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Ordered mesoporous carbon membrane prepared from liquefied larch by a soft method
Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Q1 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 61 62 63 64 65 66
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Ordered mesoporous carbon membrane prepared from liquefied larch by a soft method Xin Zhao, Wei Li, Shouxin Liu n Key Laboratory of Bio-Based Material Science and Technology, Ministry of Education, Northeast Forestry University, Harbin 150040, China
art ic l e i nf o
a b s t r a c t
Article history: Received 1 December 2013 Accepted 5 April 2014
Carbon membranes having ordered mesoporous structure were prepared via liquefaction, resinification, assembly and carbonization steps using natural renewable larch sawdust as starting material. The mesopores of the carbon membranes were formed by assembly of larch-based resin with F127 (PEO– PPO–PEO). The mesoporosity was controllable from disordered to ordered by varying the carbonization temperature. Mesoporous carbon membrane with an ordered two-dimensional hexagonal porous structure having P6mm symmetry was obtained at 700 1C. The unique ordered mesoporous structure resulted in the carbon membranes exhibiting high efficiency (permselectivity factor ¼1.97) for the separation of CO2 from a N2/CO2 mixture. & 2014 Published by Elsevier B.V.
Keywords: Liquefied larch Carbon membrane Ordered mesoporous Nanomaterials
1. Introduction The growing demand for green energy and efficient gas separation has attracted extensive research into the development of new membrane synthesis technologies and renewable starting materials. Gas separation using membranes relies on the thermal, chemical, and mechanical properties of the membrane materials. Recently, mesoporous carbon membranes (CMs) with ordered pores have appeared as promising candidates for gas separation due to their uniform pore structure [1]. Until now, ordered carbon membranes have usually been synthesized from synthetic phenolic resins using a soft-template strategy [2,3]. The hydroxyl groups of such phenolic resins interact with the PEO groups (polyethylene oxide) of the soft template F127 or P123 (PEOn–PPOm–PEOn), and form ordered mesopores [4,5]. Considering the large availability and renewable characteristics of biomass such as waste wood, the liquefaction of wood as a replacement for phenol in the synthesis of novel carbon materials with specific morphology and porous structure has proved promising [6]. It is highly expected that wood components depolymerized through liquefaction processes and reacted with specific organic reagents will produce various value-added polymer precursors or chemicals [7]. However, the preparation of ordered carbons with tunable pore structure from wood remains a challenge due to the complex intrinsic natural characteristics of wood.
n
Corresponding author. Tel./fax: þ 86 451 82191204. E-mail address: [email protected] (S. Liu).
In the present work, we focus on the preparation of ordered mesoporous carbon membrane by organic-organic assembly of copolymer F127 with liquefied larch-based resins using an evaporation-induced self-assembly (EISA) strategy. The performance of the obtained carbon in the separation of CO2 from a N2/CO2 mixture was investigated.
2. Experimental Liquefaction of larch sawdust: The procedure used to prepare the liquefied larch sawdust was based on that reported in the literature [8]; 10 g of larch sawdust, phenol (30 mL), sulfuric acid (98%, 1 mL), and phosphoric acid (85%, 2 mL) were added to a three-necked glass reactor that was equipped with a mechanical stirrer, thermometer, and condenser. The mixture was heated under reflux at a temperature of 110–120 1C for 1 h. When the reaction was finished, methanol (120 mL) was added to the liquefied product. The mixture was then filtered, the pH was adjusted to neutral using sodium hydroxide, and the mixture was filtered again to remove the resulting precipitate. The filtrate was concentrated by vacuum distillation at 40 1C to remove the methanol, yielding liquefied larch wood. Preparation of carbon membranes: In a typical synthesis, formaldehyde (37%, 90 mL) and sodium hydroxide (3 g) were added to the liquefied larch to generate larch-based resin under basic conditions. F127 (10 g) was then added and stirred for 20 h at 40 1C. Next, the pH was adjusted to 0.5 with HCl and the reaction was continued for 8 h at 50 1C. The obtained mixture was paved in ceramic ring matrices of 3 cm diameter and dried at 80 1C for 6 h.
http://dx.doi.org/10.1016/j.matlet.2014.04.027 0167-577X/& 2014 Published by Elsevier B.V.
Please cite this article as: Zhao X, et al. Ordered mesoporous carbon membrane prepared from liquefied larch by a soft method. Mater Lett (2014), http://dx.doi.org/10.1016/j.matlet.2014.04.027i
Q2
X. Zhao et al. / Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎
2
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 61 62 63 64 65 66
Finally, the carbon membranes were formed after carbonization under a N2 atmosphere at different temperatures (500 1C, 600 1C, 700 1C) for 2 h. The carbon membranes were denoted as CM-x, where x is the carbonization temperature. Characterization: The morphology of the CMs was examined by scanning electron microscopy (SEM; QUATA 200, Zeiss, Japan) operating at an accelerating voltage of 15 kV. Transmission electron microscopy images were obtained on a JEOL 2011 (FEI, Holland) operated at 200 kV. Nitrogen sorption isotherms were measured with a Micromeritics ASAP 2020 sorptometer using nitrogen as the adsorbate at 77 K. Before analysis, all samples were degassed at 300 K for more than 10 h. The surface areas were calculated using the BET (multi-point Brunauer–Emmett–Teller) method using the adsorption data in the relative pressure (P/P0) range of 0.04–0.2. The micropore surface area and volume were obtained using t-plot analysis. The pore size distributions (PSDs) were determined using non-local density functional theory (NLDFT), based on nitrogen adsorption data with a slit pore model. Gas separation test: The permeation through the carbon membranes by CO2 and N2 gases was measured at ambient temperature (20 71 1C). The carbon membrane (area E3 10 4 m2) was attached to a permeation cell and high-pressure ultra-pure gases supplied from compressed gas cylinders were placed in contact with the membranes. A manometer was used to measure the pressure. Vacuum was maintained on the low-pressure side of the membranes, and the permeation was pulled through a calibrated volume. The gas permeation and permeability of membranes was estimated from K (m3 cm/m2 h kPa) defined by K ¼ 45:8
aA=B ¼
Vδ
ð1Þ
2
d ΔP t
KA KB
ð2Þ
where V is the permeate volume, here 27.79(H2–H1); ΔP is the pressure difference, where ΔP ¼(P1 þ P2)/2; δ is the membrane thickness, d is the spherical diameter, and t is the experiment duration. aA/B is the gas permeability of the membrane for gases A and B.
3. Results and discussion Transmission electron microscopy (TEM) images of carbon membranes carbonized at different temperatures are shown in Fig. 1a–c. Both disordered and ordered mesopores (centered at 2 nm), which were formed by assembly of the PEO groups in F127 with hydroxyl groups [4] from the liquefied larch and larch-based resin, were observed. According to the TEM images, the carbonization temperature has significant effects on the formation of the porous structure. CM-500 (Fig. 1a) shows a typical disordered mesoporous structure, while ordered mesopores with 1D channels are observed for CM-600 (Fig. 1b). At a further increase in carbonization temperature, CM-700 (Fig. 1c) exhibited wellordered arrays in large domains, which indicated the formation of an ordered 2D hexagonal mesostructure with 1D channels. Because F127 decomposes at lower temperatures (o400 1C), the formation of the porous structure is closely related to the degree of Table 1 Structural parameters of CMs prepared at different carbonization temperatures. Sample
SBET (m2∕g)
Smicro/SBET (%)
Vtotal (cm3∕g)
Average pore diameter (nm)
CM-500 CM-600 CM-700 CM-800
367 400 469 346
80 83 87 78
0.198 0.214 0.250 0.126
2.15 2.14 2.13 2.63
100μ m ± 20μ m
5nm
5nm
5nm
Fig. 1. TEM and SEM images of CMs prepared at different carbonization temperatures (TEM, a: CM-500; b: CM-600; c: CM-700; SEM, d: CM-700).
Fig. 2. Nitrogen adsorption–desorption isotherms and pore diameter distribution of CMs prepared at different carbonization temperatures.
Please cite this article as: Zhao X, et al. Ordered mesoporous carbon membrane prepared from liquefied larch by a soft method. Mater Lett (2014), http://dx.doi.org/10.1016/j.matlet.2014.04.027i
X. Zhao et al. / Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎
40
27.82 23.51 16.37 500
600
14.12 700
1.97 Permselectivity
30.94
20
2.0
CO2 N2
39.77 Permeability (Barrer)
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 61 62 63 64 65 66
3
1.89 1.8
1.69 500
Temperature (oC)
600
700
Temperature (oC)
Fig. 3. Gas permeation and permeation selectivity of CMs prepared at different carbonization temperatures.
decomposition of the larch-based resin hydroxyl groups [6,8–10]. These hydroxyl groups decomposed completely as the carbonization temperature increased, resulting in the formation of a perfect pore structure. A scanning electron microscopy (SEM) image of CM-700 is shown in Fig. 1d. It is clear that the CM-700 membrane consisted of large number of carbon spheres with surface defects. This may be due to the fact that the block copolymer F127 had amphiphilic properties; the hydrophilic groups allowed the formation of spherical structure [11]. The thickness of the CM-700 membrane was measured as 100 7 20 μm, which is considered suitable for CO2/N2 separation. Fig. 2 shows the nitrogen adsorption–desorption isotherms and corresponding pore size distributions of the CMs. All samples exhibited type IV isotherm with steep increase in the adsorption– desorption cure (P/P0 o0.4) due to monolayer, multilayer adsorption in the mesopores and type H2 hysteresis loop at higher pressure (0.4 1.0 P/P0 ) corresponds to pore filling by capillary condensation [12], which is associated with capillary condensation occurring in the mesopores [9]. The shape of the hysteresis loops changed slightly with increasing carbonization temperature, which indicated that the number of mesopores decreased correspondingly. All CMs exhibited high N2 adsorption capacity at P/ P0 ¼0.1, which indicated the generation of developed micropores. In addition, more groups were decomposed and led to the generation of a more developed mesoporous structure (centered at 2 nm) with increasing carbonization temperature. The pore size distribution curves showed that the pore sizes of all of the obtained CM samples were distributed in the range of 1.5– 3.0 nm. The pore size distribution gradually became more uniform with increasing carbonization temperature, as confirmed by the TEM images. Meanwhile, the SBET, pore volume, and the micropore surface area increased with carbonization temperature from 500 1C to 700 1C. The surface area increased from 367 m2∕g to 469 m2∕g, while the percentage of microporous surface area increased from 80% to 87%, respectively. It can therefore be concluded that high carbonization temperature may be beneficial for generation of more developed micropores, as shown in Table 1. However, the SBET, pore volume, and micropore surface area decreased, while the average pore diameter increased, when the temperature was increased to 800 1C. This may have been due to collapse of the micropore walls. Fig. 3 shows the CO2 and N2 gas permeability and permeation selectivity of the CMs as calculated from Eqs. (1) and (2), respectively. While the gas permeability of the CMs obviously decreased with increasing carbonization temperature, the
permselectivity increased. Gas molecules migrate mainly through interconnecting interstitial voids. The internal pores of the CM were responsible for the separation of the gases [13]. Thus, the reductions in passing rate and gas volume were caused by a decrease in the number of pores by interstitial voids. Moreover, the mass of gas that permeated the membrane is reduced, as shown in Fig. 3a. The selectivity of the CMs was driven by the intermolecular force of the different gases, and the selectivity was enhanced as the number of micropores increased [5]. From Fig. 3b, the permselectivity increased with carbonization temperature, that is, the amount of smaller micropores also increased with temperature. This result is confirmed by the structural parameters (Table 1). The highest permselectivity factor of 1.97 was achieved for CM-700, which is higher than the Knudsen ideal separation factor of 0.79.
4. Conclusions Ordered carbon membranes with a two-dimensional hexagonal structure of P6mm symmetry were successfully prepared from larch sawdust using a soft-template method. The surface area and pore volume of the carbon membranes were in the range of 367– 469 m2∕g and 0.126–0.250 cm3∕g, respectively. The pore size distribution was centered at 2 nm. The mesoporous structure of the membranes was formed by assembly of hydroxyl groups in the liquefied larch and larch-based resin with the PEO groups of F127 (PEO–PPO–PEO). The mesopores were controllable from disordered to ordered form by varying the carbonization temperature. The unique ordered mesoporous structure obtained resulted in the carbon membranes having high efficiency (permselectivity factor¼1.97) for the separation of CO2 from a N2/CO2 mixture.
Acknowledgments This work was financially supported by the Research Fund for the Doctoral Program of Higher Education of China (2010 0062110003), the National Natural Science Foundation of China Q3 (No.31170545), and the Fundamental Research Funds for the Central Universities (DL11EB01). References [1] Kelly B, Ricard GV, Daniel MJ. Chem Eng 2010;5:169–78. [2] Tanaka S, Yasuda T, Miyake Y. J Membr Sci 2011;379:52–9.
Please cite this article as: Zhao X, et al. Ordered mesoporous carbon membrane prepared from liquefied larch by a soft method. Mater Lett (2014), http://dx.doi.org/10.1016/j.matlet.2014.04.027i
4
1 2 3 4 5 6
X. Zhao et al. / Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎
[3] Teixeira Miguel, Campo Marta C, César Magen, Mendes Adélio. Carbon 2011;49:4348–58. [4] Kimijima K, Hayashi A, Yagi I. Chem Commun 2008;44:5809–11. [5] Mahurin SM, Lee JS, Dai SJ. Membr Sci 2011;368:41–7. [6] Wang MC, Leitch M, Xu CC. J Ind Eng Chem 2009;15:870–5. [7] Lin LZ, Yao YG, Shiraishi N. Carbohydr Polym 2004;57:123–9.
[8] [9] [10] [11] [12] [13]
Meng Y, Gu D, Zhao DY. Chem Mater 2006;18:4447–64. Huang CH, Doong RA. Microporous Mesoporous Mater 2012;147:47–52. Wang R, Li W, Liu SX. J Mater Sci 2012;47:1977–84. Zhao X, Li W, Liu SX. Mater Lett 2013;107:5–8. Wang XQ, Zhu Q, Dai S. Carbon 2010;48:557–79. Chen XW, Hong L, Chan WKI. J Membr Sci 2011;379:353–60.
Please cite this article as: Zhao X, et al. Ordered mesoporous carbon membrane prepared from liquefied larch by a soft method. Mater Lett (2014), http://dx.doi.org/10.1016/j.matlet.2014.04.027i
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Q1 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 61 62 63 64 65 66
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Ordered mesoporous carbon membrane prepared from liquefied larch by a soft method Xin Zhao, Wei Li, Shouxin Liu n Key Laboratory of Bio-Based Material Science and Technology, Ministry of Education, Northeast Forestry University, Harbin 150040, China
art ic l e i nf o
a b s t r a c t
Article history: Received 1 December 2013 Accepted 5 April 2014
Carbon membranes having ordered mesoporous structure were prepared via liquefaction, resinification, assembly and carbonization steps using natural renewable larch sawdust as starting material. The mesopores of the carbon membranes were formed by assembly of larch-based resin with F127 (PEO– PPO–PEO). The mesoporosity was controllable from disordered to ordered by varying the carbonization temperature. Mesoporous carbon membrane with an ordered two-dimensional hexagonal porous structure having P6mm symmetry was obtained at 700 1C. The unique ordered mesoporous structure resulted in the carbon membranes exhibiting high efficiency (permselectivity factor ¼1.97) for the separation of CO2 from a N2/CO2 mixture. & 2014 Published by Elsevier B.V.
Keywords: Liquefied larch Carbon membrane Ordered mesoporous Nanomaterials
1. Introduction The growing demand for green energy and efficient gas separation has attracted extensive research into the development of new membrane synthesis technologies and renewable starting materials. Gas separation using membranes relies on the thermal, chemical, and mechanical properties of the membrane materials. Recently, mesoporous carbon membranes (CMs) with ordered pores have appeared as promising candidates for gas separation due to their uniform pore structure [1]. Until now, ordered carbon membranes have usually been synthesized from synthetic phenolic resins using a soft-template strategy [2,3]. The hydroxyl groups of such phenolic resins interact with the PEO groups (polyethylene oxide) of the soft template F127 or P123 (PEOn–PPOm–PEOn), and form ordered mesopores [4,5]. Considering the large availability and renewable characteristics of biomass such as waste wood, the liquefaction of wood as a replacement for phenol in the synthesis of novel carbon materials with specific morphology and porous structure has proved promising [6]. It is highly expected that wood components depolymerized through liquefaction processes and reacted with specific organic reagents will produce various value-added polymer precursors or chemicals [7]. However, the preparation of ordered carbons with tunable pore structure from wood remains a challenge due to the complex intrinsic natural characteristics of wood.
n
Corresponding author. Tel./fax: þ 86 451 82191204. E-mail address: [email protected] (S. Liu).
In the present work, we focus on the preparation of ordered mesoporous carbon membrane by organic-organic assembly of copolymer F127 with liquefied larch-based resins using an evaporation-induced self-assembly (EISA) strategy. The performance of the obtained carbon in the separation of CO2 from a N2/CO2 mixture was investigated.
2. Experimental Liquefaction of larch sawdust: The procedure used to prepare the liquefied larch sawdust was based on that reported in the literature [8]; 10 g of larch sawdust, phenol (30 mL), sulfuric acid (98%, 1 mL), and phosphoric acid (85%, 2 mL) were added to a three-necked glass reactor that was equipped with a mechanical stirrer, thermometer, and condenser. The mixture was heated under reflux at a temperature of 110–120 1C for 1 h. When the reaction was finished, methanol (120 mL) was added to the liquefied product. The mixture was then filtered, the pH was adjusted to neutral using sodium hydroxide, and the mixture was filtered again to remove the resulting precipitate. The filtrate was concentrated by vacuum distillation at 40 1C to remove the methanol, yielding liquefied larch wood. Preparation of carbon membranes: In a typical synthesis, formaldehyde (37%, 90 mL) and sodium hydroxide (3 g) were added to the liquefied larch to generate larch-based resin under basic conditions. F127 (10 g) was then added and stirred for 20 h at 40 1C. Next, the pH was adjusted to 0.5 with HCl and the reaction was continued for 8 h at 50 1C. The obtained mixture was paved in ceramic ring matrices of 3 cm diameter and dried at 80 1C for 6 h.
http://dx.doi.org/10.1016/j.matlet.2014.04.027 0167-577X/& 2014 Published by Elsevier B.V.
Please cite this article as: Zhao X, et al. Ordered mesoporous carbon membrane prepared from liquefied larch by a soft method. Mater Lett (2014), http://dx.doi.org/10.1016/j.matlet.2014.04.027i
Q2
X. Zhao et al. / Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎
2
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 61 62 63 64 65 66
Finally, the carbon membranes were formed after carbonization under a N2 atmosphere at different temperatures (500 1C, 600 1C, 700 1C) for 2 h. The carbon membranes were denoted as CM-x, where x is the carbonization temperature. Characterization: The morphology of the CMs was examined by scanning electron microscopy (SEM; QUATA 200, Zeiss, Japan) operating at an accelerating voltage of 15 kV. Transmission electron microscopy images were obtained on a JEOL 2011 (FEI, Holland) operated at 200 kV. Nitrogen sorption isotherms were measured with a Micromeritics ASAP 2020 sorptometer using nitrogen as the adsorbate at 77 K. Before analysis, all samples were degassed at 300 K for more than 10 h. The surface areas were calculated using the BET (multi-point Brunauer–Emmett–Teller) method using the adsorption data in the relative pressure (P/P0) range of 0.04–0.2. The micropore surface area and volume were obtained using t-plot analysis. The pore size distributions (PSDs) were determined using non-local density functional theory (NLDFT), based on nitrogen adsorption data with a slit pore model. Gas separation test: The permeation through the carbon membranes by CO2 and N2 gases was measured at ambient temperature (20 71 1C). The carbon membrane (area E3 10 4 m2) was attached to a permeation cell and high-pressure ultra-pure gases supplied from compressed gas cylinders were placed in contact with the membranes. A manometer was used to measure the pressure. Vacuum was maintained on the low-pressure side of the membranes, and the permeation was pulled through a calibrated volume. The gas permeation and permeability of membranes was estimated from K (m3 cm/m2 h kPa) defined by K ¼ 45:8
aA=B ¼
Vδ
ð1Þ
2
d ΔP t
KA KB
ð2Þ
where V is the permeate volume, here 27.79(H2–H1); ΔP is the pressure difference, where ΔP ¼(P1 þ P2)/2; δ is the membrane thickness, d is the spherical diameter, and t is the experiment duration. aA/B is the gas permeability of the membrane for gases A and B.
3. Results and discussion Transmission electron microscopy (TEM) images of carbon membranes carbonized at different temperatures are shown in Fig. 1a–c. Both disordered and ordered mesopores (centered at 2 nm), which were formed by assembly of the PEO groups in F127 with hydroxyl groups [4] from the liquefied larch and larch-based resin, were observed. According to the TEM images, the carbonization temperature has significant effects on the formation of the porous structure. CM-500 (Fig. 1a) shows a typical disordered mesoporous structure, while ordered mesopores with 1D channels are observed for CM-600 (Fig. 1b). At a further increase in carbonization temperature, CM-700 (Fig. 1c) exhibited wellordered arrays in large domains, which indicated the formation of an ordered 2D hexagonal mesostructure with 1D channels. Because F127 decomposes at lower temperatures (o400 1C), the formation of the porous structure is closely related to the degree of Table 1 Structural parameters of CMs prepared at different carbonization temperatures. Sample
SBET (m2∕g)
Smicro/SBET (%)
Vtotal (cm3∕g)
Average pore diameter (nm)
CM-500 CM-600 CM-700 CM-800
367 400 469 346
80 83 87 78
0.198 0.214 0.250 0.126
2.15 2.14 2.13 2.63
100μ m ± 20μ m
5nm
5nm
5nm
Fig. 1. TEM and SEM images of CMs prepared at different carbonization temperatures (TEM, a: CM-500; b: CM-600; c: CM-700; SEM, d: CM-700).
Fig. 2. Nitrogen adsorption–desorption isotherms and pore diameter distribution of CMs prepared at different carbonization temperatures.
Please cite this article as: Zhao X, et al. Ordered mesoporous carbon membrane prepared from liquefied larch by a soft method. Mater Lett (2014), http://dx.doi.org/10.1016/j.matlet.2014.04.027i
X. Zhao et al. / Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎
40
27.82 23.51 16.37 500
600
14.12 700
1.97 Permselectivity
30.94
20
2.0
CO2 N2
39.77 Permeability (Barrer)
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 61 62 63 64 65 66
3
1.89 1.8
1.69 500
Temperature (oC)
600
700
Temperature (oC)
Fig. 3. Gas permeation and permeation selectivity of CMs prepared at different carbonization temperatures.
decomposition of the larch-based resin hydroxyl groups [6,8–10]. These hydroxyl groups decomposed completely as the carbonization temperature increased, resulting in the formation of a perfect pore structure. A scanning electron microscopy (SEM) image of CM-700 is shown in Fig. 1d. It is clear that the CM-700 membrane consisted of large number of carbon spheres with surface defects. This may be due to the fact that the block copolymer F127 had amphiphilic properties; the hydrophilic groups allowed the formation of spherical structure [11]. The thickness of the CM-700 membrane was measured as 100 7 20 μm, which is considered suitable for CO2/N2 separation. Fig. 2 shows the nitrogen adsorption–desorption isotherms and corresponding pore size distributions of the CMs. All samples exhibited type IV isotherm with steep increase in the adsorption– desorption cure (P/P0 o0.4) due to monolayer, multilayer adsorption in the mesopores and type H2 hysteresis loop at higher pressure (0.4 1.0 P/P0 ) corresponds to pore filling by capillary condensation [12], which is associated with capillary condensation occurring in the mesopores [9]. The shape of the hysteresis loops changed slightly with increasing carbonization temperature, which indicated that the number of mesopores decreased correspondingly. All CMs exhibited high N2 adsorption capacity at P/ P0 ¼0.1, which indicated the generation of developed micropores. In addition, more groups were decomposed and led to the generation of a more developed mesoporous structure (centered at 2 nm) with increasing carbonization temperature. The pore size distribution curves showed that the pore sizes of all of the obtained CM samples were distributed in the range of 1.5– 3.0 nm. The pore size distribution gradually became more uniform with increasing carbonization temperature, as confirmed by the TEM images. Meanwhile, the SBET, pore volume, and the micropore surface area increased with carbonization temperature from 500 1C to 700 1C. The surface area increased from 367 m2∕g to 469 m2∕g, while the percentage of microporous surface area increased from 80% to 87%, respectively. It can therefore be concluded that high carbonization temperature may be beneficial for generation of more developed micropores, as shown in Table 1. However, the SBET, pore volume, and micropore surface area decreased, while the average pore diameter increased, when the temperature was increased to 800 1C. This may have been due to collapse of the micropore walls. Fig. 3 shows the CO2 and N2 gas permeability and permeation selectivity of the CMs as calculated from Eqs. (1) and (2), respectively. While the gas permeability of the CMs obviously decreased with increasing carbonization temperature, the
permselectivity increased. Gas molecules migrate mainly through interconnecting interstitial voids. The internal pores of the CM were responsible for the separation of the gases [13]. Thus, the reductions in passing rate and gas volume were caused by a decrease in the number of pores by interstitial voids. Moreover, the mass of gas that permeated the membrane is reduced, as shown in Fig. 3a. The selectivity of the CMs was driven by the intermolecular force of the different gases, and the selectivity was enhanced as the number of micropores increased [5]. From Fig. 3b, the permselectivity increased with carbonization temperature, that is, the amount of smaller micropores also increased with temperature. This result is confirmed by the structural parameters (Table 1). The highest permselectivity factor of 1.97 was achieved for CM-700, which is higher than the Knudsen ideal separation factor of 0.79.
4. Conclusions Ordered carbon membranes with a two-dimensional hexagonal structure of P6mm symmetry were successfully prepared from larch sawdust using a soft-template method. The surface area and pore volume of the carbon membranes were in the range of 367– 469 m2∕g and 0.126–0.250 cm3∕g, respectively. The pore size distribution was centered at 2 nm. The mesoporous structure of the membranes was formed by assembly of hydroxyl groups in the liquefied larch and larch-based resin with the PEO groups of F127 (PEO–PPO–PEO). The mesopores were controllable from disordered to ordered form by varying the carbonization temperature. The unique ordered mesoporous structure obtained resulted in the carbon membranes having high efficiency (permselectivity factor¼1.97) for the separation of CO2 from a N2/CO2 mixture.
Acknowledgments This work was financially supported by the Research Fund for the Doctoral Program of Higher Education of China (2010 0062110003), the National Natural Science Foundation of China Q3 (No.31170545), and the Fundamental Research Funds for the Central Universities (DL11EB01). References [1] Kelly B, Ricard GV, Daniel MJ. Chem Eng 2010;5:169–78. [2] Tanaka S, Yasuda T, Miyake Y. J Membr Sci 2011;379:52–9.
Please cite this article as: Zhao X, et al. Ordered mesoporous carbon membrane prepared from liquefied larch by a soft method. Mater Lett (2014), http://dx.doi.org/10.1016/j.matlet.2014.04.027i
4
1 2 3 4 5 6
X. Zhao et al. / Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎
[3] Teixeira Miguel, Campo Marta C, César Magen, Mendes Adélio. Carbon 2011;49:4348–58. [4] Kimijima K, Hayashi A, Yagi I. Chem Commun 2008;44:5809–11. [5] Mahurin SM, Lee JS, Dai SJ. Membr Sci 2011;368:41–7. [6] Wang MC, Leitch M, Xu CC. J Ind Eng Chem 2009;15:870–5. [7] Lin LZ, Yao YG, Shiraishi N. Carbohydr Polym 2004;57:123–9.
[8] [9] [10] [11] [12] [13]
Meng Y, Gu D, Zhao DY. Chem Mater 2006;18:4447–64. Huang CH, Doong RA. Microporous Mesoporous Mater 2012;147:47–52. Wang R, Li W, Liu SX. J Mater Sci 2012;47:1977–84. Zhao X, Li W, Liu SX. Mater Lett 2013;107:5–8. Wang XQ, Zhu Q, Dai S. Carbon 2010;48:557–79. Chen XW, Hong L, Chan WKI. J Membr Sci 2011;379:353–60.
Please cite this article as: Zhao X, et al. Ordered mesoporous carbon membrane prepared from liquefied larch by a soft method. Mater Lett (2014), http://dx.doi.org/10.1016/j.matlet.2014.04.027i