graphene humers method

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NEW CARBON MATERIALS

Volume 24, Issue 2, June 2009

Online English edition of the Chinese language journal

Cite this article as: New Carbon Materials, 2009, 24(2):147–152.

Received date: 18 March 2008; Revised date: 28 May 2009

*Corresponding author. E-mail: [email protected]

Copyright©2009, Institute of Coal Chemistry, Chinese Academy of Sciences. Published by Elsevier Limited. All rights reserved.

DOI: 10.1016/S1872-5805(08)60044-X

RESEARCH PAPER

In situ synthesis of graphene oxide and its composites

with iron oxide

V. K. Singh, M. K. Patra, M. Manoth, G. S. Gowd, S. R. Vadera, N. Kumar*

Defence Laboratory, Jodhpur-342011, India

Abstract: A single step method was developed for the preparation of graphene oxide/Fe2O3 composites by exfoliation of graphite ox-

ide with an oxygen-rich ferric acetyl acetonate complex. The synthesized materials were characterized by Fourier transform infrared

spectroscopy, X-ray diffraction, vibrating sample magnetometry, atomic force microscopy, and low temperature dc conductivity meas-

urements. After exfoliation, the Fourier transform infrared studies reveal the decomposition of epoxy groups and the simultaneous for-

mation of composites of iron oxide particles within the graphene oxide. Atomic force microscopy reveals the formation of an ~5nm thick

graphene oxide stack with layered morphology. The layered morphology of graphene oxide degrades at higher concentrations of iron

oxide. The vibrating sample magnetometer studies show ferromagnetic behavior of all composites in the range of 0.13-5.5 emu/g at room

temperature. The conductivity of these composites is found to be governed by a quasi 1D hopping mechanism.

Key Words: Graphite Oxide; Graphene oxide; Iron oxide; Composite

Introduction

The graphene, a two dimensional form of carbon, was

first reported in 2004[1]

and has generated curiosity among

material scientists to study its properties like very low resis-

tivity, high mobility of charge carriers, and new quantum hall

effect at room temperature[2-3]

. The interest also comes from

the presence of various oxygen bearing functional groups

(C=O, C–O, –OH) in the structure of graphene oxide[4-7]

,

which can lead to synthesis of various composites of varied

electromagnetic properties[8-9]

.

Recently, the efforts were made on making ~10 nm thick

layer of graphene on SiC/SiO2 substrate to show extraordinary

properties of ballistic charge transport leading to their poten-

tial application in various electronic devices[3, 10-11]

. At the

same time, considerable efforts have been made to synthesize

composites of graphene oxide with polymers, metals, and theiralloys in a two step chemical processes

[12-21], i.e., initially gra-

phene oxide has been prepared and then re-dispersed in

polymeric solution to tailor electrical and mechanical proper-

ties to suit various applications[12]

, e.g., Lee and Lee have

synthesized graphite–FeSi alloy composites as anode materi-

als for rechargeable lithium batteries[13]

. In contrast, Zheng

and Wong prepared poly (methyl methacrylate)

(PMMA)/ expanded graphite composites and studied their

electrical properties[14]

. It is intriguing that, so far, to the best

of our knowledge, no work has been reported on the synthesis

of composites of graphene oxide with metal oxides.

In the present work, we report insitu formation of iron ox-

ide-graphene oxide composite by exfoliation of graphite oxide

(GO) with ferric acetyl acetonate [Fe (acac) 3]. Interestingly,

structural, morphological, electrical, and magnetic properties

are observed by varying the concentration of ferric acetylacetonate.

2 Experimental

2.1 Synthesis of graphene oxide/ iron oxide composites

The synthesis of graphite oxide (GO) was carried out by

the following well known Hummer’s method[22]

, except for

replacing the step of purification, i.e., dialysis by washing the

product with pre-determined concentration of HNO3. This

modification in the process has not only enhanced oxidation of

graphite but also removes trace impurities of other metal ions.

The product was filtered and thoroughly washed by distilled

water. The golden yellow powder of GO thus obtained was

dried at room temperature for composite preparation. This

dried powder was mixed with solution of different concentra-

tions of Fe(acac)3 in acetone [A1 (9:1 GO/ Fe(acac)3)], A2 (8:2

GO/ Fe (acac)3), A3 (7:3 GO/ Fe(acac) 3), A4 (6:4GO/

Fe(acac)3), and A5 (5:5 GO/Fe(acac)3)], and grinded in a pestle

mortar by allowing the solvent to evaporate leaving behind a

dried precursor composite.

For exfoliation, these precursor composite powders were

taken into round bottom flask covered by thin aluminium foil


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V. K. Singh et al. / New Carbon Materials, 2009, 24(2): 147–152

Fig.1 (a) FTIR spectra of GO, GO/Fe (acac) 3, and S0. (b) FTIR spectra of graphene oxide/Fe2O3 composites (S1 -S5)

and placed on hot plate. It was observed that exfoliation of

GO/Fe (acac) 3 takes place at ~1500C. The resulting powders

were marked as S1, S2, S3, S4, and S5 for A1, A2, A3, A4, and A5, respectively. The concentration of iron oxide in composite

materials was estimated by dissolving the powders in conc.

HNO3 and found to be 9.8%, 18.3%, 29.4%, 38.5%, and 47%

for S1, S2, S3, S,4 and S5, respectively. For comparison, a sam-

ple of pure graphene oxide was prepared without Fe (acac)3

and named as S0.

2.2 Physical Measurements

The structural characterization of the samples was car-

ried out by powder X-ray diffraction (XRD) performed on a

Philips X’Pert Pro system by using Cu K α1 (λ =0.154 060 nm)radiation. The fourier transform infrared (FTIR) spectra were

recorded in KBr by using FTIR spectrometer Model Shmadzu

DR-8101 A. DC electrical conductivity of these materials was

measured as a function of temperature by four-probe method

using Janis closed cycle refrigerator system and Lake Shore

temperature controller model 331. Imaging of the material was

carried out by using NT–MDT Solver PRO Atomic Force

Microscope (AFM) in tapping mode. In order to take images,

samples were initially dispersed in ethanol solution and

spray-coated on a freshly cleaved mica surface by using a fine

atomizer. Room temperature magnetic measurements were

carried out by ADE model EV-5 Vibrating Sample Magne-

tometer (VSM).

3 Results and discussion

FTIR spectra of pure GO, GO/ Fe (acac) 3, and S0 are

shown in Fig.1(a). In case of pure GO, absorption peaks ap-

pearing at 1 726 cm-1

, 1 360 cm-1,

and 1 405 cm-1

are be-

cause of C=O, C–O stretching, and O-H deformation vibration,

respectively. Furthermore, bands at 1 225 cm-1

, 1 062 cm-1,

and 986 cm-1

are because of epoxy symmetrical ring deforma-

tion, C–O stretching mixed with C–OH bending, and out of

plane wagging of O–H–O, respectively. In addition, observed

broad absorption band at 3 362 cm-1

and a peak at 1 621 cm-1

correspond to vibrations of the absorbed water molecules[23]

.

In the sample S0,i.e., on exfoliation of GO, the intensity of

C=O and O–H absorption peaks are significantly reduced in

intensity with disappearance of absorption peak characteristic

to epoxy group. In case of composite samples (i.e., S1 -S5)[ Fig.1(b)], we have observed the similar FTIR spectra like S0,

with additional peaks at 637, 545, and 456 cm-1

attributed to

the presence of α - Fe2O3[24]

. Furthermore, in these composites,

a shoulder peak is also observed at 696 cm-1

suggesting the

presence of γ –Fe2O3[25-26]

. The intensity of all peaks attributed

to α – and γ –Fe2O3 increases gradually with increasing con-

centration of iron oxides.

In order to understand any initial interaction between

Fe(acac)3 and GO, FTIR spectrum was recorded of a repre-

sentative sample, i.e., GO mixed with 10% Fe(acac)3 before its

exfoliation [in Fig.1(a)]. It has been observed that, the charac-teristic peaks of GO because of carbonyl group at 1 726 cm

-1

and 1 621 cm-1

because of water are shifted to 1 712 cm-1

and

1 615 cm-1,

respectively. The observed shifts are quite signifi-

cant and suggest some interaction between carbonyl (C=O)

and hydroxyl (-OH) groups of GO and Fe (acac) 3. Such shifts

towards lower wave numbers might be correlated to the exis-

tence of hydrogen bonding[27]

between GO and Fe (acac) 3

before the exfoliation.

The diagram for the formation of graphene oxide/Iron oxide

composites has been shown in scheme.1.

XRD spectra of composite materials are shown in Fig.2.Sample (S1) prepared with ~9.8% concentration of Fe2O3

shows diffraction peaks corresponding to (002), (100), (101),

(102), (104), and (110) planes of hexagonal carbon structure,

similar to that of pure graphene oxide (S0) (shown in inset

figure). Furthermore, the higher intensity of the peak because

of (104) plane is found to be high as compared to other peaks,

suggesting planar growth of hexagonal carbon phase. How-

ever, in samples prepared with higher concentration of Fe2O3

concentrations (~18.3% -29.4%), i.e., S2 and S3, the intensities

of these peaks corresponding to hexagonal carbon phase

gradually decrease and with further increase in iron oxide

concentrations (beyond ~29.4%) in composites samples S4 and

S5, their intensity almost vanishes with formation of iron ox-

ide in both α and γ –Fe2O3 phases. Moreover, in samples S1, S2,

and S3 the peaks of iron oxides could not be observed because


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Scheme.1 Scheme for the formation of graphene oxide/ Iron

Oxide composites

Fig.2 XRD spectra of graphene oxide/Fe2O3 composites (S1-

S5). Inset figure shows XRD of graphene oxide (S0)

Fig.3 AFM images of S0, S1 and S5. Inset figure shows height profile of S0

Fig. 4 M - H curves of graphene oxide/Fe2O3 composites (S1-

S5). Inset fig: Variation of coercivity and saturation values with

respect to percentage of Fe (acac) 3.

of its low concentration. From the above observations, it is

clear that planar growth of hexagonal carbon phase has been

hindered because of the increase in concentration of iron oxide

in the composite materials beyond a limit ~29.4% of Fe2O3.

AFM images of graphene oxide as well as of composites

(S1 and S5) are shown in Fig.3. Image of graphene oxide

shows layered morphology having thickness of ∼25 nm con-

sisting of each stack thickness ~5 nm (inset figure shows

height profile of graphene oxide layers). Images of samples

(S1and S5) show formation of iron oxide particles embedded

within graphene oxide layers. Interestingly, in case of sample

S1, size of particles (~70 nm) are smaller as compared to those

found in sample S5 (~200 nm). Furthermore, the layered mor-

phology of graphene oxide significantly degrades in sample S5

with the dominance of particles that is consistent with XRD

results as the diffraction peaks of hexagonal carbon phase

diminishes with increase in concentrations of iron oxide in the

composite materials. Although, the phase of spherical particles

can not be arrived from AFM image studies, however, results

from XRD and FTIR studies suggest that they might be iron

oxide particles.

Field dependent magnetization ( M - H curves) of compos-

ite materials (S1-S5) is shown in Fig.4. All these samples show

ferromagnetic behavior, even at room temperature, because of

the presence of Fe2O3 phases. Furthermore, coercive field ( H c)

as well as saturation magnetization ( M s) values were found to

increase with increase in Fe2O3 concentration in composites

(Inset figure) with maximum saturation magnetization ( M s)

value of ~ 5.5 emu/g in case of sample S5. The higher value of

MS can be attributed mainly to the formation of bigger Fe2O3

particles as revealed in its AFM images.

Room temperature dc conductivity values (σ ) of pure

graphene oxide (S0) and its composites (S1 –S5) are listed in


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Fig.5 lnσ Vs T plot of pure graphene oxide (S0) and compos-

ites (S1 –S5). Inset fig: lnW vs ln T plot of pure graphene oxide

(S0) and composites (S1 –S5)

Table 1 Conductivity values (σ ) at room temperature and γ

values of pure graphene oxide (S0) and graphene oxide/Fe2O3

composites (S1-S5)

Sample Conductivity σ/S · cm-1 γ

S0 3.44 0.948

S1 3.2×10-2 1.120

S2 9.1×10-3 1.126

S3 3.8×10-3 1.230

S4 8.8×10-4 1.540

S5 1.9×10-3 1.837

Table.1, together with γ values obtained from their tempera-

ture dependence conductivity study curves of lnW vs. lnT

(inset Fig.5) [28]

. It is evident from the table that, graphene

oxide (S0) shows two orders higher conductivity than compos-

ite material containing lower concentration of iron oxides (S1).

Furthermore, decrease in conductivity values is observed with

increasing the concentration of iron oxide (S2 –S5). The de-

crease in conductivity values might be attributed to reduction

of graphene oxide content as well as progressive destruction

of its layered structure as indicated from their XRD and AFMstudies. From the temperature dependent dc conductivity

measurements, shown in Fig.5, the increase of conductivity

values with that of temperature suggests the semiconducting

behavior [28]

both in graphene oxide as well as its composites.

Furthermore, the conductivity mechanism in these materials

has been explained by variable range hopping model (VRH)

(as in case of other nanostructure carbon)[29]

. The experimen-

tal data have been analyzed by using the following equations:

σ (T) = σ 0 exp (-T 0/T ) γ

, (1)

W = dlnσ /dlnT , (2)

where T 0 is the characteristic temperature, γ represents

dimension of hopping, and W is activation energy. The values

of σ and γ are shown in Table.1. The γ –values are found to be

>0.5 in both composites and graphene oxide, suggesting quasi

1D hopping mechanism[30-31]

.

There are several reports regarding graphite intercala-

tion compounds (GIC)[32-33]

. In these compounds, conductiv-

ity increases because of charge transfer interaction as the

amount of intercalated particles increases. Furthermore, struc-

ture of the host matrix remains unchanged even after insertion

of intercalated particles [33]

. However, in present studies, gra-

phene oxide/Fe2O3 composites are different from GIC since

carbon layer loses their planarity because of interaction be-

tween functional groups of host matrix (graphene oxide) and

Fe2O3 particles, causing a disruption of the π –electron system.

Hence, decrease of electrical conductivity has been observed

as the amount of Fe2O3 particles increases in the graphene

oxide matrix.

4 Conclusions

We have synthesized graphite oxide (GO) by modifying

the Hummer’s method. It is demonstrated here that exfoliation

of GO with different concentrations of Fe(acac)3 leads to the

formation of light weight flaky graphene oxide/Fe2O3 com-

posites, as confirmed by FTIR and XRD studies. Furthermore,

XRD studies of composites show the formation of α and

γ –phases of Fe2O3 and degradation of graphene oxide layered

structure. AFM images show particles of Fe2O3 in graphene

oxide matrix and increase in their size together with degrada-

tion in layered structure of graphene oxide as the amount of

Fe2O3 increases. VSM studies indicate the ferromagnetic be-

havior in all composite samples and increase in magnetization

and coercivity values has been observed with increase in con-centration of Fe2O3. Semiconducting behavior of composites

with VRH model for the mechanism of their conductivity is

established from their temperature dependent conductivity

studies.

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