One step synthesis of b-FeOOH nanowire bundles/graphene oxidenanocomposites

Hao-Jie Song • Xueqiang Zhang • Tao Chen

Received: 31 March 2014 / Accepted: 4 June 2014

� Springer Science+Business Media New York 2014

Abstract A nanocomposite of graphene oxide (GO) and

b-ferric oxyhydroxide (b-FeOOH) nanowire bundles is

synthesized by in situ hydrolysis of the precursor ferric

chloride and GO nanosheets. Characterization by X-ray

diffraction, transmission electron microscopy, and ther-

mogravimetric analysis established the composite structure

of the synthesized sample. The results revealed that the

surface of GO nanosheets was uniformly assembled by

numerous nanowire bundles with diameters in the range of

30–50 nm and lengths of 100–150 nm. Furthermore, b-

FeOOH/GO nanocomposites showed a very high adsorp-

tion capacity of Congo red and thus these nanocomposites

can be used as good adsorbents and can be used for the

removal of organic dye from the waste water system.

1 Introduction

Organic dye contamination in natural water is a worldwide

problem because of its known toxicity and health hazards.

Among the technologies to remove the organic dye from

contaminated water, adsorption process has been the most

widely used because of its high removal efficiency, easy

operation, low cost and sludge-free [1, 2]. Among these

reported materials, b-ferric oxyhydroxide (b-FeOOH) have

attracted special attention due to its low cost and good

adsorption capacity for organic dye species [3–5]. How-

ever, these iron oxides adsorbents can rarely be used in real

application due to their small size and instability. To meet

the ever-increasing environment demand, therefore, it is

highly desirable but challenging to develop high-capacity

and longlifes b-FeOOH-based adsorb materials.

Graphene, an atomic-thick layer of carbon atoms, has

drawn significant attention due to its unique structure and

properties [6]. Recently, functionalized graphene as a

derivative of graphene have been explored extensively; [7,

8] the tunable functional groups on their surface can act as

binding sites to control nucleation of nanocrystals [9].

By corresponding surface modification techniques, various

materials were loaded onto the graphene sheets, such as

TiO2 nanoflower [10], Fe2O3 nanorods [11], Cu2O nano-

particles [12], etc. More importantly, the functionalized

graphene serving as molecular templates not only be

component of nanocomposites, but could also control and

improve the properties of nanocomposite materials because

of their ultrahigh electron mobility, tunable surface

chemistry, and the two-dimensional nature of their struc-

ture [13–15]. Very recently, there have been a few reports

of the synthesis of FeOOH/GO composites. For instance,

Hu et al. [16] have report on a novel infrared irradiation

approach to synthesize amorphous FeOOH with ultrafine

particles grown on mRGO nanosheets. Huang et al. [17]

have used Fe2? efficiently to reduce GO under mild con-

ditions to form FeOOH/RGO via spontaneous in situ

deposition of FeOOH nanorods onto the RGO surfaces.

Moreover, there was another report on the use of FeOOH/

GO composites as adsorbent, in which the morphology of

the composites remains to be optimized in order to achieve

higher adsorption capacities [18]. Therefore, it is highly

desirable but challenging to develop a facile and environ-

ment-friendly method to produce FeOOH/GO composites

for their large scale applications in water treatment and

others.

In this paper, we report a simple, effective and reproduc-

ible approach of preparing b-FeOOH/GO nanocomposites by

H.-J. Song (&) � X. Zhang � T. Chen

School of Materials Science and Engineering, Jiangsu

University, Zhenjiang 212013, Jiangsu, China

e-mail: songujs2014@163.com

123

J Mater Sci: Mater Electron

DOI 10.1007/s10854-014-2075-z

ultrasonic-assisted in situ hydrolysis of the precursor ferric

chloride and GO nanosheets. The b-FeOOH nanowire bun-

dles were uniformly self-assembled on the surface of GO

nanosheets. Because of advantageous combination of two-

dimensional supports with large surface areas and the highly

dispersed FeOOH nanowire bundles, the as-prepared nano-

composites exhibits high efficiency in the removal of congo

red, excellent chemical stability and mechanical strength by

introducing GO sheets when evaluated as an adsorb material.

2 Experimental section

2.1 Materials synthesis

Graphene oxide nanosheets were prepared from purified

natural graphite by the method reported by Hummers and

Offeman [19]. FeCl3�6H2O was employed as the precursor

for the synthesis of b-FeOOH. FeCl3�6H2O (5.53 g) and

6.97 g sodium dodecyl benzene sulfonate (SDBS) was first

dissolved in mixed solution of distilled water and ethanol

(50:50 mL) under magnetic stirring. After that, 1 mg of

GO were added into the aqueous solution. After 30 min

ultrasonic vibration, a brown suspension with GO homo-

geneously dispersed was obtained. The stable aqueous

suspension was then longdrawn reflux condensed in a

thermostatic water bath at the temperature of 60 �C,

ensuring the isothermal hydrolyzing of FeCl3�6H2O. After

approximately 4 h, the products were cooled to room

temperature and isolated by centrifugation, repeatedly

washed with de-ionized water and absolute ethanol several

times to remove the remaining impurities. Finally, the

products were dried in air at 50 �C for 12 h.

2.2 Materials characterization

The phase structure and phase purity of the as synthesized

powders were examined by X-ray diffraction (XRD, Hol-

land Philips X’pert X-ray diffractometer with Cu-Karadiation, k = 1.5406 A) at 40 kV, 30 mA over the 2hrange 5–70�. Raman spectra were recorded on a Dilor

Labram-1B multichannel confocal microspectrometer with

514 nm laser excitation. The morphology and microstruc-

ture of the products were further investigated by trans-

mission electron microscopy (TEM) using a JEOL JEM

2010F microscope working at 200 kV. Thermogravimetric

analysis (TGA) was conducted with a Netzsch TG 209F1

that was fitted to a air gas at 10 �C/min heating rate. Before

the tests, all the samples were carefully grinded to powders

to ensure sufficient diffusion of heat.

Congo red, a common dye in the textile industry, was

chosen as a model organic water pollutant. In a typical

adsorption test, the experiments were carried out in glass

bottles at room temperature. b-FeOOH/GO nanocompos-

ites containing different dosage were added into 30 mL of

the Congo red (100 mg L-1) solution. The suspension was

mechanically shaken at a constant speed. After desired

adsorption time, the magnetic composites were separated

and the supernatant solutions were analyzed with UV–vis

spectroscopy (Shimadzu 2450) to obtain the concentrations

of dye in the solution. The Congo red concentration was

obtained by integrating the area of the absorbance bands in

the wavelength range of 400–600 nm. b-FeOOH nanowire

bundles were also adopted as the reference to compare the

photocatalytic activity under the same experimental

conditions.

3 Results and discussion

Figure 1 shows the XRD pattern of b-FeOOH/GO nano-

composites. The diffraction pattern of GO shows a clear

peak centered at 2h = 11.9�, which is corresponding to the

[001] interlayer spacing of 0.743 nm, while other diffrac-

tion peaks match well with the (110), (200), (220), (310),

(211), (301), (321), (411), (600), (521), (002), (541) and

(730) reflections of the standard tetragonal phase of

b-FeOOH (JCPDS No. 34-1266), and no other obvious

XRD peaks due to impurities were found in the XRD

patterns. The broadening of the diffraction peaks could be

attributed to the small particle size and overlapping of the

diffraction peaks.

The morphology and microstructure of b-FeOOH/GO

nanocomposites were examined by TEM in Fig. 2,

respectively. TEM observation of the resulting products

(Fig. 2a) shows that GO nanosheets are highly transparent

with folding at the edges, suggesting a very small

Fig. 1 XRD pattern of b-FeOOH/GO nanocomposites

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123

thickness. TEM images of b-FeOOH/GO nanocomposites

(Fig. 2b) clearly illustrate that the transparent nanosheets

were decorated randomly by the nano-sized rods, and few

nanorods scattered out of the sheets, which indicates the

strong interaction between the nanorods and GO. High

magnification observation as shown in Fig. 2c, it can be

seen that the single nanosheets can be distinguished from

the backgrounds. The crumpled waves of the nanosheets

also prove that the nanorods were indeed deposited on

some transparent GO supports. It can be found that the

anchored crystal b-FeOOH nanorods are composed of

nanowire bundles, which are built on the nanorods via

oriented attachment. Further investigation of the high

magnification TEM image in Fig. 2d reveals that the length

and diameter of nanorods constructed by nanowire bundles

in the range is found to be 100–150, and 30–50 nm,

respectively.

Figure 3 shows the TG-DSC curves of b-FeOOH/GO

nanocomposites. TG curve of b-FeOOH/GO nanocom-

posites presents that the total weight loss is about 61.5 %,

containing two changes in weight between 30 and

1,000 �C. The first slow change in weight occurs at

30–200 �C, which corresponds to desorption of water and

ethanol physically absorbed on the surface of the nano-

composites. The second fast change in weight occurs at

200–450 �C, which corresponds to the decomposition of

the further desorption of the water and ethanol. The third

fast change in weight occurs at 450–900 �C, which corre-

sponds to the removal of more stable oxygen functional-

ities of GO and the oxidative decomposition of FeOOH

nanoparticles. The desorption of the water and oxygen

functionalities appears on DSC curve as an endothermic

peak. The endothermic peak at 227 and 383 �C is due to

the dehydroxylation of b-FeOOH and the exothermic peak

at 518 �C is due to the crystallization from amorphous

Fig. 2 TEM images of the as prepared GO (a); b-FeOOH/GO nanocomposites: b overall product morphology; c magnified image; d high

magnification image

Fig. 3 TG-DSC curves of b-FeOOH/GO nanocomposites

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ferric oxide to a-Fe2O3. A large exothermic peak appeared

around 818 �C which could be caused by the decomposi-

tion and/or oxidation of GO, because this peak was

accompanied by a large weight loss.

To obtain further information on the surface composi-

tion of the samples, XPS analysis was carried out. The

wide-survey XPS spectrum (Fig. 4a) of the as-prepared

nanocomposites revealed the predominant presence of

carbon, oxygen, and iron. No other hetero element was

detectable, which suggested that there were no byproducts

or unreacted precursors in the nanocomposites. The XPS

signal of Fe 2p is shown in Fig. 4b, which can be decon-

voluted into three peaks centered at 711.3, 724.7 and

718.8 eV. Among them, the peaks centered at 711.3 and

724.7 eV can be assigned to Fe 2p3/2 and Fe 2p1/2,

respectively, in good agreement with the binding energy

values of Fe3? in FeOOH [20].

Time-dependent experiments were carried out to

understand the formation process of GO-decorated

b-FeOOH nanorod nanocomposites. Figure 5 showed TEM

images of b-FeOOH/GO nanocomposites obtained with

different reaction durations. As can be seen from Fig. 5a, at

Fig. 4 a The wide-survey XPS spectrum of a-Fe2O3/GO nanocomposites obtained at 60 �C for 4 h, SDBS/Fe3? = 1:1; b Fe 2p XPS spectrum

Fig. 5 TEM images of b-FeOOH/GO nanocomposites obtained at 60 �C, SDBS/Fe3? = 1:1 for different reaction durations: a 30 min; b 1 h;

c 2 h; d 8 h

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the growth time of 0.5 h, many b-FeOOH nanorods with

diameters of about 3 nm were coated on the surface of GO

nanosheets. When the growth time was increased to 1 and

2 h (Fig. 5b, c), no appreciable change was observed in the

b-FeOOH nanorods in terms of shapes and sizes. Once the

growth time reached 8 h (Fig. 5d), it was found that many

b-FeOOH nanorods were tending to attach together to form

nanorod bundles with diameters of about 20 nm.

Based on the above experimental observations, a plau-

sible formation mechanism of b-FeOOH/GO nanocom-

posites was proposed. GO nanosheets were used as

templates for the growth of b-FeOOH nanowires, the

process was schematically shown in Fig. 6. GO nanosheets

contain abundant of epoxy, hydroxyl, and carboxyl groups

on their basal planes and edges, making them negatively

charged when those nanosheets were dispersed in aqueous

solution. Fe3? cations, formed by the dissolution of FeCl3in water, can thus favorably bind with the oxygen-con-

taining groups on GO nanosheets via electrostatic interac-

tions when they are mixed together. Upon heating the

mixture to 100 �C, hydrolysis of Fe3? accompanied via the

formation of FeOOH was expected to occur on the surface

of GO. It is worth noting that the presence of the SDBS

covering on the GO nanosheets helped to bind the iron

precursors tightly to the surface of GO nanosheets, thus

promoting the growth of FeOOH nanowires with uniform

distribution. Since the GO–SDBS had many reaction sites,

such as negatively charged groups in SDBS as well as

defects in GO, for synthesis of iron oxides, positively

charged iron precursors were more favorable for adsorption

on the GO–SDBS. In the absence of SDBS, FeOOH

nanowires with irregular distribution and aggregation on

the surface of the GO nanosheets were observed.

Figure 7a shows the adsorption spectra of congo red

solutions after being treated by b-FeOOH/GO nanocom-

posites loading amount of 1.5 g L-1 with the initial Congo

red concentration fixed at 100 mg L-1. It can be seen that

the intensity of the characteristic peak at 497 nm decreases

rapidly with the stirring time and after 30 min it completely

disappeared, suggesting the complete adsorption of Congo

red. Due to the dosage of b-FeOOH/GO nanocomposites is

an important parameter to affect the removal efficiency of

Congo red, the effect of adsorbent dosage was investigated

on Congo red removal from aqueous solutions by varying

dosage of b-FeOOH/GO nanocomposites (0, 0.2, 0.5, 0.8,

1.0 and 1.5 g L-1) at a fixed initial concentration of

100 mg L-1. The corresponding result is shown in Fig. 7b.

It can be seen that the removal efficiency of dye from the

solution was increased with the increase of adsorbent

dosage. When the dosage of b-FeOOH/GO nanocompos-

ites are 1.5 g L-1, the Congo red can be completely

removed from the water. And Fig. 7c shows the adsorption

spectra of b-FeOOH nanowire bundles. Compared with the

photocatalytic behaviors of b-FeOOH/GO nanocomposites,

the decomposition of the Congo red for b-FeOOH nano-

wire bundles is relatively slow, and the concentration

decreased to about 60 % within 30 min. The relatively high

adsorption capacity of the synthetic nanocomposites could

be attributed to GO was available for adsorption due to the

increase in active sites on the surface of b-FeOOH/GO

Fig. 6 The formation mechanism of b-FeOOH/GO nanocomposites

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123

nanocomposites with increasing adsorbent dosage. Fur-

thermore, the GO sheets possess two-dimensional struc-

ture, and nanowire bundles can be deposited on both sides

of the sheets. Thus, such integration of two-dimensional

supports with large surface areas and the highly dispersed

FeOOH nanowire bundles can be an exciting material for

the efficient removal of Congo red from water.

4 Conclusions

In summary, we have developed a simple one-pot, ‘‘green’’

method for the synthesis of the composite nanostructure of

GO and b-FeOOH nanowire bundles by in situ hydrolysis

of the precursor ferric chloride and GO. It is found that GO

were fully and homogenously coated with b-FeOOH

nanowire bundles with diameters in the range of 30–50 nm

and lengths of 100–150 nm. Furthermore, b-FeOOH/GO

nanocomposites are shown to exhibit excellent water

treatment performance with high removal capacities

towards organic dyes, advantageous over most of iron-

based materials. The superiority of this system lies in the

fact that the combination of the properties of two functional

nanoscale materials can be used to achieve a wider range of

applications.

Acknowledgments This work is supported by the National Natural

Science Foundation of China (No. 51202092, and 51372103).

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