Journal of Alloys and Compounds 433 (2007) 216–220
Hydrothermal synthesis and characterization of ␣-FeOOH and
␣-Fe
2
O
3
uniform nanocrystallines
Xiaohe Liu
a,b
, Guanzhou Qiu
b
, Aiguo Yan
b
, Zhong Wang
a
, Xingguo Li
a,∗
a
College of Chemistry & Molecular Engineering, Peking University, Beijing 100871, People’s Republic of China
b
Department of Inorganic Materials, Central South University, Changsha, Hunan 410083, People’s Republic of China
Received 18 April 2006; received in revised form 4 June 2006; accepted 6 June 2006
Available online 24 July 2006
Abstract
Inorganic nanoparticles with controlled size and shape are technologically important due to the strong correlation between these parameters
and magnetic, electrical, and catalytic properties. Herein we demonstrated that under appropriate conditions, rodlike ␣-FeOOH (goethite) and
porous fusiform ␣-Fe
2
O
3
(hematite) uniform nanocrystallines could be selectively synthesized in large quantities via a facile surfactant sodium

interesting electrical [7], magnetic [8], and catalytic [9] proper-
ties and wide variety of potential applications in various fields
∗
Corresponding author. Tel.: +86 10 62765930; fax: +86 10 62765930.
E-mail address: [email protected] (X. Li).
such as electro-optic materials [10], sorbents [11], pigments
[12], ion exchangers [13], and magnetic resonance imaging
(MRI) [14], particularly in the field of catalysis [15]. Amongst
the readily available carbon monoxide oxidation catalysts, iron
oxide-based materialshave beenfound tobe especiallyattractive
candidates as cheap and efficient catalysts [16]. Various pro-
cedures including wet chemical [17–20], electrochemical [21],
thermal decomposition techniques [22], and chemical oxidation
in polymer [23] have been successfully employed for the syn-
thesis of iron oxides nanocrystallines. As is well known, the
properties of iron oxides nanocrystallines sensitively depend on
their size and shape. In order to improve the functional proper-
ties such as catalytic activity, it is significant challenge to control
the size and shape of iron oxides nanocrystallines. Porous iron
oxides nanoparticles may provide some immediate advantages
over their solid counterparts because of their relatively low den-
sities and large surface areas for their applications. In recent
years, Oca
˜
na and co-workers have synthesized uniform iron
oxides nanoparticles via aerial oxidation and forced hydroly-
sis methods [24], however, the products of such synthesis often
involved complicated process or produced in low quantities.
In this paper, we demonstrated that rodlike goethite (␣-
FeOOH) and porous fusiform hematite (␣-Fe

), and sodium dodecyl sulfate (SDS) were of ana-
lytical grade, and which were used without further purification.
2.1. Preparation of iron oxides nanocrystallines
In a typical procedure, pure sodium dodecyl sulfate (0.001 mol) and hydrated
ferrous chloride (FeCl
2
·4H
2
O, 0.001 mol) were firstly dissolved in distilled
water to form a salmon pink micellar solution under vigorous stirring at room
temperature. Then, sodium borohydride solution (NaBH
4
, 0.5 mmol) was added
to the salmon pink solution. With the introduction of sodium borohydride solu-
tion, the color of mixed micellar solution turned immediately from salmon pink
to black. Next, the mixture was transferred to a Teflon-lined stainless steel auto-
clave of 50 mL capacity. Finally, the autoclave was filled with distilled water
up to 75% of the total volume, sealed and maintained at 140
◦
C for 4, 8, 12,
and 24 h, respectively. After the heating treatment, the autoclave was allowed to
cool down to room temperature naturally. The resulting products were filtered,
washed with distilled water and absolute ethanol, and finally dried in vacuum at
50
◦
C for 6 h.
2.2. Characterization
The rodlike ␣-FeOOH (goethite) and porous fusiform ␣-Fe
2
O

goethite (␣-FeOOH) iron oxide nanocrystallines obtained for 4,
8, and 12 h, respectively. The XRD pattern (Fig. 1a) of sample
shows that the goethite (␣-FeOOH) iron oxide nanocrystallines
Fig. 1. The evolution of the XRD patterns of the ␣-FeOOH nanocrystallines
obtained at 140
◦
C for different reaction time: (a) 4 h; (b) 8 h; (c) 12 h. (
*
␣-
Fe
2
O
3
).
obtained for 4 h were poorly crystallized. With the elongation of
reaction time, the XRD patterns of samples at the whole process
show that the crystallinities of the samples were continuously
improved. When the samples maintained for 8 h, the XRD pat-
tern of the sample is shown in Fig. 1b. The main diffraction
peaks of ␣-FeOOH are clear observed in the patterns. When
the reaction time prolonged to 12 h (in Fig. 1c), the peaks of
␣-FeOOH become slightly weak, along with the weakening of
␣-Fe
2
O
3
peaks, which indicates the transition from ␣-FeOOH
to ␣-Fe
2
O

nanocrystallines
obtained at 140
◦
C for 24 h.
218 X. Liu et al. / Journal of Alloys and Compounds 433 (2007) 216–220
Fig. 3. (A) TEM image of the sample produced at 140
◦
C for 4 h. (B) TEM image of the sample produced at 140
◦
C for 8 h. The insets of (A and B) show the SAED
pattern of the rodlike ␣-FeOOH nanocrystallines taken on a mass of ␣-FeOOH nanocrystallines.
observed, indicating the hematite (␣-Fe
2
O
3
) iron oxide success-
fully synthesized under current experimental conditions.
The size and morphology of the rodlike ␣-FeOOH (goethite)
and porous fusiform ␣-Fe
2
O
3
(hematite) nanocrystallines were
further examined by transmission electron microscopy (TEM).
Fig. 3A shows the typical TEM photograph of ␣-FeOOH
nanocrystallines obtained at 140
◦
C for 4 h through a surfac-
tant SDS assisted hydrothermal synthetic route, and its select
area electron diffraction pattern indicates the sample A is poorly

porous fusiform ␣-Fe
2
O
3
(hematite) nanocrystallines. Fusiform
␣-Fe
2
O
3
(hematite) nanocrystallines were obtained when the
reactants were treated at 140
◦
C for 24 h, as shown in Fig. 4B.
TEM observations indicates that about 100% of the products are
fusiform ␣-Fe
2
O
3
nanocrystallines whose diameter ranges from
about 50 to 70 nm with a length of up to ∼200 nm. There was an
interesting change in the morphology of the sample of ␣-Fe
2
O
3
nanocrystallines. With careful observation, the fusiform ␣-
Fe
2
O
3
nanocrystallines can be made up from many porous struc-

approach. These fusiform ␣-Fe
2
O
3
nanocrystallines have a
mean diameter of 60 nm and length of up to ∼200 nm, which
agree well with the TEM results. Fig. 5B is a higher magnifi-
cation SEM image obtained from a selected area of Fig. 5A.
Herein, fusiform ␣-Fe
2
O
3
nanocrystallines with many porous
structures can be clearly observed. The chemical compositions
of the as-prepared fusiform ␣-Fe
2
O
3
nanocrystallines have been
investigated by means of EDS. Results from EDS spectra (Fig. 6)
show that the fusiform ␣-Fe
2
O
3
nanocrystallines contain Fe and
O, and no contamination elements are detected. The atomic ratio
of Fe and O matched their stoichiometries quite well.
Associating all those results, the whole reaction to form the
␣-FeOOH and ␣-Fe
2

2
O → 4FeOOH ↓+8H
+
(3)
2FeOOH → Fe
2
O
3
↓+H
2
O (4)
Soluble ferrous chlorides will firstly dissociate in water into fer-
rous ions, which then react with sodium borohydride to form
ultrafine iron particles. The reduction of transition metal ions
for the production of ultrafine metal particles by BH
4
−
is a
ubiquitous reaction. The ultrafine iron particles may be redis-
solved under acidic conditions. Subsequently, rodlike ␣-FeOOH
(goethite) nanocrystallines will gradually form under surfactant
SDS assisted hydrothermal conditions. With the reaction time
prolonged, rodlike ␣-FeOOH nanocrystallines appear agglom-
erate and form fusiform nanocrystallines. Finally, the ␣-FeOOH
Fig. 6. The EDS spectra of the as-prepared porous fusiform ␣-Fe
2
O
3
nanocrys-
tallines.

O
3
phase. When the reaction time
prolonged to 24 h, we successfully synthesized porous fusiform
hematite (␣-Fe
2
O
3
) iron oxide nanocrystallines with good uni-
formity. The synthetic strategy presented here may have a good
prospect in the future application and provide an effective route
to synthesize other metal oxide nanocrystallines. Owing to the
excellent physical properties of the iron oxides, it is expected
the rodlike ␣-FeOOH (goethite) and porous fusiform ␣-Fe
2
O
3
(hematite) uniform nanocrystallines exhibit some important
applications in, e.g., sensors, magnetic media, catalytic fields,
etc.
Acknowledgements
Financial support of this work by National Natural Science
Foundation of China (Grant no. 50504017) and Hunan Provin-
cial Natural Science Foundation of China (Grant no. 05JJ30104)
is gratefully acknowledged.
References
[1] O.Y. Min, J L. Huang, C.L. Cheung, C.M. Lieber, Science 292 (2001) 702.
[2] X.H. Liu, Mater. Chem. Phys. 91 (2005) 212.
[3] H. Yu, J. Li, R.A. Loomis, L W. Wang, W.E. Buhro, Nat. Mater. 2 (2003)
517.

[22] J. Cheon, N J. Kang, S M. Lee, J H. Lee, J H. Yoon, S.J. Oh, J. Am.
Chem. Soc. 126 (2004) 1950.
[23] R. Ziolo, E.P. Giannelis, B.A. Weinstein, M.P. O’Horo, B.N. Ganguly, V.
Mehrotra, M.W. Russel, D.R. Huffman, Science 257 (1992) 219.
[24] R. Pozas, M. Oca
˜
na, M.P. Morales, C.J. Serna, J. Colloid Interface Sci. 254
(2002) 87.