- Email: [email protected]
Large-pore ordered mesoporous carbons with tunable structures and pore sizes templated from poly(ethylene oxide)-b-poly(methyl methacrylate)
Solid State Sciences 13 (2011) 784e792
Contents lists available at ScienceDirect
Solid State Sciences journal homepage: www.elsevier.com/locate/ssscie
Large-pore ordered mesoporous carbons with tunable structures and pore sizes templated from poly(ethylene oxide)-b-poly(methyl methacrylate) Jing Wei, Yonghui Deng, Junyong Zhang, Zhenkun Sun, Bo Tu, Dongyuan Zhao* Department of Chemistry, Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, the Key Laboratory of Molecular Engineering of Polymers of Ministry of Education and Advanced Materials Laboratory, Fudan University, Shanghai 200433, PR China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 12 February 2010 Accepted 9 March 2010 Available online 17 March 2010
Ordered mesoporous carbons (OMCs) with possible face-centered cubic (space group Fm3m) and 2-D hexagonal (p6mm) symmetries have been successfully synthesized by using lab-made poly(ethylene oxide)-block-poly(methyl methacrylate) diblock polymers (PEO-b-PMMA) with different PEO/PMMA ratios as a template. The synthesis process undergoes an evaporation induced self-assembly (EISA) at 100 C by using low-molecular weight phenolic resol as a carbon source and tetrahydrofuran (THF) as the solvent. The atom transfer radical polymerization (ATRP) method was used to prepare the diblock copolymers with different molecular weight and compositions of PEO and PMMA segments by simply changing the PEO initiator and polymerization time. For the first time, we have obtained OMCs with hexagonal p6mm symmetry and large pore size (8.6e12.1 nm) by using PEO-b-PMMA with long PMMA segment as the templates. Notably, the pore size of the ordered mesoporous carbons can be tuned in the range of 8.6e22.0 nm by slightly adjusting the hydrophobic PMMA length of the template or adding desired amount of PMMA homopolymer as a pore expander. Additionally, it is found that the pore wall thickness of OMCs with possible face-centered cubic symmetry can be adjusted from 8.1 to 10.4 nm by simply increasing the weight ratio of resol to the template (Rw). Ó 2010 Elsevier Masson SAS. All rights reserved.
Keywords: Mesoporous materials Carbon Synthesis Block copolymer Template Self-assembly
1. Introduction Ordered mesoporous carbons (OMCs) have received considerable attention owing to their high surface areas, large pore sizes with narrow distribution, high chemical inertness and mechanical stability, all of which lead to potential applications in adsorption and separation, catalysis, electrochemistry and sensors [1e8]. It is believed that the precise control of their pore structures, pore sizes and wall thickness can greatly enhance their suitability for the applications. Particularly, OMCs with large pore sizes can provide fast mass transfer and thus are highly desirable for biomacromolecular separation and biocatalysis involving large sized molecules [9]. Great efforts have been made to synthesize OMCs with tunable pore size through the nanocasting approach by using various ordered mesoporous silicas as the hard templates. Ryoo and coworkers reported the synthesis of OMCs with pore sizes tunable in a narrow range of 2.2e3.3 nm by using mesoporous silica templates with different wall thicknesses [10]. Using boric acid as
* Corresponding author. Tel.: þ86 21 55664194; fax: þ86 21 65641740. E-mail address: [email protected] (D.Y. Zhao). 1293-2558/$ e see front matter Ó 2010 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.solidstatesciences.2010.03.008
a pore expanding agent, Kim et al. successfully synthesized OMCs with controllable pore size ranging from 3 to 10 nm [11]. However, the nanocasting method suffers drawbacks such as the time-consuming, costly procedure, and the reliance of pore structures on the templates. Moreover, the pore size, depending on the wall thickness of template, is difficult to be adjusted in a wide range. Recently, the organic-organic self-assembly of amphiphilic block copolymers and carbon precursors has been demonstrated to be a versatile route to fabricate ordered mesoporous polymers and carbons [12e19]. It has been realized that the composition and feature of the block copolymer templates play key roles in the formation of mesostructures, and the volume of hydrophobic segment is close relative to the pore size of OMCs. Previous reports on the mesoporous carbons based on the selfassembly of poly(ethylene oxide)-block-poly(propylene oxide)block-poly (ethylene oxide) (PEO-b-PPO-b-PEO) and phenolic resols have shown that, by increasing hydrophilic/hydrophobic ratio of the templates, OMCs with cubic Ia3d, hexagonal p6mm, and cubic Im3m mesostructures can be obtained in order [14,15]. However, due to the limitation of the molecular weight, the common commercially available amphiphilic PEO-b-PPO-b-PEO failed to adjust the pore size or wall thickness of the mesoporous carbons in a relative wide range.
J. Wei et al. / Solid State Sciences 13 (2011) 784e792
More recently, the design of novel amphiphilic block copolymer templates has turned out to be an efficient approach to synthesize OMCs with new mesostructures, tunable pore size and wall thickness. OMCs with face-centered cubic Fd3m symmetry were obtained by using the reverse PPO-b-PEO-b-PPO triblock copolymers prepared in the laboratory from the anionic copolymerization as a template [20]. By using polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) as a structure-directing agent, the synthesis of ordered mesoporous carbon thin films with two-dimensional (2-D) hexagonal p6mm mesostructure and large pore size of w36 nm was reported by Dai and co-workers [21]. The preparation procedure involves a complicated stepwise assembly process assisted with a solvent annealing treatment using mixed vapor of benzene and dimethyl formamide. The ultra-large pore size relates to the large molecular weight of the hydrophobic segment and the solvent annealing treatment. However, only mesoporous carbon films could be obtained via this method. Our group has reported the synthesis of ultra-large pore OMCs by using a lab-made diblock copolymer PEO-b-PS as a soft template via the simple evaporation induced self-assembly (EISA) method. The pore size can reach to 22.6 nm [22]. By adding PS homopolymer as a pore expander, the pore size can be controlled from 22.9 to 37.4 nm [23]. By using the novel PEO-b-PMMA diblock copolymer as a template, OMCs with large pore (w12 nm) and thick pore wall (w11 nm) can be synthesized by virtue of the interactions occurred between the resol and hydrophilic segments EO or/and partial ester groups of the PMMA hydrophobic segments [24]. Lab-made triblock copolymer PEO-b-PMMA-b-PS was also designed as a template to synthesize OMCs with tunable pore wall thickness from 10 to 19 nm by increasing the resol/ template ratio [25]. All these reports reveal that the lab-made block copolymer templates hold great promise for templating OMCs with various mesostructures, tunable pore size and wall thickness. Up to now, most of the OMCs obtained from the lab-made block copolymers with long hydrophobic segment have 3-D cubic mesostructures from closed packing and large spherical pores and small-sized window, which hinders the large guest molecules from transfer. OMCs with large pores and channel-like mesostructure such as p6mm would favor the transfer to solve this problem. However, OMCs with large cylindrical mesopore have been scarcely reported. In this paper, lab-made block copolymers PEO-b-PMMA with different molecular weight and composition such as EO125-bMMA174 (22,400 g/mol) and EO44-b-MMA103 (12300 g/mol) were used as the templates to prepare large-pore OMCs with possible face-centered cubic ðFm3mÞ and 2-D hexagonal (p6mm) symmetries via an EISA process. It was the first example to synthesize OMCs with p6mm symmetry and large cylindrical mesopore using block copolymer PEO-b-PMMA via an EISA approach. The composition and molecular weight of PEO-b-PMMA, the weight ratio of resol to PEO-b-PMMA, and PMMA homopolymer used as a pore expander were studied to understand the synthesis of various mesoporous carbons with adjustable pore structure, pore size and pore wall thickness. 2. Experimental 2.1. Chemicals Monomethoxy poly(ethylene oxide) (PEO5k and PEO2k with molecular weight of 5000, 2000 g/mol, respectively) and 2-bromoisobutyryl bromide were purchased from Aldrich. N,N,N0 ,N0 ,N00 pentamethyldiethylenetriamine (PMDETA) was purchased from Acros. Methyl methacrylate (MMA), tetrahydrofuran (THF) (>99%), pyridine (>99%), copper bromide (CuBr), and anhydrous ether (>99%) were purchased from Shanghai Chemical Corp. MMA was
785
purified by filtering through an Al2O3 column to remove the polymerization inhibitor. The phenolic resol dissolved in THF (20 wt %) was prepared according to the previous report [22]. 2.2. Preparation of PEO-b-PMMA diblock copolymer The PEO-b-PMMA diblock copolymers were prepared by using the atom transfer radical polymerization (ATRP) technique. The initiator PEO2k-Br was synthesized as the previous report [22]. Typically, 4.0 g of PEO2k was dissolved in a mixture solvent of THF (30 mL) and pyridine (15 mL). The resulting solution was cooled in an ice-water bath and 1.38 g of 2-bromoisobutyryl bromide was added dropwise under stirring. Afterwards, the solution was stirred at 30 C for 12 h and then filtered to remove impurities. Subsequently, 60 mL of ether was added into the filtrate to obtain the white precipitate. After washing with ether and vacuum drying at 25 C, PEO2k-Br macroinitiator was obtained. Then, the PEO2k-bPMMA-4 h was prepared by polymerizing MMA using the PEO2k-Br as an initiator. Typically, 1.5 g of PEO2k-Br, 0.078 g of CuCl, 10 mL of MMA, 0.14 g of PMDETA and 20 mL of THF were added into an ampoules bottle. After the removal of air by bubbling with Ar gas, the reaction system was sealed and placed in a thermostated oil bath at 60 C for the polymerization under stirring. After 4 h, the system was cooled to room temperature, and 50 mL of THF was added to dissolve the product. After that, the obtained solution was filtered through an Al2O3 column to remove the Cu complex. 200 mL of cold ether was poured into the clear filtrate to precipitate PEO-b-PMMA diblock copolymer. The precipitate product was collected by filtration and dried under vacuum. PEO5k-b-PMMA-5h was synthesized as follows: 2.5 g of PEO5kBr, 0.50 g of CuCl, 10 mL of MMA, 0.22 g of PMDETA and 20 mL of THF were used as reactants. The react time was 5 h. Except for these differences; other conditions were identical to the typical procedure described above. 2.3. Synthesis of mesoporous carbons Mesoporus carbons were prepared through an EISA process by using PEO-b-PMMA as a template, phenolic resol as a carbon source and THF as a solvent. In a typical synthesis, 0.25e1.25 g of the resol precursor in the THF solution (20 wt %) was added to 2.5 g of THF solution of PEO5k-b-PMMA-5h (2.0 wt %, containing 0.05 g of copolymer) with stirring to form a homogeneous solution. The transparent films were obtained by pouring the solution into Petri dishes to evaporate THF solvent at room temperature for 12 h, followed by further heating in an oven at 100 C for 24 h. The as-made products were scraped and crushed into powders for pyrolysis. The pyrolysis was carried out in a tubular furnace under N2 at different temperatures (450 or 800 C) for 3 h. The heating rate was 1 C/min below 600 C and 5 C/min above 600 C. The final products were designated as EO5k-OMC-X-Y, where X refers to the weight ratio of resol to PEO5k-b-PMMA-5h; Y refers to the pyrolysis temperature and EO5k refers to the template PEO5k-bPMMA-5h. The synthesis of EO2k-OMC-X-Y samples was similar to EO5kOMC-X-Y except that the weight ratio of resol to PEO2k-b-PMMA-4h was changed from 2.5 to 3.0, where X refers to the weight ratio of resol to PEO2k-b-PMMA-4h; Y refers to the pyrolysis temperature and EO2k refers to the template PEO2k-b-PMMA-4h. Mesoporous carbons with ultra-large pore (denoted as EO2kMPC-X-450) were synthesized by adding different amount of PMMA homopolymer (Mw ¼ 9000 g/mol) as a pore expander together with the PEO2k-b-PMMA-4h template in the above procedure, where X refers to the pore size. The weight ratio of PEO2k-b-PMMA-4h: resol: PMMA was 1:2.5:0.17, 0.34, 0.50, 0.67
786
J. Wei et al. / Solid State Sciences 13 (2011) 784e792
and 0.87, corresponding to EO2k-MPC-9.8-450, EO2k-MPC-10.8-450, EO2k-MPC-12.6-450, EO2k-MPC-15.0-450 and EO2k-MPC-17.7-450. The other procedure was the same to EO2k-OMC-2.5-450. 2.4. Characterization 1
H Nuclear Magnetic Resonance (NMR) spectra were recorded at on a DMX 500 MHz spectrometer (Bruker, Germany) with 25 tetramethylsilane as an internal standard and CD3COCD3 as a solvent. Gel permeation chromatography (GPC) was performed on an Agilent 1100 gel permeation chromatographer with a refractive index detector and UV-vis detector (wavelength 190e950 nm, USA) with the use of THF as an eluent (1.0 mL min1). GPC was calibrated with a monodisperse polystyrene standard. Fourier transform infrared (FT-IR) spectra were collected on Nicolet Fourier spectrophotometer (USA) using KBr pellets. Small angle Xray scattering (SAXS) measurements were taken on a Nanostar U small angle X-ray scattering system (Bruker, Germany) using Cu Ka radiation (40 kV, 35 mA). The d-spacing values were calculated by the formula d ¼ 2p/q. The wall thickness was calculated from pffiffiffi WT ¼ 2a=2 DðFm3mÞ or WT ¼ a D (p6mm), where a represents the unit cell parameter and D is the pore diameter calculated from the N2 sorption measurements. Nitrogen sorption isotherms were measured at 77 K with a Micromeritics Tristar 3000 analyzer (USA). Before measurements, the samples were degassed in a vacuum at 180 C for at least 6 h. The BrunauereEmmetteTeller (BET) method was utilized to calculate the specific surface areas. By using the Broekoff-de Boer (BdB) or Barrett-Joyner-Halenda (BJH) model, the pore volumes and pore size distributions were derived from the adsorption branches of isotherms, and the total pore volumes (V) were estimated from the adsorbed amount at a relative pressure P/P0 of 0.992. Transmission electron microscopy (TEM) experiments were conduced on a JEOL 2011 microscope (Japan) operated at 200 kV. C
Fig. 1. 1H NMR spectrum of compolymer PEO5k-b-PMMA-5h, (insert) GPC of two different molecular weight PEO-b-PMMA diblock copolymers: (a) PEO5k-b-PMMA-5h and (b) PEO2k-b-PMMA-4h.
respectively, suggesting monodisperse molecular weight distributions. Through the versatile ATRP approach, the PEO-b-PMMA templates can be readily varied with respect to the chain lengths of hydrophilic PEO and hydrophobic PMMA blocks by using macroinitiators PEO-Br with different chain length of PEO and controlling the polymerization time, respectively. 3.2. 2-D hexagonal mesoporous carbon Using EO44-b-MMA103 as the template and through an EISA process, homogenously transparent PEO-b-PMMA/resol composite
3. Results
The synthetic procedure of PEO-b-PMMA involves two steps: the preparation of macroinitiator by reacting monomethoxy PEO5k or PEO2k with 2-bromoisobutyryl bromide, and the polymerization of methyl methacrylate (MMA). The synthesis of diblock copolymers PEO-b-PMMAs was characterized by FT-IR, 1H NMR spectroscopy and gel permeation chromatography (GPC). The FT-IR spectra display absorption bands at 1120e1150 cm1 originated from EO units, a carbonyl stretching band at 1740 cm1 for the macroinitiator PEO-Br formed by the acetylation reaction, and a strong carbonyl stretching band at 1740 cm1 attributed to the PMMA segment (Fig. S1, Supporting Information). These results imply the successful preparation of PEO-Br and PEO-b-PMMA via the ATRP method. The chemical structure of PEO5k-b-PMMA-5h was further confirmed by 1H NMR spectra, which was also used to determine the composition (Fig. 1). The signals around 3.70 (i) and 1.90 ppm (ii) are associated with EO units and the eCH3 group, respectively, the latter is originated from 2-bromoisobutyryl bromide. The signals at 0.8e1.2 (iii), 1.7e2.0 (v), and 3.6 (iv) ppm are attributed to MMA units. 1H NMR spectra of the copolymer PEO2k-b-PMMA-4h is similar to that of PEO5k-b-PMMA-5h except for the intensity of each signal (Fig. S2). The molecular weight and compositions of PEO5k-b-PMMA-5h and PEO2k-b-PMMA-4h are 22,400, 12,300 g/mol from the results of 1H NMR, confirming the structural formula of EO125-b-MMA174, and EO44-b-MMA103, respectively. The GPC analyses show polydispersity index (PDI) of 1.09 and 1.07 for EO125-b-MMA174 and EO44-b-MMA103,
Ln I (a.u.)
3.1. Synthesis of diblock copolymer PEO-b-PMMA
d
c
10
11
b
22
a 0.0
0.5
1.0
-1
1.5
2.0
q(nm ) Fig. 2. SAXS patterns of mesoporous carbons synthesized with EO44-b-MMA103 and EO125-b-MMA174: (a) EO2k-OMC-2.5-450; (b) EO2k-OMC-3.0-450; (c) EO5k-OMC-1.0450; and (d) EO5k-OMC-1.0-800.
J. Wei et al. / Solid State Sciences 13 (2011) 784e792
787
Fig. 3. TEM images of mesoporous carbon EO2k-OMC-2.5-450 (a, b) and EO2k-OMC-3.0-450 (c, d) after pyrolysis at 450 C.
films can be obtained after thermosetting at 100 C. After pyrolysis above 450 C, PEO-b-PMMA was removed from the composites [24], then, mesoporous carbons with open frameworks are obtained. The SAXS pattern of the mesoporous carbon EO2k-OMC2.5-450 sample synthesized with the resol/EO44-b-MMA103 weight ratio (Rw) of 2.5 after calcination at 450 C shows three wellresolved scattering peaks at q of 0.40, 0.70 and 1.1, which can be indexed to the 10, 11, 22 reflections, corresponding to ordered 2-D
hexagonal (p6mm) mesostructure (Fig. 2a). As increasing the Rw to 3.0, the EO2k-OMC-3.0-450 sample shows similar SAXS pattern, indicating that the same hexagonal mesostructure is obtained (Fig. 2b). The unit cell parameter increases from 15.8 to 19.0 nm as the Rw increases from 2.5 to 3.0. TEM images and corresponding Fourier diffractograms of the sample EO2k-OMC-2.5-450 show a highly ordered degree of periodicity, viewed from [10] and [01] directions, further confirming
2.5
12.1nm
2.0
300
200
3 -1 -1 dV/dD ) cm g nm )
3
Adsorption volume ) cm /g )
400
a b
100
0 0.0
0.2 0.4 0.6 0.8 Relative pressure ) p/po)
1.0
8.6nm 1.5
1.0
0.5
0.0 0
10 20 30 40 50 60 70 80 90 100
Pore size(nm)
Fig. 4. Nitrogen adsorption-desorption isotherm plots (left) and pore size distribution (right) of the mesoporous carbons (a) EO2k-OMC-2.5-450 and (b) EO5k-OMC-1.0-450 after pyrolysis at 450 C.
788
J. Wei et al. / Solid State Sciences 13 (2011) 784e792
Fig. 5. The nitrogen sorption isothermals (a), its pore size distribution (b) of mesoporous carbon EO2k-OMC-3.0-450 prepared with a high resol/compolymer ratio of 3.0 after pyrolysis at 450 C. TEM images (c, d) of mesoporous carbon EO5k-OMC-1.0-450, showing disordered mesochannels structure.
the 2-D hexagonal p6mm mesostructure (Fig. 3a, b). The sample EO2k-OMC-3.0-450 prepared with a high Rw of 3.0 also shows ordered hexagonal p6mm symmetry and curved cylindrical mesochannel (Fig. 3c and d). While some domains show obvious blocked mesochannles caused by the structure faults (see the denoted area). Nitrogen sorption isotherms of EO2k-OMC-2.5-450 sample reveal representative type IV curves with an obvious H1-type
hysteresis loop and a sharp capillary condensation step (Fig. 4a), corresponding to a cylindrical mesopore with uniform pore size. The pore size, BET surface area and pore volume are calculated to be 8.6 nm, 637 m2/g and 0.51 cm3/g, respectively. Nitrogen sorption isotherms of the EO2k-OMC-3.0-450 prepared with a high Rw of 3.0 also show the type IV curves with an obvious H2-type hysteresis loop (Fig. 5a and b), suggesting that the cylindrical mesopores are
Table 1 Physicochemical properties of ordered mesoporous carbons synthesized by using diblock copolymer PEO-b-PMMA as the template via the EISA method. Samples
Unit cell parametera (nm)
pore sizeb (nm)
Wall thicknessc (nm)
BET surface area (m2/g)
Pore volume (cm3/g)
EO2k-OMC-2.5-450 EO2k-OMC-3.0-450 EO2k-MPC-9.8-450 EO2k-MPC-10.8-450 EO2k-MPC-12.6-450 EO2k-MPC-15.0-450 EO2k-MPC-17.7-450 EO5k-OMC-1.0-450 EO5k-OMC-1.0-800 EO5k-OMC-4.2-450 EO5k-OMC-4.2-800 EO5k-OMC-5.0-450
15.8 19.0 16.7 17.0 18.4 21.5 22.1 17.9 17.0 32.9 30.0 32.5
8.6 10.8 9.8 10.8 12.6 15.0 17.7 12.1 10.9 15.6 14.1 12.6
7.2 8.2 6.9 6.2 5.8 6.5 4.4 5.8 6.1 7.7 7.3 10.4
637 385 598 554 604 533 525 466 1001 590 842 506
0.51 0.12 0.58 0.50 0.66 0.52 0.81 0.14 0.29 0.20 0.30 0.16
a
The unit cell parameters were calculated from the SAXS results. Calculated by the BJH model (for OMCs with hexagonal p6mm symmetry) and BdB model (for OMCs pffiffiffiwith possible cubic Fm3m symmetry) from sorption data. Calculated by the formulas WT ¼ a D (for OMCs with hexagonal p6mm symmetry) and WT ¼ 2a=2 D (for OMCs with possible cubic Fm3m symmetry) , where a represents the unit cell parameter and D is the pore diameter. b c
Ln I (a.u.)
J. Wei et al. / Solid State Sciences 13 (2011) 784e792
111
c 220
b 420
620 a
0.0
0.5
1.0
1.5
2.0
789
irregular and partly blocked, consistent with TEM results. The pore size, BET surface area and pore volume are calculated to be 10.8 nm, 385 m2/g and 0.12 cm3/g (Table 1), which are lower than that of the sample EO2k-OMC-2.5-450 with a low Rw. It further suggests the partly blocked mesopores. Diblock copolymer EO125-b-MMA174 with higher molecular weight of PMMA segment was also used as the template to synthesize mesoporous carbon. The SAXS pattern of the mesoporous carbon EO5k-OMC-1.0-450 sample templated from EO125-bMMA174 with a low Rw of 1.0 after pyrolyzed at 450 C shows the similar hexagonal mesostructure to EO2k-OMC-2.5-450 parepared by a short EO segment copolymer of EO44-b-MMA103 (Fig. 2c). The unit cell parameter is calculated to be as large as 17.9 nm. After pyrolysis at 800 C, the corresponding SAXS peak moves to higher q value and becomes a little weak, suggesting that the mesostructural ordering becomes inferior slightly (Fig. 2b). The unit cell parameter decreases from 17.9 to 17.0 nm, suggesting a small (5%) shrinkage. TEM images of the EO5k-OMC-1.0-450 sample also show ordered cylindrical mesopore, but the mesopore becomes irregular (Fig. 5c and d). Nitrogen sorption isotherms of EO5k-OMC-1.0-450 show uniform mesopores, similar to that of EO2k-OMC-2.5-450 sample. The pore size, BET surface and pore volume are 12.1 nm, 466 m2/g and 0.14 cm3/g, respectively.
-1
q(nm ) 3.3. Face-centered cubic mesoporous carbon Fig. 6. SAXS patterns of mesoporous carbons: (a) EO5k-OMC-4.2-450, (b) EO5k-OMC4.2-800 and (c) EO5k-OMC-5.0-450.
When EO125-b-MMA174 diblock copolymer is used as the template, increasing Rw ratio from 1.0 to 4.2, the SAXS pattern of EO5k-OMC-4.2-450 sample shows four resolved scattering peaks at q-values of 0.33, 0.55, 0.86 and 1.20, which is possibly indexed to
Fig. 7. TEM images of mesoporous carbon EO5k-OMC-4.2-450 viewed from (a) [100]; (b) [110]; (c, d) [211] directions. The insert shows corresponding FFT diffractorgram.
790
J. Wei et al. / Solid State Sciences 13 (2011) 784e792
400
0.0030
3
Adsorption volume(cm /g)
300
a
250
b 200 150
dV/dD(cm3g-1nm-1)
a: 15.4nm 350
0.0025
0.0020
b:12.6nm 0.0015
0.0010
100
0.0005
50 0.0000
0 0.0
0.2
0.4
0.6
0.8
1.0
0
Relative pressure(p/po)
20
40
60
80
100
Pore size(nm)
B
1000
800
Ln I (a.u.)
3
A
Adsorption volume(cm /g)
Fig. 8. The nitrogen sorption isotherms (left) and pore size distributions (right) of mesoporous carbons: (a), EO5k-OMC-4.2-450 and (b), EO5k-OMC-5.0-450 after pyrolysis at 450 C.
e d c b a
0.0
0.5
1.0 -1 q(nm )
1.5
600
e
400
d c
200
b a
0 0.0
2.0
0.2 0.4 0.6 0.8 Relative pressure(p/p0)
1.0
25 2.5
c
D
e
20
Pore size(nm)
b
2.0
a
3
-1
-1
dV/d log(w)(cm g nm )
C
d
1.5
15
10 1.0
5 0.5
0 0
0.0 0
10
20 30 40 pore size(nm)
50
20 40 60 80 PMMA homopolymer/ PEO-b-PMMA(wt%)
100
Fig. 9. (A) SAXS patterns, (B) nitrogen sorption isothermal plots, and (C) pore size distributions of mesoporous carbons: (a) EO2k-MPC-9.8-450, (b) EO2k-MPC-10.8-450, (c) EO2kMPC-12.6-450, (d) EO2k-MPC-15.0-450 and (e) EO2k-MPC-17.6-450. (D) The dependence of the pore size on the weight ratio of PMMA homopolymer to EO44-b-MMA123.
J. Wei et al. / Solid State Sciences 13 (2011) 784e792
calculated to be as low as 8 %. Further increasing the Rw value to 5.0, the SAXS pattern shows that the EO5k-OMC-5.0-450 sample has the same ordered cubic mesostructure with the unit cell parameter of 32.5 nm (Fig. 6c). Representative TEM images for EO5k-OMC-4.2-450 sample taken from [100], [110], [211] directions with corresponding Fourier diffractograms further confirm the possible well-ordered facecentered cubic mesostructure (Fig. 7). The unit cell parameter estimated from TEM images is about 33.1 nm, very close to that calculated from the SAXS pattern (32.9 nm). Nitrogen sorption isotherms of both EO5k-OMC-4.2-450 and EO5k-OMC-5.0-450 reveal type IV curves with an obvious H2-type hysteresis loop and a sharp capillary condensation step, corresponding to spherical mesopore with uniform pore size distribution (Fig. 8). According to the BdB sphere model, the pore sizes are calculated to be 15.6 and 12.6 nm, respectively. The BET surface area and pore volume are 590, 506 m2/g and 0.20, 0.16 cm3/g, respectively. The wall thicknesses for both EO5k-OMC-4.2-450 and EO5kOMC-5.0-450 samples based on the SAXS and nitrogen sorption results are 7.7 and 10.4 nm, respectively.
18 16
L n I ( a .u .)
14 12 10
MPC-84 MPC-68
8
MPC-61 MPC-52
6
MPC-36 MPC-20
4
MPC-12 MPC-0
2 0 0.0
0.5
1.0
1.5
-1
791
2.0
3.4. Tunable pore size
q(nm ) Fig. 10. SAXS patterns of large-pore mesoporous carbon templated by EO44-b-MMA123 with adding different amount of PMMA homopolymer as a pore expander agent. The numbers 0, 12, 20, 36, 52, 61, 68 and 84 are the percent of PMMA homopolymer in the template.
the 111, 220, 420 and 620 reflections of a possible face-centered cubic mesostructure with space group Fm3m (Fig. 6a). It suggests that a highly ordered mesoporous carbon is obtained. The unit cell parameter is calculated to be as large as 32.9 nm. After pyrolysis at 800 C, the well-resolved SAXS pattern is also observed (Fig. 6b), suggesting a thermal stability of the carbon framework for EO5kOMC-4.2-800 sample. The cell parameter decreases from 32.9 to 30.2 nm (Table 1), as a result, the mesostructural shrinkage is
A 1400
In order to get OMCs with the large tunable pore size and large windows, PMMA homopolymer is firstly used as a pore expander. SAXS patterns of all mesoporous carbons EO2k-OMC-2.5-450 synthesized from EO44-b-MMA103 with different amount of homopolymer PMMA show two resolved scattering peaks with a little weak intensity, suggesting a similar hexagonal mesostructure with a slightly poor ordering (Fig. 9A). The cell parameter increases from 16.7 to 22.1 nm as the amount of PMMA homopolymer increases (Table 1), further suggesting a pore expander. The nitrogen sorption isotherms of all the mesoporous carbons prepared by adding the homopolymer as the pore expander show typical type IV curves with an obvious H1-type hysteresis loop and a sharp capillary condensation step, corresponding to cylindrical mesopore with the uniform pore size distribution. The pore size increases from 8.6 to
B 3.0 MPC-0
1200
MPC-12
1000
dV/d log(w) (cm3 g -1 nm -1 )
3
Adsorption volume(cm /g)
2.5
MPC-84 MPC-68
800
MPC-61
600
MPC-52
400
MPC-20
MPC-36
MPC-12
200
22.0nm
MPC-20 MPC-36 MPC-52
2.0
MPC-61 MPC-68 MPC-84
11.2nm
1.5
1.0
0.5
MPC-0
0.0
0 0.0
0.2
0.4
0.6
0.8
Relative pressure(p/p0)
1.0
0
10
20
30
40
50
Pore size(nm)
Fig. 11. (A) nitrogen sorption isothermals and (B) pore size distribution curves of large-pore ordered mesoporous carbon templated by EO44-b-MMA123 with adding different amount of PMMA homopolymer as a pore expander agent. The values 0, 12, 20, 36, 52, 61, 68 and 84 correspond to the percent of PMMA homopolymer in the template.
792
J. Wei et al. / Solid State Sciences 13 (2011) 784e792
17.7 nm as the amount of PMMA increases from 17 to 87 wt% relative to the template (Fig. 9B and C). The BET surface area (525e604 m2/g) and pore volume (0.50e0.81 cm3/g) are showed in Table 1. When the diblock copolymer EO-b-MMA template with the longer hydrophobic segment (MMA), such as EO44-b-MMA123, is used to synthesize mesoporous carbon, a little larger pore size of 11.2 nm is obtained (Figs. 10 and 11). The pore size of ordered mesoporous carbons increases continuously (from 11.2 to 22.0 nm) as the amount of PMMA homopolymer increases (Fig. 9D). 4. Discussion Our results show that using copolymer EO125-b-PMMA174 as the template and phenolic resol as the carbon precursor, the weight ratio (Rw) of resol to the template can significantly affect the mesostructure of carbon. When Rw increases from 1.0 to 4.2, the hydrophilic/hydrophobic ratio increases, inducing the mesostructure of OMCs transferred from 2-D hexagonal to possible 3-D cubic Fm3m symmetry. This can be explained in terms of the change of hydrophilic/hydrophobic ratio in the resol/surfactant mesophase. Since the phenolic resol molecules can interplay with PEO segments of copolymer PEO-b-PMMA by hydrogen-bonds, the increase of Rw can result in the increase of hydrophilic/hydrophobic ratio in the micelles and cause the increase of the interfacial curvature, then, the hexagonal mesostruture can be transformed to possible facecentered cubic mesostructure. Further increasing Rw from 4.2 to 5.0, the mesostructure is unchanged, but the pore wall thickness increases from 7.7 to 10.4 nm and the pore size decreases from 15.6 to 12.6 nm. It is due to the gradual invasion of resol molecules into the hydrophobic domain of PMMA segment of diblock copolymer PEO-b-PMMA by hydrogenbond-interaction, therefore, leading to thick pore wall and reduce the pore size. Such a phenomenon has been observed previously for FDU-18 mesoporous carbons [24]. Using EO44-b-MMA103 as the soft template, 2-D hexagonal (p6mm) OMCs with large cylindrical mesopore can be obtained. Increasing Rw from 2.5 to 3.0, the mesostructure keeps unchanged, but the pore channels become curved and partially blocked. It is because the template with too short hydrophilic segments could not endure the wide variation of Rw value. Further increasing the Rw, or using other composites of PEO-b-PMMA with shorter PMMA segments such as EO44-b-MMA43 and EO44-b-MMA73 as the template, no ordered mesoporous carbon can be obtained. This is due to the weak microphase separation ability of the diblock copolymer duing the EISA process. The nitrogen sorption results show longer hydrophobic segment (e.g. EO125-b-MMA174) copolymer can yield larger pore size than shorter one (e.g. EO44-bMMA103). The pore size increases from 8.6 to 12.1 nm as PMMA segment enlarges from 10,300 to 17,400 g/mol, implying a positive proportion increase. The pore size can be further adjusted in the range of 8.6e22.0 nm by adding a desired amount of PMMA homopolymer as the pore expander. The pore expanding effect is mainly ascribed to the hydrophobic interaction of the homopolymer with PMMA segment of PEO-b-PMMA block copolymers. During the EISA process, PMMA homopolymer resides in hydrophobic part of PEO-b-PMMA/resol composites, leading to the increase of both the pore size and unit cell. 5. Conclusion In this paper, several amphiphilic PEO-b-PMMA diblock copolymers were designed by using the versatile ATRP technique for templating synthesis of mesoporous carbons, and through an EISA approach, phenolic resol as a carbon precursor and THF as a solvent. We demonstrated that it is a feasible and simple method to control the synthesis of OMCs with desired mesostructure, pore size and
wall thickness, via varying hydrophilic/hydrophobic ratio, the size of hydrophobic part and the amount of the carbon precursor. We have shown for the first time that OMCs with hexagonal p6mm symmetry and large pore size (8.6e12.1 nm) can be synthesized by using PEOb-PMMA with long PMMA segment as a template. Increasing resol/ template weight ratio (Rw) from 1.0 to 4.2, the mesostructure can be transferred from 2-D hexagonal p6mm to possible 3-D cubic Fm3m, owing to the change of interface curvature. Further increasing Rw from 4.2 to 5.0, the mesopore wall thickness can increase from 8.1 to 10.4 nm. Adding homopolymer PMMA as the pore expander, the pore size of hexagonal mesoporous carbon can be precisely and continuously adjusted from 8.6 to 22.0 nm. Our results show that the lab-made amphiphilic block copolymers, such as PEO-b-PS and PEOb-PMMA-b-PS et al, their hydrophilic/hydrophobic ratio and the size of hydrophobic part can also be controlled by ATRP method, which are favorable to synthesize mesoporous carbons, silicas and metal oxides with tunable parameters. Acknowledgements This work was supported by NSF of China (2089012, 20721063, 20821140537, 20871030), State Key Basic Research Program of PRC (2006CB932302), Shanghai Leading Academic Discipline Project (B108), Shanghai Rising Star Program for Young Research Scientists (08QA14010), Doctoral Program Foundation of State Education Commission of China (200802461013), and Science & Technology Commission of Shanghai Municipality ( 08DZ2270500). Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.solidstatesciences.2010.03.008 References [1] J. Lee, J. Kim, T. Hyeon, Adv. Mater. 18 (2006) 2073. [2] C.D. Liang, Z.J. Li, S. Dai, Angew. Chem. Int. Ed. 47 (2008) 2e26. [3] A.H. Lu, W. Schmidt, N. Matoussevitch, H. Bönnemann, B. Spliethoff, B. Tesche, E. Bill, W. Kiefer, F. Schüth, Angew. Chem. Int. Ed. 43 (2004) 4303. [4] T. Ohkubo, J. Miyawaki, K. Kaneko, R. Ryoo, N.A. Seaton, J. Phys. Chem. B 106 (2002) 6523. [5] J. Lee, S. Yoon, T. Hyeon, S.M. Oh, K.B. Kim, Chem. Commun. (1999) 2177. [6] X.L. Ji, K.T. Lee, L.F. Nazar, Nat. Mater. 6 (2009) 500. [7] S.H. Joo, S.J. Choi, I. Oh, J. Kwak, Z. Liu, O. Terasaki, R. Ryoo, Nature 412 (2001) 169. [8] K. Ariga, A. Vinu, Q. Ji, O. Ohmori, J.P. Hill, S. Acharya, J. Koike, S. Shiratori, Angew. Chem. Int. Ed. 47 (2008) 7254. [9] D. Lee, J. Lee, J. Kim, J. Kim, H.B. Na, B. Kim, C.H. Shin, J.H. Kwak, A. Dohnalkova, J.W. Grate, T. Hyeon, H.S. Kim, Adv. Mater. 17 (2005) 2828. [10] J.S. Lee, S.H. Joo, R. Ryoo, J. Am. Chem. Soc. 124 (2002) 1156. [11] H.I. Lee, J.H. Kim, D.J. You, J.E. Lee, J.M. Kim, W.S. Ahn, C. Pak, S.H. Joo, H. Chang, D. Seung, Adv. Mater. 20 (2008) 757. [12] S. Tanaka, N. Nishiyama, Y. Egashira, K. Ueyama, Chem. Commun (2005) 2125. [13] C.D. Liang, S. Dai, J. Am. Chem. Soc. 128 (2006) 5316. [14] Y. Meng, D. Gu, F.Q. Zhang, Y.F. Shi, H.F. Yang, Z. Li, C.Z. Yu, B. Tu, D.Y. Zhao, Angew. Chem. Int. Ed. 44 (2005) 7053. [15] Y. Meng, D. Gu, F.Q. Zhang, Y.F. Shi, L. Cheng, D. Feng, Z.X. Wu, Z.X. Chen, Y. Wan, A. Stein, D.Y. Zhao, Chem. Mater. 18 (2006) 4447. [16] F.Q. Zhang, Y. Meng, D. Gu, Y. Yan, C.Z. Yu, B. Tu, D.Y. Zhao, J. Am. Chem. Soc. 127 (2005) 13508. [17] F.Q. Zhang, Y. Meng, D. Gu, Y. Yan, C.Z. Yu, B. Tu, D.Y. Zhao, Chem. Mater. 18 (2006) 5279. [18] Y. Wan, Y.F. Shi, D.Y. Zhao, Chem. Commun (2007) 897. [19] Y. Wan, D.Y. Zhao, Angew. Chem. Int. Ed. 107 (2007) 2821. [20] Y. Huang, H.Q. Cai, T. Yu, F.Q. Zhang, F. Zhang, Y. Meng, D. Gu, Y. Wan, X.L. Sun, B. Tu, D.Y. Zhao, Angew. Chem. Int. Ed. 46 (2007) 1089. [21] C.D. Liang, K.L. Hong, G.A. Guiochon, J.W. Mays, S. Dai, Angew. Chem. Int. Ed. 43 (2004) 5785. [22] Y.H. Deng, T. Yu, Y. Wan, Y.F. Shi, Y. Meng, D. Gu, L.J. Zhang, Y. Huang, C. Liu, X.J. Wu, D.Y. Zhao, J. Am. Chem. Soc. 129 (2007) 1690. [23] Y.H. Deng, J. Liu, C. Liu, D. Gu, Z.K. Sun, J. Wei, J.Y. Zhang, L.J. Zhang, B. Tu, D.Y. Zhao, Chem. Mater. 20 (2008) 7281. [24] Y.H. Deng, C. Liu, D. Gu, T. Yu, B. Tu, D.Y. Zhao, J. Mater. Chem. 18 (2008) 91. [25] J.Y. Zhang, Y.H. Deng, J. Wei, Z.K. Sun, D. Gu, H. Bongard, C. Liu, H.H. Wu, B. Tu, F. Schüth, D.Y. Zhao, Chem. Mater. 21 (2009) 3996.
Contents lists available at ScienceDirect
Solid State Sciences journal homepage: www.elsevier.com/locate/ssscie
Large-pore ordered mesoporous carbons with tunable structures and pore sizes templated from poly(ethylene oxide)-b-poly(methyl methacrylate) Jing Wei, Yonghui Deng, Junyong Zhang, Zhenkun Sun, Bo Tu, Dongyuan Zhao* Department of Chemistry, Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, the Key Laboratory of Molecular Engineering of Polymers of Ministry of Education and Advanced Materials Laboratory, Fudan University, Shanghai 200433, PR China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 12 February 2010 Accepted 9 March 2010 Available online 17 March 2010
Ordered mesoporous carbons (OMCs) with possible face-centered cubic (space group Fm3m) and 2-D hexagonal (p6mm) symmetries have been successfully synthesized by using lab-made poly(ethylene oxide)-block-poly(methyl methacrylate) diblock polymers (PEO-b-PMMA) with different PEO/PMMA ratios as a template. The synthesis process undergoes an evaporation induced self-assembly (EISA) at 100 C by using low-molecular weight phenolic resol as a carbon source and tetrahydrofuran (THF) as the solvent. The atom transfer radical polymerization (ATRP) method was used to prepare the diblock copolymers with different molecular weight and compositions of PEO and PMMA segments by simply changing the PEO initiator and polymerization time. For the first time, we have obtained OMCs with hexagonal p6mm symmetry and large pore size (8.6e12.1 nm) by using PEO-b-PMMA with long PMMA segment as the templates. Notably, the pore size of the ordered mesoporous carbons can be tuned in the range of 8.6e22.0 nm by slightly adjusting the hydrophobic PMMA length of the template or adding desired amount of PMMA homopolymer as a pore expander. Additionally, it is found that the pore wall thickness of OMCs with possible face-centered cubic symmetry can be adjusted from 8.1 to 10.4 nm by simply increasing the weight ratio of resol to the template (Rw). Ó 2010 Elsevier Masson SAS. All rights reserved.
Keywords: Mesoporous materials Carbon Synthesis Block copolymer Template Self-assembly
1. Introduction Ordered mesoporous carbons (OMCs) have received considerable attention owing to their high surface areas, large pore sizes with narrow distribution, high chemical inertness and mechanical stability, all of which lead to potential applications in adsorption and separation, catalysis, electrochemistry and sensors [1e8]. It is believed that the precise control of their pore structures, pore sizes and wall thickness can greatly enhance their suitability for the applications. Particularly, OMCs with large pore sizes can provide fast mass transfer and thus are highly desirable for biomacromolecular separation and biocatalysis involving large sized molecules [9]. Great efforts have been made to synthesize OMCs with tunable pore size through the nanocasting approach by using various ordered mesoporous silicas as the hard templates. Ryoo and coworkers reported the synthesis of OMCs with pore sizes tunable in a narrow range of 2.2e3.3 nm by using mesoporous silica templates with different wall thicknesses [10]. Using boric acid as
* Corresponding author. Tel.: þ86 21 55664194; fax: þ86 21 65641740. E-mail address: [email protected] (D.Y. Zhao). 1293-2558/$ e see front matter Ó 2010 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.solidstatesciences.2010.03.008
a pore expanding agent, Kim et al. successfully synthesized OMCs with controllable pore size ranging from 3 to 10 nm [11]. However, the nanocasting method suffers drawbacks such as the time-consuming, costly procedure, and the reliance of pore structures on the templates. Moreover, the pore size, depending on the wall thickness of template, is difficult to be adjusted in a wide range. Recently, the organic-organic self-assembly of amphiphilic block copolymers and carbon precursors has been demonstrated to be a versatile route to fabricate ordered mesoporous polymers and carbons [12e19]. It has been realized that the composition and feature of the block copolymer templates play key roles in the formation of mesostructures, and the volume of hydrophobic segment is close relative to the pore size of OMCs. Previous reports on the mesoporous carbons based on the selfassembly of poly(ethylene oxide)-block-poly(propylene oxide)block-poly (ethylene oxide) (PEO-b-PPO-b-PEO) and phenolic resols have shown that, by increasing hydrophilic/hydrophobic ratio of the templates, OMCs with cubic Ia3d, hexagonal p6mm, and cubic Im3m mesostructures can be obtained in order [14,15]. However, due to the limitation of the molecular weight, the common commercially available amphiphilic PEO-b-PPO-b-PEO failed to adjust the pore size or wall thickness of the mesoporous carbons in a relative wide range.
J. Wei et al. / Solid State Sciences 13 (2011) 784e792
More recently, the design of novel amphiphilic block copolymer templates has turned out to be an efficient approach to synthesize OMCs with new mesostructures, tunable pore size and wall thickness. OMCs with face-centered cubic Fd3m symmetry were obtained by using the reverse PPO-b-PEO-b-PPO triblock copolymers prepared in the laboratory from the anionic copolymerization as a template [20]. By using polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) as a structure-directing agent, the synthesis of ordered mesoporous carbon thin films with two-dimensional (2-D) hexagonal p6mm mesostructure and large pore size of w36 nm was reported by Dai and co-workers [21]. The preparation procedure involves a complicated stepwise assembly process assisted with a solvent annealing treatment using mixed vapor of benzene and dimethyl formamide. The ultra-large pore size relates to the large molecular weight of the hydrophobic segment and the solvent annealing treatment. However, only mesoporous carbon films could be obtained via this method. Our group has reported the synthesis of ultra-large pore OMCs by using a lab-made diblock copolymer PEO-b-PS as a soft template via the simple evaporation induced self-assembly (EISA) method. The pore size can reach to 22.6 nm [22]. By adding PS homopolymer as a pore expander, the pore size can be controlled from 22.9 to 37.4 nm [23]. By using the novel PEO-b-PMMA diblock copolymer as a template, OMCs with large pore (w12 nm) and thick pore wall (w11 nm) can be synthesized by virtue of the interactions occurred between the resol and hydrophilic segments EO or/and partial ester groups of the PMMA hydrophobic segments [24]. Lab-made triblock copolymer PEO-b-PMMA-b-PS was also designed as a template to synthesize OMCs with tunable pore wall thickness from 10 to 19 nm by increasing the resol/ template ratio [25]. All these reports reveal that the lab-made block copolymer templates hold great promise for templating OMCs with various mesostructures, tunable pore size and wall thickness. Up to now, most of the OMCs obtained from the lab-made block copolymers with long hydrophobic segment have 3-D cubic mesostructures from closed packing and large spherical pores and small-sized window, which hinders the large guest molecules from transfer. OMCs with large pores and channel-like mesostructure such as p6mm would favor the transfer to solve this problem. However, OMCs with large cylindrical mesopore have been scarcely reported. In this paper, lab-made block copolymers PEO-b-PMMA with different molecular weight and composition such as EO125-bMMA174 (22,400 g/mol) and EO44-b-MMA103 (12300 g/mol) were used as the templates to prepare large-pore OMCs with possible face-centered cubic ðFm3mÞ and 2-D hexagonal (p6mm) symmetries via an EISA process. It was the first example to synthesize OMCs with p6mm symmetry and large cylindrical mesopore using block copolymer PEO-b-PMMA via an EISA approach. The composition and molecular weight of PEO-b-PMMA, the weight ratio of resol to PEO-b-PMMA, and PMMA homopolymer used as a pore expander were studied to understand the synthesis of various mesoporous carbons with adjustable pore structure, pore size and pore wall thickness. 2. Experimental 2.1. Chemicals Monomethoxy poly(ethylene oxide) (PEO5k and PEO2k with molecular weight of 5000, 2000 g/mol, respectively) and 2-bromoisobutyryl bromide were purchased from Aldrich. N,N,N0 ,N0 ,N00 pentamethyldiethylenetriamine (PMDETA) was purchased from Acros. Methyl methacrylate (MMA), tetrahydrofuran (THF) (>99%), pyridine (>99%), copper bromide (CuBr), and anhydrous ether (>99%) were purchased from Shanghai Chemical Corp. MMA was
785
purified by filtering through an Al2O3 column to remove the polymerization inhibitor. The phenolic resol dissolved in THF (20 wt %) was prepared according to the previous report [22]. 2.2. Preparation of PEO-b-PMMA diblock copolymer The PEO-b-PMMA diblock copolymers were prepared by using the atom transfer radical polymerization (ATRP) technique. The initiator PEO2k-Br was synthesized as the previous report [22]. Typically, 4.0 g of PEO2k was dissolved in a mixture solvent of THF (30 mL) and pyridine (15 mL). The resulting solution was cooled in an ice-water bath and 1.38 g of 2-bromoisobutyryl bromide was added dropwise under stirring. Afterwards, the solution was stirred at 30 C for 12 h and then filtered to remove impurities. Subsequently, 60 mL of ether was added into the filtrate to obtain the white precipitate. After washing with ether and vacuum drying at 25 C, PEO2k-Br macroinitiator was obtained. Then, the PEO2k-bPMMA-4 h was prepared by polymerizing MMA using the PEO2k-Br as an initiator. Typically, 1.5 g of PEO2k-Br, 0.078 g of CuCl, 10 mL of MMA, 0.14 g of PMDETA and 20 mL of THF were added into an ampoules bottle. After the removal of air by bubbling with Ar gas, the reaction system was sealed and placed in a thermostated oil bath at 60 C for the polymerization under stirring. After 4 h, the system was cooled to room temperature, and 50 mL of THF was added to dissolve the product. After that, the obtained solution was filtered through an Al2O3 column to remove the Cu complex. 200 mL of cold ether was poured into the clear filtrate to precipitate PEO-b-PMMA diblock copolymer. The precipitate product was collected by filtration and dried under vacuum. PEO5k-b-PMMA-5h was synthesized as follows: 2.5 g of PEO5kBr, 0.50 g of CuCl, 10 mL of MMA, 0.22 g of PMDETA and 20 mL of THF were used as reactants. The react time was 5 h. Except for these differences; other conditions were identical to the typical procedure described above. 2.3. Synthesis of mesoporous carbons Mesoporus carbons were prepared through an EISA process by using PEO-b-PMMA as a template, phenolic resol as a carbon source and THF as a solvent. In a typical synthesis, 0.25e1.25 g of the resol precursor in the THF solution (20 wt %) was added to 2.5 g of THF solution of PEO5k-b-PMMA-5h (2.0 wt %, containing 0.05 g of copolymer) with stirring to form a homogeneous solution. The transparent films were obtained by pouring the solution into Petri dishes to evaporate THF solvent at room temperature for 12 h, followed by further heating in an oven at 100 C for 24 h. The as-made products were scraped and crushed into powders for pyrolysis. The pyrolysis was carried out in a tubular furnace under N2 at different temperatures (450 or 800 C) for 3 h. The heating rate was 1 C/min below 600 C and 5 C/min above 600 C. The final products were designated as EO5k-OMC-X-Y, where X refers to the weight ratio of resol to PEO5k-b-PMMA-5h; Y refers to the pyrolysis temperature and EO5k refers to the template PEO5k-bPMMA-5h. The synthesis of EO2k-OMC-X-Y samples was similar to EO5kOMC-X-Y except that the weight ratio of resol to PEO2k-b-PMMA-4h was changed from 2.5 to 3.0, where X refers to the weight ratio of resol to PEO2k-b-PMMA-4h; Y refers to the pyrolysis temperature and EO2k refers to the template PEO2k-b-PMMA-4h. Mesoporous carbons with ultra-large pore (denoted as EO2kMPC-X-450) were synthesized by adding different amount of PMMA homopolymer (Mw ¼ 9000 g/mol) as a pore expander together with the PEO2k-b-PMMA-4h template in the above procedure, where X refers to the pore size. The weight ratio of PEO2k-b-PMMA-4h: resol: PMMA was 1:2.5:0.17, 0.34, 0.50, 0.67
786
J. Wei et al. / Solid State Sciences 13 (2011) 784e792
and 0.87, corresponding to EO2k-MPC-9.8-450, EO2k-MPC-10.8-450, EO2k-MPC-12.6-450, EO2k-MPC-15.0-450 and EO2k-MPC-17.7-450. The other procedure was the same to EO2k-OMC-2.5-450. 2.4. Characterization 1
H Nuclear Magnetic Resonance (NMR) spectra were recorded at on a DMX 500 MHz spectrometer (Bruker, Germany) with 25 tetramethylsilane as an internal standard and CD3COCD3 as a solvent. Gel permeation chromatography (GPC) was performed on an Agilent 1100 gel permeation chromatographer with a refractive index detector and UV-vis detector (wavelength 190e950 nm, USA) with the use of THF as an eluent (1.0 mL min1). GPC was calibrated with a monodisperse polystyrene standard. Fourier transform infrared (FT-IR) spectra were collected on Nicolet Fourier spectrophotometer (USA) using KBr pellets. Small angle Xray scattering (SAXS) measurements were taken on a Nanostar U small angle X-ray scattering system (Bruker, Germany) using Cu Ka radiation (40 kV, 35 mA). The d-spacing values were calculated by the formula d ¼ 2p/q. The wall thickness was calculated from pffiffiffi WT ¼ 2a=2 DðFm3mÞ or WT ¼ a D (p6mm), where a represents the unit cell parameter and D is the pore diameter calculated from the N2 sorption measurements. Nitrogen sorption isotherms were measured at 77 K with a Micromeritics Tristar 3000 analyzer (USA). Before measurements, the samples were degassed in a vacuum at 180 C for at least 6 h. The BrunauereEmmetteTeller (BET) method was utilized to calculate the specific surface areas. By using the Broekoff-de Boer (BdB) or Barrett-Joyner-Halenda (BJH) model, the pore volumes and pore size distributions were derived from the adsorption branches of isotherms, and the total pore volumes (V) were estimated from the adsorbed amount at a relative pressure P/P0 of 0.992. Transmission electron microscopy (TEM) experiments were conduced on a JEOL 2011 microscope (Japan) operated at 200 kV. C
Fig. 1. 1H NMR spectrum of compolymer PEO5k-b-PMMA-5h, (insert) GPC of two different molecular weight PEO-b-PMMA diblock copolymers: (a) PEO5k-b-PMMA-5h and (b) PEO2k-b-PMMA-4h.
respectively, suggesting monodisperse molecular weight distributions. Through the versatile ATRP approach, the PEO-b-PMMA templates can be readily varied with respect to the chain lengths of hydrophilic PEO and hydrophobic PMMA blocks by using macroinitiators PEO-Br with different chain length of PEO and controlling the polymerization time, respectively. 3.2. 2-D hexagonal mesoporous carbon Using EO44-b-MMA103 as the template and through an EISA process, homogenously transparent PEO-b-PMMA/resol composite
3. Results
The synthetic procedure of PEO-b-PMMA involves two steps: the preparation of macroinitiator by reacting monomethoxy PEO5k or PEO2k with 2-bromoisobutyryl bromide, and the polymerization of methyl methacrylate (MMA). The synthesis of diblock copolymers PEO-b-PMMAs was characterized by FT-IR, 1H NMR spectroscopy and gel permeation chromatography (GPC). The FT-IR spectra display absorption bands at 1120e1150 cm1 originated from EO units, a carbonyl stretching band at 1740 cm1 for the macroinitiator PEO-Br formed by the acetylation reaction, and a strong carbonyl stretching band at 1740 cm1 attributed to the PMMA segment (Fig. S1, Supporting Information). These results imply the successful preparation of PEO-Br and PEO-b-PMMA via the ATRP method. The chemical structure of PEO5k-b-PMMA-5h was further confirmed by 1H NMR spectra, which was also used to determine the composition (Fig. 1). The signals around 3.70 (i) and 1.90 ppm (ii) are associated with EO units and the eCH3 group, respectively, the latter is originated from 2-bromoisobutyryl bromide. The signals at 0.8e1.2 (iii), 1.7e2.0 (v), and 3.6 (iv) ppm are attributed to MMA units. 1H NMR spectra of the copolymer PEO2k-b-PMMA-4h is similar to that of PEO5k-b-PMMA-5h except for the intensity of each signal (Fig. S2). The molecular weight and compositions of PEO5k-b-PMMA-5h and PEO2k-b-PMMA-4h are 22,400, 12,300 g/mol from the results of 1H NMR, confirming the structural formula of EO125-b-MMA174, and EO44-b-MMA103, respectively. The GPC analyses show polydispersity index (PDI) of 1.09 and 1.07 for EO125-b-MMA174 and EO44-b-MMA103,
Ln I (a.u.)
3.1. Synthesis of diblock copolymer PEO-b-PMMA
d
c
10
11
b
22
a 0.0
0.5
1.0
-1
1.5
2.0
q(nm ) Fig. 2. SAXS patterns of mesoporous carbons synthesized with EO44-b-MMA103 and EO125-b-MMA174: (a) EO2k-OMC-2.5-450; (b) EO2k-OMC-3.0-450; (c) EO5k-OMC-1.0450; and (d) EO5k-OMC-1.0-800.
J. Wei et al. / Solid State Sciences 13 (2011) 784e792
787
Fig. 3. TEM images of mesoporous carbon EO2k-OMC-2.5-450 (a, b) and EO2k-OMC-3.0-450 (c, d) after pyrolysis at 450 C.
films can be obtained after thermosetting at 100 C. After pyrolysis above 450 C, PEO-b-PMMA was removed from the composites [24], then, mesoporous carbons with open frameworks are obtained. The SAXS pattern of the mesoporous carbon EO2k-OMC2.5-450 sample synthesized with the resol/EO44-b-MMA103 weight ratio (Rw) of 2.5 after calcination at 450 C shows three wellresolved scattering peaks at q of 0.40, 0.70 and 1.1, which can be indexed to the 10, 11, 22 reflections, corresponding to ordered 2-D
hexagonal (p6mm) mesostructure (Fig. 2a). As increasing the Rw to 3.0, the EO2k-OMC-3.0-450 sample shows similar SAXS pattern, indicating that the same hexagonal mesostructure is obtained (Fig. 2b). The unit cell parameter increases from 15.8 to 19.0 nm as the Rw increases from 2.5 to 3.0. TEM images and corresponding Fourier diffractograms of the sample EO2k-OMC-2.5-450 show a highly ordered degree of periodicity, viewed from [10] and [01] directions, further confirming
2.5
12.1nm
2.0
300
200
3 -1 -1 dV/dD ) cm g nm )
3
Adsorption volume ) cm /g )
400
a b
100
0 0.0
0.2 0.4 0.6 0.8 Relative pressure ) p/po)
1.0
8.6nm 1.5
1.0
0.5
0.0 0
10 20 30 40 50 60 70 80 90 100
Pore size(nm)
Fig. 4. Nitrogen adsorption-desorption isotherm plots (left) and pore size distribution (right) of the mesoporous carbons (a) EO2k-OMC-2.5-450 and (b) EO5k-OMC-1.0-450 after pyrolysis at 450 C.
788
J. Wei et al. / Solid State Sciences 13 (2011) 784e792
Fig. 5. The nitrogen sorption isothermals (a), its pore size distribution (b) of mesoporous carbon EO2k-OMC-3.0-450 prepared with a high resol/compolymer ratio of 3.0 after pyrolysis at 450 C. TEM images (c, d) of mesoporous carbon EO5k-OMC-1.0-450, showing disordered mesochannels structure.
the 2-D hexagonal p6mm mesostructure (Fig. 3a, b). The sample EO2k-OMC-3.0-450 prepared with a high Rw of 3.0 also shows ordered hexagonal p6mm symmetry and curved cylindrical mesochannel (Fig. 3c and d). While some domains show obvious blocked mesochannles caused by the structure faults (see the denoted area). Nitrogen sorption isotherms of EO2k-OMC-2.5-450 sample reveal representative type IV curves with an obvious H1-type
hysteresis loop and a sharp capillary condensation step (Fig. 4a), corresponding to a cylindrical mesopore with uniform pore size. The pore size, BET surface area and pore volume are calculated to be 8.6 nm, 637 m2/g and 0.51 cm3/g, respectively. Nitrogen sorption isotherms of the EO2k-OMC-3.0-450 prepared with a high Rw of 3.0 also show the type IV curves with an obvious H2-type hysteresis loop (Fig. 5a and b), suggesting that the cylindrical mesopores are
Table 1 Physicochemical properties of ordered mesoporous carbons synthesized by using diblock copolymer PEO-b-PMMA as the template via the EISA method. Samples
Unit cell parametera (nm)
pore sizeb (nm)
Wall thicknessc (nm)
BET surface area (m2/g)
Pore volume (cm3/g)
EO2k-OMC-2.5-450 EO2k-OMC-3.0-450 EO2k-MPC-9.8-450 EO2k-MPC-10.8-450 EO2k-MPC-12.6-450 EO2k-MPC-15.0-450 EO2k-MPC-17.7-450 EO5k-OMC-1.0-450 EO5k-OMC-1.0-800 EO5k-OMC-4.2-450 EO5k-OMC-4.2-800 EO5k-OMC-5.0-450
15.8 19.0 16.7 17.0 18.4 21.5 22.1 17.9 17.0 32.9 30.0 32.5
8.6 10.8 9.8 10.8 12.6 15.0 17.7 12.1 10.9 15.6 14.1 12.6
7.2 8.2 6.9 6.2 5.8 6.5 4.4 5.8 6.1 7.7 7.3 10.4
637 385 598 554 604 533 525 466 1001 590 842 506
0.51 0.12 0.58 0.50 0.66 0.52 0.81 0.14 0.29 0.20 0.30 0.16
a
The unit cell parameters were calculated from the SAXS results. Calculated by the BJH model (for OMCs with hexagonal p6mm symmetry) and BdB model (for OMCs pffiffiffiwith possible cubic Fm3m symmetry) from sorption data. Calculated by the formulas WT ¼ a D (for OMCs with hexagonal p6mm symmetry) and WT ¼ 2a=2 D (for OMCs with possible cubic Fm3m symmetry) , where a represents the unit cell parameter and D is the pore diameter. b c
Ln I (a.u.)
J. Wei et al. / Solid State Sciences 13 (2011) 784e792
111
c 220
b 420
620 a
0.0
0.5
1.0
1.5
2.0
789
irregular and partly blocked, consistent with TEM results. The pore size, BET surface area and pore volume are calculated to be 10.8 nm, 385 m2/g and 0.12 cm3/g (Table 1), which are lower than that of the sample EO2k-OMC-2.5-450 with a low Rw. It further suggests the partly blocked mesopores. Diblock copolymer EO125-b-MMA174 with higher molecular weight of PMMA segment was also used as the template to synthesize mesoporous carbon. The SAXS pattern of the mesoporous carbon EO5k-OMC-1.0-450 sample templated from EO125-bMMA174 with a low Rw of 1.0 after pyrolyzed at 450 C shows the similar hexagonal mesostructure to EO2k-OMC-2.5-450 parepared by a short EO segment copolymer of EO44-b-MMA103 (Fig. 2c). The unit cell parameter is calculated to be as large as 17.9 nm. After pyrolysis at 800 C, the corresponding SAXS peak moves to higher q value and becomes a little weak, suggesting that the mesostructural ordering becomes inferior slightly (Fig. 2b). The unit cell parameter decreases from 17.9 to 17.0 nm, suggesting a small (5%) shrinkage. TEM images of the EO5k-OMC-1.0-450 sample also show ordered cylindrical mesopore, but the mesopore becomes irregular (Fig. 5c and d). Nitrogen sorption isotherms of EO5k-OMC-1.0-450 show uniform mesopores, similar to that of EO2k-OMC-2.5-450 sample. The pore size, BET surface and pore volume are 12.1 nm, 466 m2/g and 0.14 cm3/g, respectively.
-1
q(nm ) 3.3. Face-centered cubic mesoporous carbon Fig. 6. SAXS patterns of mesoporous carbons: (a) EO5k-OMC-4.2-450, (b) EO5k-OMC4.2-800 and (c) EO5k-OMC-5.0-450.
When EO125-b-MMA174 diblock copolymer is used as the template, increasing Rw ratio from 1.0 to 4.2, the SAXS pattern of EO5k-OMC-4.2-450 sample shows four resolved scattering peaks at q-values of 0.33, 0.55, 0.86 and 1.20, which is possibly indexed to
Fig. 7. TEM images of mesoporous carbon EO5k-OMC-4.2-450 viewed from (a) [100]; (b) [110]; (c, d) [211] directions. The insert shows corresponding FFT diffractorgram.
790
J. Wei et al. / Solid State Sciences 13 (2011) 784e792
400
0.0030
3
Adsorption volume(cm /g)
300
a
250
b 200 150
dV/dD(cm3g-1nm-1)
a: 15.4nm 350
0.0025
0.0020
b:12.6nm 0.0015
0.0010
100
0.0005
50 0.0000
0 0.0
0.2
0.4
0.6
0.8
1.0
0
Relative pressure(p/po)
20
40
60
80
100
Pore size(nm)
B
1000
800
Ln I (a.u.)
3
A
Adsorption volume(cm /g)
Fig. 8. The nitrogen sorption isotherms (left) and pore size distributions (right) of mesoporous carbons: (a), EO5k-OMC-4.2-450 and (b), EO5k-OMC-5.0-450 after pyrolysis at 450 C.
e d c b a
0.0
0.5
1.0 -1 q(nm )
1.5
600
e
400
d c
200
b a
0 0.0
2.0
0.2 0.4 0.6 0.8 Relative pressure(p/p0)
1.0
25 2.5
c
D
e
20
Pore size(nm)
b
2.0
a
3
-1
-1
dV/d log(w)(cm g nm )
C
d
1.5
15
10 1.0
5 0.5
0 0
0.0 0
10
20 30 40 pore size(nm)
50
20 40 60 80 PMMA homopolymer/ PEO-b-PMMA(wt%)
100
Fig. 9. (A) SAXS patterns, (B) nitrogen sorption isothermal plots, and (C) pore size distributions of mesoporous carbons: (a) EO2k-MPC-9.8-450, (b) EO2k-MPC-10.8-450, (c) EO2kMPC-12.6-450, (d) EO2k-MPC-15.0-450 and (e) EO2k-MPC-17.6-450. (D) The dependence of the pore size on the weight ratio of PMMA homopolymer to EO44-b-MMA123.
J. Wei et al. / Solid State Sciences 13 (2011) 784e792
calculated to be as low as 8 %. Further increasing the Rw value to 5.0, the SAXS pattern shows that the EO5k-OMC-5.0-450 sample has the same ordered cubic mesostructure with the unit cell parameter of 32.5 nm (Fig. 6c). Representative TEM images for EO5k-OMC-4.2-450 sample taken from [100], [110], [211] directions with corresponding Fourier diffractograms further confirm the possible well-ordered facecentered cubic mesostructure (Fig. 7). The unit cell parameter estimated from TEM images is about 33.1 nm, very close to that calculated from the SAXS pattern (32.9 nm). Nitrogen sorption isotherms of both EO5k-OMC-4.2-450 and EO5k-OMC-5.0-450 reveal type IV curves with an obvious H2-type hysteresis loop and a sharp capillary condensation step, corresponding to spherical mesopore with uniform pore size distribution (Fig. 8). According to the BdB sphere model, the pore sizes are calculated to be 15.6 and 12.6 nm, respectively. The BET surface area and pore volume are 590, 506 m2/g and 0.20, 0.16 cm3/g, respectively. The wall thicknesses for both EO5k-OMC-4.2-450 and EO5kOMC-5.0-450 samples based on the SAXS and nitrogen sorption results are 7.7 and 10.4 nm, respectively.
18 16
L n I ( a .u .)
14 12 10
MPC-84 MPC-68
8
MPC-61 MPC-52
6
MPC-36 MPC-20
4
MPC-12 MPC-0
2 0 0.0
0.5
1.0
1.5
-1
791
2.0
3.4. Tunable pore size
q(nm ) Fig. 10. SAXS patterns of large-pore mesoporous carbon templated by EO44-b-MMA123 with adding different amount of PMMA homopolymer as a pore expander agent. The numbers 0, 12, 20, 36, 52, 61, 68 and 84 are the percent of PMMA homopolymer in the template.
the 111, 220, 420 and 620 reflections of a possible face-centered cubic mesostructure with space group Fm3m (Fig. 6a). It suggests that a highly ordered mesoporous carbon is obtained. The unit cell parameter is calculated to be as large as 32.9 nm. After pyrolysis at 800 C, the well-resolved SAXS pattern is also observed (Fig. 6b), suggesting a thermal stability of the carbon framework for EO5kOMC-4.2-800 sample. The cell parameter decreases from 32.9 to 30.2 nm (Table 1), as a result, the mesostructural shrinkage is
A 1400
In order to get OMCs with the large tunable pore size and large windows, PMMA homopolymer is firstly used as a pore expander. SAXS patterns of all mesoporous carbons EO2k-OMC-2.5-450 synthesized from EO44-b-MMA103 with different amount of homopolymer PMMA show two resolved scattering peaks with a little weak intensity, suggesting a similar hexagonal mesostructure with a slightly poor ordering (Fig. 9A). The cell parameter increases from 16.7 to 22.1 nm as the amount of PMMA homopolymer increases (Table 1), further suggesting a pore expander. The nitrogen sorption isotherms of all the mesoporous carbons prepared by adding the homopolymer as the pore expander show typical type IV curves with an obvious H1-type hysteresis loop and a sharp capillary condensation step, corresponding to cylindrical mesopore with the uniform pore size distribution. The pore size increases from 8.6 to
B 3.0 MPC-0
1200
MPC-12
1000
dV/d log(w) (cm3 g -1 nm -1 )
3
Adsorption volume(cm /g)
2.5
MPC-84 MPC-68
800
MPC-61
600
MPC-52
400
MPC-20
MPC-36
MPC-12
200
22.0nm
MPC-20 MPC-36 MPC-52
2.0
MPC-61 MPC-68 MPC-84
11.2nm
1.5
1.0
0.5
MPC-0
0.0
0 0.0
0.2
0.4
0.6
0.8
Relative pressure(p/p0)
1.0
0
10
20
30
40
50
Pore size(nm)
Fig. 11. (A) nitrogen sorption isothermals and (B) pore size distribution curves of large-pore ordered mesoporous carbon templated by EO44-b-MMA123 with adding different amount of PMMA homopolymer as a pore expander agent. The values 0, 12, 20, 36, 52, 61, 68 and 84 correspond to the percent of PMMA homopolymer in the template.
792
J. Wei et al. / Solid State Sciences 13 (2011) 784e792
17.7 nm as the amount of PMMA increases from 17 to 87 wt% relative to the template (Fig. 9B and C). The BET surface area (525e604 m2/g) and pore volume (0.50e0.81 cm3/g) are showed in Table 1. When the diblock copolymer EO-b-MMA template with the longer hydrophobic segment (MMA), such as EO44-b-MMA123, is used to synthesize mesoporous carbon, a little larger pore size of 11.2 nm is obtained (Figs. 10 and 11). The pore size of ordered mesoporous carbons increases continuously (from 11.2 to 22.0 nm) as the amount of PMMA homopolymer increases (Fig. 9D). 4. Discussion Our results show that using copolymer EO125-b-PMMA174 as the template and phenolic resol as the carbon precursor, the weight ratio (Rw) of resol to the template can significantly affect the mesostructure of carbon. When Rw increases from 1.0 to 4.2, the hydrophilic/hydrophobic ratio increases, inducing the mesostructure of OMCs transferred from 2-D hexagonal to possible 3-D cubic Fm3m symmetry. This can be explained in terms of the change of hydrophilic/hydrophobic ratio in the resol/surfactant mesophase. Since the phenolic resol molecules can interplay with PEO segments of copolymer PEO-b-PMMA by hydrogen-bonds, the increase of Rw can result in the increase of hydrophilic/hydrophobic ratio in the micelles and cause the increase of the interfacial curvature, then, the hexagonal mesostruture can be transformed to possible facecentered cubic mesostructure. Further increasing Rw from 4.2 to 5.0, the mesostructure is unchanged, but the pore wall thickness increases from 7.7 to 10.4 nm and the pore size decreases from 15.6 to 12.6 nm. It is due to the gradual invasion of resol molecules into the hydrophobic domain of PMMA segment of diblock copolymer PEO-b-PMMA by hydrogenbond-interaction, therefore, leading to thick pore wall and reduce the pore size. Such a phenomenon has been observed previously for FDU-18 mesoporous carbons [24]. Using EO44-b-MMA103 as the soft template, 2-D hexagonal (p6mm) OMCs with large cylindrical mesopore can be obtained. Increasing Rw from 2.5 to 3.0, the mesostructure keeps unchanged, but the pore channels become curved and partially blocked. It is because the template with too short hydrophilic segments could not endure the wide variation of Rw value. Further increasing the Rw, or using other composites of PEO-b-PMMA with shorter PMMA segments such as EO44-b-MMA43 and EO44-b-MMA73 as the template, no ordered mesoporous carbon can be obtained. This is due to the weak microphase separation ability of the diblock copolymer duing the EISA process. The nitrogen sorption results show longer hydrophobic segment (e.g. EO125-b-MMA174) copolymer can yield larger pore size than shorter one (e.g. EO44-bMMA103). The pore size increases from 8.6 to 12.1 nm as PMMA segment enlarges from 10,300 to 17,400 g/mol, implying a positive proportion increase. The pore size can be further adjusted in the range of 8.6e22.0 nm by adding a desired amount of PMMA homopolymer as the pore expander. The pore expanding effect is mainly ascribed to the hydrophobic interaction of the homopolymer with PMMA segment of PEO-b-PMMA block copolymers. During the EISA process, PMMA homopolymer resides in hydrophobic part of PEO-b-PMMA/resol composites, leading to the increase of both the pore size and unit cell. 5. Conclusion In this paper, several amphiphilic PEO-b-PMMA diblock copolymers were designed by using the versatile ATRP technique for templating synthesis of mesoporous carbons, and through an EISA approach, phenolic resol as a carbon precursor and THF as a solvent. We demonstrated that it is a feasible and simple method to control the synthesis of OMCs with desired mesostructure, pore size and
wall thickness, via varying hydrophilic/hydrophobic ratio, the size of hydrophobic part and the amount of the carbon precursor. We have shown for the first time that OMCs with hexagonal p6mm symmetry and large pore size (8.6e12.1 nm) can be synthesized by using PEOb-PMMA with long PMMA segment as a template. Increasing resol/ template weight ratio (Rw) from 1.0 to 4.2, the mesostructure can be transferred from 2-D hexagonal p6mm to possible 3-D cubic Fm3m, owing to the change of interface curvature. Further increasing Rw from 4.2 to 5.0, the mesopore wall thickness can increase from 8.1 to 10.4 nm. Adding homopolymer PMMA as the pore expander, the pore size of hexagonal mesoporous carbon can be precisely and continuously adjusted from 8.6 to 22.0 nm. Our results show that the lab-made amphiphilic block copolymers, such as PEO-b-PS and PEOb-PMMA-b-PS et al, their hydrophilic/hydrophobic ratio and the size of hydrophobic part can also be controlled by ATRP method, which are favorable to synthesize mesoporous carbons, silicas and metal oxides with tunable parameters. Acknowledgements This work was supported by NSF of China (2089012, 20721063, 20821140537, 20871030), State Key Basic Research Program of PRC (2006CB932302), Shanghai Leading Academic Discipline Project (B108), Shanghai Rising Star Program for Young Research Scientists (08QA14010), Doctoral Program Foundation of State Education Commission of China (200802461013), and Science & Technology Commission of Shanghai Municipality ( 08DZ2270500). Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.solidstatesciences.2010.03.008 References [1] J. Lee, J. Kim, T. Hyeon, Adv. Mater. 18 (2006) 2073. [2] C.D. Liang, Z.J. Li, S. Dai, Angew. Chem. Int. Ed. 47 (2008) 2e26. [3] A.H. Lu, W. Schmidt, N. Matoussevitch, H. Bönnemann, B. Spliethoff, B. Tesche, E. Bill, W. Kiefer, F. Schüth, Angew. Chem. Int. Ed. 43 (2004) 4303. [4] T. Ohkubo, J. Miyawaki, K. Kaneko, R. Ryoo, N.A. Seaton, J. Phys. Chem. B 106 (2002) 6523. [5] J. Lee, S. Yoon, T. Hyeon, S.M. Oh, K.B. Kim, Chem. Commun. (1999) 2177. [6] X.L. Ji, K.T. Lee, L.F. Nazar, Nat. Mater. 6 (2009) 500. [7] S.H. Joo, S.J. Choi, I. Oh, J. Kwak, Z. Liu, O. Terasaki, R. Ryoo, Nature 412 (2001) 169. [8] K. Ariga, A. Vinu, Q. Ji, O. Ohmori, J.P. Hill, S. Acharya, J. Koike, S. Shiratori, Angew. Chem. Int. Ed. 47 (2008) 7254. [9] D. Lee, J. Lee, J. Kim, J. Kim, H.B. Na, B. Kim, C.H. Shin, J.H. Kwak, A. Dohnalkova, J.W. Grate, T. Hyeon, H.S. Kim, Adv. Mater. 17 (2005) 2828. [10] J.S. Lee, S.H. Joo, R. Ryoo, J. Am. Chem. Soc. 124 (2002) 1156. [11] H.I. Lee, J.H. Kim, D.J. You, J.E. Lee, J.M. Kim, W.S. Ahn, C. Pak, S.H. Joo, H. Chang, D. Seung, Adv. Mater. 20 (2008) 757. [12] S. Tanaka, N. Nishiyama, Y. Egashira, K. Ueyama, Chem. Commun (2005) 2125. [13] C.D. Liang, S. Dai, J. Am. Chem. Soc. 128 (2006) 5316. [14] Y. Meng, D. Gu, F.Q. Zhang, Y.F. Shi, H.F. Yang, Z. Li, C.Z. Yu, B. Tu, D.Y. Zhao, Angew. Chem. Int. Ed. 44 (2005) 7053. [15] Y. Meng, D. Gu, F.Q. Zhang, Y.F. Shi, L. Cheng, D. Feng, Z.X. Wu, Z.X. Chen, Y. Wan, A. Stein, D.Y. Zhao, Chem. Mater. 18 (2006) 4447. [16] F.Q. Zhang, Y. Meng, D. Gu, Y. Yan, C.Z. Yu, B. Tu, D.Y. Zhao, J. Am. Chem. Soc. 127 (2005) 13508. [17] F.Q. Zhang, Y. Meng, D. Gu, Y. Yan, C.Z. Yu, B. Tu, D.Y. Zhao, Chem. Mater. 18 (2006) 5279. [18] Y. Wan, Y.F. Shi, D.Y. Zhao, Chem. Commun (2007) 897. [19] Y. Wan, D.Y. Zhao, Angew. Chem. Int. Ed. 107 (2007) 2821. [20] Y. Huang, H.Q. Cai, T. Yu, F.Q. Zhang, F. Zhang, Y. Meng, D. Gu, Y. Wan, X.L. Sun, B. Tu, D.Y. Zhao, Angew. Chem. Int. Ed. 46 (2007) 1089. [21] C.D. Liang, K.L. Hong, G.A. Guiochon, J.W. Mays, S. Dai, Angew. Chem. Int. Ed. 43 (2004) 5785. [22] Y.H. Deng, T. Yu, Y. Wan, Y.F. Shi, Y. Meng, D. Gu, L.J. Zhang, Y. Huang, C. Liu, X.J. Wu, D.Y. Zhao, J. Am. Chem. Soc. 129 (2007) 1690. [23] Y.H. Deng, J. Liu, C. Liu, D. Gu, Z.K. Sun, J. Wei, J.Y. Zhang, L.J. Zhang, B. Tu, D.Y. Zhao, Chem. Mater. 20 (2008) 7281. [24] Y.H. Deng, C. Liu, D. Gu, T. Yu, B. Tu, D.Y. Zhao, J. Mater. Chem. 18 (2008) 91. [25] J.Y. Zhang, Y.H. Deng, J. Wei, Z.K. Sun, D. Gu, H. Bongard, C. Liu, H.H. Wu, B. Tu, F. Schüth, D.Y. Zhao, Chem. Mater. 21 (2009) 3996.