Synthesis of ultrathin mesoporous carbon through bergman cyclization of enediyne self-assembled monolayers in SBA-15

Article abstract of DOI:10.1021/la1005727

In this work, a bottom-up synthesis of ultrathin mesoporous carbon was developed through Bergman cyclization of enediyne containing compounds immobilized inside of SBA-15 nanochannels and followed by pyrolysis. Raman spectroscopy confirmed the occurrence of thermal Bergman cyclization inside the channels. Further heating under elevated temperature produced nanotube arrays in good yield. TEM images revealed the formation of interconnected tubular carbon due to the microtunnels of template. Raman spectra showed moderate degree of graphitization. Formation of enediyne SAMs on a template followed by the processing sequence developed in this work is promising to construct carbon materials with various nanoscopic morphology, such as carbon nanotube, graphene, and giant fullerene.

Full text of DOI:10.1021/la1005727

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© 2010 American Chemical Society
Synthesis of Ultrathin Mesoporous Carbon through Bergman Cyclization of
Enediyne Self-Assembled Monolayers in SBA-15
Xi Yang, Zhiwen Li, Jian Zhi, Jianguo Ma, and Aiguo Hu*
Key Laboratory for Ultrafine Materials of Ministry of Education, School of Materials Science and Engineering,
East China University of Science and Technology, Shanghai, 200237, China
Received February 7, 2010. Revised Manuscript Received April 6, 2010
In this work, a bottom-up synthesis of ultrathin mesoporous carbon was developed through Bergman cyclization of
enediyne containing compounds immobilized inside of SBA-15 nanochannels and followed by pyrolysis. Raman
spectroscopy confirmed the occurrence of thermal Bergman cyclization inside the channels. Further heating under
elevated temperature produced nanotube arrays in good yield. TEM images revealed the formation of interconnected
tubular carbon due to the microtunnels of template. Raman spectra showed moderate degree of graphitization.
Formation of enediyne SAMs on a template followed by the processing sequence developed in this work is promising to
construct carbon materials with various nanoscopic morphology, such as carbon nanotube, graphene, and giant
fullerene.
Introduction
been widely demonstrated in catalyst supports, gas storage,
nanofiltration, fuel cell, and electrode materials.16-22
Carbon, as one of the most important substances, possesses a
broad range of properties due to the existence of different
allotropes as well as various microstructures. Seminal work by
Smalley1 et al. on carbon buckyball, Iijima2 on carbon nanotubes
and Geim et al.3 on graphene had initiated tremendous research
efforts on many preparation methods of these nanoscopic materi-
als, including arc discharge, chemical vapor deposition (CVD),
laser evaporation, thermal decomposition, ion beam irradiation,
and nanocasting.4-16 The applications of these materials had also
Morphology control is generally very critical in the synthesis of
nanomaterials since the properties of nanomaterials are highly
structural dependent. Tremendous work had been focused on
synthesizing nanomaterials with various shapes, including rods,
tubes, pipes, prisms, cubes, spheres, capsules, and sheets. Among
all these efforts, templated synthesis15,23-30 belongs to one of the
most important approaches to achieve nanomaterials with unique
shapes that could not be easily obtained through other methods.
Elegant work on controlled synthesis of mesoporous silica31-34
had provided a variety of hard templates, which facilitate the
construction of different types of nanomaterials. Ryoo et al.35
accomplished the synthesis of ordered carbon nanopipes inside
rigid mesoporous silica templates by filling the voids with furfuryl
alcohol through incipient-wetness technique followed by pyroly-
sis under elevated temperature. The obtained carbon nanopipes
were proven to be good supports for Platinum nanoparticles in
electrocatalytic reduction of oxygen. Following this strategy, a
number of researches had been conducted either by switch-
ing carbon precursors from furfuryl alcohol to phenol resin,
*Corresponding author. E-mail: hagmhsn@ecust.edu.cn.
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11244 DOI: 10.1021/la1005727
Published on Web 04/29/2010
Langmuir 2010, 26(13), 11244–11248

Yang et al.
Article
polyacrylonitrile, acenaphthene, etc. or by using other templates,
such as anodic aluminum oxide (AAO) or metal-organic frame-
works (MOF).36-50 However, pyrolysis reactions are chemically
complicated and difficult to control, and void-filling technique is
not suitable for making replica of flat or external surface of
templates. Formation of self-assembled monolayers (SAMs) of
multifunctional precursors on template followed by cross-linking
reaction had been established in the synthesis of poly-
(arylenediacetylene) monolayers of different shapes.51 Biphenyl
thiol SAMs on gold surface irradiated with electron beam
followed by high temperature pyrolysis has recently be proven
to produce ∼1 nm thick conducting aromatic nanosheets.52 Single
layer graphene sheets were prepared using oxidative cross-linked
polypyrrole as carbon source through a confined self-assembled
approach.53 We deduce that with rational designed monomers,
infinite sp2 carbon network could be synthesized in “bottom-up”
manner under suitable polymerization conditions, which will
facilitate construction of graphitic monolayers with various
morphologies. Herein, we wish to reportour work onsynthesizing
ultrathin mesoporous carbon through processing Bergman cycli-
zation of enediyne SAMs on internal surface of mesoporous silica
SBA-15.
and synthesizing biosimilar compounds as potential anticancer
agents.56-60 Bergman cyclization had also been used in surface
functionalization of multilayered carbon nano-onion and C60,61,62
initiating free radical polymerization,63 and formation of glassy
carbon.64-66 It is well established that with properly designed
enediyne precursors, extensive polyarene network can be ob-
tained through Bergman cyclization, which is essential for for-
mationof sp2 carbonmonolayers insidethe channels of SBA-15in
this work.
Experimental Section
Materials. Tetrahydrofuran (THF) and triethylamine (Et3N)
were distilled over sodium or calcium hydride under nitrogen
prior to use. Other reagents used in the reactions were analytically
pure and used as received. All of the reactions and manipulations
were carried out under a nitrogen atmosphere and using Schlenk
techniques. 4-(2-(trimethylsilyl)ethynyl)benzaldehydeand 4-ethy-
nylbenzaldehyde (1) were synthesized according to literature
procedure with minor modification,67 detailed information could
also be found in Supporting Information. All chromatographic
purifications were performed on silica-gel (200-300 mesh) using
the indicated solvent systems.
Characterization. 1H NMR (400 MHz) and 13C NMR
(100 MHz) spectra were recorded in chloroform-d (CDCl3) on
an Ultra Shield 400 spectrometer (BRUKER BIOSPIN AG,
Magnet System 400 MHz/54 mm). Onset and peak temperature
of the model compound were studied with Differential Scanning
Calorimetry (DSC) using a Pyris Diamond thermal analysis
workstation equipped with a model 822e DSC module under a
constant nitrogen flow. FT-IR spectroscopy measurements were
performed from KBr pellets on a Nicolet Magna 5700 FTIR
spectrometer. Mass spectra were obtained with a Micromass
LCTTM mass spectrometer using EI method. X-ray diffraction
(XRD) patterns were conducted on a Bruker D8 ADVANCE
(Karlsruhe, Germany) X-ray diffractometer (Cu KR radiation
generated at 40 kV and 40 mA). The sample for TEM dispersed in
anhydrous isopropanol was deposited on a grid of holey carbon
film and transferred to a JEM-2100F highresolution transmission
electron microscope operating at 200 kV. Raman measurements
were performed on an inViaþReflex Raman spectrometer
(Renishaw, 514 nm). Nitrogen adsorption/desorption isotherms
Bergman cyclization is the intramolecular cyclization of en-
ediyne compounds first studied by Bergman et al.54 It was later
found that many naturally occurring enediyne-containing com-
pounds exhibited strong antibiotic activities through in situ
triggered Bergman cyclization.55 Extensive research had been
focused on elucidation of the mechanism of Bergman cyclization
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zene (10.47 g, 37 mmol), Pd(PPh3)2Cl2 (0.71 g, 1.02 mmol), and
CuI (0.19 g, 1.02 mmol) in 35 mL of anhydrous Et3N was heated
at 60 °C overnight under a nitrogen atmosphere. After cooling,
the resulting solution was concentrated and then partitioned
with saturated aqueous NaCl, 1 M HCl, and ethyl acetate. The
organic layer was dried over anhydrous MgSO4. After filtration,
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Langmuir 2010, 26(13), 11244–11248
DOI: 10.1021/la1005727 11245

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Yang et al.
purified by silica gel chromatography with petroleum ether/
ethyl acetate (20/1) as eluent to give 7.37 g of product as yellow
crystal. Yield: 76%. 1H NMR (CDCl3, ppm): 10.03 (s, -HCdO,
1H), 7.61-7.79 (m, O=CH-Ph-H, 4H), 7.13-7.55 (m, Br-
Ph-H, 4H). 13C NMR (CDCl3, ppm): 190.1, 134.4, 132.2, 131.3,
130.9, 128.8, 128.3, 127.8, 125.9, 124.6, 123.4, 91.5, 90.6. MS: m/z
calcd for C15H9BrO, 284.0; found, 284.0.
highly corrosive and toxic] with 30 min sonication, and heated at
90 °C for 24 h. After activation, the resulting mixture was
centrifuged (9500 rpm, 15 min) and rinsed with deionized water
to neutrality and then washed with anhydrous ethanol repeatedly
to obtain a white powder (SBA-15-Cal/P).
Immobilization. Imine 5 (1.06 g) and activated SBA-15(1.18 g)
were mixed in 50 mL Schlenk flask, and then 20 mL of anhydrous
ethanol was added under a nitrogen atmosphere. After stirred for
40 h at 85 °C, the resulting solution was centrifuged (9500 rpm, 15
min) and rinsed with anhydrous ethanol repeatedly to obtain a
pale yellow powder (EDY-SBA-15-Cal/P, note: EDY represents
enediyne). Weightpercentages of EDY immobilizedonsilicawere
between 35% and 40%.
4-(2-(2-(2-(Trimethylsilyl)ethynyl)phenyl)ethynyl)benzalde-
hyde (3). A degassed solution of 2 (7.37 g, 26 mmol), Pd-
(PPh3)2Cl2 (0.54 g, 0.78 mmol), and CuI (0.15 g, 0.78 mmol) in
70mLofanhydrous Et3N wastreated withtrimethylsilylacetylene
(TMSA) (26.3 mL, 182 mmol). The mixture was heated in the seal
tube at 80 °C for 3 days. After cooling, the resulting solution was
concentrated and then partitioned with saturated aqueous NaCl
and ethyl acetate. The organic layer was dried over anhydrous
MgSO4. After filtration, the solvent was removed under vacuum
and the residue was purified by silica chromatography with
hexane/ethyl acetate (35/1) as eluent to give 5.98 g of yellow oily
liquid. Yield: 73%. 1H NMR (CDCl3, ppm): 10.02 (s, -HCdO,
1H), 7.69-7.89 (m, O=CH-Ph-H, 4H), 7.30-7.55 (m, (CH3)3-
Si-CtC-Ph-H, 4H), 0.27 (s, -Si-(CH3)3, 9H). 13C NMR
(CDCl3, ppm): 191.1, 135.2, 132.3, 132.1, 131.9, 131.6, 129.3,
129.2, 128.3, 128.0, 125.7, 124.9, 102.9, 98.8, 92.0, 91.9, 0.28. MS:
m/z calcd for C20H18OSi, 302.1; found, 302.1.
Bergman Cyclization. All the Bergman cyclization (BC)
reactions were performed under vacuum in a sealed glass tube
with EDY-SBA-15-Cal/P inside and diphenyl ether outside as
reflux bath (259 °C) for 8 h to obtain a brown powder (BC-EDY-
SBA-15-Cal/P).
Pyrolysis. All the pyrolysis reactions were performed in a tube
furnace with a continuous nitrogen flow. BC-EDY-SBA-15-Cal/
P was heated in a furnace while the temperature was increased to
750 °C at a rate of 2.0 °C min-1, and then maintained for 1 h to
obtain a black powder (CNT-SBA-15-Cal/P). After pyrolysis, the
weight-loss ratio of sample was approximately 25%.
4-(2-(2-Ethynylphenyl)ethynyl)benzaldehyde (4). A degassed
solution of 3 (5.98 g, 19 mmol), tetrabutylammonium fluoride
(TBAF) (9.94 g, 38 mmol) and p-toluenesulfonic acid (PTSA)
(3.27 g, 19 mmol) in 60 mL of anhydrous THF was stirred under a
nitrogen atmosphere for 10 min at room temperature. The solvent
was removed under vacuum and the residue was purified by silica
gel chromatography with petroleum ether/ethyl acetate (7/1) as
eluent to give 4.33 g of yellow oily liquid. Yield: 99%. 1H NMR
(CDCl3, ppm): 10.00 (s, -HCdO, 1H), 7.68-7.86 (m, OdCH-
Ph-H, 4H), 7.32-7.56 (m, HCtC-Ph-H, 4H), 3.41 (s, -Ct
CH, 1H). 13C NMR (CDCl3, ppm): 191.7, 135.8, 133.0, 132.5,
132.2, 129.8, 129.6, 128.9, 125.7, 125.2, 92.7, 92.0, 82.2, 81.8. MS:
m/z calcd for C17H10O, 230.1; found, 230.1.
Removal of Template. Silicon etching was performed in a
PTFE griffin beaker at ambient temperature. CNT-SBA-15-Cal/
P was treated with 40% HF and stirred vigorously at ambient
temperature overnight to remove the silicon template.
Results and Discussion
Synthesis of Enediyne-Containing Imine (5). Enediyne 4
was synthesized by three consecutive Sonogashira coupling reac-
tions in high yields. 4-ethynylbenzaldehyde (1) was first synthesized
through a known procedure (see Supporting Information).67
Reaction of 1 with commercial available o-bromoiodobenzene
afforded 2 in good yield. In this reaction, iodine was selectively
substituted while bromine was intact according to NMR and MS
analysis. Subsequent installation of trimethylsilylacetylene (TMSA)
took place in a sealed tube under elevated temperature, and then
the trimethylsilyl protection group was completely removed using a
solution of TBAF and PTSA in THF. TBAF is typically used as a
selective and mild deprotection reagent for the trimethylsilyl
(TMS) group. However, we found that lots of unidentified
byproduct formed when using solely TBAF to remove TMS group
of 3. This phenomenon was speculated as due to the strong basicity
of fluorine anions in TBAF solution. To solve this problem, a half
equivalent of PTSA was added to the reaction mixture to neutralize
fluorine anions into bifluoride. With this combo deprotection
reagent, the reaction took place cleanly to form 4 in quantitative
yield. The final imine product 5 was successfully formed by reacting
4 with APTES in anhydrous ethanol. A slight excess of enediyne 4
was used in this reaction to avoid incorporation of free APTES
(enediyne void in SAMs) on templates in the subsequent immobi-
lization step (Scheme 1).
Formation of Carbon Monolayers. With this enediyne
containing imine (5) in hand, SAMs formation could be processed
straightforwardly on various substrates. In this work, we chose
internal surface of SBA-15 as the substrate to construct tubular
carbon monolayers. Pretreated SBA-15 powder was added to a
reflux solution of 5 in anhydrous ethanol, the immobilization was
conducted under nitrogen atmosphere for 40 h. After thoroughly
rinsed with anhydrous ethanol, a pale yellow powder was
obtained. The enediyne grafted SBA-15 was then heated to 260 °C
under vacuum. Differential calorimetry scan (DSC) analysis
showed that Bergman cyclization of 4 takes place rapidly at over
N-(4-(2-(2-Ethynylphenyl)ethynyl)benzylidene)-3-(triethoxy-
silyl)propan-1-amine (5). A degassed solution of 4 (4.33 g,
19 mmol), 3-aminopropyltriethoxysilane (APTES) (3.98 g, 18 mmol),
and 1 g of MgSO4 in 40 mL of anhydrous ethanol was stirred at
room temperature overnight under a nitrogen atmosphere. The
resulting solutionwasfiltrated and thesolvent was removed under
vacuum to give 8.07 g of yellow oily liquid. Yield: 98%. 1H NMR
(CDCl3, ppm): 8.13 (s, -HCdN, 1H), 7.58-7.72 (m, -NdCH-
Ph-H, 4H), 7.29-7.55 (m, HCtC-Ph-H, 4H), 3.79-3.85 (m,
(CH3-CH2-O)3-Si-, 6H), 3.61-3.64 (t, -CH2-NdCH-,
2H), 3.38 (s, -CtCH, 1H), 1.81-1.85 (t, -CH2-CH2-NdCH-,
2H), 1.18-1.24 (m, (CH3-CH2-O)3-Si-, 9H), 0.65-0.70 (t,
-CH2-Si-(OCH2CH3)3, 2H). 13C NMR (CDCl3, ppm): 160.4,
136.2, 132.6, 132.0, 131.9, 128.6, 128.1, 128.0, 126.1, 125.2, 124.7,
93.3, 89.6, 82.1, 81.3, 64.4, 58.4, 24.3, 18.3, 8.1. MS: m/z calcd for
C26H31NO3Si, 433.2; found, 433.3.
Synthesis of SBA-15. Mesoporous silica SBA-15 was synthe-
sized according to published procedures.31,32,68 In a typical
synthesis, 5 g of triblock copolymer surfactant EO20PO70EO20
(Pluronic P123, Sigma-Aldrich) was dissolved in 159.5 g of
distilled water and 26.5 mL of 12 M HCl with stirring, followed
by addition of 10.4 g of tetraethoxysilane (TEOS) at 40 °C. This
gel was continuously stirred for 20 h and then hydrothermally
treated at 100 °C for 24 h. After crystallization, the solid product
was filtered, washed with distilled water, and dried in air at 40 °C.
The material was calcinated in air at 550 °C for 5 h to remove the
surfactant template and obtain a white powder (as-synthesized
SBA-15). As-synthesized SBA-15 was dispersed in piranha solu-
tion (H2SO4:H2O2=7:3, volume ratio) [Caution! Piraha solution is
(68) Cui, T.; Zhang, J. H.; Wang, J. Y.; Cui, F.; Chen, W.; Xu, F. B.; Wang, Z.;
Zhang, K.; Yang, B. Adv. Funct. Mater. 2005, 15, 481–486.
11246 DOI: 10.1021/la1005727
Langmuir 2010, 26(13), 11244–11248

Yang et al.
Article
Scheme 1. Synthesis of Enediyne Containing Iminea
a Key: (a) 4-ethynylbenzaldehyde (1), Pd(PPh3)2Cl2, CuI, Et3N, 60°C, 76%. (b) TMSA, Pd(PPh3)2Cl2, CuI, Et3N, 80°C, 73%. (c) TBAF, PTSA, THF,
99%. (d) APTES, EtOH, RT, 98%.
Figure 1. Schematic illustration of formation of 2D carbon net-
work inside SBA-15 channels.
200 °C (seeSupportingInformation). After thermal Bergman cyc-
lization, the powder turned to light brown. Raman analysis con-
firmed the reaction was complete according to the disappearance
of the alkyne moieties (∼2220 cm-1). The powder was heated in a
Figure 2. TEM images viewed along [110] (A) and [001] (B) dir-
ections, SAED (inset) pattern of tubular carbon monolayers, and
EDX spectrum (C) of tubular carbon monolayers after removal of
template.
tube furnace at 750 °C for 1 h to eliminate any volatile compo-
nents. The black powder obtained was treated with aqueous HF
solution to give the carbonous material. This powder was heated
under vacuum at 900 °C to further fix the carbon network.
Si-OH were maintained for further functionalization. To avoid
As shown in Figure 1, the formation of densely packed SAMs is
using this relative harsh condition with operating highly corrosive
the fundamental prerequisite in construction of an infinite sp2
acid under high pressure and high temperature, we chose an
carbon network. The choice of template is thus highly important.
alternative strategy to activate the silica surface by treating the
SBA-15 prepared from conventional methods, either by calcina-
calcinated SBA-15 with Piranha solution. IR analysis clearly
tion or solvent extraction, did not meet with this criterion.
Irregular flakes or giant semitransparent carbonous materials
showed intense Si-OH bending band at around 960 cm-1. After
immobilization of 5, this band was completely disappeared (see
were obtained after removal of templates due to lost of some
Supporting Information), indicative of formation of densely
surface hydroxy groups during calcination or channel collapse
packed enediyne SAMs. With this activated SBA-15 as template,
during solvent extraction (see Supporting Information). Zhao
well-defined tubular carbon monolayers were obtained as shown
et al.69 reported that treating as-synthesized SBA-15 through a
in TEM images (Figure 2).
high pressure microwave digestion process in the presence of
The pore structure of SBA-15 is revealed as a complex
concentrated nitric acid and hydrogen peroxide, most surface
combination of meso-channels and significant amount of
microtunnels.70 Most of replica method for preparation of other
(69) Tian, B. Z.; Liu, X. Y.; Yu, C. Z.; Gao, F.; Luo, Q.; Xie, S. H.; Tu, B.; Zhao,
mesoscopic materials relied on these microtunnels to hold the
D. Y. Chem. Commun. 2002, 1186–1187.
Langmuir 2010, 26(13), 11244–11248
DOI: 10.1021/la1005727 11247

Article
Yang et al.
Figure 3. Nitrogen adsorption isotherm of tubular carbon mono-
layers.
nanowires together after removal of silica template. From TEM
images, it is obvious that nanotubes prepared through this
method were holding together through irregular nanorods.
Fast Fourier transform (FFT) diffractograms also showed main-
tenance of mesophase (see Supporting Information). Energy
dispersive X-ray spectroscopy (EDX) measurement showed no
detectable silicon signal (Figure 2), which confirmed that these
tubular carbon monolayers were interconnected with carbon-
ous matter originated from replica of microtunnels of SBA-15
template. The carbon bridges are relatively weak, after sonication
in isopropanol for prolonged time (TEM sampling), some dis-
crete carbon nanotube arrays or single nanotubes can be found in
TEM (see Supporting Information). Select area electron diffrac-
tion (SAED) of carbon networks showed two well separated
rings with d spacings of 0.217 and 0.126 nm, which could be
interpreted as to correspond to the major indices [100] (0.123 nm)
and [110] (0.213 nm) of graphite nanostructure. The fact that the
[100] ring appear to be more intense than the [110] ring further
reflects the single-layer nature of the tubular arrays.53 To prepare
independent carbon nanotubes, micropore-less template like
MCM-41 or SBA-15 prepared in the presence of concentrated
inorganic salts70 could be used. This work will be presented in the
future.
Nitrogen adsorption data (Figure 3 and Supporting In-
formation) showed that tubular carbon monolayers exhibited
high surface areas (around 1500 m2/g) and large pore volumes
(above 1.0 cm3/g, BJH) with significant amount of micropores
(∼0.2 cm3/g, BJH). The mesopores of all samples have uniform
size distribution centered at 3.8 nm, which is comparable to the
mean diameter of carbon channels measured from TEM images.
The XRD of SBA-15 template showed three well-resolved peaks
revealing a highly ordered hexagonal (p6mm) pore structure
similar to reported data.31,32 After removal of silica, tubular
carbon monolayers showed much less intense diffraction peaks,
indicative of less ordered structures.
Figure 4. Raman spectra of tubular carbon monolayers.
active in graphitic materials exhibiting structure defects.71 After
annealing at 900 °C, the G-peak shifted to higher wavenumber,
reaching 1598 cm-1 (Figure 3). The intensity ratios of ID/IG of
carbon nanotubes are around 0.8-0.9 for these nanotubes, which
are comparable to other graphitic nanostructures prepared thro-
ugh catalytic polymerization followed by pyrolysis,39,52,53 indica-
tive of moderate graphitization degrees in these samples.
Control experiments were conducted using simple aromatic
imines synthesized from APTES with benzaldehyde or 2-naph-
thaldehyde. These imines were first immobilized onto activated
SBA-15 and then pyrolyzed under continuous nitrogen flow. All
organic components were completely burned off when the samples
were heated to 750 °C. These results unambiguously confirmed
the necessity of Bergman cyclization in constructing infinite carbon
network and final tubular carbon monolayers in this work.
Conclusion. We have developed a universal and simple
method to synthesize ultrathin mesoporous carbon inside nano
channels of mesoporous silica. The integrity of tubular shape of
silica was fully maintained after etching off the template. The
facial synthesis and structural variability of enediyne precursors
allow bottom-up construction of a family of graphitic monolayers
on various substrates, which can further be extended to the
synthesis of giant fullerene and mass production of graphene.
These works are currently underway in our lab.
Acknowledgment. The support of National Natural Science
Foundation of China (20874026, 20704013), Shanghai Pujiang
Program (07PJ14024), ShuguangProject (07SG33), New Century
Excellent Talents in University, and Shanghai Leading Academic
Discipline Project (B502) is gratefully acknowledged. AH thanks
Dr. Lingyun Zhang for her valuable comments on this paper.
Supporting Information Available: Text giving detailed
experimental procedures for starting materials, figures show-
ing NMR spectra, DSC curve, TGA analysis, IR spectra,
Raman spectrum, XRD patterns, and TEM images, and a
table ofBET data. This material is available free of charge via
the Internet at http://pubs.acs.org
Raman spectra (Figure 4) showed two broad peaks centered at
1350 and 1590 cm-1 corresponding to so-called D, G bands. The
G band is related to the in-plane E2 g vibration mode of graphite
sp2-bonded carbon atoms in a 2D hexagonal lattice, while D-peak
is due to the breathing mode of the aromatic rings, which are
(70) Sayari, A.; Yang, Y. Chem. Mater. 2005, 17, 6108–6113.
(71) Ferrari, A. C.; Robertson, J. Phys. Rev. B 2001, 64, 075414.
11248 DOI: 10.1021/la1005727
Langmuir 2010, 26(13), 11244–11248