- Email: [email protected]
Intercalation of various organic molecules into pillared carbon
CARBON
5 0 ( 2 0 1 2 ) 2 2 8 0 –2 2 8 6
Available at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/carbon
Intercalation of various organic molecules into pillared carbon Yoshiaki Matsuo *, Kentaro Konishi Department of Materials Science and Chemistry, Graduate School of Engineering, University of Hyogo, 2167 Shosha Himeji, Hyogo 671-2280, Japan
A R T I C L E I N F O
A B S T R A C T
Article history:
Intercalation of various organic molecules into pillared carbon prepared from the pyrolysis
Received 18 November 2011
of graphite oxide silylated with methyltrichlorosilane for three times was investigated.
Accepted 13 January 2012
Liquid n-alkylamine molecules with various alkyl chain lengths were intercalated into
Available online 24 January 2012
the resulting pillared carbon and the interlayer spacing increased with increasing in the alkyl chain length, until it became a constant value of 2.24 nm for chains having more than six carbon atoms. This suggests that the length of the pillar is 1.9 nm. Various organic molecules including non-polar xylene isomers and alcohol molecules can also penetrate into pillared carbon. The n-hexadecylamine molecules with a higher melting point than room temperature were intercalated into pillared carbon simply by mixing them with pillared carbons in hexane, though the interlayer spacing was smaller. The space between the layers of pillared carbon was saturated with n-hexadecylamine molecules when 1.8 molecules per 40 carbon atoms were added. The n-hexadecylamine molecules occupied 51% of the micropore volume of pillared carbon. For the intercalation of organic molecules into pillared carbon, the shorter axis of them should be smaller than 0.87 nm. 2012 Elsevier Ltd. All rights reserved.
1.
Introduction
Porous materials with controlled pore structures are attracting much attention for the support of catalysts, gas storage, adsorbents, electrode of electric double layer capacitor and so on. These include mesoporous silicas, meso- or microporous carbons, metal organic frameworks (MOF)/porous coordination polymers (PCP), zeolites, pillared layered materials, etc. [1–6]. Most of these materials possess rigid frameworks and structural change is not usually observed during adsorption, however, some of the PCP/MOF showed unique adsorption behaviors for small molecules, accompanied by a reversible structural change [7–15]. It would be very interesting for catalysts, sensors, etc., if conducting and chemically stable carbon based materials show similar properties. In this context, we have recently prepared pillared carbons by pyrolysis of silylated graphite oxide and the adjacent
carbon layers of them are connected with each other by silica or silsesquioxane pillars through CAOASi and SiAOASi bondings [16–19]. Moreover, we have also found that polar organic molecules were size-selectively intercalated into the pillared carbon prepared from graphite oxide repeatedly silylated with methyltrichlorosilane, which was accompanied by large interlayer expansions [20]. Considering the minimum molecular widths of the intercalated organic molecules, this indicated that the width between two adjacent pillars for the entrance of organic molecules is well controlled between 0.36 and 0.4 nm. At the same time, the pillars connecting the adjacent carbon layers should incline from the normal against the carbon layers and the length of the pillars should be larger than 1.72 nm. In this study, the intercalation behaviors of various organic molecules into the above mentioned pillared carbon were investigated in detail.
* Corresponding author: Fax: +81 792 67 4898. E-mail address: [email protected] (Y. Matsuo). 0008-6223/$ - see front matter 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbon.2012.01.047
CARBON
Experimental
250
Adsorbed N2 / mLSTP/g
2.
2281
5 0 ( 20 1 2 ) 2 2 8 0–22 8 6
Preparation of pillared carbon was performed in the same manner as reported in our previous studies [18,20]. Graphite oxide (hereafter abbreviated as GO) was prepared from natural graphite powder (57–74 lm) in fuming nitric acid using potassium chlorate, based on the Brodie’s method [21] and oxidation procedure was repeated five times. The composition of the resulting GO was C8H3.0O4.5. GO was silylated as follows, according to our previous studies [22,23]. GO (100 mg) was mixed with n-butylamine (C4H9NH2, hereafter abbreviated as C4, 2 mL; 32 mol per GO unit (C8H3.0O4.5)) as an exfoliating reagent in a sealed glass vial under an Argon atmosphere and the resulting solution was sonicated, then heated at 60 C for 1 h. Dry toluene (5 mL, water content <30 ppm) was added to this solution and the solution was again sonicated. Methyltrichlorosilane, CH3SiCl3, abbreviated as C1Si: 0.90 mL) was added to the resulting dispersion and then it was allowed to stand for 2 day at 60 C. After centrifugation at 4000 rpm for 20 min, the precipitate was washed with dry toluene, ethanol and finally acetone. The obtained silylated GO samples were silylated with C1Si in the same manner as described above for 1 day. This was repeated for two times. The composition of silylated GO was determined from the weight of residual SiO2 after thermogravimetric analysis, assuming that 0.4 n-butylamine molecules per C8 GO unit were intercalated [23] and (C1Si)2.1GO was obtained. The content of C1Si in GO was slightly smaller than that obtained in our previous study [20]. The resulting silylating GO was heated at 500 C under dynamic vacuum and pillared carbon was obtained. Here, the temperature increase rate was 1 C/min and the amount of the sample was less than 200 mg in order to avoid the deflagration of GO layers due to the heat generate during the removal oxygen from GO layers. These samples were analyzed by X-ray diffraction (Rigaku, Rint-2100, CuKa), thermogravimetric (TG; Shimadzu, TGA-50), N2 gas adsorption at 196 C (Bel Japan, BELSORP-Max) and scanning electron microscopy (SEM; JEOL, JSM-5600). TG measurement was performed under air with the temperature increase rate of 5 C/min between room temperature and 800 C. Intercalation behavior of organic molecules into pillared carbons was investigated as follows. Pillared carbon was immersed in the solutions of organic molecules of n-alkylamines with various alkyl chain lengths, n-octanol and xylenes for 24 h and the resulting samples were analyzed by X-ray diffractometry without drying. The evaporation of organic molecules was avoided during measurement by covering the samples with kapton film. In case of the intercalation of solid n-hexadecylamine molecules, they were mixed with pillared carbons in a pestle and then a small amount of hexane was added as reported previously [24,25]. The mixture was mechanically ground until the hexane was evaporated and then the resulting sample was dried at 60 C.
676 m2/g which was slightly higher than that observed in our previous study (550 m2/g) [20]. Moreover, hysteresis during desorption was not observed. The slightly lower pillar density in the present pillared carbon than that of the previous sample [20] could be responsible for the higher BET surface area and easier diffusion of N2 molecules in it. However, the selective intercalation of propylene carbonate, dimethylsulfoxide, diethoxyethane and vinylene carbonate was commonly observed, indicating that the distance between the pillars for the entrance of the organic molecules is almost the same. The pore distribution of pillared carbon estimated based on the HK method is shown in Fig. 2 and a sharp peak at 0.46 nm was observed. The pores in pillared carbon are very small and they are distributed quite uniformly in the gallery of it.
3.
Results and discussion
3.2. Intercalation behavior of liquid organic molecules into pillared carbon
3.1.
N2 gas adsorption behavior of pillared carbon
The N2 adsorption isotherm of the pillared carbon at 196 C was type I as shown in Fig. 1 and the BET surface area was
Adsorbed N2 / mLSTP/g
200 150 100 50
250 200 150 100 50 0 1.0E-08
1.0E-04 P / P0
0 0
0.2
0.4
1.0E+00
0.6
0.8
1
P / P0 Fig. 1 – N2 gas adsorption isotherm of pillared carbon at 196 C. Filled and open marks indicate the data during adsorption and desorption, respectively. Inset shows the logarithm plot for relative pressure.
1.2
dVp/d(dp)
1 0.8 0.6 0.4 0.2 0 0
1
2
3
4
Pore diameter / nm Fig. 2 – Pore size distribution of pillared carbon determined based on the HK method.
Fig. 3 shows the X-ray diffraction patterns of pillared carbon prepared from (C1Si)2.1GO after immersion in the solutions of n-alkylamine molecules with various alkyl chain lengths. The diffraction peak of pillared carbon observed at 2h = 13.5
CARBON
***
5 0 ( 2 0 1 2 ) 2 2 8 0 –2 2 8 6
* **
*
(F)
Intensity/A.U.
(E) (D) (C) (B) (A) 2
6
10
14
18
22
26
30
2θ/ deg. CuKα Fig. 3 – X-ray diffraction patterns of pillared carbon prepared from (C1Si)2.1GO (A): before and after immersion in nalkylamines with various alkyl chain lengths of (B) 3, (C) 4, (D) 6, (E) 8 and (F) 12. The peaks marked with ‘‘*’’ indicate the residual n-alkylamines crystallized on the surface of pillared carbon.
(d = 1.31 nm) and 20.3 (d = 0.658 nm) shifted to lower angle after immersion in the solutions of alkylamines. This indicates that alkylamine molecules were intercalated into the pillared carbon. The shift of the diffraction peak became larger for alkylamines with longer alkyl chains and then became almost constant for alkylamines with six carbon atoms or more. The sharp diffraction peaks at 2h = 4.54, 3.68 and 2.46 (d = 1.95, 2.40 and 3.94 nm, respectively) are due to excess alkylamines crystallized on the surface of pillared carbons. Here, note that the plate like morphology of the pillared carbon [20] was almost unchanged even after immersion in n-butylamine. Fig. 4 shows the relationship between the alkyl chain length of alkylamines and the interlayer space of pillared carbon after intercalation of liquid alkylamines. The interlayer spacing after intercalation of organic molecules increased with increasing in the length of them. It reached 2.24 nm and then became constant even when the molecular length further increased. This fact strongly suggests that the adjacent carbon layers are well connected with each other by silsesquioxane pillars, otherwise further increase of the interlayer spacing is expected. Based on the interlayer spacing of pillared carbon containing alkylamines and the thickness of the carbon layers (0.34 nm), the minimum length of the pillar was calculated to be 1.90 nm (2.24– 0.34 nm). This value was very similar to that of the length of the fully extended Si12O20(CH3)12 pillars proposed in our previous study (1.85 nm) [20] and this suggests the perpendicular orientation of them against the carbon layers. Considering that the in-plane orientation of pillars hardly changes, the volume expansion of pores in pillared carbons is calculated from the interlayer expansion and 96% ((2.24–0.34)/(1.31– 0.34) · 100–100) is obtained. This value is smaller than those observed for pyridine or diethylformamide included chromium(III) dicarboxylates, however, is larger than most of those reported previously [26,27]. Based on these results, intercalation of n-alkylamine molecule into pillared carbon is schematically shown in Fig. 5. Fig. 6 shows the X-ray diffraction patterns of pillared carbon after immersion in the solutions of m-xylene and n-octanol
Interlayer distance of pillared carbon after inclusion of alkylamines / nm
2282
2.5 2 1.5 1 0.5 0 0
5
10
15
Number of carbon atoms in alkyl chains
Fig. 4 – Relationship between interlayer distance of pillared carbon from (C1Si)2.3GO after intercalation of n-alkylamines and number of carbon atoms in them.
molecules (minimum molecular widths of 0.33 and 0.36 nm, respectively). In both cases, the diffraction peaks shifted to lower angles and a series of (0 0 ‘) lines was observed. The interlayer spacing increased to 2.07 and 2.10 nm, respectively and they were also intercalated into pillared carbon. The immersion of pillared carbon in o- and p-isomers of xylene molecules also resulted in the increase in the interlayer spacing to 2.00 and 1.86 nm, respectively. These results show that a wide variety of liquid molecules are introduced between the layers of pillared carbon independently of their polarity or shape if the minimum molecular width of them is enough small. The pillars contain hydrophobic SiACH3 groups, together with polar OASiAO groups, therefore, various weak interactions such as van der Waals, p–p and CH–p interactions are also available even for non-polar molecules.
3.3. Intercalation of n-hexadecylamine molecules into pillared carbon Fig. 7 shows the X-ray diffraction patterns of pillared carbon after the addition of different amount of n-hexadecylamine molecules. As the increase in the added amounts of n-hexadecylamine molecules, the diffraction peak shifted to lower angle, then reached 2h = 9.7 (d = 0.91 nm), when the n-hexadecylamine/pillared carbon weight ratio reached 0.4. Alkylamine molecules with a higher melting point than room temperature (46.8 C) were also introduced into the interlayer gallery of pillared carbons. The broad peak at 2h = 20–21 (d value of about 0.43 nm) which slightly shifted to higher angle with increasing in the amount of added n-hexadecylamine molecules could be ascribed to the in-plane orientation of the intercalated alkylamines and/or that of pillars in pillared carbons. The peak positions were unchanged for the samples containing larger amounts of n-hexadecylamine molecules. At the same time, the diffraction peak at 2h = 21.8 due to the excess n-hexadecylamine crystal deposited on the surface of the samples was observed. These indicate that the interlayer space of pillared carbon was saturated by n-hexadecylamine molecules for this sample. In addition, the diffraction peak of the sample containing n-hexadecylamine after washed with ethanol shifted to 2h = 13.5 which is the same as that observed for the pristine pillared carbon. The
CARBON
2283
5 0 ( 20 1 2 ) 2 2 8 0–22 8 6
O O H3C Si O Si CH3 O O H C Si O Si CH3 3
Carbon layer 1.31 nm
= Pillar
Pillared carbon
O H3C Si O O H3C Si O O H3C Si O O H3C Si O O
O Si CH 3 O Si CH3 O Si CH3 O Si CH3 O
CnH2n+1NH2 n≥6
CnH2n+1NH2 n<6
Carbon layer
Carbon layer 1.52 nm R H2N
R H2N
R NH2
R H2N
R NH2
R NH2
2.24 nm
n-alkylamine-intercalated pillared carbon Fig. 5 – Schematic of the intercalation of n-alkylamine molecules into pillared carbon.
(G) (F)
Intensity/A.U.
Intensity/A.U.
(C)
(B)
(E) (D) (C) (B) (A)
(A) 2
6
10
14
18
22
26
30
2θ/ deg. CuKα Fig. 6 – X-ray diffraction patterns of pillared carbon from (C1Si)2.1GO (A) before and after intercalation of (B) m-xylene and (C) n-octanol.
intercalated n-hexadecylamine molecules were completely removed from the interlayer space of pillared carbon. The intercalation/deintercalation of n-hexadecylamine molecules and accompanying structural changes are reversible. Fig. 8 shows the SEM image of the n-hexadecylamine intercalated pillared carbon before and after washing with ethanol, together with that of the pristine pillared carbon. The plate like morphology of the starting graphite powder is well preserved for pristine pillared carbon as shown in our previous study [20]. After the addition of n-hexadecylamine, many smaller particles were observed. However, the morphology of the sample after the removal of n-hexadecylamine was almost unchanged. This indicates that the smaller particles are not ascribed to the deposited n-hexadecylamine crystals but to pillared carbon fragments formed as the result of the mechanical grinding of it. These strongly show that the nhexadecylamine molecules are inserted between the layers of pillared carbon.
2
6
10
14
18
22
26
30
2θ/deg.CuKα Fig. 7 – X-ray diffraction patterns of pillared carbon prepared from (C1Si)2.1GO (A) before and after intercalation of n-hexadecylamine molecules with various n-hexadecylamine/ pillared carbon weight ratios of (B) 0.1, (C) 0.2, (D) 0.3, (E) 0.4 and (F) 0.5, together with (G) that of the sample containing nhexadecylamine after washed with ethanol.
Fig. 9 shows that the TG data of pillared carbon containing n-hexadecylamine molecules with n-hexadecylamine/pillared carbon weight ratios of 0.2 and 0.4, together with that of the pristine pillared carbon. After showing a slight decrease of the weight below 100 C due to the removal of water, the weight decrease ascribed to the oxidation of pillared started above 480 C. The oxidation of pillared carbon was completed below 600 C and white powder remained. On the other hand, for pillared carbon containing n-hexadecylamine with n-hexadecylamine/pillared carbon weight ratio of 0.4, the weight decreased stepwisely (room temperature – 140 C, 210–360 C and above 480 C). The last weight decrease should be ascribed to the oxidation of pillared carbon, therefore, the others are due to the elimination of n-hexadecylamine molecules. In case of the sample with a lower n-hexadecylamine content, the first step of weight decrease was not observed. This indicates that
2284
CARBON
5 0 ( 2 0 1 2 ) 2 2 8 0 –2 2 8 6
100
(C)
80 60
Intensity/A.U.
Weight / initial weight / %
Fig. 8 – SEM images of (A) pillared carbon, n-hexadecylamine-intercalated pillared carbon (B) before and (C) after washing with ethanol.
(A) (B) (C)
40 20
(B)
(A)
0 0
100
200
300
400
500
600
700
800
o
Temperature / C
2
6
10
14
18
22
26
30
2θ/deg.CuKα
Fig. 9 – TG data of pillared carbon containing n-hexadecylamine molecules with n-hexadecylamine/pillared carbon weight ratios of (A) 0.2 and (B) 0.4, together with that of (C) pristine samples.
Fig. 10 – X-ray diffraction patterns of pillared carbon (A) before and after intercalation of (B) 18-crown-6 and (C) 1aminopyrene.
it is assigned to the removal of n-hexadecylamine deposited on the surface of pillared carbons, though they are not apparently detected by X-ray diffraction measurement shown in Fig. 7. Consequently, the elimination of n-hexadecylamine molecules intercalated between the layers of pillared carbon is responsible for the second step weight decrease. Based on the weight decrease between 210 and 480 C observed for the sample with a higher amine content, the saturated n-hexadecylamine/pillared carbon ratio was more precisely determined to be 0.33. Based on the ladder-type silsesquioxane pillar with the composition of Si12O20(CH3)12, this saturated composition corresponds to C40{Si12O20(CH3)12}Æ1.8C16H33NH2. Here, interestingly, the interlayer spacing observed for the pillared carbon saturated by n-hexadecylamine molecules was a smaller value of 1.85 nm, though the molecular length of n-hexadecylamine (2.31 nm) is larger than that of the fully extended pillars (1.90 nm). The volume occupied by n-hexadecylamine corresponds to 0.245 mL/g (0.2963 · 1021 · 1.8 · (6.023 · 1023)/ 1312 = 0.245). Here, Avogadro number of 6.023 · 1023, formula weight of 1312 for pillared carbon with the composition of C40{Si12O20(CH3)12} and the van der Waals volume of n-hexadecylamine (0.2963 nm3) [28] were used. This value was similar to the micropore volume (0.317 mL/g) obtained from the as analysis of N2 gas adsorption isotherm using carbon black as a reference [29,30]. Considering the change of the interlayer spacing after intercalation of n-hexadecylamine molecules
from 1.31 to 1.86 nm, the micropore volume should be 1.57 times ((1.86–0.34)/(1.31–0.34)) larger than that of the pristine pillared carbon, assuming the thickness of carbon layer as 0.34 nm. Accordingly, 51% of the micropore volume is occupied by n-hexadecylamine molecules. Fig. 10 shows the X-ray diffraction patterns of pillared carbon before and after intercalation of 1-aminopyrene and 18-crown-6 molecules. Here, note that the solvent for the intercalation of 1-aminopyrene, dimethylformamide was used instead of hexane. While the peak positions of X-ray diffraction were unchanged for the sample after the addition of 18crown-6 molecules, they shifted to lower angles when 1-aminopyrene molecules were added. This means that only 1-aminopyrene molecules were intercalated into pillared carbon. As shown in Fig. 11, the minimum widths of the 1-aminopyrene and 18-crown-6 molecules are 0.30 and 0.36 nm, respectively and they are almost the same as those of vinylene carbonate and diethoxyethane molecules both of which were successfully intercalated into pillared carbon in our previous study [20]. Therefore, it should be possible for these molecules to enter the interlayer gallery of pillared carbon through the space between two adjacent pillars. Considering the size of the 18-crown-6 and 1-aminopyrene molecules and the observations shown above, the shorter axis of the 18-crown-6 molecules (0.87 nm) was too large to be accommodated in the micropores of pillared carbon.
CARBON
Top view
2285
5 0 ( 20 1 2 ) 2 2 8 0–22 8 6
0.70 nm
0.87 nm
hydrogen oxygen carbon
Side view
0.36 nm 0.87 nm 18-crown-6
0.30 nm
nitrogen
0.9 nm 1-aminopyrene
Fig. 11 – Molecular structure and size of 18-crown-6 and 1-aminopyrene molecules.
It can be concluded that for the intercalation of organic molecules into pillared carbon, the shorter axis of the organic molecules should be smaller than 0.87 nm, in addition to the minimum molecular width smaller than 0.4 nm.
4.
Conclusions
Intercalation of various organic molecules into pillared carbon prepared from silylated graphite oxide was investigated. When liquid n-alkylamine molecules are intercalated, the interlayer spacing increased with increasing in the alkyl chain lengths and reached a constant value of 2.24 nm, when the alkyl chain lengths became 6 of more. This indicates that the length of pillar is 1.90 nm, which is almost the same as that of fully extended ladder type pillar with the composition of Si12O20(CH3)12. Non-polar xylene isomers and n-octanol molecules were also intercalated into pillared carbon, which indicated that organic molecules can penetrate into pillared carbon if their minimum molecular widths are enough small, independent of their polarity. The n-hexadecylamine molecules with a higher melting point than room temperature were also intercalated into pillared carbon simply by mixing them with pillared carbons, though the interlayer spacing of the resulting sample was smaller. The saturated amount of n-hexadecylamine estimated form the thermogravimetric analysis was 1.8 molecules per 40 carbon atoms of pillared carbon. The n-hexadecylamine molecules occupied 53% of the micropore volume of the pillared carbon. The 1-aminopyrene molecules were also intercalated into pillared carbon, while 18-crown-6 molecules were not accommodated in it, indicating that the shorter axis of the organic molecules should be smaller than 0.87 nm for the intercalation into it. These results indicate that pillared carbon would be useful for molecular recognition, selective adsorbents, host of functional molecules, etc. Moreover, pillared carbons are electrically conductive and they would be promising for sensors and energy storage materials.
Acknowledgements Financial supports from Canon Research Foundation and Japan Science Technology Agency are greatly acknowledged.
R E F E R E N C E S
[1] Bagshaw SA, Prouzet E, Pinnavaia TJ. Templating of mesoporous molecular sieves by nonionic polyethylene oxide surfactants. Science 1995;269:1242–4. [2] Kyotani T. Synthesis of various types of nano carbons using the template technique. Bull Chem Soc Jpn 2006;79:1322–37. [3] Rosseinski MJ. Recent development in metal-organic framework chemistry: design, discovery, permanent porosity and flexibility. Microporous Mesoprous Mater 2004;73:15–30. [4] Fe´rey G, Mellot-Draznieks C, Serre C, Millange F. Crystallized frameworks with giant pores: are there limits to the possible? Acc Chem Res 2005;38:217–25. [5] Yaghi OM, O’Keefe M, Ocwig NW, Chae HK, Eddaoudi M, Kim. Reticular synthesis and the design of new materials. J Nat 2003;423:705–14. [6] Kitagawa S, Kitaura R, Noro Si. Functional porous coordination polymers. Angew Chem Int Ed 2004;43:2334–75. [7] Ma¨kinen SK, Melcer NJ, Paverez M, Shimizu GKH. Highly selective guest uptake in a silver sulfonate network imparted by a tetragonal to triclinic shift in the solid state. Chem Eur J 2001;7:5176–82. [8] Uemura K, Kitagawa S, Kondo M, Fukui K, Kitaura R, Chang H-C, et al. Novel flexible frameworks of porous cobalt(II) coordination polymers which show selective guest adsorption based on switching of hydrogen bond pairs of amide groups. Chem Eur J 2002;8:3586–600. [9] Zhao X, Xiao B, Fretcher AJ, Thomas KM, Bradshaw D, Rosseinsky MJ. Hysteretic adsorption and desorption of hydrogen by nanoporous metal-organic frameworks. Science 2004;306:1012–5. [10] Choi HJ, Dicnca´ M, Long JR. Broadly hysteretic H2 adsorption in the microporous metal-organic framework Co(1,4benzenedipyrazolate). J Am Chem Soc 2008;130:7848–50. [11] Kondo A, Noguchi H, Carlussim L, Proserpio DM, Ciani G, Kaijiro H, et al. Double-step gas sorption of a twodimensional meta1-organic framework. J Am Chem Soc 2007;129:12362–3. [12] Kitaura R, Fujimoto K, Noro S-i, Kondo M, Kitagawa S. An unprecedented mixed-charged state in a supramolecular assembly of ligand-based mixed-valence redox isomers (ET 0 +3 [CrIII(Cl4 SQ)2 (Cl4 Cat)] [CrIII(Cl4 SQ)(Cl4 Cat)2]2. Angew Chem Int Ed 2002;41:133–5. [13] Uemura K, Matsuda R, Kitagawa S. Flexible microporous coordination polymers. J Solid State Chem 2005;178:2420–9. [14] Kitagawa S, Uemura K. Dynamic porous properties of coordination polymers inspired by hydrogen bonds. Chem Soc Rev 2005;34:109–19.
2286
CARBON
5 0 ( 2 0 1 2 ) 2 2 8 0 –2 2 8 6
[15] Fletcher AJ, Thomas KM, Rosseinsky MJ. Flexibility in metalorganic framework materials: impact on sorption properties. J Solid State Chem 2005;178:2491–510. [16] Matsuo Y, Sakai Y, Fukutsuka T, Sugie Y. Preparation of pillared carbon from pyrolysis of silylated graphite oxide. Chem Lett 2007;36:1050–1. [17] Matsuo Y, Sakai Y, Fukutsuka T, Sugie Y. Preparation and characterization of pillared carbons obtained by pyrolysis of silylated graphite oxides. Carbon 2009;47:804–11. [18] Matsuo Y, Komiya T, Sugie Y. The effect of alkyl chain length on the structure of pillared carbons prepared by the silylation of graphite oxide with alkyltrichlorosilanes. Carbon 2009;47:2782–8. [19] Matsuo Y, Komiya T, Sugie Y. Preparation of microporous pillared carbons from the silylated graphite oxide prepared by a two-step method. J Phys Chem Solids, [accepted for publication]. Available from: http://dx.doi.org/10.1016/ j.jpcs.2011.10.045. [20] Matsuo Y, Konishi K. Size-dependent selective inclusion of organic molecules into elastic pillared carbons. Chem Coummn 2011;47:4409–11. [21] Brodie MBC. Sur le poids atomique du graphite. Ann Chim Phys 1860;59:466–72. [22] Matsuo Y, Fukunaga T, Fukutsuka T, Sugie Y. Silylation of graphite oxide. Carbon 2005;42:2117–9. [23] Matsuo Y, Tabata T, Fukunaga T, Fukutsuka T, Sugie Y. Preparation and characterization of silylated graphite oxide. Carbon 2005;43:2875–82.
[24] Matsuo Y, Watanabe K, Fukutsuka T, Sugie Y. Characterization of n-hexadecylalkylamine-intercalated graphite oxides as sorbents. Carbon 2003;41:1545–50. [25] Matsuo Y, Miyabe T, Fukutsuka T, Sugie Y. Preparation and characterization of alkylamine-intercalated graphite oxide. Carbon 2007;45:1005–7. [26] Serre C, Millange F, Thouvenot C, Nogue`s M, Marsolier G, Loue¨r D, et al. Very large breathing effect in the first nanoporous chromium(III)-based solids: MIL-53 or CrIII(OH)Æ{O2CC6H4CO2}Æ{HO2CC6H4CO2H}xÆH2Oy. J Am Chem Soc 2002;124:13519. [27] Serre C, Mellot-Draznieks C, Surble´ S, Audebrand N, Filinchuk Y, Fe´rey G. Role of solvent-host interactions that lead to very large swelling of hybrid frameworks. Science 2007;315:1828–31. [28] Zhao YH, Abraham MH, Zissimos AM. Fast calculation of van der Waals volume as a sum of atomic and bond contributions and its application to drug compounds. J Org Chem 2003;68:7368–73. [29] Sing KSW, Evrett DH, Haul RAW, Moscou L, Pierotti RA, Rouquerol J, et al. Reporting physisorption data for gas/solid systems with special reference to the determination of surface area and porosity. Pure Appl Chem 1985;57:603. [30] Kaneko K, Ishii C, Kanoh H, Hanzawa Y, Setoyama N, Suzuki T. Characterization of porous carbons with high resolution as-analysis and low temperature magnetic susceptibility. Adv Colloid Inerface Sci 1998;76–77:295–320.
5 0 ( 2 0 1 2 ) 2 2 8 0 –2 2 8 6
Available at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/carbon
Intercalation of various organic molecules into pillared carbon Yoshiaki Matsuo *, Kentaro Konishi Department of Materials Science and Chemistry, Graduate School of Engineering, University of Hyogo, 2167 Shosha Himeji, Hyogo 671-2280, Japan
A R T I C L E I N F O
A B S T R A C T
Article history:
Intercalation of various organic molecules into pillared carbon prepared from the pyrolysis
Received 18 November 2011
of graphite oxide silylated with methyltrichlorosilane for three times was investigated.
Accepted 13 January 2012
Liquid n-alkylamine molecules with various alkyl chain lengths were intercalated into
Available online 24 January 2012
the resulting pillared carbon and the interlayer spacing increased with increasing in the alkyl chain length, until it became a constant value of 2.24 nm for chains having more than six carbon atoms. This suggests that the length of the pillar is 1.9 nm. Various organic molecules including non-polar xylene isomers and alcohol molecules can also penetrate into pillared carbon. The n-hexadecylamine molecules with a higher melting point than room temperature were intercalated into pillared carbon simply by mixing them with pillared carbons in hexane, though the interlayer spacing was smaller. The space between the layers of pillared carbon was saturated with n-hexadecylamine molecules when 1.8 molecules per 40 carbon atoms were added. The n-hexadecylamine molecules occupied 51% of the micropore volume of pillared carbon. For the intercalation of organic molecules into pillared carbon, the shorter axis of them should be smaller than 0.87 nm. 2012 Elsevier Ltd. All rights reserved.
1.
Introduction
Porous materials with controlled pore structures are attracting much attention for the support of catalysts, gas storage, adsorbents, electrode of electric double layer capacitor and so on. These include mesoporous silicas, meso- or microporous carbons, metal organic frameworks (MOF)/porous coordination polymers (PCP), zeolites, pillared layered materials, etc. [1–6]. Most of these materials possess rigid frameworks and structural change is not usually observed during adsorption, however, some of the PCP/MOF showed unique adsorption behaviors for small molecules, accompanied by a reversible structural change [7–15]. It would be very interesting for catalysts, sensors, etc., if conducting and chemically stable carbon based materials show similar properties. In this context, we have recently prepared pillared carbons by pyrolysis of silylated graphite oxide and the adjacent
carbon layers of them are connected with each other by silica or silsesquioxane pillars through CAOASi and SiAOASi bondings [16–19]. Moreover, we have also found that polar organic molecules were size-selectively intercalated into the pillared carbon prepared from graphite oxide repeatedly silylated with methyltrichlorosilane, which was accompanied by large interlayer expansions [20]. Considering the minimum molecular widths of the intercalated organic molecules, this indicated that the width between two adjacent pillars for the entrance of organic molecules is well controlled between 0.36 and 0.4 nm. At the same time, the pillars connecting the adjacent carbon layers should incline from the normal against the carbon layers and the length of the pillars should be larger than 1.72 nm. In this study, the intercalation behaviors of various organic molecules into the above mentioned pillared carbon were investigated in detail.
* Corresponding author: Fax: +81 792 67 4898. E-mail address: [email protected] (Y. Matsuo). 0008-6223/$ - see front matter 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbon.2012.01.047
CARBON
Experimental
250
Adsorbed N2 / mLSTP/g
2.
2281
5 0 ( 20 1 2 ) 2 2 8 0–22 8 6
Preparation of pillared carbon was performed in the same manner as reported in our previous studies [18,20]. Graphite oxide (hereafter abbreviated as GO) was prepared from natural graphite powder (57–74 lm) in fuming nitric acid using potassium chlorate, based on the Brodie’s method [21] and oxidation procedure was repeated five times. The composition of the resulting GO was C8H3.0O4.5. GO was silylated as follows, according to our previous studies [22,23]. GO (100 mg) was mixed with n-butylamine (C4H9NH2, hereafter abbreviated as C4, 2 mL; 32 mol per GO unit (C8H3.0O4.5)) as an exfoliating reagent in a sealed glass vial under an Argon atmosphere and the resulting solution was sonicated, then heated at 60 C for 1 h. Dry toluene (5 mL, water content <30 ppm) was added to this solution and the solution was again sonicated. Methyltrichlorosilane, CH3SiCl3, abbreviated as C1Si: 0.90 mL) was added to the resulting dispersion and then it was allowed to stand for 2 day at 60 C. After centrifugation at 4000 rpm for 20 min, the precipitate was washed with dry toluene, ethanol and finally acetone. The obtained silylated GO samples were silylated with C1Si in the same manner as described above for 1 day. This was repeated for two times. The composition of silylated GO was determined from the weight of residual SiO2 after thermogravimetric analysis, assuming that 0.4 n-butylamine molecules per C8 GO unit were intercalated [23] and (C1Si)2.1GO was obtained. The content of C1Si in GO was slightly smaller than that obtained in our previous study [20]. The resulting silylating GO was heated at 500 C under dynamic vacuum and pillared carbon was obtained. Here, the temperature increase rate was 1 C/min and the amount of the sample was less than 200 mg in order to avoid the deflagration of GO layers due to the heat generate during the removal oxygen from GO layers. These samples were analyzed by X-ray diffraction (Rigaku, Rint-2100, CuKa), thermogravimetric (TG; Shimadzu, TGA-50), N2 gas adsorption at 196 C (Bel Japan, BELSORP-Max) and scanning electron microscopy (SEM; JEOL, JSM-5600). TG measurement was performed under air with the temperature increase rate of 5 C/min between room temperature and 800 C. Intercalation behavior of organic molecules into pillared carbons was investigated as follows. Pillared carbon was immersed in the solutions of organic molecules of n-alkylamines with various alkyl chain lengths, n-octanol and xylenes for 24 h and the resulting samples were analyzed by X-ray diffractometry without drying. The evaporation of organic molecules was avoided during measurement by covering the samples with kapton film. In case of the intercalation of solid n-hexadecylamine molecules, they were mixed with pillared carbons in a pestle and then a small amount of hexane was added as reported previously [24,25]. The mixture was mechanically ground until the hexane was evaporated and then the resulting sample was dried at 60 C.
676 m2/g which was slightly higher than that observed in our previous study (550 m2/g) [20]. Moreover, hysteresis during desorption was not observed. The slightly lower pillar density in the present pillared carbon than that of the previous sample [20] could be responsible for the higher BET surface area and easier diffusion of N2 molecules in it. However, the selective intercalation of propylene carbonate, dimethylsulfoxide, diethoxyethane and vinylene carbonate was commonly observed, indicating that the distance between the pillars for the entrance of the organic molecules is almost the same. The pore distribution of pillared carbon estimated based on the HK method is shown in Fig. 2 and a sharp peak at 0.46 nm was observed. The pores in pillared carbon are very small and they are distributed quite uniformly in the gallery of it.
3.
Results and discussion
3.2. Intercalation behavior of liquid organic molecules into pillared carbon
3.1.
N2 gas adsorption behavior of pillared carbon
The N2 adsorption isotherm of the pillared carbon at 196 C was type I as shown in Fig. 1 and the BET surface area was
Adsorbed N2 / mLSTP/g
200 150 100 50
250 200 150 100 50 0 1.0E-08
1.0E-04 P / P0
0 0
0.2
0.4
1.0E+00
0.6
0.8
1
P / P0 Fig. 1 – N2 gas adsorption isotherm of pillared carbon at 196 C. Filled and open marks indicate the data during adsorption and desorption, respectively. Inset shows the logarithm plot for relative pressure.
1.2
dVp/d(dp)
1 0.8 0.6 0.4 0.2 0 0
1
2
3
4
Pore diameter / nm Fig. 2 – Pore size distribution of pillared carbon determined based on the HK method.
Fig. 3 shows the X-ray diffraction patterns of pillared carbon prepared from (C1Si)2.1GO after immersion in the solutions of n-alkylamine molecules with various alkyl chain lengths. The diffraction peak of pillared carbon observed at 2h = 13.5
CARBON
***
5 0 ( 2 0 1 2 ) 2 2 8 0 –2 2 8 6
* **
*
(F)
Intensity/A.U.
(E) (D) (C) (B) (A) 2
6
10
14
18
22
26
30
2θ/ deg. CuKα Fig. 3 – X-ray diffraction patterns of pillared carbon prepared from (C1Si)2.1GO (A): before and after immersion in nalkylamines with various alkyl chain lengths of (B) 3, (C) 4, (D) 6, (E) 8 and (F) 12. The peaks marked with ‘‘*’’ indicate the residual n-alkylamines crystallized on the surface of pillared carbon.
(d = 1.31 nm) and 20.3 (d = 0.658 nm) shifted to lower angle after immersion in the solutions of alkylamines. This indicates that alkylamine molecules were intercalated into the pillared carbon. The shift of the diffraction peak became larger for alkylamines with longer alkyl chains and then became almost constant for alkylamines with six carbon atoms or more. The sharp diffraction peaks at 2h = 4.54, 3.68 and 2.46 (d = 1.95, 2.40 and 3.94 nm, respectively) are due to excess alkylamines crystallized on the surface of pillared carbons. Here, note that the plate like morphology of the pillared carbon [20] was almost unchanged even after immersion in n-butylamine. Fig. 4 shows the relationship between the alkyl chain length of alkylamines and the interlayer space of pillared carbon after intercalation of liquid alkylamines. The interlayer spacing after intercalation of organic molecules increased with increasing in the length of them. It reached 2.24 nm and then became constant even when the molecular length further increased. This fact strongly suggests that the adjacent carbon layers are well connected with each other by silsesquioxane pillars, otherwise further increase of the interlayer spacing is expected. Based on the interlayer spacing of pillared carbon containing alkylamines and the thickness of the carbon layers (0.34 nm), the minimum length of the pillar was calculated to be 1.90 nm (2.24– 0.34 nm). This value was very similar to that of the length of the fully extended Si12O20(CH3)12 pillars proposed in our previous study (1.85 nm) [20] and this suggests the perpendicular orientation of them against the carbon layers. Considering that the in-plane orientation of pillars hardly changes, the volume expansion of pores in pillared carbons is calculated from the interlayer expansion and 96% ((2.24–0.34)/(1.31– 0.34) · 100–100) is obtained. This value is smaller than those observed for pyridine or diethylformamide included chromium(III) dicarboxylates, however, is larger than most of those reported previously [26,27]. Based on these results, intercalation of n-alkylamine molecule into pillared carbon is schematically shown in Fig. 5. Fig. 6 shows the X-ray diffraction patterns of pillared carbon after immersion in the solutions of m-xylene and n-octanol
Interlayer distance of pillared carbon after inclusion of alkylamines / nm
2282
2.5 2 1.5 1 0.5 0 0
5
10
15
Number of carbon atoms in alkyl chains
Fig. 4 – Relationship between interlayer distance of pillared carbon from (C1Si)2.3GO after intercalation of n-alkylamines and number of carbon atoms in them.
molecules (minimum molecular widths of 0.33 and 0.36 nm, respectively). In both cases, the diffraction peaks shifted to lower angles and a series of (0 0 ‘) lines was observed. The interlayer spacing increased to 2.07 and 2.10 nm, respectively and they were also intercalated into pillared carbon. The immersion of pillared carbon in o- and p-isomers of xylene molecules also resulted in the increase in the interlayer spacing to 2.00 and 1.86 nm, respectively. These results show that a wide variety of liquid molecules are introduced between the layers of pillared carbon independently of their polarity or shape if the minimum molecular width of them is enough small. The pillars contain hydrophobic SiACH3 groups, together with polar OASiAO groups, therefore, various weak interactions such as van der Waals, p–p and CH–p interactions are also available even for non-polar molecules.
3.3. Intercalation of n-hexadecylamine molecules into pillared carbon Fig. 7 shows the X-ray diffraction patterns of pillared carbon after the addition of different amount of n-hexadecylamine molecules. As the increase in the added amounts of n-hexadecylamine molecules, the diffraction peak shifted to lower angle, then reached 2h = 9.7 (d = 0.91 nm), when the n-hexadecylamine/pillared carbon weight ratio reached 0.4. Alkylamine molecules with a higher melting point than room temperature (46.8 C) were also introduced into the interlayer gallery of pillared carbons. The broad peak at 2h = 20–21 (d value of about 0.43 nm) which slightly shifted to higher angle with increasing in the amount of added n-hexadecylamine molecules could be ascribed to the in-plane orientation of the intercalated alkylamines and/or that of pillars in pillared carbons. The peak positions were unchanged for the samples containing larger amounts of n-hexadecylamine molecules. At the same time, the diffraction peak at 2h = 21.8 due to the excess n-hexadecylamine crystal deposited on the surface of the samples was observed. These indicate that the interlayer space of pillared carbon was saturated by n-hexadecylamine molecules for this sample. In addition, the diffraction peak of the sample containing n-hexadecylamine after washed with ethanol shifted to 2h = 13.5 which is the same as that observed for the pristine pillared carbon. The
CARBON
2283
5 0 ( 20 1 2 ) 2 2 8 0–22 8 6
O O H3C Si O Si CH3 O O H C Si O Si CH3 3
Carbon layer 1.31 nm
= Pillar
Pillared carbon
O H3C Si O O H3C Si O O H3C Si O O H3C Si O O
O Si CH 3 O Si CH3 O Si CH3 O Si CH3 O
CnH2n+1NH2 n≥6
CnH2n+1NH2 n<6
Carbon layer
Carbon layer 1.52 nm R H2N
R H2N
R NH2
R H2N
R NH2
R NH2
2.24 nm
n-alkylamine-intercalated pillared carbon Fig. 5 – Schematic of the intercalation of n-alkylamine molecules into pillared carbon.
(G) (F)
Intensity/A.U.
Intensity/A.U.
(C)
(B)
(E) (D) (C) (B) (A)
(A) 2
6
10
14
18
22
26
30
2θ/ deg. CuKα Fig. 6 – X-ray diffraction patterns of pillared carbon from (C1Si)2.1GO (A) before and after intercalation of (B) m-xylene and (C) n-octanol.
intercalated n-hexadecylamine molecules were completely removed from the interlayer space of pillared carbon. The intercalation/deintercalation of n-hexadecylamine molecules and accompanying structural changes are reversible. Fig. 8 shows the SEM image of the n-hexadecylamine intercalated pillared carbon before and after washing with ethanol, together with that of the pristine pillared carbon. The plate like morphology of the starting graphite powder is well preserved for pristine pillared carbon as shown in our previous study [20]. After the addition of n-hexadecylamine, many smaller particles were observed. However, the morphology of the sample after the removal of n-hexadecylamine was almost unchanged. This indicates that the smaller particles are not ascribed to the deposited n-hexadecylamine crystals but to pillared carbon fragments formed as the result of the mechanical grinding of it. These strongly show that the nhexadecylamine molecules are inserted between the layers of pillared carbon.
2
6
10
14
18
22
26
30
2θ/deg.CuKα Fig. 7 – X-ray diffraction patterns of pillared carbon prepared from (C1Si)2.1GO (A) before and after intercalation of n-hexadecylamine molecules with various n-hexadecylamine/ pillared carbon weight ratios of (B) 0.1, (C) 0.2, (D) 0.3, (E) 0.4 and (F) 0.5, together with (G) that of the sample containing nhexadecylamine after washed with ethanol.
Fig. 9 shows that the TG data of pillared carbon containing n-hexadecylamine molecules with n-hexadecylamine/pillared carbon weight ratios of 0.2 and 0.4, together with that of the pristine pillared carbon. After showing a slight decrease of the weight below 100 C due to the removal of water, the weight decrease ascribed to the oxidation of pillared started above 480 C. The oxidation of pillared carbon was completed below 600 C and white powder remained. On the other hand, for pillared carbon containing n-hexadecylamine with n-hexadecylamine/pillared carbon weight ratio of 0.4, the weight decreased stepwisely (room temperature – 140 C, 210–360 C and above 480 C). The last weight decrease should be ascribed to the oxidation of pillared carbon, therefore, the others are due to the elimination of n-hexadecylamine molecules. In case of the sample with a lower n-hexadecylamine content, the first step of weight decrease was not observed. This indicates that
2284
CARBON
5 0 ( 2 0 1 2 ) 2 2 8 0 –2 2 8 6
100
(C)
80 60
Intensity/A.U.
Weight / initial weight / %
Fig. 8 – SEM images of (A) pillared carbon, n-hexadecylamine-intercalated pillared carbon (B) before and (C) after washing with ethanol.
(A) (B) (C)
40 20
(B)
(A)
0 0
100
200
300
400
500
600
700
800
o
Temperature / C
2
6
10
14
18
22
26
30
2θ/deg.CuKα
Fig. 9 – TG data of pillared carbon containing n-hexadecylamine molecules with n-hexadecylamine/pillared carbon weight ratios of (A) 0.2 and (B) 0.4, together with that of (C) pristine samples.
Fig. 10 – X-ray diffraction patterns of pillared carbon (A) before and after intercalation of (B) 18-crown-6 and (C) 1aminopyrene.
it is assigned to the removal of n-hexadecylamine deposited on the surface of pillared carbons, though they are not apparently detected by X-ray diffraction measurement shown in Fig. 7. Consequently, the elimination of n-hexadecylamine molecules intercalated between the layers of pillared carbon is responsible for the second step weight decrease. Based on the weight decrease between 210 and 480 C observed for the sample with a higher amine content, the saturated n-hexadecylamine/pillared carbon ratio was more precisely determined to be 0.33. Based on the ladder-type silsesquioxane pillar with the composition of Si12O20(CH3)12, this saturated composition corresponds to C40{Si12O20(CH3)12}Æ1.8C16H33NH2. Here, interestingly, the interlayer spacing observed for the pillared carbon saturated by n-hexadecylamine molecules was a smaller value of 1.85 nm, though the molecular length of n-hexadecylamine (2.31 nm) is larger than that of the fully extended pillars (1.90 nm). The volume occupied by n-hexadecylamine corresponds to 0.245 mL/g (0.2963 · 1021 · 1.8 · (6.023 · 1023)/ 1312 = 0.245). Here, Avogadro number of 6.023 · 1023, formula weight of 1312 for pillared carbon with the composition of C40{Si12O20(CH3)12} and the van der Waals volume of n-hexadecylamine (0.2963 nm3) [28] were used. This value was similar to the micropore volume (0.317 mL/g) obtained from the as analysis of N2 gas adsorption isotherm using carbon black as a reference [29,30]. Considering the change of the interlayer spacing after intercalation of n-hexadecylamine molecules
from 1.31 to 1.86 nm, the micropore volume should be 1.57 times ((1.86–0.34)/(1.31–0.34)) larger than that of the pristine pillared carbon, assuming the thickness of carbon layer as 0.34 nm. Accordingly, 51% of the micropore volume is occupied by n-hexadecylamine molecules. Fig. 10 shows the X-ray diffraction patterns of pillared carbon before and after intercalation of 1-aminopyrene and 18-crown-6 molecules. Here, note that the solvent for the intercalation of 1-aminopyrene, dimethylformamide was used instead of hexane. While the peak positions of X-ray diffraction were unchanged for the sample after the addition of 18crown-6 molecules, they shifted to lower angles when 1-aminopyrene molecules were added. This means that only 1-aminopyrene molecules were intercalated into pillared carbon. As shown in Fig. 11, the minimum widths of the 1-aminopyrene and 18-crown-6 molecules are 0.30 and 0.36 nm, respectively and they are almost the same as those of vinylene carbonate and diethoxyethane molecules both of which were successfully intercalated into pillared carbon in our previous study [20]. Therefore, it should be possible for these molecules to enter the interlayer gallery of pillared carbon through the space between two adjacent pillars. Considering the size of the 18-crown-6 and 1-aminopyrene molecules and the observations shown above, the shorter axis of the 18-crown-6 molecules (0.87 nm) was too large to be accommodated in the micropores of pillared carbon.
CARBON
Top view
2285
5 0 ( 20 1 2 ) 2 2 8 0–22 8 6
0.70 nm
0.87 nm
hydrogen oxygen carbon
Side view
0.36 nm 0.87 nm 18-crown-6
0.30 nm
nitrogen
0.9 nm 1-aminopyrene
Fig. 11 – Molecular structure and size of 18-crown-6 and 1-aminopyrene molecules.
It can be concluded that for the intercalation of organic molecules into pillared carbon, the shorter axis of the organic molecules should be smaller than 0.87 nm, in addition to the minimum molecular width smaller than 0.4 nm.
4.
Conclusions
Intercalation of various organic molecules into pillared carbon prepared from silylated graphite oxide was investigated. When liquid n-alkylamine molecules are intercalated, the interlayer spacing increased with increasing in the alkyl chain lengths and reached a constant value of 2.24 nm, when the alkyl chain lengths became 6 of more. This indicates that the length of pillar is 1.90 nm, which is almost the same as that of fully extended ladder type pillar with the composition of Si12O20(CH3)12. Non-polar xylene isomers and n-octanol molecules were also intercalated into pillared carbon, which indicated that organic molecules can penetrate into pillared carbon if their minimum molecular widths are enough small, independent of their polarity. The n-hexadecylamine molecules with a higher melting point than room temperature were also intercalated into pillared carbon simply by mixing them with pillared carbons, though the interlayer spacing of the resulting sample was smaller. The saturated amount of n-hexadecylamine estimated form the thermogravimetric analysis was 1.8 molecules per 40 carbon atoms of pillared carbon. The n-hexadecylamine molecules occupied 53% of the micropore volume of the pillared carbon. The 1-aminopyrene molecules were also intercalated into pillared carbon, while 18-crown-6 molecules were not accommodated in it, indicating that the shorter axis of the organic molecules should be smaller than 0.87 nm for the intercalation into it. These results indicate that pillared carbon would be useful for molecular recognition, selective adsorbents, host of functional molecules, etc. Moreover, pillared carbons are electrically conductive and they would be promising for sensors and energy storage materials.
Acknowledgements Financial supports from Canon Research Foundation and Japan Science Technology Agency are greatly acknowledged.
R E F E R E N C E S
[1] Bagshaw SA, Prouzet E, Pinnavaia TJ. Templating of mesoporous molecular sieves by nonionic polyethylene oxide surfactants. Science 1995;269:1242–4. [2] Kyotani T. Synthesis of various types of nano carbons using the template technique. Bull Chem Soc Jpn 2006;79:1322–37. [3] Rosseinski MJ. Recent development in metal-organic framework chemistry: design, discovery, permanent porosity and flexibility. Microporous Mesoprous Mater 2004;73:15–30. [4] Fe´rey G, Mellot-Draznieks C, Serre C, Millange F. Crystallized frameworks with giant pores: are there limits to the possible? Acc Chem Res 2005;38:217–25. [5] Yaghi OM, O’Keefe M, Ocwig NW, Chae HK, Eddaoudi M, Kim. Reticular synthesis and the design of new materials. J Nat 2003;423:705–14. [6] Kitagawa S, Kitaura R, Noro Si. Functional porous coordination polymers. Angew Chem Int Ed 2004;43:2334–75. [7] Ma¨kinen SK, Melcer NJ, Paverez M, Shimizu GKH. Highly selective guest uptake in a silver sulfonate network imparted by a tetragonal to triclinic shift in the solid state. Chem Eur J 2001;7:5176–82. [8] Uemura K, Kitagawa S, Kondo M, Fukui K, Kitaura R, Chang H-C, et al. Novel flexible frameworks of porous cobalt(II) coordination polymers which show selective guest adsorption based on switching of hydrogen bond pairs of amide groups. Chem Eur J 2002;8:3586–600. [9] Zhao X, Xiao B, Fretcher AJ, Thomas KM, Bradshaw D, Rosseinsky MJ. Hysteretic adsorption and desorption of hydrogen by nanoporous metal-organic frameworks. Science 2004;306:1012–5. [10] Choi HJ, Dicnca´ M, Long JR. Broadly hysteretic H2 adsorption in the microporous metal-organic framework Co(1,4benzenedipyrazolate). J Am Chem Soc 2008;130:7848–50. [11] Kondo A, Noguchi H, Carlussim L, Proserpio DM, Ciani G, Kaijiro H, et al. Double-step gas sorption of a twodimensional meta1-organic framework. J Am Chem Soc 2007;129:12362–3. [12] Kitaura R, Fujimoto K, Noro S-i, Kondo M, Kitagawa S. An unprecedented mixed-charged state in a supramolecular assembly of ligand-based mixed-valence redox isomers (ET 0 +3 [CrIII(Cl4 SQ)2 (Cl4 Cat)] [CrIII(Cl4 SQ)(Cl4 Cat)2]2. Angew Chem Int Ed 2002;41:133–5. [13] Uemura K, Matsuda R, Kitagawa S. Flexible microporous coordination polymers. J Solid State Chem 2005;178:2420–9. [14] Kitagawa S, Uemura K. Dynamic porous properties of coordination polymers inspired by hydrogen bonds. Chem Soc Rev 2005;34:109–19.
2286
CARBON
5 0 ( 2 0 1 2 ) 2 2 8 0 –2 2 8 6
[15] Fletcher AJ, Thomas KM, Rosseinsky MJ. Flexibility in metalorganic framework materials: impact on sorption properties. J Solid State Chem 2005;178:2491–510. [16] Matsuo Y, Sakai Y, Fukutsuka T, Sugie Y. Preparation of pillared carbon from pyrolysis of silylated graphite oxide. Chem Lett 2007;36:1050–1. [17] Matsuo Y, Sakai Y, Fukutsuka T, Sugie Y. Preparation and characterization of pillared carbons obtained by pyrolysis of silylated graphite oxides. Carbon 2009;47:804–11. [18] Matsuo Y, Komiya T, Sugie Y. The effect of alkyl chain length on the structure of pillared carbons prepared by the silylation of graphite oxide with alkyltrichlorosilanes. Carbon 2009;47:2782–8. [19] Matsuo Y, Komiya T, Sugie Y. Preparation of microporous pillared carbons from the silylated graphite oxide prepared by a two-step method. J Phys Chem Solids, [accepted for publication]. Available from: http://dx.doi.org/10.1016/ j.jpcs.2011.10.045. [20] Matsuo Y, Konishi K. Size-dependent selective inclusion of organic molecules into elastic pillared carbons. Chem Coummn 2011;47:4409–11. [21] Brodie MBC. Sur le poids atomique du graphite. Ann Chim Phys 1860;59:466–72. [22] Matsuo Y, Fukunaga T, Fukutsuka T, Sugie Y. Silylation of graphite oxide. Carbon 2005;42:2117–9. [23] Matsuo Y, Tabata T, Fukunaga T, Fukutsuka T, Sugie Y. Preparation and characterization of silylated graphite oxide. Carbon 2005;43:2875–82.
[24] Matsuo Y, Watanabe K, Fukutsuka T, Sugie Y. Characterization of n-hexadecylalkylamine-intercalated graphite oxides as sorbents. Carbon 2003;41:1545–50. [25] Matsuo Y, Miyabe T, Fukutsuka T, Sugie Y. Preparation and characterization of alkylamine-intercalated graphite oxide. Carbon 2007;45:1005–7. [26] Serre C, Millange F, Thouvenot C, Nogue`s M, Marsolier G, Loue¨r D, et al. Very large breathing effect in the first nanoporous chromium(III)-based solids: MIL-53 or CrIII(OH)Æ{O2CC6H4CO2}Æ{HO2CC6H4CO2H}xÆH2Oy. J Am Chem Soc 2002;124:13519. [27] Serre C, Mellot-Draznieks C, Surble´ S, Audebrand N, Filinchuk Y, Fe´rey G. Role of solvent-host interactions that lead to very large swelling of hybrid frameworks. Science 2007;315:1828–31. [28] Zhao YH, Abraham MH, Zissimos AM. Fast calculation of van der Waals volume as a sum of atomic and bond contributions and its application to drug compounds. J Org Chem 2003;68:7368–73. [29] Sing KSW, Evrett DH, Haul RAW, Moscou L, Pierotti RA, Rouquerol J, et al. Reporting physisorption data for gas/solid systems with special reference to the determination of surface area and porosity. Pure Appl Chem 1985;57:603. [30] Kaneko K, Ishii C, Kanoh H, Hanzawa Y, Setoyama N, Suzuki T. Characterization of porous carbons with high resolution as-analysis and low temperature magnetic susceptibility. Adv Colloid Inerface Sci 1998;76–77:295–320.