34

37.8

39 This

Pebax

®

CNTs

2

25

Dry state

87

19

53 work

Humidifi Pebax

®

CNTs

2

25

This 567

35

70

ed state

work

1000 

Robeson upper bound 2008

CO2/CH4 selectivity

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 31

Pebax -NIPAM@CNTs 

Pebax Other MMMs

100

10 Robeson upper bound 1991

1

1

10

100

1000


22


10000

Page 23 of 31

1000 

Pebax -NIPAM@CNTs 

CO2/N2 selectivity

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Pebax Other MMMs 100

Robeson upper bound 2008 10

1

1

10

100

1000

10000

CO2 permeability (Barrer) Figure 9. Robeson plots for: (a) CO2/CH4 separation and (b) CO2/N2 separation. 4. CONCLUSIONS In this work, a NIPAM-CNTs composite filler was designed to construct efficient CO2 pathways. A high-performance MMM was fabricated by incorporating NIPAM-CNTs composite fillers. The extraordinary smooth one-dimensional nanochannels of CNTs and super water hydroscopicity of NIPAM hydrogels are key factors contributing the efficient CO2 separation in MMM. The NIPAM-CNTs fillers show a good dispersion in membrane matrix without agglomeration. The obtained MMMs containing NIPAM-CNTs enhance CO2 permeability and selectivity for CO2/CH4 and CO2/N2 mixed-gas compared with the Robeson upper bound and other CNTs-based MMMs. Remarkably, MMM containing 5 wt% NIPAM-CNTs can increase CO2 permeability and ideal selectivity by 35% and 11% respectively compared with pure membrane. The results demonstrated that the designed composite 23



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filler with fast transport pathways and super water hydroscopicity is indeed an effective strategy to improve gas separation performance of MMMs, and this will be extended to fabricate other kinds of advanced membrane materials. AUTHOR INFORMATION Corresponding author *X.

Li.

Tel.:

86-993-2057277.

Fax:

86-993-2057210.

E-mail

address:

[email protected]. Notes The authors declare no competing financial interest. ACKNOWLEDGEMENTS The authors gratefully acknowledge the support from the Start-Up Foundation for Young Scientists of Shihezi University (RCZX201508) and the Start-Up Foundation for Young Scientists of Shihezi University (RCZX201507).

24


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Table of Contents

31


Mixed-Matrix Membranes Containing Carbon Nanotubes Composite

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