Interesante Publicación que describe la forma de obtener Grafeno mediante el uso de un Molino de Tres Rodillos.

1. Continuous mechanical exfoliation of graphene sheets via three-roll mill†
Jinfeng Chen, Miao Duan and Guohua Chen*
Received 11th June 2012, Accepted 3rd August 2012
DOI: 10.1039/c2jm33740a
In this work, single and few-layer graphene sheets have been
successfully peeled from natural graphite through continuous
mechanical exfoliation by a three-roll mill machine with a polymer
adhesive. The inspiration takes root in the ‘‘Scotch tape’’ method.
Characterizations show that the thickness of the resultant graphene
sheets is 1.13–1.41 nm. The presented scalable process can be
effective for the high-yield and low-cost production of graphene
sheets or in situ fabrication of polymer/graphene nanocomposites.
Graphene, consisting of a single atomic layer of graphite, is an
exciting material for future advanced applications. Because of the
excellent electrical, optical, mechanical and thermal properties,1
it has
emerged as a rapidly rising star in diverse fields such as super-
capacitors,2
semiconductor devices, support for catalysts, conductive
transparent electrodes, biosensors3
and batteries, among others.4
To date, there have been several widely used techniques to produce
‘‘pristine’’ graphene: micromechanical exfoliation,5
epitaxial growth
on SiC,6
chemical vapour deposition (CVD)7
and chemical exfolia-
tion of graphite oxide (GO),8
etc. Of these reported approaches, the
micromechanical cleavage of graphite using the ‘‘Scotch tape’’
method is the original, which was the first used to mechanically split
graphite into individual atomic planes and provided the best
graphene for the study of its fundamental properties. However, this
method is unlikely to be suitable for large scale production. Other-
wise, large-area single-layer 30 inch graphene films have been grown
by CVD, which is one of the best techniques to grow graphene film
on various metals by using gaseous hydrocarbon sources. Unsatis-
factorily, this is an extremely careful fabrication process, considered
to be too tedious and too expensive for mass production.9
The
chemical exfoliation of graphite oxide can be easily dispersed in
aqueous solution in favour of the materials processing and funda-
mental characterization, but in fact it results in considerable disrup-
tion of the electronic structure of graphene.10
Thus, a simple,
economic and facile approach to produce significant quantities of
defect free, un-oxidised graphene to facilitate its applications and
studies is urgently required.
This work is inspired by the ‘‘Scotch tape’’ method and presents a
novel and simple method for the low-cost and large scale production
of monolayer and few-layer graphene sheets via continuous direct
exfoliation of natural graphite by a three-roll mill, which is a common
machine in the rubber industry.
Firstly, 2.0 g poly vinyl chloride (PVC) was dispersed in 50 ml
dioctyl phthalate (DOP) at 250
C for 30 min by a magnetic stirrer to
prepare an adhesive. 1.0 g of natural graphite with an average size of
500 mm was pre-dried at 100
C for 24 h and then the adhesive was
placed between the feed and the centre rolls of the three-roll mill.
Once the rolls started moving, the prepared natural graphite was
spread gradually on the adhesive to achieve maximum contact with
the rolls, followed by the uniform dispersion and exfoliation of the
graphite in the adhesive. Exfoliation was carried out at room
temperature for 12 h. After that, the material from the mill was
collected and steeped in alcohol to remove the DOP, followed by the
burning out of the PVC resin in the muffle at 500
C for 3 h in order
to extract the pure graphene product. A schematic of the preparation
process is illustrated in Fig. 1, and a video of the exfoliation process is
included in the ESI.†
In this work, the three-roll mill consisted of three adjacent cylin-
drical rolls (80 mm in diameter), which rotated at the same velocity.
The first and the third rolls, known as the feed and apron rolls, rotate
in the same direction while the centre roll rotates in the opposite
direction (Fig. 1). The gap and speed settings on the mill can be
controlled. With the help of force, the graphite runs in an inverted S
curve from the feed roll to the apron roll, then turns back towards the
feed roll. In this way, the graphite can be continuously exfoliated,
Fig. 1 Schematic illustration of the approach used to exfoliate natural
graphite by a three-roll mill.
Department of Polymer Science Engineering, Huaqiao University,
Xiamen, 361021, China. E-mail: hdcgh@hqu.edu.cn; Fax: +86-592-
6166296; Tel: +86-592-6166296
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c2jm33740a
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2. which is the crucial difference between this method and the ‘‘Scotch
tape’’ method (Fig. S1†). Fig. S2† shows SEM images of the gra-
phene produced in the three-roll mill steps. As the edge defects come
into existence during the three-roll mill exfoliation, the conductivity
of the graphene product after 12 h exfoliation is 7.5 Â 103
S mÀ1
,
while that of the natural graphite is 2.5 Â 104
S mÀ1
. The conduc-
tivity is higher compared to graphene obtained from the chemical
exfoliation of graphite oxide due to the structure of the graphene have
been retained well.
The prepared graphene sheets were characterized by high-resolu-
tion transmission electron microscopy (HRTEM, JEM-2010) and
selected-area electron diffraction. The HRTEM specimens were
prepared by loading the microtomed epoxy composite slices of the as-
obtained graphene onto standard TEM grids.11
Atomic force
microscopy (AFM, NanoScope IIIa) was used to determine accu-
rately the thicknesses of the graphene sheets and a high resolution
dispersive Raman microscope (LabRAM Aramis) with an excitation
laser witha wavelength of 532 nm was carried out to further char-
acterize the graphene structure.
The HRTEM image in Fig. 2a shows that the sizes of the graphene
sheets are homogeneous and have lateral dimensions on the submi-
cron scale. The cross-sections of the obtained graphene sheets are
shown in Fig. 2b and the number of layers can be visualized directly:
a single-layer and a three-layer sheet of graphene are marked in
Fig. 2b. It confirms that the graphene product is likely to be in forms
of single- or few-layer sheets. As one dark line dominates a single
atomic carbon layer, the thickness is about $0.5 nm. The typical
selective electron area diffraction (SAED) pattern (Fig. 2c) demon-
strates that the graphene sheets have good crystallinity, in which spots
(0–110) and (À1010) are more intense than spots (1–210) and
(À2110), reconfirming the single-layer feature of the graphene.12
Fig. 3a shows the typical tapping-mode AFM image of graphene
deposited on a mica substrate. In Fig. 3b the cross-sectional analysis
shows that the graphene sheet has a thickness of 1.13–1.41 nm, and it
canbeobservedthatthegraphenesheethasasizeof$2.7Â 5.0mm.At
a high resolution, the apparent thickness obtained by AFM may be a
layerofabsorbedwaterorsolventbetweenthegraphenesheetsandthe
substrate for the chemical and van der Waals contrast. Furthermore,
an instrumental offset of $ ca. 0.5 nm (caused by different interaction
forces) always exists, which is even larger than the thickness of a single
layer of graphene, so graphene films of the theoretical thickness (ca.
0.34nm)arerarelyobservedbyAFM,13
andthicknessesofca.1nmare
reported normally.14
Thus the graphene sheets found can be estimated
assingle-layerordouble-layergraphenesheets.Thisresultisconsistent
with the above HRTEM observation. It was proved that with the help
of mechanical force the polymer adhesive is sufficient to overcome the
van der Waals forces between the graphene sheets, which successfully
amplified the ‘‘Scotch tape’’ method.
To further investigate the graphene product structure, Raman
spectroscopy of the natural graphite and graphene product were
carried out. Fig. 4 shows the Raman spectra of natural graphite
(green line) and graphene sheets (red line). The two most intense
features of the graphene sheets and the graphite are the G peak at
$1580 cmÀ1
and 2D peak at $2700 cmÀ1
. A single and symmetric
Lorentzian 2D peak (2690 cmÀ1
) is generated in the red line, indi-
cated that the graphene product is probably a single-layer graphene
sheet. In addition, the 2D position is 29–30 cmÀ1
lower than that of
natural graphite. This down-shift and the sharp peak is similar to the
thin graphene data reported previously.15
What is more, the D/G
peak intensity ratio (ID/IG) for the graphene product is 0.06, which is
lower than the value for the chemical exfoliation of graphite oxide,
indicating the perfect structure of the resultant graphene.8
Interest-
ingly, the G peak is also gradually down-shifted towards that of the
natural graphite. Similar phenomena have been reported, in which,
because of the chemical doping effects,16
the frequency shift of the G
peak is a more significant modification in thinner graphene sheets.17
However, the reason attributed to this phenomenon is not clear.
Fig. 2 (a) and (b) High-resolution TEM imaging of graphene products
embedded in epoxy resin slice. (c) The SAED pattern corresponding to
the inset TEM image of the graphene sheets thin edge and the intensity
scan along the solid line.
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3. Evidently, with the help of mechanical force, the polymer adhesive
is sufficient to peel the natural graphite into single and few-layer
graphene sheets. As many flakes were observed in the HRTEM, we
count the number of graphene layers per flake for a number of flakes
from Fig. 2b and the additional image shown in Fig. S3† to
approximately calculate that the ratio of the single and few-layer
(#10) graphene sheets is around 90%, with the single-layer sheets
constituting at least 50%.14
However, based on the current results, it is
reasonable to deduce that an eventual increase of the yield of single-
layer graphene sheets can be accomplished by optimizing the exfoli-
ation conditions such as the rolling time, the speed of rolling, the
properties of the polymer adhesive and so on.
In conclusion, mechanical delamination by a three-roll mill
machine with a polymer adhesive offers the possibility of the large-
scale production of graphene monolayers or ultrathin graphene
layers starting from natural graphite. As a very common industrial
technique in the rubber industry, the method can be applicable for the
industrial production of graphene product. Obviously, the process
could also be applicable for the preparation of polymer/graphene
composites, as long as one is careful to choose the polymer and
exfoliation parameters properly.
Further work will be focused on the properties of the polymer
adhesive and the exfoliation conditions such as the rolling time,
temperature, speed of rolling, etc.
Acknowledgements
This work was funded by Natural Science Foundation of China
(20574025, 50373015) and Science Foundation of Xiamen
(3502Z20103032).
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