Experimental Study on Graphene-Based Nanocomposite Membrane

Accepted Manuscript Title: Experimental Study on Graphene-Based Nanocomposite Membrane for Hydrogen Purification: Effect of Temperature and Pressure Authors: Rahman Zeynali, Kamran Ghasemzadeh, Alireza Behrooz Sarand, Farshad Kheiri, Angelo Basile PII: DOI: Reference:

S0920-5861(18)30667-9 https://doi.org/10.1016/j.cattod.2018.05.047 CATTOD 11477

To appear in:

Catalysis Today

Received date: Revised date: Accepted date:

6-2-2018 3-5-2018 23-5-2018

Please cite this article as: Zeynali R, Ghasemzadeh K, Sarand AB, Kheiri F, Basile A, Experimental Study on Graphene-Based Nanocomposite Membrane for Hydrogen Purification: Effect of Temperature and Pressure, Catalysis Today (2018), https://doi.org/10.1016/j.cattod.2018.05.047 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Experimental Study on Graphene-Based Nanocomposite Membrane for Hydrogen Purification: Effect of Temperature and Pressure Rahman Zeynali1, Kamran Ghasemzadeh1, Alireza Behrooz Sarand1, Farshad Kheiri1, Angelo Basile2*

Engineering Faculty, Urmia University of Technology, Urmia, Iran

2CNR-ITM,

corresponding Author: [email protected]

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*Email

Via P. Bucci c/o University of Calabria Cubo 17/C, Rende (CS) – 87046, Italy

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1Chemical

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Graphical abstract

Highlights:

Graphene oxide (GO) nanocomposite membrane was synthesized by vacuum dip-

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

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coating method.

For preparation of GO membrane, the modified gamma-alumina support was used.

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GO nanocomposite membrane indicated promising results for hydrogen separation.

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

Abstract In the last five recent years, molecular-sieve Graphene Oxide (GO) membranes have shown a great potential to realize high-flux and high-selectivity mixture separation, at low energy cost. Hence, in this study, GO nanocomposite membranes were fabricated on modified γ-alumina

tubes for hydrogen separation. As a high-performance process, H2-permselective GO membrane derived from graphite source was developed by using a modified hummer method. In fact, the GO nanocomposite membranes, referred to here as carbon membranes, were prepared via vacuum dip coating of the modified γ-alumina tubes using single-layer GO solution. Special attention was devoted to obtain high H2/CO2 selectivity, high H2 permeance, and good stability in separation process. Hence, the effects of the operating conditions (temperature, and pressure on quality and performance of the GO membranes) were

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investigated. At the best condition, the synthesized GO membrane exhibited good H2/CO2 selectivity (>57) and high H2 permeance (in the order of 7.9×10-7 mol.Pa-1.m-2.s-1). Moreover,

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it was found that the GO membrane selectivities (H2/CO2 and H2/N2) were decreased by temperature increasing, while selectivity trends were improved by increasing pressure gradient. It should be noted that all permeation tests were reported after time durability of

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around 48 h.

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Keywords: Hydrogen separation, GO nanocomposite membrane, single-layer graphene oxide (GO), GO membrane selectivity.

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1. Introduction

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In last two decades, membranes for gas separation are increasingly becoming a significant and convenient technology for the hydrogen recovery from gas mixtures, oxygen enrichment,

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gas sweeting of natural gas, CO2 capturing, vapour-vapour separation and air dehydration [1]. It should be noted that the main reason of this affinity is that the membrane technology can

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successfully separate gas mixtures under low pressure, obviously reducing the required industry area and minimizing the necessary energy consumption with relatively low

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contamination, compared to traditional separation technologies [2-4]. Up till now, numerous papers about gas separation membranes are focused on achieving high flux and surprising selectivity [see for example: 5-7]. Recently, considerable interest has been observed by the emerging two-dimensional

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structural materials, such as MoS2 [8, 9], Phosphorene [10], ZIF-7 [11], and graphene based material [12], due to their ultra-thin thickness and unique separation property. Utilizing twodimensional intriguing materials to fabricate thin membranes is considered as a useful and effective way to overcome the current performance (permeability/selectivity) [13,14] which often occurred in traditional polymer membranes [14,15]. Among the mentioned options, there is no doubt that graphene based material, a two-dimensional monolayer of sp2

hybridized carbon atoms arrayed in a honeycomb pattern, shows the most outstanding prospect, owing to a series of unique physical/chemical properties, such as good chemical stability, excellent thermal conductance and strong mechanical strength [12, 16-19]. Hitherto, some exciting and encouraging works have been achieved [20, 21]. However, because of the complicated membrane preparation process [22-24], it is very hard to transfer their membrane to the practical application. On the other hand, the attractive ultrathin membrane structure brings another critical issue: how to bear complex and harsh long-term operation

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environments in the real industry (such as high pressure and unstable gas flow). Hence, the remarkable interest in graphene based material must be complemented by insistent efforts to

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develop new membrane materials with much higher performance (permeance and selectivity) for more energy-efficient membrane processes.

In the last five years, some of theoretical and experimental papers on porous graphene and graphene oxide (GO) nanocomposite membranes have been presented for gas separation

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applications. Recently, the progress on graphene-based membranes has been nicely reviewed

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[25–27]. In general, extremely careful manipulations are needed for few-layers GO

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membranes preparation [28, 29]. Therefore, it is still necessary to design GO membranes which can satisfy the practical requirements and explore their gas separation.

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In order to make up above shortages, in this work, we try to prepare porous γ-alumina supported GO membranes, because alumina substrates not only can decrease thickness of

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membranes to realize high flux obviously, but also can offer a good mechanical strength for composite membranes [30, 31]. Moreover, it can be forecasted good matching of alumina

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substrate with GO layer. Therefore, in this study, the porous modified γ-alumina tube was selected as the substrates due to its characteristic configuration (low mass transfer resistance and high-packing density) and good thermal and chemical stability [32].

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Here, a convenient and rapid vacuum dip-coating method to prepare GO membranes on the modified γ-alumina tubular substrate, which exhibited excellent Knudsen permeation mechanism [30]. The special configuration makes GO membranes very easy to be scaled-up.

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Moreover, the GO nanosheets stacked to form a cylinder shell around the ceramic tubular substrate, keeping it more stable than flat GO membranes. Herein, as a first approach, this work reports our finding that can fulfill the details about highquality GO nanocomposite membranes on modified γ-alumina tubular substrate with excellent hydrogen separation. In particular, effects of operating parameters such as pressure and temperature on the performance of synthesized GO nanocomposite membrane were analyzed in terms of hydrogen purification.

2. Experimental procedure 2.1. Material In this experimental study, the material sources used as follows: nitric acid (HNO3, 65%, Merck) as catalyst for boehmite sol preparation, and Poly vinyl alcohol (PVA, Merck, MW: 72,000) as stabilizer, aluminum-tri-sec-butoxide (ATSB) (97%, Sigma Aldrich) as source of

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γ-alumina, graphite as source of GO solution, NaNO3 (98%, Merck), H2SO4 (98%, Merck),

H3PO4 (99%, Sigma Aldrich), H2O2 (30%, Merck), HCL (37%, Merck) and KMnO4 (99%, Sigma Aldrich) for GO solution preparation, the high purity gases of H2, CO2 and N2 (99.999

water was also employed in the whole experiments.

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2.2. Nanocomposite graphene membrane preparation

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%, Nanjing Special Gas Co., LTD) as the gas sources for permeance tests, and deionized

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2.2.1. Fabrication of α-alumina support

The home-produced supports used for GO membrane synthesis were α-alumina tubes with

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thickness of 3 mm, outer diameter of 10 mm, length of 70 mm, average pore size of ~ 550 nm

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and average porosity of 39.4%. It should be mentioned that α-alumina tube support were fabricated by gel casting method as in our previous work [33]. Before the γ-alumina layer

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synthesis, the α-alumina supports were cleaned in distilled water by an ultrasonic system for 5 min and then dried at 313 K for 24 h.

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2.2.2. Preparation of γ-Alumina sub-layer

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Regarding to Author’s previous works [33], a new successful strategy was used for surface modification of α-alumina support, in which a particles size control of boehmite sol was applied. In this case, the boehmite sol was prepared by adding aluminum-tri-sec-butylate drop-wise to distilled water, in which about 1.5 L of water was added per mole alkoxide at 80 C and under vigorous stirring. A white solution was obtained, which was peptized with nitric

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acid (0.07 mol HNO3 per mole alkoxide was added). The resulting colloidal suspension was kept boiling until the most of the butanol be evaporated. The PVA solution was made by dissolving PVA (1 wt % of sol) in distilled water under vigorous stirring, then added to sol. The nitric acid was added to decrease the range of pH till 3-4 and after this step sol was refluxed for 16 h to form a stable boehmite sol. The dip-coating process was performed at

room temperature. The substrate speed and dip-time were 1 mm/s and 10 s, respectively. After the dipping step, the membranes were dried in a climate chamber at 313 K at least for 24 h. Subsequently, the γ-alumina layer was formed by calcining at 973 K for 3h in atmospheric condition with a heating and cooling rate of 0.5 C/min. The whole processes of dipping, drying and calcining were repeated 4 times. The optical picture of surface modified alumina substrate has been shown in Figure 1.

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Figure 1: Optical image from prepared γ–alumina support

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2.2.3. Synthesis of graphene oxide solution

In detail, 5 g of graphite and 2.5 g of NaNO3 were mixed with 108 mL H2SO4 and 12 mL H3PO4 and stirred in an ice bath for 10 min. Next, 15 g of KMnO4 were slowly added so that

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the temperature of the mixture remains below 278 K. The suspension was then reacted for 2 h in an ice bath and stirred for 60 min. Again being stirred in a 313 K water bath for 60 min.

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The temperature of the mixture was adjusted to a constant 371 K for 60 min, while water was

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added continuously, deionized water was further added so that the volume of the suspension

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was 400 mL, 15 mL of H2O2 was added after 5 min. The reaction product was centrifuged and washed with deionized water and 5% HCl solution repeatedly. Finally, the product

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diluted in deionized water and the solution of GO was obtained with concentration of 1

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mg/mL [34].The picture of synthesized GO solution for coating process is shown in Figure 2.

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Figure 2: Optical image from synthesized single-layer GO (SLGO) solution

2.2.4. Fabrication of graphene oxide (GO) membrane A typical process to prepare GO membranes is described as follows.

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Firstly, preparation of GO aqueous solution. The GO powder (achieved by freezing dry method from prepared GO solution in Section 2.2.3) was dissolved into deionized water, and at the same time the mixture solution was treated by ultrasound equipment for 1 h to form a high concentration GO aqueous solution. In this step, GO powder was exfoliated to nanosheets. Then, above GO solution was centrifuged at 3000 r/min for 10 min in order to remove agglomerated powder and impurity. After this, the as-prepared solution was diluted 1000 times to form a very low concentration solution (0.001 mg/mL).

Secondly, fabrication of GO membranes. One side of the ceramic tube was sealed and the other side was connected to a vacuum pump (0.1 bar). Then, the whole hollow fiber was immersed in the GO aqueous solution. With the pressure driving, GO flakes were stacked on the surface in order. Through changing the operation time, different thickness GO membranes were fabricated. Finally, the as-prepared GO membrane was dried in a vacuum oven at 318 K over 48 h. The quality of as-prepared GO membranes was examined by testing the H2 and CH4 single gas

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permeation. Figures 3 and 4 give a picture of synthesized nanocomposite GO membrane

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before and after characterization tests, respectively.

Figure 3: Optical image from fabricated GO membrane after permeance tests

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Figure 4: Optical image from fabricated GO membrane before permeance tests

2.3. Characterization methods

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The surface-sectional and cross-sectional images of the α-alumina and modified γ-alumina

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supports were obtained by scanning electron microscopy (SEM- Cam Scan MV 2300,

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Czechoslovakia) and the surface and cross-sectional images of SLGO and synthesized GO membrane by high resolution field emission scanning electron microscopy (FESEM- MIRA3

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FEG-SEM, Czechoslovakia). The working parameters for FESEM tests were a voltage (HV) of 20 kV and a work distance (WD) of 8 mm. Fourier transform infrared spectroscopy for characterization of SLGO were recorded by using a FTIR spectrophotometer (AVATAR-FT-

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IR-360, Thermo Nicolet, USA) over the range of 4000-500 cm-1.

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2.4. Set up of permeance test

The permeation tests were carried out using a custom-made stainless steel module, designed for 70 mm tubular membranes. The membrane ends were sealed in the module using Viton

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O-rings, which allows measuring at temperatures up to 473 K. Pure gas (H2, N2 and CO2) was fed in the range of 0.5-3 bar over ambient and the permeation rates were measured by a bubble flow meter at atmospheric pressure (see Figure 5). The GO membrane performance was investigated at 298, 373 and 473 K versus a pressure difference of 0.5 bar. Therefore, the permselectivity was obtained by the ratio of single gases permeances. The permeance test process was carried out in accordance with the method and experimental homemade apparatus. In a simple style, gas permeance set up is schematically illustrated in Figure 5.

Figure 5: Schematic diagram of the gas separation setup.

3. Results and discussion 3.1. Characterization analysis 

γ-alumina intermediate layer

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In order to prepare microporous composite membranes, the quality of the support is very effective on the membrane layer integrity. The surface roughness and homogeneity of the

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support determines not only the integrity of the membrane layer, but also the minimal

thickness of the membrane layer for complete surface coverage [35]. The use of thin intermediate layers is an attractive alternative which can be used: a) to generate a smooth surface; b) to improve the chemical adhesion of the graphene layer to the support; c) to limit

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the effect of differential thermal expansion coefficients, and finally d) to limit the diffusion of

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the GO sol in the support pores.

The γ-alumina layer is however almost exclusively used as an intermediate membrane layer

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for the development of gas separation membranes. These layers are not susceptible to crack-

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formation and peeling-off effects during the firing process [33]. To modify the homemade α-alumina tubular supports, a γ-alumina intermediate layer using alkoxide source was

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synthesized. Hence, Figure 6 and Figure 7 show SEM and FESEM images of α-alumina and modified γ-alumina supports, respectively.

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Figure 6: SEM image of α-alumina surface support

Figure

7:

FESEM

image

showing

the

cross

(a)

and

surface

(b)-sectional

morphology

of

modified alumina support

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As seen, a homogeneous γ-alumina layer was formed by boehmite sol prepared by ATSB. This is due to the stability of the ATSB boehmite sol which is probably related to the zeta potential in this medium. 

Top GO membrane layer

As we know, the properties of membrane materials have great effect on the separation performance. Before permeation tests, basic properties of GO materials were characterized,

including FESEM and FTIR spectrum. Firstly, as mentioned before, after synthesis of singlelayer GO sol by modified hummer method, FTIR (see Figure 8) and FESEM (see Figure 9) analyses were carried out to characterize of the GO flakes. As illustrated in Figure 8, the FTIR spectrum of GO flakes proves the presences of O–H stretching vibrations (3400 cm-1), C=O stretching vibrations from carbonyl and carboxylic groups (1720 cm-1), unoxidized sp2 C=C bonds in the carbon lattice (1600 cm-1), C-OH stretching vibrations from hydroxyl groups (1220 cm-1), and C–O stretching vibrations from

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epoxy groups (1060 cm-1).

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Figure 8: FTIR spectrum characterization of GO sol

Figure 9 depicts the FESEM image of GO flakes in solution (1mg/ml). The size of GO flake is about 1 µm size. Regarding to the thickness of GO sheets shown in Figure 9, formation of

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single-layer GO solution can be indicated.

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Figure 9: FESEM image of single-layer GO solution

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On the other hand, the FESEM images of GO membrane surface and cross sections are shown in Figure 10. As depicted, the GO membrane layer separately is apparent and the

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homogeneous crack-free membrane layer was formed on the γ-alumina modified support.

Figure 10: FESEM image showing the cross (a) and surface (b)-sectional morphology of synthesized GO

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membrane

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3.2. Performance of the synthesized GO nanocomposite membrane The effects of pressure gradient on modified γ-alumina substrate and α-alumina support for hydrogen and nitrogen permeances are shown in Figure11.

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Figure 11: Gas permeances of N2 and H2 for α-alumina and modified γ-alumina supports versus pressure gradient at room temperature

As presented in this figure, the slope of H2 and N2 permeances is decreased after modifying the support with γ-alumina layer, and in fact, pressure dependency of gas permeance is reduced. So, after modification of alumina support, the Knudsen diffusion can be considered

as dominant mechanism. It should be noted, for synthesis of defect-free GO layer, that it is necessary to fine the pores with surface modification which is illustrative in gas permeance results. Figure 12 shows the single gas permeation results of GO membrane in the range of 298-473 K. The permeation of H2 (dk = 2.9 Å), CO2 (dk = 3.3 Å) and N2 (dk = 3.64 Å) molecules increases with increasing the temperature. These gas permeance results satisfy the Arrhenius dependence when adsorption is in Henry’s region [36]:

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(1)

J = Pe(Pret - Pper )

Pe = J 0 exp (

- (Ed  ΔH ad ) ) RT

(2)

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where J is the flux (mol m-2 s-1) through membrane and Pe is the permeation of the gas considered through the membrane (mol/m2.Pa.S), J0 is flux coefficient, R is the gas constant,

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T is the absolute temperature and Ea (kJ. mol-1) is the apparent activation energy.

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Figure 12: Arrhenius temperature dependence of H2, CO2 and N2 permeances in the synthesized GO membrane;

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(at pressure gradient of 0.5 bar)

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The activation energy for single gas permeation as indicated in Figure 12 was calculated using Eq. (2) and the achieved parameters are listed in Table 1.

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Ea is the sum of two contributions: the heat of sorption of the molecule that is a negative number ( ΔH ad ), because adsorption is an exothermic process in which heat is released, and

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the positive activation energy of mobility of the permeating molecule inside the membrane matrix (Ed). Since these two terms have opposite signs, the apparent activation energy can be

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positive or negative depending on their relative magnitudes [37].

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Table 1: Activation energy and permeation coefficient for single gas permeation

The activation energy of H2, CO2 and N2 molecules permeation in GO membrane is positive and the molecules have greater permeances at higher temperatures. Increased mobility of the molecules causes this, which has positive sign at the activation energy contribution. N2 gas molecules, with the largest kinetic diameter, permeance increases with increasing temperature. This is due to the presence of larger pores in the GO thin film.

3.2.1. Evaluation of pressure and temperature effect on GO membrane performance To evaluate one most promising parameters, single gas permeations of synthesized GO membrane, including H2, CO2 and N2, were tested in detail. As shown in Figure 13-(a) and Figure 13-(b), the permeances of hydrogen and hydrogen selectivities (H2/CO2 and H2/N2) were studied versus increasing temperature in the range of 298-473 K. As indicated in these Figures, hydrogen and also other gases permeances are increased by increasing temperature.

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This is due to an activated diffusion mechanism in the GO membrane. However, the corresponding hydrogen selectivities show a decreasing trend, indicating that some inevitable pores were formed in the GO laminates by heating. Indeed, these irreversible pores would

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also contribute to improving the permeance. Therefore, low temperature ranges (room temperature) are most suitable for GO membrane used in gas separation processes.

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Figure 13: (a); Values of hydrogen permeances and H2/CO2 selectivity (b); Values of hydrogen permeances and H2/N2 selectivity (for GO membrane versus increasing temperatures at pressure gradient 1 bar)

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On the other hand, in contrast of molecular sieve mechanism in microporous membranes, CO2 shows a lower permeance and higher hydrogen selectivity with respect to N2, which can

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be attributed to the chemical nature of GO material. As we know, there are numerous carboxylic acid groups distributed at the edge of GO flakes. Strong interplay between these

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polar groups and C-O bonds in the nonpolar CO2 molecules would happen. For CO2 transfer, CO2 as a Lewis acid or a Lewis base participates in hydrogen bonding, which inhibits it from

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transferring within the stacked GO structure [38]. A similar phenomenon was also found in the porous metal-organic framework (MOF) ZIF-78 membrane [39].

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Furthermore, as a first approach, the pure gas H2 permeance and H2/CO2 selectivity (Figure 14-(a)) and H2/N2 selectivity (Figure 14-(b)) versus increasing pressure gradient for the synthesized GO composite membrane are presented.

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Figure 14: (a); Values of hydrogen permeances and H2/CO2 selectivities (b); Values of hydrogen permeances and H2/N2 selectivities (for GO membrane versus increasing pressure gradient at room temperature)

As shown in these Figures, hydrogen selectivities (H2/CO2 and H2/N2) are increased by enhancement of pressure gradient for GO membrane. Regarding to molecular sieve mechanism, performance of this GO membrane is reasonable.

As we know, a direct comparison among all the experimental data from literatures, as reported in Figure 15, is not possible due to the different operating conditions adopted by each author. Nevertheless, from only a qualitative point of view, it is possible to observe that most of the H2/CO2 permselectivity and hydrogen permeance values for microporous membrane are focused. GO membranes at room temperature show higher performance in the hydrogen separation from carbon dioxide.

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Figure 15: Comparing performance of synthesized GO membrane in this work with literatures data

Indeed, this aspect visualizes to the reader a scenario in which great performance is

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achievable by the synthesized GO membrane. According to the use of a similar vacuum dip

coating method for synthesizing of GO layer by in literature [38], the higher performance of GO membrane in this work probably is related to good surface modification of α-alumina

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support by γ–alumina intermediate layers.

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4. Conclusion

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The GO nanocomposite membrane with high quality was synthesized by vacuum dip coating

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method showing a temperature and pressure dependency flux of molecular sieve mechanism. During synthesis of GO nanocomposite membrane a new successful strategy was used for

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surface modification of α-alumina support, in which a particles size control of boehmite sol was applied. The permeance test results strongly show that the higher quality of surface modification of supports can affect directly the GO membrane performance. Hence, the

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improvement of GO membrane performance can be used in various application. According to the results of gas permeance tests of GO nanocomposite membrane, pressure gradient effect

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was positive on gas permeances, while negative effect on H2/CO2 and H2/N2 selectivities was found. A similar effect was shown for hydrogen selectivities versus temperature increasing. Regarding to low cost of GO nanocomposite membrane with respect to other hydrogenselective membranes such as palladium and silica membranes, the GO membranes have

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acceptable (H2/CO2 and H2/N2) selectivities and permeance values (7.9×10-7 mol.m-2.s-1.Pa-1), while permeance temperature tests in ambient condition present lower energy consumption. Hence, in particular, regarding to pressure and temperature effects, the best performance of the synthesized GO nanocomposite membrane was specified at 298 K and 3 bar.

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[40] Z. Hong, F. Sun, D. D. Chen, C. Zhang, X. H. Gu, N. P. Xu, Improvement of hydrogen-separating performance by on-stream catalytic cracking of silane over hollow fiber MFI zeolite membrane, Int. J. Hydrogen Energy, 38 (2013) 8409−8414. membranes at high temperatures, AIChE J, 54 (2008)1478−1486.

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[41] M. Kanezashi, J. O’Brien-Abraham, Y. S. Lin, K. Suzuki, Gas permeation through DDR-type zeolite

[42] Ch. Chi, X. Wang, Y. Peng, Y. Qian, Z. Hu, J. Dong, and D. Zhao, Facile Preparation of Graphene Oxide

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Membranes for Gas Separation, Chem. Mater, 28 (2016) 2921-2927.

Figures and Tables captions: Figure 1: Optical image from prepared γ–alumina support Figure 2: Optical image from synthesized single-layer GO (SLGO) solution Figure 3: Optical image from fabricated GO membrane after permeance tests Figure 4: Optical image from fabricated GO membrane before permeance tests Figure 5: Schematic diagram of the gas separation setup. Figure 6: SEM image of α-alumina surface support

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Figure 7: FESEM image showing the cross (a) and surface (b)-sectional morphology of modified alumina support Figure 8: FTIR spectrum characterization of GO sol

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Figure 10: FESEM image showing the cross (a) and surface (b)-sectional morphology of synthesized GO membrane

Figure 11: Gas permeances of N2 and H2 for α-alumina and modified γ-alumina supports

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versus pressure gradient at room temperature

Figure 12: Arrhenius temperature dependence of H2, CO2 and N2 permeances in the synthesized GO

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membrane; (at pressure gradient of 0.5 bar)

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Table 1: Activation energy and permeation coefficient for single gas permeation

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Figure 1: Optical image from prepared γ–alumina support

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Figure 1

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Figure 2

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Figure 2: Optical image from synthesized single-layer GO (SLGO) solution

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Figure 3

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Figure 3: Optical image from fabricated GO membrane after permeance tests

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Figure 4

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Figure 4: Optical image from fabricated GO membrane before permeance tests

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Figure 5

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Figure 5: Schematic diagram of the gas separation setup.

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Figure 6: SEM image of α-alumina surface support

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Figure 7

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Figure 7: FESEM image showing the cross (a) and surface (b)-sectional morphology of modified

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γ-alumina support

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Figure 8

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Figure 8: FTIR spectrum characterization of GO sol

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Figure 9

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Figure 10

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GO layer

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Gama-alumina layer

Figure 10: FESEM image showing the cross (a) and surface (b)-sectional morphology of synthesized GO

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membrane

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Figure 11

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Figure 11: Gas permeances of N2 and H2 for α-alumina and modified γ-alumina supports versus pressure gradient at room temperature

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Figure 12

Figure 12: Arrhenius temperature dependence of H2, CO2 and N2 permeances in the synthesized GO membrane;

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(at pressure gradient of 0.5 bar)

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Figure 13


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Figure 15

70 Silica-alumina-[24] GO-alpha-alumina[38] Zeolite-DDR-[41]

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GO-AAO-[42] GO-gama-alumina-[This work]

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H2/CO2 Selectivity [-]

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Silica-alumina-[24]

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0 0

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Table 1

Table 1: Activation energy and permeation coefficient for single gas permeation (Ed- ΔH ad )=Ea (kJ/mol)

J0 (mol/m2.Pa.S)

H2

4.42

141.76*10-8

CO2

7.53

4.55*10*-8

N2

7.36

8*10-8

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Gases