A simple one-pot strategy for the synthesis of ternary reduced graphite oxide/SnO2/Au hybrid nanomaterials

C A R B O N 4 9 ( 2 0 1 1 ) 3 5 3 8 – 3 5 4 3

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A simple one-pot strategy for the synthesis of ternary reducedgraphite oxide/SnO2/Au hybrid nanomaterials

Jun Zhang, Xianghong Liu, Liwei Wang, Taili Yang, Xianzhi Guo, Shihua Wu,Shoumin Zhang, Shurong Wang *

Department of Chemistry, TKL of Metal- and Molecule-Based Material Chemistry and Key Laboratory of Advanced Energy Materials

Chemistry (MOE), Nankai University, Tianjin 300071, China

A R T I C L E I N F O

Article history:

Received 30 September 2010

Accepted 15 April 2011

Available online 22 April 2011

0008-6223/$ - see front matter � 2011 Elsevidoi:10.1016/j.carbon.2011.04.053

* Corresponding author: Fax: +86 22 2350 245E-mail address: [email protected] (S. W

A B S T R A C T

A simple, time-saving, and user-friendly one-pot strategy is demonstrated for the synthesis

of a novel ternary reduced graphite oxide/SnO2/Au hybrid nanomaterials using exfoliated

graphite oxide, SnCl2 and HAuCl4 as the staring materials. The synthesis process can be fin-

ished within 2 h in a solution phase, without using any surfactant and toxic or harsh

reagent such as hydrazine, which is highly efficient, cost-effective and can be easily scaled

up for production. This easy one-pot procedure offers a new pathway to produce complex

graphene-based hybrid nanomaterials, which would hold great promise for a variety of

applications.

� 2011 Elsevier Ltd. All rights reserved.

1. Introduction

Graphene, known as ‘‘the thinnest material in our universe’’

with only one-atom thickness [1], has attracted tremendous

attention from both experimental and theoretical perspec-

tives since its discovery in 2004 [2–4]. Its unique features such

as light weight, high surface area, high electron mobility and

mechanical strength makes graphene highly promising for a

wide range of applications such as supercapacitors, nanoelec-

tronics, sensors, hydrogen storage and so forth [1–5]. Chemical

reduction of exfoliated graphite oxide (GO) using reductant

such as hydrazine is probably the most easy and popular

method to obtain graphene [6–8]. GO can form well-dispersed

aqueous colloids, even in the absence of stabilizers, due to

electrostatic repulsion of the versatile oxygen-containing

groups (OCGs) such as carboxylic acid, phenol, hydroxyl and

epoxy groups distributed on the basal plane (Fig. 1a) [9–11].

Of particular interest is that the aqueous colloidal dispersion

of GO can be used as the starting support material for fabricat-

ing advanced graphene-based nanomaterials [9,12].

er Ltd. All rights reserved

8.ang).

In recent years, the synthesis of graphene-based hybrid

nanomaterials has sparked enormous research interest

[5,12–15]. The hybridization of graphene or GO with a second

component such as noble metals [13,16–21] or metal oxides

[13,22–38] to obtain a binary composite, which combines the

merits of the two materials, could provide superior properties

over their single components in various applications. For in-

stance, the graphene/SnO2 composite holds great promise

for Li-ion batteries and photocatalysis [33,35–38]. GO is insu-

lating and it should be converted to conducting graphene be-

fore practical uses. To obtain graphene-based hybrid

nanomaterials, two methods are usually employed. One ap-

proach is to first produce a GO-based composite, followed

by conversion to graphene-based hybrids using chemical

reduction (e.g., hydrazine). An alternative procedure is to first

reduce exfoliated GO to graphene, which is then used as a

support to load a second material. In this case, a surfactant

stabilizer must be used to protect the graphene sheets from

re-stacking, which may have a negative effect on the intrinsic

properties of the materials [9]. While great success has been

.

Fig. 1 – (a) Procedure to fabricate ternary rGO/SnO2/Au hybrids and (b) photos of the GO dispersion at different reaction time.

C A R B O N 4 9 ( 2 0 1 1 ) 3 5 3 8 – 3 5 4 3 3539

made in producing graphene-based hybrid nanomaterials,

the previous methods suffer from several drawbacks such

as time-consuming multi-steps, the use of various surfac-

tants, organic solvent and toxic reagent like hydrazine, and

thus are not user/environmentally friendly. While recent ad-

vances have been made in the synthesis of graphene using

a green reductant such as ascorbic acid [39,40] and reducing

sugars [41], the synthesis of graphene-based hybrids using a

straightforward green one-step method still remains unsuc-

cessful. It is therefore very important to develop a simple,

user-friendly and cost-effective method for the synthesis of

complex graphene-based hybrids.

On the other hand, extensive attention has been focused

on binary graphene-based composites, while relatively little

attention has been paid to the synthesis of ternary graph-

ene-based hybrids, which represent another new class of

nanomaterials that combine the advantages of three or

more different compositions. Very recently Guo et al. [42] re-

ported the preparation of a ternary Pt/Pd/graphene electro-

catalyst by using a multi-step wet-chemical method using

PVP-functionalized graphene as the support. In the past dec-

ades carbon nanotubes (CNTs)-based hybrid nanomaterials

integrating the properties of multi-components have been

extensively studied from the viewpoints of both science

and technology [43–46]. It has been mentioned that graph-

ene is a promising substitute for CNTs for next-generation

nanoelectronic devices due to its easy preparation and low

cost [5,7,47]. In this regard, an easy, efficient and general

method for the synthesis of multicomponent graphene-

based nanohybrids is of great significance. Herein, we pres-

ent a straightforward sonication-assisted one-pot route to

fabricate a ternary reduced graphite oxide(rGO)/SnO2/Au

nanomaterial using aqueous dispersion of exfoliated GO as

the support and SnCl2 as the tin source and the reductant

for both rGO and Au nanoparticles. This easy procedure

has several obvious advantages, which will be discussed la-

ter in this work. This approach provides a new pathway for

preparing a new class of graphene-based multicomponent

nanomaterials.

2. Experimental

2.1. Preparation of GO

GO was prepared by Hummer’s method [48] with minor mod-

ifications. Briefly, 1 g of graphite powder was added to 25 mL

of concentrated H2SO4 (in ice-water bath). 3 g of KMnO4 was

added gradually into the mixture under stirring. After being

stirred for 45 min, the mixture was heated in a water bath

at 35 �C for another 1 h, followed by slow addition of 50 mL

of water to cause an increase in temperature to 98 �C. The

mixture was maintained at that temperature for 15 min.

The reaction was terminated by adding 140 mL of water fol-

lowed by 1 mL of 30% H2O2 solution. After 30 min, the yellow

product was collected by centrifugation, and washed with

water until pH 4–5.

2.2. Preparation of rGO/SnO2/Au hybrids

This is an easy, one-pot and time-saving procedure, which

can be finished within 2 h, based on the literature method

for preparing SnO2-coated CNTs [49]. In a typical synthesis,

25 mL of GO dispersion (0.2 mg/mL) was exfoliated by sonica-

tion for 30 min to get a homogeneous yellow-brown colloidal

(Fig. 1a (GO)). Then 1 g of SnCl2 and 1 mL of HCl (38%) was

added to the GO colloidal, which was sonicated for 40 min,

followed by adding 0.5 mL of HAuCl4 (0.01 M). After further

sonicating for 30 min, the black product was harvested by

centrifugation and washed with water and ethanol several

times, and dried at 60 �C for several hours.

2.3. Characterizations

The samples were characterized by means of powder X-ray

diffraction (XRD, Rigaku D/max-2500, Cu Ka, k = 1.5418 A),

transmission electron microscope (TEM, Philips FEI Tecnai

20ST, 200 kV), thermogravimetric analysis (TGA, ZRY-2P,

10 �C/min), X-ray photoelectron spectroscopy (XPS, Kratos

Axis Ultra DLD spectrometer, Al Ka X-ray monochromator).

Fig. 3 – XRD pattern of ternary rGO/SnO2/Au hybrids.

Fig. 4 – TEM images of GO.

3540 C A R B O N 4 9 ( 2 0 1 1 ) 3 5 3 8 – 3 5 4 3

3. Results and discussion

3.1. The role of SnCl2

Our one-pot procedure for preparing rGO/SnO2/Au hybrids is

illustrated in Fig. 1a, which was conducted in water without

using any organic solvent and surfactant and can be finished

within 2 h. We deduce that Sn(II) can be absorbed onto the

graphene plane and then nucleate and grow therein, as

shown in Fig. 2, due to two reasons. First, it is known that

GO obtained using chemical oxidation carries negative

charges; positive Sn(II) can be absorbed onto the negative

GO due to electrostatic interaction. On the other hand, the

large amount of OCGs on graphene sheets can serve as the

anchor sites for Sn(II) to be oxidized into Sn(IV) of SnO2 by

the OCGs according to reaction (1) in Fig. 1a. The formed

SnO2 nanoparticles could in turn act as a spacer to separate

the GO nanosheets during sonication.

The reaction process has been monitored by the digital

photos shown in Fig. 1b taken at different sonication time.

Only after 10 min, the dispersion shows an obvious color

change from yellow-brown to brown, the dispersion also be-

come turbid from transparent. After 40 min sonication, the

dispersion became totally black, indicating the reduction of

GO to rGO. With the sonication time further prolonged to

70 min, a homogeneous black dispersion is finally obtained,

suggesting the reduction of GO by Sn(II). Furthermore, the

black product can be easily collected by centrifugation at

4000 rpm for 10 min due to its high density, while GO disper-

sion can not be harvested at the same centrifugation condi-

tions, further indicating the successful formation of the

hybrids.

Importantly, the in situ formed rGO/SnO2 dispersion can be

used as a starting material for further functionalization. For

example, after sonication for 40 min, the addition of aqueous

HAuCl4 to the dispersion would give rise to a ternary rGO/

SnO2/Au composites. The linked Sn(II) species [50] on GO

and excess Sn(II) in the solution can reduce the HAuCl4 to

metallic Au based on reaction (2) in Fig. 1a. To our best knowl-

edge, this is the first report on the synthesis of a ternary rGO/

SnO2/Au hybrids, which represent another new kind of

nanomaterials.

3.2. Structure and composition

The phase composition of the ternary hybrids is analyzed by

XRD (Fig. 3), showing four highly broadened peaks at 25.9�,

Fig. 2 – Nucleation and growth of SnO2 nanoparticles on GO

sheets.

33.6�, 51.3� and 65.1�, which can be ascribed to the (1 1 0),

(1 0 1), (2 0 0) and (2 1 1) planes of tetragonal rutile SnO2

(JCPDS 41-1445). The wide peaks suggest that the SnO2 in

the hybrids has a very small size, which is observed from

the TEM images. However, no obvious peaks for Au could be

seen in Fig. 3. This may be due to the low content and the

Fig. 5 – TEM images of ternary rGO/SnO2/Au hybrids.

Fig. 6 – TGA curves of GO and ternary rGO/SnO2/Au hybrids.

C A R B O N 4 9 ( 2 0 1 1 ) 3 5 3 8 – 3 5 4 3 3541

small size of Au nanoparticles in the hybrids. Fig. 4 displays

the TEM images of the well-dispersed GO. It is seen that the

GO has a smooth and clean plane surface.

The nanosheets have a size of several micrometers, with

some surface wrinkles in some places. Fig. 5 displays the

TEM images of the ternary rGO/SnO2/Au hybrids. From

Fig. 5a and b, it can be observed that the products exhibit a

rough surface, which is significantly different from that of

the pristine GO in Fig. 4. By close observation from Fig. 5b

and c, one can see that a large amount of nanoparticle dots

are attached on the nanosheets surface, with a size of no

more than 3 nm, which is also reflected by the wide diffrac-

tion peaks of the XRD pattern in Fig. 3. It should be noted that

Au nanoparticles can not be easily distinguished among the

nanoparticles dots, probably due to their small size, although

in Fig. 5d of a high-resolution, some black dots with a darker

Fig. 7 – XPS spectra of (a) C 1s of graphene oxide, (b) C 1s,

contrast against the background can be observed, which may

be Au nanoparticles. In Fig. 5c, some nanoparticles can be

seen out of the hybrid nanosheet, which may be SnO2 that

was not attached on GO. Furthermore, the high density of

the nanoparticles anchored on the sheets (Fig. 5c and d) sug-

gests a high loading content of SnO2. According to TGA in

Fig. 6, the hybrids exhibits a total weight loss of ca. 30% until

600 �C, while the pristine GO shows a weight loss of 80% be-

fore 650 �C and continues to lose its weight after this temper-

ature. Both of the weight losses are due to the evaporation of

adsorbed water and combustion of the carbon skeleton of GO.

The surface composition of the ternary rGO/SnO2/Au hy-

brids has been further analyzed by XPS. Fig. 7 shows the C

1s XPS spectra for pristine GO and C 1s, Sn 3d and Au 4f spec-

tra for the hybrids. Fig. 7a reveals that four different types of

carbon species exist in the GO, i.e., CAC at 284.5 eV, CAOH at

285.4 eV, C (epoxy) at 286.7 eV and C@O at 288.6 eV. In Fig. 7b,

although the four types of carbon species can still be seen in

the rGO/SnO2/Au hybrids, the XPS peaks corresponding to C

(epoxy) and C@O (carboxylic) are severely weakened in com-

parison to Fig. 7a, indicating that GO has been highly reduced

by Sn(II). The high-resolution XPS spectrum in Fig. 7c shows

two peaks at 487.5 eV for Sn 3d5/2 and 496.1 eV for Sn 3d3/2,

which are attributed to Sn(IV). The presence of Au in the hy-

brids is confirmed by Fig. 7d, showing significant signals at

84.3 and 87.9 eV corresponding to metallic Au, however, a

miner peak at 86.3 eV due to Au(I) is also detected. The Au

4f signal of metallic Au shows a higher intensity than that

of Au(I), suggesting that most of Au is of zero valence and ex-

its in the metallic form. According to our XPS data, the con-

tent of Sn and Au element in the composite is 63.82% and

1.38%, respectively.

(c) Sn 3d and (4) Au 4f of ternary rGO/SnO2/Au hybrids.

3542 C A R B O N 4 9 ( 2 0 1 1 ) 3 5 3 8 – 3 5 4 3

4. Conclusions

A highly efficient, user-friendly one-pot strategy is success-

fully developed for synthesizing a new type of ternary rGO/

SnO2/Au hybrid nanomaterials using only GO dispersion

and SnCl2 as the starting materials, without using any surfac-

tant stabilizers and toxic reductant such as hydrazine. This

easy procedure, in comparison to the previous reports, offers

several significant advantages. First, the procedure is highly

efficient and time-saving, as the whole synthesis process

can be finished in 2 h. Second, only GO dispersion and SnCl2are used as the staring materials for the synthesis of hybrid

nanomaterials. The reduction of GO and loading of SnO2

simultaneously occurred in situ without using any surfactant

stabilizers and toxic reagent such as hydrazine. Third, in the

sonication process, by adding HAuCl4 into the reaction sys-

tem one can obtain a new class of ternary hybrids, thus pro-

viding a potential for preparing other multi-component

hybrids based on different metal precursors. This new type

of ternary rGO/SnO2/Au hybrids is expected to be useful for

a variety of applications such as lithium-ion battery, chemical

sensor, electrocatalysis and so forth.

Acknowledgments

This work was supported by the National Natural Science

Foundation of China (No. 20871071) and the Applied Basic

Research Programs of Science and Technology Commission

Foundation of Tianjin (Nos. 09JCYBJC03600 and

10JCYBJC03900).

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