Facile synthesis and shape control of Fe3O4 nanocrystals with good dispersion and stabilization

Article abstract of DOI:10.1039/c3ce40123e

We have reported a facile solution-based strategy for shape-controllable synthesis of Fe₃O₄ nanocrystals (NCs) with high yield, uniform shape and good stability. The low-cost polyisobutene succimide (PIBSI), Fe(oleate)₃ an

Full text of DOI:10.1039/c3ce40123e

CrystEngComm
View Article Online
View Journal | View Issue
PAPER
Facile synthesis and shape control of Fe O nanocrystals
3
4
with good dispersion and stabilization3
Cite this: CrystEngComm, 2013, 15,
366
3
Buhe Bateer, Chungui Tian, Yang Qu, Shichao Du, Taixing Tan, Ruihong Wang,
Guohui Tian and Honggang Fu*
We have reported a facile solution-based strategy for shape-controllable synthesis of Fe
O
3 4
nanocrystals
(
NCs) with high yield, uniform shape and good stability. The low-cost polyisobutene succimide (PIBSI),
Fe(oleate)
3
and paraffin oil, are separately used as surfactant, iron precursor and solvent. By controlling the
NCs with cubic, cuboctahedral and octahedral morphology can
be successfully prepared with narrow size-distribution and high crystallinity via the thermal decomposition
method. The key to realizing shape control of small size (¡15 nm) Fe nanocrystals is choosing PIBSI as
the surfactant. It played an important role in tuning the morphology of Fe NCs. Also, its characteristics
of a long chain with plentiful non-polar groups can dramatically improve the stability and dispersibility of
the Fe NCs in the reaction solvent (paraffin oil). The paraffin oil, in which Fe NCs are dispersed,
becomes a magnetic fluid with high stability.
3 4
heating rate and growth time, the Fe O
3 4
O
Received 21st January 2013,
Accepted 21st February 2013
3 4
O
DOI: 10.1039/c3ce40123e
O
3 4
3 4
O
www.rsc.org/crystengcomm
the size- and shape-controlled Fe
3
O
4
NCs with high crystal-
linity. Guardia et al. have prepared cube-octahedral iron
oxide NCs with different sizes by using Fe(acac) as iron
Introduction
1
5
Shape-controlled synthesis of nanocrystals (NCs) has become a
hot topic due to morphology-dependent electronic, optical,
3
precursors in dibenzyl ether assisted by decanoic acid, and the
particle size can be controlled by changing the amount of
1
,2
and magnetic properties and applications of nanomaterials.
In the past few decades, success has been achieved in the areas
16
decanoic acid. However, the above iron precursors are
3
4,5
of metals and metal oxides etc. Iron oxide has rich magnetic
relatively expensive and toxic, which is still a major drawback
for greener technological applications.
The first use of inexpensive and nontoxic Fe(oleate) as an
iron precursor was reported by Hyeon’s group. By this
method, the monodisperse spherical iron oxide NCs with
different sizes could be obtained. Since then, more research on
6
properties due to the dominating role of anisotropy in
17
7
magnetism. Magnetic performance of iron oxide is largely
3
influenced by the size and shape. For example, Lee et al. have
synthesized ferromagnetic iron oxide nanocubes with a high
saturation magnetization, and found it had extremely high r
relativity for highly sensitive in vivo MRI of tumors. But in
18
2
8
3 4
using iron carboxylate in the shape-control of Fe O NCs are
fact, the research on them is not well developed.
19
carried out. Maksym et al. has prepared superparamagnetic
iron oxide cubes and bipyramids with different magnetization
properties at low temperatures, in which Fe(oleate)3 was
decomposed in the presence of stabilizers (sodium oleate,
NaOl, or a mixture of NaOl, oleic acid and various oleic acid
9
Fe O can be synthesized by numerous methods. Therein,
3
4
coprecipitation and thermal decomposition are the most
common methods for synthesizing Fe O NCs. The method
3 4
has the advantages of low cost, high yields and easily scalable
production for industrial applications, but the disadvantages
of relatively poor size uniformity and long-term stability
1
0
20
salts). Hofmann et al. synthesized spherical and polyhedral
3 4
Fe O NCs by decomposing iron carboxylate in a mixture of
1
1
restraining its application.
The thermal decomposition
21
TOA and OA. Bronstein et al. demonstrated that the reaction
method is the most common method for synthesizing shape
controlled magnetic Fe O NCs. Different types of precursors,
conditions in thermal decomposition of long-chain iron
carboxylates, such as Fe(oleate) , palmitate and myristate
3
was important for controlling the size and morphology.
However, the iron oxide NCs obtained are usually larger than
3
4
1
2
13
14
such as FeCup, Fe(CO)
5
,
Fe(acac)
3
,
are used to synthesize
22
Key Laboratory of Functional Inorganic Material Chemistry, Ministry of Education of
the People’s Republic of China, Heilongjiang University, 150080 Harbin, P. R. China.
E-mail: fuhg@vip.sina.com; Fax: +86-451-86673647; Tel: +86-451-86604330
2
0 nm with poor stability and dispersibility, which would limit
largely its applications. The synthesis of small-sized Fe
less than 20 nm) with uniform morphology is still a great
challenge. Clearly, it is desirable to develop a strategy for
shape-controlled syntheses of Fe
3 4
O
(
3
Electronic supplementary information (ESI) available: Photographs of
loudspeaker use paraffin based magnetic fluid, photographs of cubic Fe
3 4
O
dispersed in different carriers, different shapes of Fe
paraffin. See DOI: 10.1039/c3ce40123e
3 4
O NCs dispersed in
3 4
O .
3
366 | CrystEngComm, 2013, 15, 3366–3371
This journal is ß The Royal Society of Chemistry 2013

View Article Online
CrystEngComm
Paper
Surfactants are significant for the shape control of
nanoscaled materials. Oleic acid and oleylamine can be
summarized as the most widely employed surfactants for the
subsequently cooled to room temperature and the paraffin oil
based cubic Fe O magnetic fluid is then prepared. The
3 4
control experiments were carried out by changing the heating
rate, heating temperature (310 and 350 uC) and adding
polyisobutene succimide (0.25 and 0.75 g) without varying
the other conditions. By changing the heating rate to 5 uC
2
3
shape-controlled synthesis of Fe
3 4
O NCs. However, their
poor stability and dispersibility, short molecular chains
2
4
restrain their application in oil based magnetic fluid. So,
for overcoming the shortages of the oleic-type surfactants in
shape control of NCs and improving the compatibility of NCs
simultaneously, it is of great importance to find a suitable
amphipathic surfactant with both polar and nonpolar long
chain groups. Polyisobutene succimide (PIBSI) is a stable oil-
soluble polymer surfactant with a polar head and two long
chain nonpolar tails. The polar groups may help the surfactant
to be well adsorbed on the magnetic NCs, and the nonpolar
long chains can improve the stability and dispersibility of the
magnetic NCs to prepare magnetic fluid. Therefore, PIBSI
entirely meets the requirements of the desirable surfactant,
but it is rarely used in the preparation of nanomaterial.
Based on the above considerations, we designed a thermal
2
1
min , the cuboctahedral Fe O magnetic fluid can be
3
4
2
1
obtained. Changing the heating rate to 2 uC min
and
maintaining at 330 uC for 3 h, the octahedral Fe O particles
3
4
can be fabricated.
Characterization
X-ray powder diffraction (XRD) patterns were obtained by a
Bruker D8 diffractometer using Cu Ka radiation (l = 1.5406 Å).
Transmission electron microscopy (TEM) test was performed
on a JEM-2100 electron microscope (JEOL, Japan) with an
acceleration voltage of 200 kV. Carbon coated copper grids
were used as the sample holders. Magnetization of Fe O4
3
magnetic NCs and magnetic fluids was measured at 300 K with
a Lake Shore Vibrating Sample Magnetometer Model 7404,
applying a field strength of up to 20 kOe.
decomposition method of Fe(oleate) and PIBSI dissolved in
3
3 4
paraffin oil for shape-controlled synthesis of Fe O NCs. The
morphology of the products can be easily controlled by
adjusting the reaction conditions, such as heating rate and
growth time of the NCs. In this way, we can easily prepare the
Results and discussion
Shape-control of Fe O NCs
3
4
3 4
cubic, cuboctahedral and octahedral Fe O NCs with small
size, narrow size distribution, good magnetic properties and
dispersion. In addition, the materials used in the method are
very cheap, which make the method very simple and easy to
industrialize.
The formation of NCs is a crystallization process on the
nanometer scale. The solvent–thermal reaction of Fe(oleate)
is the primary step in the synthesis of Fe NCs, and this
process (Scheme 1) includes the formation of thermal free
radicals, the resultant free radicals addition and/or substitu-
3
O
3 4
tion and the combination of Fe(oleate) containing free
3
2
5
radicals. Here, PIBSI is used as surfactant, the nucleation
and growth speed are controlled by varying the heating rate
and reaction time. The NCs can be tuned in the form of
small size cubic, cuboctahedral, and little truncated octahe-
Experimental
2
6
Chemicals
3 2
Ferric chloride (FeCl ?6H O, 99%), ethanol, sodium oleate,
dral shapes. TEM images of the cubic Fe
Fig. 1. We can see from Fig. 1A and B that the cubic Fe
3
O
4
NCs are shown in
NCs
deionized water and heptane were purchased from Sinopharm
Chemical Reagent Co. Ltd. Polyisobutene succimide (PIBSI),
paraffin oil, polyalphaolefin (PAO-40) and polyisobutene
3 4
O
are about 10 nm in size. The lattice fringe of {400} planes with
the interplanar distance of 0.208 nm is shown in Fig. 1C. In
Fe O cube, the {400} planes are entirely parallel to the {100}
(PB450, molecular weight 450) were purchased from China
3
4
Petrochemical Corporation.
planes of Fe O . At the same time, the exposure of distinct
3
4
surfaces offers an ideal platform for studying the surface-
related properties. The equilibrium crystal structure with
minimum surface energy increasingly dominates the shape
Synthesis of Fe(oleate)
The Fe(oleate) was prepared by reaction of sodium oleate and
In a typical synthesis, 40 mmol of FeCl , 120 mmol of
sodium oleate, 100 mL of H O, 100 mL of ethanol, and 200 mL
3
3
2
0
FeCl
3
.
3
of the Fe
The original Fe
111} faces. The gradual decrease in monomer concentration
3
O
4
NCs within increasing monomer concentration.
2
3 4
O
NCs are faceted with both the {100} and
of hexane were mixed and heated at 60 uC for 4 h. The
{
Fe(oleate) was obtained by separation of the water phase and
3
triggered the difference in the growth rate of various planes.
subsequent evaporation of the residual ethanol and hexane at
Under this circumstance, a relative faster growth along the
7
0 uC and water at 110 uC.
Shape-controlled synthesis of Fe
The pre-prepared 5 g of Fe(oleate)
21
[111] directions at the relative fast heating rate (10 uC min
)
results in the eventual formation of cube-shaped NCs with
3
O
4
NCs
, 50 mL of paraffin oil and
.5 g of PIBSI were mixed and magnetically stirred under
3
0
2
protection of N in a three-necked flask and heated firstly to
1
1
N
50 uC for 1 h, and then heated to 330 uC with a heating rate of
2
1
0 uC min and maintained at this temperature for 2 h under
flow with continuous stirring. The reaction mixture was
3 4
Scheme 1 Schemed procedure process for synthesis of Fe O .
2
This journal is ß The Royal Society of Chemistry 2013
CrystEngComm, 2013, 15, 3366–3371 | 3367

View Article Online
Paper
CrystEngComm
Fig. 1 TEM images of cubic Fe
3
O
4
NCs (11 nm), (A) and (B) at different
Fig. 2 TEM images of iron oxide NCs synthesized by varying the relative
magnifications. (C) Higher-magnification TEM image (D) corresponding SAED
pattern.
concentration of PIBSI and reaction temperature (A) 0.25 g per 50 ml (B) 0.75 g
per 50 ml and syntheses at the reaction temperature of (C) 310 uC, (D) 350 uC.
terminated{100} facets. The NCs tend to be bounded by {100}
planes, and thus form nanocubes, which has also been
solution. The changes of shape and size of the Fe
3 4
O NCs are
shown in Fig. 2. The size distribution of the Fe O NCs was
3
4
2
7,28
observed for synthesis of other magnetic nanocrystals.
Fe O has a cubic inverse spinel structure with a space
very wide with a variety of morphologies. In addition, due to
the decrease of the amount of surfactant, the Fe NCs can’t
O
3 4
3
4
2
2
grouping of Fd3-m. The unit cell of Fe
which are regular cubic close packed along the [110] direction.
The lattice constant is a = 0.839. The crystal structure of Fe
3
O
4
has 32 O ions,
be well dispersed in hexane (Fig. 2A). Secondly, we increased
the surfactant amount (Fig. 2B). In this case, although the
Fe O NCs are well dispersed in solution, they do not exhibit a
3 4
3
O
4
consists of two different iron sites: tetrahedral sites occupied
by Fe(III) and octahedral sites occupied by both Fe(II) and
uniform size and morphology. PIBSI, which is composed of
two long non-polar tails and a polar head, is better than the
commonly used oleic acid in shape control. The polar heads
Fe(III). Generally, Fe
3 4
O crystals are overlaid with octahedral
and mixed octahedral–tetrahedral layers along the [111]
direction. The high-index planes usually have higher surface
energy.
The sequence of c(111) , c(100) , c(110) , c(220) for the
face-centered-cubic phase can be generated from the distance
between those planes and the central Wulff’s point. As a result,
attach themselves to Fe O NCs, while the long non-polar tails
3 4
2
9
keep themselves in the reaction solution (paraffin oil). When
PIBSI (MW = 1000) is in a high concentration, a large amount
of long non-polar tails restrain the nucleus from regular
growing.
To understand the formation process of the cubic struc-
tures, the experiments were monitored by drawing out 1 mL of
reaction solution at 310 and 350 uC, the TEM image (Fig. 2C)
shows that the NCs at 310 uC have no regular shape because
the bubbling effect is an important factor of the formation of
3 4
the Fe O NCs are surrounded mostly by {111}, and exhibit
octahedral morphology. However, the crystal shape is defined
by the ratio (R) of growth rate in the [100] direction to that in
the [111] direction. Thus, faster growth along the [100]
direction can lead to octahedral particles, while faster growth
along the [111] direction can generate cubic particles. To get
various morphologies, it is necessary to control the growth rate
of different facets of the nuclei. The inherent crystal structure
during the initial nucleation stage and the subsequent growth
stage, which governs the growth rate of different facets of the
nuclei, is greatly affected by reaction conditions, such as
surfactant, temperature, and time. That means the crystal
3
2
uniform Fe O . The main components of liquid paraffin is a
3
4
mixture of normal alkanes from C16 to C20, there are no
bubbles at 310 uC because it doesn’t reach the boiling point of
the most abundant alkanes C18 in the paraffin oil. At 330 uC,
most of the Fe O NCs are uniform with a cubic shape because
3
4
there is already a lot of bubbles at this temperature. The
formation of boiling bubbles has more influence on the
nucleation of NCs than on their growth. Research proves that
solvent boiling bubbles can substantially promote the primary
nucleation of iron oxide NCs, which can successfully suppress
secondary nucleation and yield mono-dispersed NCs products.
However, at 350 uC (Fig. 2D), an excess of bubbles makes the
NCs continuously grow up to nearly 20 nm. We have
3
0
structure can be controlled by tuning these external factors.
Surfactants have a great effect on the shape and size of
3
1
Fe O NCs. In our research, the Fe O NCs with three
3
4
3 4
different shapes were synthesized with PIBSI as surfactant.
First of all, we decreased the surfactant amount in the reaction
3
368 | CrystEngComm, 2013, 15, 3366–3371
This journal is ß The Royal Society of Chemistry 2013

View Article Online
CrystEngComm
Paper
Fig. 4 X-ray diffraction of the Fe
octahedral Fe NCs.
3
O
4
NCs (a) cubic, (b) cuboctahedral and (c)
3 4
O
Fig. 3 TEM and HRTEM images of (A and B) cuboctahedral (13 nm) and (C and
3 4
D) octahedral (15 nm) Fe O NCs.
cuboctahedral NCs including six {111} faces and six {100} faces
is obtained. Fig. 3C and D are respectively TEM and HRTEM
3 4
images of octahedral Fe O NCs of about 15 nm. And the much
performed the synthesis at low temperature below 300 uC
primarily (290 uC). The product has a small size about 2 nm
and poor crystallinity (Fig. S1, ESI ). This result indicates the
3
large effect of temperature on the resulting product.
With identical decomposition temperature and surfactant
2
1
lower heating rate (2 uC min ) results in a much lower
concentration of crystal nucleus (Scheme 2). The {100} facets
grow with enough iron precursor concentration at the
beginning of the growth stage. But after the formation of
cubic NCs, the {111} faces grow relatively faster than the {100}
facets with enough iron precursor concentration, and the {100}
facets tend to be bounded by {111} faces until an octahedral
Fe O NP is formed. The dependence of the shape on the
amount, cuboctahedral and octahedral Fe
synthesized by changing the heating rate and reaction time
3 4
Fig. 3). Fig. 3A is a TEM image of typical cuboctahedral Fe O
3 4
O NCs can be
(
NCs with size about 13 nm. The NCs are monodispersed with
the largest vertex-to-vertex distance. Fig. 3B clearly shows the
lattice fringe of {111} planes with the interplanar distance of
3 4
heating rate and reaction time is shown in Scheme 2.
The structure of Fe NCs is examined by XRD, which is
3 4
O
shown in Fig. 4. All the diffraction peaks can be indexed as the
face-centered magnetite (Fe O ) crystallite (JCPDS card No. 74-
0
.478 nm. As shown, a slow nucleation caused by a lower
2
1
heating rate (5 uC min ) results in a low concentration of
crystal nucleus (Scheme 2), and the slow heating rate makes
the {111} faces form at a relatively fast growth compared with
that of the {100} facets, but there is not enough iron precursor
for the formation of all the {111} faces. In this case, a
3 4
0
748), indicating the formation of magnetite NCs. The
diffraction peaks of the as-synthesized Fe NCs at 18.1,
0.0, 35.5, 37.0, 43.0, 53.0, 57.0 and 62.6 are respectively
ascribed to the (111), (220), (311), (222), (400), (422), (511) and
3 4
O
3
(
440) planes of the magnetite, which is in accordance with
3
3
pure spinel Fe
stronger as the morphology of Fe O
3 4
3
O
4
.
Moreover, the {111} facet becomes
NCs transfers from cubic
to cuboctahedral and octahedral, which is consistent with the
above explanation of determining the plane of the three
shapes. Actually, there are some weak diffraction peaks at 24u
in Fig. 4. They may be caused by the presence of trace amounts
of Fe O which may reduce the saturated magnetization of the
2
3
sample. More work should be performed to study the effect of
this.
Bulk Fe O is ferrimagnetic at room temperature, but below
3
4
a critical particle size, it becomes superparamagnetic and
displays zero coercivity with no remanence. Magnetization
properties of the as-prepared three shapes of Fe
investigated at 300 K and 20 kOe by measuring magnetization
curves (Fig. 5). The hysteresis loops for Fe display zero
3 4
O NCs are
Scheme 2 Schematic illustration of the shape control of Fe
3
O
4
through
3 4
O
adjusting the heating rate.
coercivity with no remanence, indicating the superparamag-
This journal is ß The Royal Society of Chemistry 2013
CrystEngComm, 2013, 15, 3366–3371 | 3369

View Article Online
Paper
CrystEngComm
Fig. 6 Magnetization hysteresis curve (a) the viscosity versus at temperature (b)
stability index (c) and of magnet adsorption before and after (d) the Fe
in paraffin (10%).
3 4
O NCs
3 4
Fig. 5 Magnetic hysteresis curves of the Fe O NCs at 300 K (a) cubic, (b)
3 4
cuboctahedral and (c) octahedral Fe O NCs.
netic behaviour of the samples because the size of all magnetic
particles is under the critical particle size of superparamag-
show the magnetic fluid exhibits relatively big viscosity and
low viscosity–temperature relation. The density of the Fe O4
3
netic (the octahedral Fe
5 nm). All the samples show a typical superparamagnetic
behaviour with negligible coercivity and remanence, which is
3
O
4
NCs with the largest size of about
magnetic fluid remains 0.951 even for 90 days (Fig. 6c), and no
1
Fe O NCs are precipitated out, which indicates that the PIBSI-
3
4
coated Fe O are not separated under a long time strong
3
4
3
4
often observed at room temperature with magnetite NCs.
The saturation magnetization of the three shapes of Fe O is
magnetic field (Fig. S2, ESI ).
3
3
4
The magnetic fluid has good stability due to the super-
2
1
respectively 61.73, 65.43 and 67.99 emu g , smaller than that
dispersibility of cubic Fe
3 4
O NCs coated with PIBSI. The polar
2
1 35,36
of the theoretical value of bulk magnetite (94 emu g ),
which can be attributed to the small size of the NCs. Due to the
bigger size of the Fe NCs, the saturation magnetization of
them becomes larger.
heads of PIBSI attach themselves to the Fe O NCs, while the
3
4
long hydrocarbon (non-polar) tails can keep suspension of
PIBSI in either low or high-boiling point solutions (Fig. S3,
ESI ). The magnetic fluids prepared by this method have the
3
3 4
O
advantages of facile handling, low cost and long-term stability.
The magnetic fluids made of cuboctahedral and octahedral
3 4
Application of cubic Fe O NCs in magnetic fluids
3
7
Magnetic fluids are colloidal dispersions of magnetic NCs. At
present, most of the applications of magnetic NCs use
Fe
3
O
4
NCs have a good dispersion and stability as well (Fig. S4,
ESI
3
).
3 4 3 4
polydispersity spherical Fe O NCs. The Fe O NCs with a
3
8
larger particle size are easy to settle. Generally, magnetic
fluids have been prepared by coating the magnetic particle
3
9
Conclusions
with a fatty acid such as oleic acid. There is a problem since
the oleic-type surfactant only adheres to the surface of the fine
In summary, we have demonstrated a one-pot method to
synthesize cubic, cuboctahedral and octahedral Fe O NCs
3 4
with polyisobutene succimide as the surfactant. The particles
have a small size (10, 13 and 15 nm for cubic, cuboctahedral
4
0
ferromagnetic particles through electrostatic attraction. So
the surfactant would dissociate from the particle surface if
they are affected by an external effect such as a polar solvent or
the thermal and applied external current, causing agglomera-
tion of the particles. Thus, the magnetic fluids prepared by the
conventional method can’t keep a stable dispersion after long-
and octahedral Fe
The saturation magnetization of the three kinds of Fe
3
O
4
NCs), good stability and dispersibility.
NCs
3 4
O
2
1
4
1,42
is respectively 61.73, 65.43 and 67.99 emu g . They can be
well-dispersed in either low or high-boiling point solutions,
such as hexane, paraffin oil, polyalphaolefin (PAO-40) and
polyisobutene (PB450) to obtain magnetic fluids. The stability
test of paraffin oil-based cubic Fe O NCs magnetic fluid
term utilization.
The magnetic property of the stable magnetic fluids made of
the cubic Fe O NCs has been determined. Fig. 6a shows the
3
4
initial magnetization curve of the magnetic fluid with 10%
mass percentage of Fe NCs in paraffin. We can learn from
3 4
O
3
4
Fig. 6a that the magnetization of the magnetic fluid increases
with the increase of the magnetic field (H) simultaneously
until it tends to be saturated with no remanence. Its saturation
magnetization is 6.2 emu g . The viscosity dependence of the
magnetic fluid on temperature is analyzed. Data in Fig. 6b
shows that it was stable at room temperature for more than 90
days.
2
1
3
370 | CrystEngComm, 2013, 15, 3366–3371
This journal is ß The Royal Society of Chemistry 2013

View Article Online
CrystEngComm
Paper
1
9 W. W. Yu, J. C. Falkner, C. T. Yavuz and V. L. Colvin, Chem.
Commun., 2004, 2306.
Acknowledgements
We gratefully acknowledge the support of this research by the
Key Program Projects of the National Natural Science
Foundation of China (No. 21031001), the National Natural
Science Foundation of China (No. 51272070, 91122018,
20 M. V. Kovalenko, M. I. Bodnarchuk, R. T. Lechner,
G. Hesser, F. Sch ¨a ffler and W. Heiss, J. Am. Chem. Soc.,
2007, 129, 6352.
21 C. Hofmann, I. Rusakova, T. Ould-Ely, D. Prieto-Centuri o´ n,
K. B. Hartman, A. T. Kelly, A. L u¨ ttge and K. H. Whitmire,
Adv. Funct. Mater., 2008, 18, 1661.
21201058, 51102082), the Cultivation Fund of the Key
Scientific and Technical Innovation Project, Ministry of
Education of China (No. 708029), Special Research Fund for
the Doctoral Program of Higher Education of China
22 L. M. Bronstein, J. E. Atkinson, A. G. Malyutin, F. Kidwai, B.
D. Stein, D. Morgan, J. M. Perry and J. A. Karty, Langmuir,
2011, 27, 3044.
(20112301110002).
2
2
2
2
2
2
2
3 H. Wang, Y. Wu, Y. Bai, W. Zhou, Y. An, J. Li and L. Guo, J.
Mater. Chem., 2011, 21, 10189.
4 H. G. Cha, C. W. Kim, S. W. Kang, B. K. Kim and Y. S. Kang,
J. Phys. Chem. C, 2010, 114, 9802.
5 D. Gatteschi, A. Caneschi, L. Pardi and R. Sessoli, Science,
Notes and references
1
2
3
4
H. Zhang, S. Peng, C. b. Rong, J. P. Liu, Y. Zhang, M.
J. Kramer and S. Sun, J. Mater. Chem., 2011, 21, 16873.
G. M. Cragg, P. G. Grothaus and D. J. Newman, Chem. Rev.,
1
994, 265, 1054.
6 T. Mokari, M. Zhang and P. Yang, J. Am. Chem. Soc., 2007,
29, 9864.
1
2009, 109, 3012.
7 N. Bao, L. Shen, W. An, P. Padhan, C. H. Turner and A. Gupta,
Chem. Mater., 2009, 21, 3458.
8 Y. Wei, R. Klajn, A. O. Pinchuk and B. A. Grzybowski, Small,
Y. Li, Y. Jiang, M. Chen, H. Liao, R. Huang, Z. Zhou, N. Tian,
S. Chen and S. Sun, Chem. Commun., 2012, 48, 9531.
M. D’Arienzo, J. Carbajo, A. Bahamonde, M. Crippa,
S. Polizzi, R. Scotti, L. Wahba and F. Morazzoni, J. Am.
Chem. Soc., 2011, 133, 17652.
2008, 4, 1635.
9 U. Schwertmann and R. M. Cornell, Iron Oxides in the
Laboratory, Wiley-VCH, Weinheim, 2000.
5
6
M. H. Huang and P. H. Lin, Adv. Funct. Mater., 2012, 22, 14.
J. Mohapatra, A. Mitra, D. Bahadur and M. Aslam, CrystEngComm,
3
3
0 C. Yang, J. Wu and Y. Hou, Chem. Commun., 2011, 47, 5130.
1 C. H. Ho, C. P. Tsai, C. C. Chung, C. Y. Tsai, F. R. Chen, H.
J. Lin and C. H. Lai, Chem. Mater., 2011, 23, 1753.
2 J. Lynch, J. Zhuang, T. Wang, D. LaMontagne, H. Wu and Y.
C. Cao, J. Am. Chem. Soc., 2011, 133, 12664.
2
013, 15, 524.
L. Zhang, J. Wu, H. Liao, Y. Hou and S. Gao, Chem. Commun.,
009, 4378.
N. Lee, Y. Choi, Y. Lee, M. Park, W. K. Moon, S. H. Choi and
T. Hyeon, Nano Lett., 2012, 12, 3127.
7
8
9
3
3
3
2
3 G. Xie, P. Xi, H. Liu, F. Chen, L. Huang, Y. Shi, F. Hou,
Z. Zeng, C. Shao and J. Wang, J. Mater. Chem., 2012, 22, 1033.
4 T. J. Daou, G. Pourroy, S. Begin-Colin, J. M. Greneche,
C. Ulhaq-ouillet, P. Legare, P. Bernhardt, C. Leuvrey and
G. Rogez, Chem. Mater., 2006, 18, 4399.
A. S. Arico, P. Bruce, B. Scrosati, J. M. Tarascon and W.
V. Schalkwijk, Nat. Mater., 2005, 4, 366.
1
1
1
0 H. Lee, E. Lee, D. K. Kim, N. K. Jang, Y. Y. Jeong and S. Y. Jon,
J. Am. Chem. Soc., 2006, 128, 7383.
1 A. Shavel, B. Rodr ´ı guez-Gonz ´a lez, J. Pacifico, M. Spasova,
M. Farle and L. M. Liz-Marz ´a n, Chem. Mater., 2009, 21, 1326.
2 J. Rockenberger, E. C. Scher and P. A. Alivisatos, J. Am.
Chem. Soc., 1999, 121, 11595.
35 X. L. Liu, H. M. Fan, J. B. Yi, Y. Yang, E. S. G. Choo, J. M. Xue,
D. D. Fan and J. Ding, J. Mater. Chem., 2012, 22, 8235.
36 M. F. Casula, A. Corrias, P. Arosio, A. Lascialfari, T. Sen,
P. Floris and I. J. Bruce, J. Colloid Interface Sci., 2011, 357, 50.
37 N. Jain, X. Zhang, B. S. Hawkett and G. G. Warr, ACS Appl.
Mater. Interfaces, 2011, 3, 662.
1
1
3 S. Sun and H. Zeng, J. Am. Chem. Soc., 2002, 124, 8204.
4 Q. Jia, J. Zeng, R. Qiao, L. Jing, L. Peng, F. Gu and M. Gao, J.
Am. Chem. Soc., 2011, 133, 19512.
38 B. Qin, Z. Zhao, R. Song, S. Shanbhag and Z. Tang, Angew.
Chem., Int. Ed., 2008, 47, 9875.
1
1
1
1
5 H. Qu, H. Ma, A. Riviere, W. Zhou and C. J. O’Connor, J.
Mater. Chem., 2012, 22, 3311.
6 G. Wang, W. Lu, J. Li, J. Choi, J. B. Park, M. K. Ryu and
K. Lee, Small, 2006, 2, 1436.
7 P. Guardia, N. Perez, A. Labarta and X. Batlle, Langmuir, 2010, 26,
39 P. Yecko, W. K. Lee, A. D. Trubatch and M. Vieira, J. Magn.
Magn. Mater., 2011, 323, 1288.
40 B. Wang, B. Wang, P. Wei, X. Wang and W. Lou, Dalton
Trans., 2012, 41, 896.
41 J. A. Gomes, G. M. Azevedo, J. Depeyrot, J. Mestnik-Filho, G.
J. D. Silva, F. A. Tourinho and R. Perzynski, J. Magn. Magn.
Mater., 2011, 323, 1203.
5843.
8 J. Park, K. An, Y. Hwang, J. G. Park, H. J. Noh, J. Y. Kim, J.
H. Park, N. M. Hwang and T. Hyeon, Nat. Mater., 2004, 3,
42 S. Feng, Z. Ren, Y. Wei, B. Jiang, Y. Liu, L. Zhang, W. Zhang
and H. Fu, Chem. Commun., 2010, 46, 6276.
891.
This journal is ß The Royal Society of Chemistry 2013
CrystEngComm, 2013, 15, 3366–3371 | 3371