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Cite this: J. Mater. Chem., 2011, 21, 9491

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Conversion of carbon dioxide to few-layer graphene

Amartya Chakrabarti,†ab Jun Lu,†c Jennifer C. Skrabutenas,a Tao Xu,*a Zhili Xiao,*c John A. Maguireb

and Narayan S. Hosmane*a

Received 22nd March 2011, Accepted 19th May 2011

DOI: 10.1039/c1jm11227a

Burningmagnesiummetal in dry ice resulted in few-layer nanosheets

of graphene in high yields. These carbon nanomaterials were

characterized by Raman spectroscopy, energy-dispersive X-ray

analysis, X-ray powder diffraction and transmission electron

microscopy. This work provides an innovative route for producing

one of the most promising carbon nanostructures by capturing

carbon dioxide that is popularly known as the greenhouse gas.

Within the last few years, graphene has received special attention

from the scientific world due to its unique mechanical and electrical

properties.1 The widespread application of graphene is not just

limited to the fields of sensors,2 nanoelectronics,3 composites,4

hydrogen storage,5 lithium-ion batteries,6 but also shown promise in

medicine as antibacterialmaterials.7The diversity of the technological

applications of graphene materials drives the search for facile routes

to produce graphenes in high yields. Recent research for synthesis of

such materials involved either chemical or electrochemical reduction

of exfoliated graphite oxide.8Most of these techniques require the use

of strong oxidizing agents, e.g., H2SO4/KMnO4, while some of them

claimed to have utilized greener chemicals. A recent report described

the production of graphene via reduction of CO using Al2S3.9

Nonetheless, a well-controlled large scale production protocol for

graphene structures is still in great demand and thus we embarked on

research involving graphene synthesis with a particular emphasis on

green chemistry. Consequently, our work described here provides

a new methodology that can be potentially scaled up in directly

capturing CO2 to produce few-layer graphene as useful solid carbon

materials.

Thus, burning magnesium metal in a CO2 environment produces

carbon materials as shown in eqn. (1). Although the metal–CO2

propulsion system for Mars missions has been explored,10 the

conversion of CO2 into solid nanostructured carbon materials has

not been reported. Therefore, our approach involving combustion of

magnesium metal in carbon dioxide to form few-layer graphene is

aDepartment of Chemistry and Biochemistry, Northern Illinois University,DeKalb, IL, 60115, USA. E-mail: hosmane@niu.edu; txu@niu.edubDepartment of Chemistry, Southern Methodist University, Dallas, TX,75275, USAcDepartment of Physics, Northern Illinois University, DeKalb, IL, 60115,USA. E-mail: zxiao@niu.edu

† Authors contributed equally to the work.

This journal is ª The Royal Society of Chemistry 2011

unprecedented and provides further incentives for exploration of

a number of environmentally friendly ways for capturing carbon

dioxide.11

2MgðsÞ þ CO2ðgÞ/2MgOðsÞ þ CðsÞ (1)

In a typical experiment, 3 g of Mg ribbon was ignited inside a dry

ice bowl, covered up by another dry ice slab. After the combustion

of Mg in CO2 was completed, the black products were collected

and transferred to a beaker containing 100 ml of 1 M HCl. The

product was stirred in the acid solution at room temperature

overnight to remove the MgO formed and any remaining Mg

metal. Both Mg and MgO react with hydrochloric acid to form

MgCl2 which is soluble in water and thus it can easily be removed

to get pure carbon material as the product. The mixture was then

filtered, washed with deionized water several times until the filtrate

turned out to be of neutral pH. Finally, the isolated solid carbon

product was dried under high vacuum overnight at 100 �C and the

yield was 680 mg (92%). This product was characterized by

transmission electron microscope (TEM, high-resolution TEM was

done in a Philip CM-30 with an acceleration voltage of 250 kV and

low-resolution TEM was performed in a Hitachi H-600

transmission electron microscope at an acceleration voltage of

75 kV), Raman spectroscopy (Renishaw system 2000 microfocus

Raman spectrometer), Energy-dispersive X-ray analysis (EDX,

studies done using field emission scanning electron microscope

Hitachi S-4700-II) and X-ray powder diffraction (XRD, Rigaku

MiniFlex, Cu, 30 kV, 15 mA X-ray) techniques.

Raman spectroscopy is considered to be an effective tool for

characterization of mono- or few-layer graphenes, and several

theoretical and experimental studies have been reported

recently.12–16 Raman spectrum of the nanostructured carbon species

obtained during our experiments is depicted in Fig. 1. The two

major components of the spectrum consisted of peaks at 1570 cm�1

and 2645 cm�1, which are commonly designated as the G-band and

the G0-band or 2D-band respectively. In a recent study on the

structure of graphene, Ferrari et al. demonstrated clearly that the

number of layers in a graphene structure can be revealed from the

Raman peaks, and thus, graphite can be easily distinguished from

graphenes.12,14 The position and shape of the G0 band in the

Raman spectrum identify the presence and the number of layers of

the graphene structures respectively. With a 633 nm Raman, the G0

band peak of graphene was found at about 2645 cm�1,12 which

closely matches our finding as shown in Fig. 1. In the case of

J. Mater. Chem., 2011, 21, 9491–9493 | 9491

Fig. 1 633 nm Raman spectrum of the carbon species exhibiting

a G0-band at 2645 cm�1, a G-band at 1570 cm�1 and a D-band at

1325 cm�1. Inset: the expanded view of the G0-band showing the splitting

pattern of the peak.

Fig. 2 TEM images of few-layer graphene. (a) Graphenes with an

average length of 50–100 nm. (b) Larger size graphene sheets, average

length 300 nm. (c) Crystalline graphenes with an average length of

200 nm. (d) High-resolution TEM image of few-layer graphenes, the

number of layers ranging from 3–7. Inset: the electron diffraction pattern

of graphenes.

Fig. 3 XRD pattern of the carbon species.

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monolayer graphene, the G0 band is a sharp single peak; while in

the case of bi- or multi-layer graphenes, there are splittings

generated either from the phonon branches or the electronic bands.

The G0 band shifted more towards 2700 cm�1 in the case of

graphenes with more than 7–10 layers, which is indistinguishable

from graphite.12 From the observed spectrum, splitting of the 2D

band (inset of Fig. 1) and its position provided a strong evidence in

favor of few-layer graphene as the major product. Moreover, the

peak intensities of the G-band and the G0-band are also related to

the number of layers of the graphene structures. Gupta et al.

compared the peak intensities of different layer structures of

graphene and found that with the number of layers of five or more

the G-band grows higher with respect to the intensity than that of

the G0-band,13 which again was a confirmation of our product to be

few-layer graphene. The other band found in the spectrum is the

D-band at 1325 cm�1, which is of significantly lower intensity and

represents some lattice defects present in the structure.17

Fig. 2a and b show TEM images of the few-layer graphene,

prepared by our new method described above, in which graphene

sheets with varying lengths between 50 nm and 300 nm have been

found. While large crystalline graphene structures are evidently

observed inFig. 2c, high-resolution TEM (Fig. 2d) clearly exhibits the

signature image of the few-layer graphene with the number of layers

ranging from 3–7. Themeasured lattice space of this material is about

3.5�A, which is in good agreement with the thickness of a mono-layer

graphene (3.4 �A). The inset image in Fig. 2d, corresponding to the

diffraction pattern of few-layer graphene, is indicative of the

crystallization.

An X-ray diffraction pattern of our sample is described in Fig. 3.

The prominent 002 peak at 26.3 degree is observed along with the

101 peak at 44.6 degree. The other characteristic peak for graphene

structure is 100 peak located at 2q of 43.2 degree, which is overlapped

with one ofMgOpeaks.While we examined the purity of the product

viaEDX spectroscopy, the absence of any impurity other than a trace

amount ofMg andO in the product was confirmed (Fig. 4). The trace

amount of Mg (2.38 atomic weight percent) and O (7.30 atomic

weight percent) is mainly due to the trapped MgO and some

absorbedO2. Therefore, the contribution ofMgO to the peak at 2q of

43.2 degree is small, and this peak can be readily assigned to

100 diffraction of graphenes.

9492 | J. Mater. Chem., 2011, 21, 9491–9493

Although the exact mechanism of the formation of graphene is still

under investigation, the high temperature generated during the

burning of magnesium metal undoubtedly plays a crucial role. It is

possible that the combustion of the solid magnesium in gaseous CO2

favors the rapid flee of the solid product from the reaction center. As

such, the retention time of the sp2 carbon atoms in the reaction core is

not long enough to form multi-layer graphene (graphite). Instead,

only few-layer graphene is kinetically favored. Experiments on the

effect of catalysts on formation of monolayer graphenes with higher

yields using similar techniques are presently underway in our

laboratories.

In conclusion, the current methodology produces few-layer

graphene captured directly from CO2 by burning Mg in it. The

structure of few-layer graphene product was confirmed by TEM,

Raman spectroscopy and XRD and they are all consistent with the

This journal is ª The Royal Society of Chemistry 2011

Fig. 4 EDX spectrum of the graphene nanosheets, C 90.32 (atm wt%);

Mg 2.38 (atm wt%); O 7.30 (atm wt%).

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data available in the literature. The synthetic process is cost effective

and can be used to produce few-layer graphene in large quantities.

Furthermore, the use of non-toxic chemicals and recyclable

materials during the synthesis constitutes this work as part of green

chemistry.

Acknowledgements

This work was supported by multiple grants from the National

Science Foundation (CHE-0840504 and CHE-0906179 to NSH),

Petroleum Research Fund administered by the American Chemical

Society (Type G 46374-G10 to TX), the Department of Energy

(DE-FG02-06ER46334 to ZX), and Robert A. Welch Foundation

(N-1322 to JAM). NSH also acknowledges the Inaugural Board of

Trustees Professorship from Northern Illinois University and the

Alexander von Humboldt Foundation’s Research Prize for Senior

Scientists. Structural and compositional analyses were performed at

the Electron Microscopy Center (EMC) of Argonne National

Laboratory which is funded by DOE BES under the contract

DE-AC02-06CH11357. The timely help of Lori Bross at NIU

Biology Department in obtaining TEM images is hereby gratefully

acknowledged.

This journal is ª The Royal Society of Chemistry 2011

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