Organic functionalisation of graphene catalysed by ferric perchlorate

Article abstract of DOI:10.1039/c4cc07647h

We have developed a method to prepare covalently functionalised graphene using ferric perchlorate as the catalyst. The resulting functionalised graphene was characterised by Raman spectroscopy, TGA, XPS, AFM, and dispersibility tests in organic or aqueous

Full text of DOI:10.1039/c4cc07647h

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Organic functionalisation of graphene catalysed
by ferric perchlorate†
Cite this:DOI: 10.1039/c4cc07647h
Lei Yang and Junpo He*
Received 28th September 2014,
Accepted 27th October 2014
DOI: 10.1039/c4cc07647h
www.rsc.org/chemcomm
We have developed a method to prepare covalently functionalised Table 1 Summary of graphene functionalisation reactions in the literature
graphene using ferric perchlorate as the catalyst. The resulting
Type of reactions
Radical reaction
Examples
Ref.
functionalised graphene was characterised by Raman spectroscopy,
TGA, XPS, AFM, and dispersibility tests in organic or aqueous media.
Aryl radicals, carbon radicals,
halogen radicals
11–17
Cycloaddition
Nitrene addition, Bingel reaction,
aryne cycloaddition, Diels–Alder
reaction, 1,3-dipolar cycloaddition
Friedel–Crafts acylation,
18–22
Graphene is a two-dimensional carbon material that can be
1
prepared by mechanical exfoliation of bulk graphite, chemical
Substitution
23
2
3
vapour deposition, epitaxial growth, thermal annealing of
hydrogen-lithium exchange
4
5
SiC, unzipping of carbon nanotubes, as well as bottom-up
organic synthesis. These preparation approaches have been graphene–silicon hybrid materials. The basal plane of graphene may
remarkably improved with the assistance of laser, microwave
and sonication with respect to size controllability, homogeneity ylide as well as malonate derivatives. In addition, graphene
6
18
7
8
19
also serve as a substrate for cycloaddition of aryne, azomethine
9
20
21
and the ability for pattern formation.
can act as either a diene or a dienophile in Diels–Alder reaction in a
22
Chemical functionalisation of graphene is an important reversible manner under mild conditions. Graphene can also be
23
strategy to tune its electronic properties and to increase its functionalised by substitution reaction. Despite this, the number
dispersibility in water or organic solvents and compatibility of organic reactions that can be employed for chemical modification
with matrix materials. Graphene can be functionalised either of graphene is still very limited (Table 1). Exploring new reactions of
1
0
through harsh oxidation by H SO /HNO
or through mild graphene will undoubtedly facilitate the research and application of
organic reactions. Oxidation of pristine graphene into graphene graphene based materials.
2
4
3
oxide (GO) may cause severe disruption of p-conjugation.
Organic reactions may be used to introduce functional groups xH
In this communication, we use a ferric salt, e.g., Fe(ClO
4
)
3
Á
2
O, as a catalyst to activate benzonitriles that makes them
without significant damage to the basal plane. Regarding the active enough to functionalize graphene (Scheme 1). It has been
high stability of the fused p-conjugated system, only very active shown by Wang and coworkers that fullerenes react with various
organic species, such as radicals or carbene, can be used in the nitriles to afford corresponding fullerooxazoles in the presence
2
4
functionalisation reaction. For instance, carbon radicals derived of Fe(ClO ) ÁxH O. In the present work, we demonstrate that
4
3
2
1
1
12
13
from benzoyl peroxide, diazonium salts, alkyl iodides, or graphene can also be functionalised using benzonitrile derivatives
1
4
a-naphthylacetic acid, as well as halogen radicals generated by with various R groups.
1
5
16
laser irradiation of chlorine or fluoropolymers, can be readily
We used commercially available graphene (multi-layer graphene)
added to the graphene basal plane. Halogenation of graphene (Xiamen Knano Graphene Technology Corp., Ltd) and four
1
7
was also achieved by heat treatment in the presence of XeF
2
.
benzonitrile derivatives as the starting materials. The benzonitriles
Nitrene is another active organic species which has been used contain methoxy (1), chloromethyl (2), dodecyl (3), and oligo-
for efficient functionalisation of graphene and fabrication of (ethylene oxide) (4) as functional groups, respectively. First, pristine
graphene (24 mg) was dispersed in o-dichlorobenzene (ODCB,
13
100 mL) and sonicated for 1 hour to obtain graphene dispersion.
The State Key Laboratory of Molecular Engineering of Polymers,
Department of Macromolecular Science, Fudan University, Shanghai, 200433,
China. E-mail: jphe@fudan.edu.cn
A mixture of nitrile 1 (or 2, 3, 4, 10 mmol) and ferric perchlorate
hexahydrate (46.0 mg, 0.10 mmol) was placed in a 250 mL round-
bottom flask and melted in an oil bath at 120 1C. After 30 min,
graphene dispersion was added and the resulting solution was
†
Electronic supplementary information (ESI) available. See DOI: 10.1039/
c4cc07647h
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Fig. 2 (a) High-resolution XPS C 1s core level spectrum of graphene and
FG-4. (b) High-resolution XPS N 1s core level spectrum of benzonitrile
derivative 1 and FG-1.
Scheme 1 Functionalisation of graphene with benzonitrile derivatives
catalysed by ferric perchlorate. The proposed mechanism is based on
24
the use of fullerene as the substrate.
its nitrile group. After reaction with graphene, the peak shifts to
402.3 eV corresponding to N atoms in the formed oxazole. The full
spectra of all the FGs are presented in the electronic supplementary
information (Fig. S1, ESI†). From the intensities of all the elements,
the atomic percentages can be calculated as shown in Table 2.
According to FGs’ nitrogen content, the degree of functionalisation
is estimated to be one functional group in 40 (FG-1), 50 (FG-2),
heated with stirring at 120 1C under a nitrogen atmosphere for
days. After completion of the reaction, the functionalised graphene
FG) was separated from the mixture by filtration using a PVDF filter
pore size 0.45 mm), washed thoroughly with tetrahydrofuran (THF),
ethanol and acetone, and then collected and dried under vacuum.
Raman spectroscopy, TGA, XPS and AFM were utilized to confirm
the attachment of these functional groups to graphene.
2
(
(
110 (FG-3) and 60 (FG-4) graphene carbon atoms, respectively.
The notably low functionality of FG-3 is possibly due to the low
miscibility of the ferric salt and the hydrocarbon chain.
Thermogravimetric analysis (TGA) also provides indirect
evidence of the organic group on graphene sheets. All the
Fig. 1 shows the Raman spectra of pristine graphene and FGs,
which were recorded using 633 nm laser excitation. While pristine
graphene shows a sharp G band and a very weak D band due to the
defects at the edges of the graphene plane, all FGs show obvious D
À1
samples were heated to 600 1C at a rate of 20 1C min under N2.
3
2
The results are given in Fig. 3. While pristine graphene shows a
remarkable thermal stability, FGs undergo degradation in the
temperature range 200–420 1C, which is attributed to the pyrolysis
of the covalently grafted organic groups on graphene. The weight
loss of all FGs up to 420 1C is 24% (FG-1), 16% (FG-2), 13% (FG-3)
and 35% (FG-4), respectively. These values fall in the range of
functionalities calculated from XPS results shown in Table 1. Further
weight loss above 420 1C is due to the thermal decomposition of
and G bands that correspond to sp and sp hybridization states of
the C atoms on graphene, respectively. The intensities of D bands
À1
of FGs at 1330 cm are much higher than that of pristine
2
graphene, indicating a partial change of C atoms from the sp to
3
sp state after functionalisation. The ratio of the intensities of D
25
and G bands also reflects the degree of functionalisation.
X-ray photoelectron spectroscopy (XPS) was utilized to determine
the surface elemental composition of all the FGs. Fig. 2 shows the
high-resolution XPS scans for C 1s peaks of pristine graphene and
FG-4. The peak at 285.2 eV is due to the CQC bonds of graphene.
After functionalisation reaction, a new shoulder peak appears at
21
defects formed at sites where functionalisation occurred. A similar
26
behaviour was also observed for functionalised carbon nanotubes.
Fig. 4 shows the AFM images of pristine graphene, FG-3 and
FG-4. Sonicating the purchased graphene in ODBC led to the
formation of multi-layer graphene, with the height of B3 nm
measured by AFM. After functionalisation, single-layer graphene is
easily obtained with the thickness of less than 1 nm. Thus, it seems
that the functional groups with short aliphatic hydrocarbon or
ether chains prevent graphene sheets from agglomerating. Further-
more, the side chains render the graphene sheet hydrophilic and
hydrophobic, respectively (Fig. 4d and e). FG-3 disperses well in
289.3 eV in C1s core level spectrum of FG-4, corresponding to the
presence of C–O and C–N bonds. Moreover, the N 1s core level
spectrum of benzonitrile derivative 1 shows a peak at 398.8 eV due to
Table 2 Elemental contents of pristine and functionalised graphenes
a
Sample
C (%)
O (%)
N (%)
Cl (%)
F
G
92.5
74.9
83.1
86.5
74.8
7.5
23.1
13.4
12.8
23.9
—
—
—
1.7
—
—
—
FG-1
FG-2
FG-3
FG-4
2.0
1.8
0.7
1.3
1/40
1/50
1/110
1/60
a
Fig. 1 Raman data of (a) pristine graphene, (b) FG-1, (c) FG-2, (d) FG-3,
Functionality (F) is presented as the number of functional groups
(e) FG-4.
divided by the number of graphene carbon atoms.
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The mechanism of the reaction is proposed according to
2
4
Wang and coworkers. Thus, benzonitriles first react with one
molecule of H O in the presence of Fe(ClO ) ÁxH O to form a
2
4 3
2
hydroxylimine–Fe(III) complex. The complex then undergoes a
stepwise addition towards graphene at N and O atoms involving the
release of Fe(II) and combination of the intermediate radicals,
resulting in the formation of an oxazole bridge between graphene
and the incoming phenyl ring bearing the functional groups.
In conclusion, we have, for the first time, functionalised
4 3 2
graphene using Fe(ClO ) ÁxH O-catalysed cycloaddition between
benzonitrile and unsaturation in graphene. The products were
analyzed using Raman, XPS, TGA and AFM. The analytical
results proved the successful covalent attachment of the organic
molecules to graphene. By changing the R groups in benzonitrile
derivatives, we obtained functionalised graphene with methoxy,
chloromethyl, dodecyl and oligo(ethylene oxide) functionalities,
respectively. Therefore, the present reaction can be used as a
novel tool for the organic functionalisation of graphene under
mild conditions.
Fig. 3 TGA of pristine graphene and functionalised graphenes.
toluene or ODCB, whereas FG-4 forms stable dispersion in
water. This macroscopic evidence demonstrates that graphene
was indeed functionalised.
Benzonitriles with electron-withdrawing groups such as
4
-nitro-benzonitrile did not react with graphene. XPS showed no
signal of nitrogen on the collected graphene species by filtration
after washing thoroughly with organic solvents) (Fig. S2, ESI†).
We thank the financial support from the National Basic
Research Program of China (grant no. 2011CB605701).
(
This also indicates that the product purification process used in
this work is efficient to remove any physically adsorbed organic
molecule.
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