10862 Chem. Commun., 2012, 48, 10862–10864 This journal is c The Royal Society of Chemistry 2012

Cite this: Chem. Commun., 2012, 48, 10862–10864

Graphene oxide/polyaniline nanostructures: transformation of 2D sheet

to 1D nanotube and in situ reductionw

Utpal Rana and Sudip Malik*

Received 21st August 2012, Accepted 17th September 2012

DOI: 10.1039/c2cc36052g

The formation of unique polyaniline nanotubes has been reported

in presence of graphene oxide (GO) which plays crucial dual role

as dopant and soft template, simultaneously. GO in nanotubes is

in situ reduced to reduced GO with restoration of electrical

conductivities and enhanced thermal stabilities.

Graphene has generated a tremendous attention among the

researchers working in multidiscipline areas because its superior

electronic, optical and mechanical properties, excellent controll-

ability and manipulability compared to its analogue.1 However,

the presence of large aromatic conjugated backbone composed of

an sp2-hybridized single-layer of carbon atoms has limited its

much anticipated applications in aqueous environments. Making

graphene oxide that is processable and compatible with various

substrates has overcome the problem of manufacturing graphene

based nanomaterials and electronic devices.2 However, GO is an

electrically insulating material consisting of a large number of

defect sites generated by the presence of epoxide, phenoxides and

carboxylic acids on its surface. Removal of these defects either by

chemical or thermal reduction technique produces reduced

graphene oxide (RGO) and it simultaneously allows one to restore

the electrical properties.3 RGO sheets have been used for field

effect transistors FETs,4 chemical sensors,5 organic solar cells, as

well as transparent electrodes in photovoltaic devices.6

Polyaniline (PANI) is one of the popular conducting polymers

due to its facile synthesis, exceptional solution processability,

good environmental stability as well as simple doping/dedoping

chemistry.7 In particular, making nanostructures of PANI could

offer the exciting properties that will ultimately lead to potential

applications in separation, sensors, batteries, electro-optic and

electro-chromic devices, antistatic coating and correction

protection.8 However, the control of size and morphology

during the synthesis of nanostructured PANI still remains a

challenge. Taking the advantage of facile synthesis of PANI,

hydrophilic nature of GO and the presence of carboxylic acid

group which is prerequisite for polymerization of aniline, we

wonder if we could generate directly nanostructures of graphene/

PANI that will show improved performance in flexible plastic

electronics.9

PANI composites have been prepared typically by the

dispersion of aniline (102 mg, 1.1 mmol) and the required amount

of GO in water with sonicating for 30 min followed by stirring for

one hour. After cooling the mixture at 10 1C for 30 min, an

aqueous solution of ammonium persulphate ((NH4)2S2O8, APS,

250 mg, 1.1 mmol) was added over 30 min and the mixture was

allowed to keep at low temperature (Table S1, ESIw). The

resultant precipitate was filtered and washed several times with

water and methanol to remove APS and oligoaniline. Finally, it

was dried under vacuum for 24 h to receive GO/PANI composites

prior to analysis with the multiple techniques, such as electron

microscopy, Fourier transformed infra-red spectroscopy, Raman

spectroscopy, UV-vis spectroscopy and XRD analysis (Fig. 1).

As compared to the conventional sheet-like morphology of

GO, one dimensional tubular fibers of GO/PANI composites

are clearly visible from FESEM images (Fig. 2a–f) for all

compositions. Moreover, nanofibers have a high length/diameter

ratio: they exhibit an average diameter of 200–220 nm. Their

lengths reach to 2–3 micrometers. HRTEM image (Fig. 3a) of

GO/PANI nanostructures reveals that the clear contrast between

the edge and the central part indicates the formation of GO/PANI

nanotubes. GO exists in a zigzag form in water. After addition

of aniline, protons from the carboxylic acid of GO transfer to

the aniline to form anilinium ion covered GO sheets which

initiate polymerization of aniline in the presence of APS and

simultaneously PANI embedded a two dimensional GO sheets

stack to form a nanotube at low temperature.10 Hence, GO

plays dual role: dopant acid for emeraldine salt formation of

PANI and efficient soft template for aniline nucleation and

polymerization particularly for nanotube formation11 through

possible interactions of p–p stacking, electrostatic interactions,

Fig. 1 A schematic presentation of polyaniline emeraldine salt-GO

composites.

Polymer Science Unit, Indian Association for the Cultivation ofScience, 2A & 2B Raja S. C. Mullick Road, Jadavpur, Kolkata,700032, India. E-mail: psussm2@iacs.res.inw Electronic supplementary information (ESI) available: Synthesisand characterization of GO and PANI with Fluorescence, FT-IR,XRD, TGA, I–V, C–V analysis and SEM and TEM images. See DOI:10.1039/c2cc36052g

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This journal is c The Royal Society of Chemistry 2012 Chem. Commun., 2012, 48, 10862–10864 10863

hydrogen bonding and donor–acceptor interactions.12 Careful

investigation of the HRTEM image and its SAED profile show

the multiple spots (Fig. 3b) indicative of the polycrystalline

nature of composites. Magnified image produces the lattice

fringe of distance 0.33 nm (2y = 26.851) citing the possibility

of the presence of RGO in the composites.

XRD patterns of GO/PANI composite (Fig. S3, ESIw)reveal that, along with the characteristic peak of GO at

9.951 (002) there are present three characteristic peaks for

PANI 2y=14.21 (011), 19.951 (100) and 25.151 (110), revealing the

crystalline nature of observed PANI nanotubes and interaction

between GO with PANI chains.13 The peak position at 2y =

19.951 and 25.151 are for periodicity in the parallel and

perpendicular direction to the polymer chains, respectively.8,14

With decreasing concentration of GO in the GO/PANI

composites, there is significant increase of the (002) plane of GO

[GP50 (d = 10.1 A) to GP1 (d = 12.7 A)], indicating intercalation

of PANI chains into GO layers15 Thermogravimetric analysis

(Fig. S4, ESIw) show the enhancement of the thermal stability

of GO/PANI composites with respect to GO only, further

supporting intercalation of PANI chains into GO layers which

are acting as a thermal barrier.15d

The presence of a typical stretching band in FTIR spectra

(Fig. S5, ESIw) at 1595, 1487, 1294, 1110 and 795 cm�1 is

pointing to the formation of PANI. gCQC in the benzenoid rings

of PANI chains are prominently red-shifted from 1595 cm�1 for

GP50 to 1556 cm�1 for GP1, indicating the p–p interaction and

hydrogen bonding between GO and PANI chains. Significant

increase of the ratio of the relative intensities of quinoid to

benzenoid ring stretching (Iquinoid/Ibenzenoid) as well as the

disappearance of the carbonyl stretching band of –COOH

group (1724 cm�1) are reflecting the presence of more of imine

units than amine units in the PANI chains.16

The Raman spectra (Fig. 4a) show significant structural

changes occurring during GO/PANI synthesis. Both GO

and GO/PANI have a couple of Raman-active bands in the

spectra, with the D band at 1350 cm�1 corresponding to

defects or edge areas and G band at 1598 cm�1 related to the

vibration of sp2-hybridized carbon. Raman spectra show that

an increase in the D/G ratio, from 0.76 for GO to B1.10 for

GO/PANI and shifting the D-band 1359 to 1321, indicating

the in situ reduction of GO to RGO during polymerisation of

aniline in presence of APS and this important observation is

novel and rare in the literature.17 Apart from the G/D bands,

there are two new peaks appearing at 1167 and 1468 cm�1, which

are ascribed to C–H vibrations in quinoid and semiquinone

structure of PANI, reflecting the growing of PANI chains are

on the surfaces of the GO.

UV-Vis absorption spectra (Fig. 4b) of GO/PANI composites

have three characteristics absorption bands at 355 nm (p - p*transition), 445 nm (polaron - p* transition) and 840 nm (p -

polaron transition) with a free tail extended to the IR region due to

delocalized polaron transitions. With decreasing concentration of

doped GO, the position of p–polaron band is shifted from 815 nm

to 840 nm and the intensity gradually increases, implying the

simultaneous increase of effective conjugation length in PANI

nanostructures. Moreover, the relative absorption intensities

at l= 355 and 445 nm are enhanced from GP50 to GP1, and is

attributed to the greater conjugation of the molecule, indicating

existence of the p–p interactions between PANI and graphene

sheet.18

The partial reduction of GO in GO/PANI composites is judged

by current–voltage diagrammeasured at room temperature (Fig. 5).

All the I–V curves are non-linear but symmetrical in nature.

Fig. 2 FESEM images of GO/PANI nanostructures at different ratios

of GO to aniline (w/w) (a) GO, (b) GP50, (c) GP25, (d) GP10 (e) GP5 and

(f) GP1.

Fig. 3 (a) Representative HRTEM image of GO/PANI nanostructures

and (b) corresponding SAED profile of GP25 (inset: showing crystalline

fringe of GO).

Fig. 4 (a) Raman spectra of GO and GO/PANI composite,

(b) UV-vis spectra, GO/PANI composites dispersed at different ratio

of GO to aniline (w/w, indicated on the plot, path length = 1.0 cm).

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10864 Chem. Commun., 2012, 48, 10862–10864 This journal is c The Royal Society of Chemistry 2012

The non-linearity of the curve decreases with decreasing the GO

concentration in the composite surmising the presence of the

large number of charge trap states formed during polymeriza-

tion.19 When GO is produced by oxidation, some C–C bonds

that are breaking, creating vacancies during the reduction to

RGO in GO/PANI nanotubes and subsequently a large number

of trap states are formed. This partial reduction behavior of

GO in GO/PANI is also supported by the fluorescence spectra

(Fig. S6, ESIw) and cyclic voltammetry (Fig. S7, ESIw).Fluorescence spectra show that the enhancement of the

peak intensity with decreasing the GO/aniline ratio. These

results are consistent with our expectation that with decreasing

concentration more and more reduction occurs, i.e., the percentage

of strongly localized sp2 sites increases with decreasing GO concen-

tration, thereby improving PL intensity.20 Cyclic voltammetry

studies provide further insight into the interactions between GO

and PANI, also the reduction behaviour of GO. Moreover, the

increased area of GO/PANI (GP50 to GP1) compared to GO

clearly points out GO/PANI higher capacity due to its enhanced

electrical conductivity and large surface area RGO sheets.12

In conclusion, a novel kind of PANI nanotubes doped with

graphene oxide have easily synthesized via chemical oxidation

of aniline in the presence of GO and APS. These nanotubes are

crystalline and have high thermal stability. Graphene oxide in

the composite is reduced to reduced graphene oxide that

restores the electrical properties. We believe that this finding

will help to build flexible plastic electronics based on PANI.

U. R. is indebted to CSIR, New Delhi, India for financial

support. Thanks to Mr Somnath Roy of PSU for I–V measure-

ments, S. Bandyopadhyay and Dr. A. Dey for CV measurements

and Unit of Nano science (DST, Govt. of India) at IACS.

Notes and references

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Fig. 5 Current–Voltage diagram of different GO/PANI composites

at different ratios of GO to aniline (w/w).

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