Synthesis and characterisation of metal doped Graphene-PVA
nano composite
Principal investigator; George. V. Thomas
Research and Post Graduate Department of Chemistry
St. Joseph’s college, Arakulam P. O., Moolamattom, Pin 685 591
Introduction
The synthesis of metal doped graphene nano sheets with different morphologies such as nano
rods1, nano wires2, nano tubes3 has attracted great attention because of their wide applications in
many fields such as solar cell4, sensor5, optical filters6, optical recording materials7, laser
materials8 and conductivity fields. In this project the synthesis of metal doped grapheme-pva
nano composite by chemical reduction of graphite oxide and it’s subsequent characterization
using different techniques such asX- ray diffraction IR,Raman ,NMR,TGA technique has been
described.The metals chosen for the study are selenium and tungsten as wo3.
Materials
Graphite and Hydrazine Hydrate were supplied by Loba Chemicals, NaNO3 from
Nice
Chemicals, KMnO4 and H2O2 from Merk.
Experimental Section
a) Preparation of Graphite Oxide from Graphene
In the experimental section graphite oxide was prepared by the oxidation of high purity
graphite powder with H2SO4 / KMnO4 according to the method of Hummers and Offeman9.
About 1 g Graphite, 0.5 g NaNO3 and 23ml concentrated H2SO4 are taken in a beaker and
mixed well. The temperature should be Kept at 0ºC (ie. In ice). 3 g of KMnO4 was added to the
suspension. Rate of the addition was controlled carefully to prevent the temperature from
exceeding 20ºC. Ice bath is now removed. Temperature is allowed to raise to 40ºC and maintained
for 30 minutes. As the reaction progressed the mixture become thickened and become brownish
grey in colour. At the end of 30 minutes 46ml of water was then added in to the mixture with
constant stirring causing violet effervescence. The diluted suspension was brown in colour. It was
then treated with 5ml 30% hydrogen peroxide to remove excess KMnO4.The solution is filtered to
get yellowish brown cake. It is then suspended in hot water and centrifuged. The centrifugate is
dried in room temperature under vacuum to get graphite oxide.
b) Preparation of selenium doped graphene nano sheet
0.1 g of graphite oxide was dispersed in 20ml of water until a homogeneous yellow
dispersion was obtained. The solution was placed inside a conventional microwave oven after
adding 0.2 g of the reducing agent hydrazine hydrate and 1ml 0.1M sodium selenate solution. The
microwave oven was operated at full power 2.45 GHz in 30 s cycle (on for 10s off and stirring
for 20s) for a total reaction time 60s.
Yellow dispersion of graphite oxide gradually changed to reddish black indicating the
complete reduction of graphite oxide to selenium doped graphene. The selenium doped graphene
sheet was separated by centrifugation and dried under vacuum over night.
c) Preparation of WO3 doped graphene nano sheet
0.1 g of graphite oxide was dispersed in 20ml of water until a homogeneous yellow
dispersion was obtained. The solution was placed inside a conventional microwave oven after
adding 0.2 g of the reducing agent hydrazine hydrate and 1ml 0.1M sodium tungstate solution. The
microwave oven was operated at full power 2.45 GHz in 30 s cycle (on for 10s off and stirring
for 20s) for a total reaction time 60s.
Yellow dispersion of graphite oxide gradually changed to reddish black indicating the
complete reduction of graphite oxide to wo3 doped graphene. The wo3 doped graphene sheet was
separated by centrifugation and dried under vacuum over night.
Measurement
X – Ray analysis of the sample was carried out using a Brucker AXS D8 advanced
instrument. The XRD pattern was measured in the 2θ range 20 - 70º using CuKα radiation. Raman
spectra was taken using Brucker FT Raman spectrometer. 13C nmr was carried out using Brucker
111Advance 500 MHz. TG analysis was carried out usingperkin elmer Diamond TGA/DTA. SEM
analysis was carried out using JEOL JSM scanning electron microscope. AFM analysis was carried
out using Brucker AFM
Result and discussion
Selenium and wo3doped graphene sheet has been synthesised by Chemical Reduction
of exfoliated Graphite Oxide with Hydrazine Hydrate in presence of Sodium Selenate
solution and sodium tugstate solution separatly. It is characterized by X-Ray
analysis,TGA,13CNMR,SEM ,AFM and Raman. The results obtained are discussed below.
The XRD of graphite powder in Fig. 1 shows a typical sharp diffraction peak at 2θ =26.753°
with d spacing 3.32962A°.
XRD pattern of graphite oxide in Fig. 2 shows no diffraction peaks of the parent
graphite material but a new peak at 2θ=9.356° with d spacing 9.44474A° .This indicates that
the distance between the carbon sheets has increased due to insertion of interplanar group
such as hydroxyl and epoxy group between the carbon sheets mainly on the centers while the
carbonyl groups are typically inserted on the terminal and lateral sides of the sheets. The
insertion of these groups leads to decreasing the van der Waals forces between the graphite
sheets in the graphite oxide.
FIGURE 3
X – RAY DIFFRACTOGRAM OF GRAPHENE
Fig. 3 shows the XRD of Graphene.The characteristic peak of graphite oxide at 9.356° is
absent in this XRD. This shows the complete reduction of graphite oxide to graphene by
hydrazine hydrate
Fig 4: X-Ray Diffractogram of Selenium Doped Graphene
Fig 5: X-Ray Diffractogram of Tungsten oxide Doped Graphene
Fig. 4 displays XRD of selenium doped graphene nano composite. Peaks at 23.200º
and 29.451° are assigned to selenium. Fig.5 shows the xrd of wo3 of WO3doped graphene
TGAnalysis
TG analysis of the samples was carried out and the results are shown in fig6,7,8,9.In the
thermogram of graphite( fig .6) a single stage decomposition pattern is seen. Go is thermally
stable and starts to lose mass upon heating even below 1000C .
Fig 6:Thermogram of graphite
Fig 7:Thermogram of graphite oxide
Go shows10% weight loss around 1000C and more than 40% loss at 2000C resulting
from the removal of oxygen containing functional group such as CO,CO2.and steam.Hence the
thermal decomposition of GO can be accompanied by a vigorous release of gas resulting in a
rapid thermal expansion of the material. This is evident by both a large volume expansion
and a larger mass loss..Graphene sheets shows much higher thermal stability with no significant
mass loss upto 7500C. Removal of the thermally labile oxygen functional groups by chemical
reduction results in much increased thermal stability for graphene
Fig 8:Thermogram of graphene
Graphene sheets shows much higher thermal stability with no significant mass loss
upto 7500C. Removal of the thermally labile oxygen functional groups by chemical reduction
results in much increased thermal stability for graphene
Fig 9:Thermogram of se doped graphene
NMR studies
13
CNmr spectra of GO and Graphene indicate significant structural change by
reduction. In the spectrum of GO the peaks at 57 ppm and 68 ppm represent 13C nuclei in the
epoxide andhydroxyl groups .The peak at 130ppm belongs to the epoxidised sp2 carbon
atomsof the graphene net work and that at 188ppm arises from carbonyl group.
FIG10 13C
NMR spectra of GO and Graphene
SEM Studies
Fig.11:sem of graphene
In pure graphene a uniform plane surface is seen. In wo3 doped grapheme
flower shaped wo3particles are found embedded in grapheme surface wh ere as
in selenium doped graphen e elongated se particle s are seen formed on the
graphene surface
Fig.12:sem ofwo3 doped graphene
Fig.13:sem of selenium doped graphene
Fig 14 . AFM of graphene oxide
Raman Spectra
The Raman spectrum of pristine graphite displays a prominent peak G peak at
1581cm-1.In the Raman spectrum GO G bands shifted to 1594cm-1and a D band at 1363cm-1
becomes prominent showing the reduction in size of the in plane sp2domains due to
extensive oxidation .Raman spectra of graphene contains both G and D band at 1584cm-1and
1352 cm-1
References
1.
W. Z. Wang , Y. Geng , P. Yan , F. Y. Liu , Y. Xie , Y. T. Qian , Inorg. Chem. Commun.
2 (1999) 83.
2.
Q. Li, M. A. Brown, J. C. Hemminger, R. M. Penner, Chem. Mater. 18 (2006) 3432.
3.
H. M. Cui , H. Liu , X. Li , J. Y. Wang , F. Han , X. D. Zhang, R. I. Boughton , J. Solid
State Chem. 177 (2004) 4001.
4.
S. T. Lakshmikvmar, Sol. Energy Mater. Sol. Cells 32 (1994) 7.
5.
A. Hagfeldt, M. Gratzel, Chem. Rev. (% (1995) 49.
6.
W. Z. Wang, Y. Geng , P Yan, F. Y. Liu, Y. Xie , Y. T. Qian , J Am. Chem. Soc. 121
(1999) 4602.
7.
F. Mongellaz , A. Fillot , R. Griot , J. De Lallee , Proc. SPIE – Int. Soc. Opt. Eng. 156
(1994) 2227
8.
O. Tatsuya, O. Satoru, J. Non – Cryst. Solids 250 – 252 (1999) 344.
9.
W. S. Hummers Jr. and R. E. Offeman, Preparation of graphite oxide. J. Am.Chem. Soc.,
1958, 80, 1339.