Solvothermal synthesis of NiCo alloy icosahedral nanocrystals

Article abstract of DOI:10.1021/ic201763j

New dimensional NiCo alloy icosahedral nanocrystals with controllable size have been first reported and synthesized through an Ostwald ripening process in a template-absent solvothermal reaction system. The proposed synthesis is corroborated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction analysis (XRD), energy-dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS). The as-obtained NiCo icosahedral nanocrystals exhibit the size- and component-dependent magnetic behaviors. The coercivity (H_c) depends on both the magnetocrystalline and structure anisotropy, and the saturation magnetizations (M_s) decided by the content of Co. H_c decreases from 189.02 to 147.95 Oe with the increase of the icosahedral NCs size from 200 to 850 nm. Especially, the H_c of the icosahedral NCs at 157.38 Oe is higher than that of nanospheres at 104.02 Oe. In addition, M_s and H_c increased with the increasing Co content. It can be an ideal building block for applications in magnetic media, sensors, and other devices.

Full text of DOI:10.1021/ic201763j

Article
pubs.acs.org/IC
Solvothermal Synthesis of NiCo Alloy Icosahedral Nanocrystals
Mingzhu Cheng, Ming Wen,* Shiqing Zhou, Qingsheng Wu,* and Baolei Sun
Department of Chemistry, Tongji University, Shanghai 200092, The People’s Republic of China
*
S Supporting Information
ABSTRACT: New dimensional NiCo alloy icosahedral nano-
crystals with controllable size have been first reported and
synthesized through an Ostwald ripening process in a
template-absent solvothermal reaction system. The proposed
synthesis is corroborated by scanning electron microscopy
(
SEM), transmission electron microscopy (TEM), X-ray
diffraction analysis (XRD), energy-dispersive X-ray spectros-
copy (EDX), and X-ray photoelectron spectroscopy (XPS).
The as-obtained NiCo icosahedral nanocrystals exhibit the
size- and component-dependent magnetic behaviors. The
coercivity (H ) depends on both the magnetocrystalline and
c
structure anisotropy, and the saturation magnetizations (M ) decided by the content of Co. H decreases from 189.02 to 147.95
s
c
Oe with the increase of the icosahedral NCs size from 200 to 850 nm. Especially, the H of the icosahedral NCs at 157.38 Oe is
c
higher than that of nanospheres at 104.02 Oe. In addition, M and H increased with the increasing Co content. It can be an ideal
s
c
building block for applications in magnetic media, sensors, and other devices.
15
1. INTRODUCTION
NiCo nanoparticles. In our continuous efforts to improve the
16
synthesis of magnetic nanoalloys, we herein first report on the
one-step template-absent synthesis of uniform magnetic NiCo
alloy icosahedral NCs ranging in size from 200 to 850 nm in
solvothermal reaction system. To the best of our knowledge, it
is a very rare case to obtain icosahedral NCs in a NiCo alloy
system, especially generated by a solvothermal chemistry
reaction, and this facile method can easily suggest the large
industrial production in contrast to the electrochemical
treatment.
In this work, new dimensional NiCo alloy icosahedral NCs
with controllable size and magnetism are synthesized in a
solvothermal template-absent system through an Ostwald
ripening process. The morphology, structure, formation
mechanism, magnetic property, and relativity have been
investigated. The measurement results show that magnetic
behavior is dependent on size and component, in which
Uniform polyhedral nanocrystals (NCs) have attracted
remarkable attention because their catalytic, electrical, and
magnetic performance can be finely tuned either by their
composition, which mediates electron structure, or their shapes,
which determine surface atomic arrangement and coordina-
1
−8
tion.
Because the surface structure changes as a function of
9
size, shape, and number of components of a particle, and the
large particle surface area results in increased interaction with
their environment, these effects may lead to a radical alteration
in chemical reactivity. Therefore, the reactivity and selectivity of
catalysts greatly depend upon the arrangement of surface atoms
and the number of dangling bonds on the crystal planes. For
the purpose of higher catalytic activity, the polyhedron with
uniform nanocrystal plane is expected to be prepared due to the
different kinds of active sites with different reactivity for
different exposed crystal planes, since the different exposed
crystal planes have different kinds of active sites and present
coercivity (H ) decreases with increasing icosahedral NC size.
c
10,11
different reactivities.
Recently, most of the reported investigations concerned the
In addition, saturation magnetization (M ) and H increased
s
c
with increasing Co content. This new dimensional NiCo alloy
icosahedral NC can be an ideal building block for applications
in magnetic carriers, sensors, and other devices.
10
noble metal NCs, such as Pt tetrahexahedrons; Au−Cu
1
1
nanocubes; Au−Pd core−shell nanocrystals with tetrahex-
12
ahedral, concave octahedral, and octahedral structures; and so
on, which are synthesized by solvothermal routes and
electrochemical treatment within template direction. However,
it is a large challenge to obtain shape- and size-controlled
magnetic noble-metal-free alloy polyhedral NCs with better
productivity, in spite of the tunable composition and shape
which have technological applications including magnetic
2. EXPERIMENTAL SECTION
2.1. Chemicals. All the reagents used in this work, including
nickel(II) acetate hydrate (Ni(Ac)
·4H O, 99%), cobalt(II) acetate
2
2
hydrate (Co(Ac) ·4H O, 99%), sodium hydroxide (NaOH, 99%),
2
2
polyvinyl pyrrolidone (PVP, average molecular weight is 30 000),
absolute ethyl alcohol (C H OH, 99%), and propylene glycol
2
5
13,14
carriers, biosensors, and bioseparation.
Until now, few
reports are known about magnetic NiCo alloy NCs with
icosahedral shape although there are some template-assisted
Received: August 13, 2011
Published: January 18, 2012
©
2012 American Chemical Society
1495
dx.doi.org/10.1021/ic201763j | Inorg. Chem. 2012, 51, 1495−1500

Inorganic Chemistry
Article
(
C H O , 99%), were purchased from Sinopharm Chemical Reagent
3 8 2
3. RESULTS AND DISCUSSION
.1. Synthesis and Characterization of Icosahedral
Co., Ltd., and were used without further purification.
.2. Synthesis. NiCo icosahedra nanocrystals were synthesized
through an Ostwald ripening process in a solvothermal system.
Ni(Ac) ·4H O, Co(Ac) ·4H O, NaOH, and PVP were used as
precursors. As an example of a typical process, the synthesis process
of Ni Co icosahedral nanocrystals was described as follows: 3 mL of
3
2
NiCo Nanocrystals. The formation of NiCo icosahedral NCs
is carried out through the reduction of Co2+ and Ni by
ethylene glycol in a solvothermal template-absent system. The
2+
2
2
2
2
17
formation reaction underneath can be suggested as follows. In
48
52
2
+
ethyl alcohol was mixed with 0.06 mmol Ni(Ac) ·4H O, 0.06 mmol
Co(Ac) ·4H O, 1.2 mmol NaOH, and 0.24 mmol PVP at room
the present basic reaction condition (pH = 11.5), Co and
2
2
2
+
2
2
Ni become the stable intermediate phase of Co(OH) and
2
2+
2+
temperature. The mixture was dissolved by ultrasonic decomposition.
Then, 7 mL of propylene glycol was injected into this mixture and
transferred to the autoclave in room temperature. The autoclave was
sealed and maintained at 210 °C for 6 h. After the reaction was cooled
to room temperature, the NiCo icosahedral nanocrystals were
collected at the bottom of the container. The products were
alternately washed by distilled water and ethanol with centrifugation
thrice, and then were redispersed and stored in ethanol. In addition,
the series of NiCo nanoalloys were prepared using the initial molar
Ni(OH) , which is a storehouse of Co and Ni , and can
2
control the reaction process through the controlling of the
2+
2+
release of Co and Ni in solution.
−
−
Ni(OH) (s) + 2e = Ni + 2OH (aq)
2
θ
ϕ
= −0.72 (V)
Ni(OH) /Ni
(1)
(2)
2
2+
2+
ratios of Ni :Co at 100:0, 83:17, 75:25, 50:50, 25:75, 17:83, and
:100, for the component of Ni, Ni Co , Ni Co , Ni Co ,
−
−
Co(OH) (s) + 2e = Co + 2OH (aq)
2
0
82
18
76
24
48
52
θ
Ni Co , Ni Co , and Co, respectively. Detailed data of as-obtained
nanoalloy components and their magnetic parameters are summarized
in Table S1.
25
75
16
84
ϕ
= −0.73 (V)
Co(OH) /Co
2
On the basis of the Nernst function, at pH = 11.5 this equation
follows:
2
.3. Atomic Absorption Experiments. Atomic absorption
experiments are used to confirm the elemental percentages. The
detail experiment is carried out as follows. The as-obtained NiCo
nanocrystals were freeze-dried overnight. A 1.25 mg sample of dried
NiCo nanoalloy was recovered after ensuring that they were
completely dry. Then, 2 mL of aqua regia was added to the vial to
digest the serials of NiCo nanoalloys. The resulting solution was
heated to ∼50 °C for 3 h. The solution turned from a light yellow to a
bright neon green. After digestion, the solution was allowed to cool
down and was diluted down with deionized water to the appropriate
concentration for atomic absorption experiments. The results show
that NiCo nanoalloys contain (by weight) 100% Ni for Ni(S1); 81% of
Ni and 19% of Co for Ni Co (S2); 72% of Ni and 28% of Co for
2
0.059 ⎡ 1 ⎤
ϕ
= ϕθ
+
log
Ni(OH) /Ni
Ni(OH) /Ni
⎢
⎣
⎥
⎦
2
2
2
OH
=
−0.72 − 0.059(14 − pH)
= −0.72 − 0.059(14 − 11.5)
−0.5725 (V)
=
Simultaneously
82
18
Ni Co (S3); 45% of Ni and 55% of Co for Ni Co (S4); 23% of
76
24
48
52
ϕCo(OH)2 /Co = −0.5825 (V)
Ni and 77% of Co for Ni Co (S5); 15% of Ni and 85% of Co for
25
75
Ni Co (S6); 100% of Co for Co (S7), respectively. The contents of
16
84
Ni and Co are basically consistent with the initial molar ratios between
Ni and Co .
On the other hand, as reducer
2+
2+
2
−
−
2.4. Characterization. The morphology and size of as-synthesized
C O (aq) + 8H O(1) + 8e
2
4
2
samples were determined by using Hitachi S-4800 scanning electron
microscopy (FE-SEM), JEOL JEM-1200EX (Japan) transmission
electron microscopy (TEM), and high resolution transmission
electron microscopy (HRTEM). Scanning transmission electron
microscopy (STEM) and elemental maps were carried out under
the bright field (BF) mode on JEOL JEM-2100 F microscope. Selected
area energy dispersive X-ray spectroscopy (EDXS) was conducted at
−
= C H O (1) + 10OH (aq)
2
6
2
θ
ϕ
2−
= −0.91 (V)
C O /C H O
(3)
2
4
2
6
2
When pH = 11.5
20 keV on a TN5400 EDS instrument (Oxiford), and all samples were
handled under air atmosphere. Powder element analyses of Ni and Co
were measured at λ = 232.0 and 240.7 nm by graphite furnace atomic
absorption spectrometer (AAS) (6810, Shanghai Chromatogram
Technology Company, China). The powder X-ray diffraction (XRD)
analysis patterns were recorded using Bruker D8 (German)
diffractometer with a Cu Kα X-ray radiation source (λ = 0.154 056
nm). X-ray photoelectron spectroscopy (XPS) experiments were
carried out on a RBD upgraded PHI-5000C ESCA system (Perkin-
Elmer) with Al Kα radiation (hν = 1486.6 eV). The whole spectra (0−
= ϕθ
ϕC2O42−
2−
C2O4 /C2H6O2
/C2H6O2
1
0
+ 0
.059
8
log
⎡ 1 ⎤
⎢
⎣
⎥
⎦
OH
=
−0.91 + 0.074(14 − pH)
= −0.91 + 0.074(14 − 11.5)
=
−0.725 (V)
1100 eV) and the narrow spectra of all the elements with much high
resolution were both recorded by using RBD 147 interface (RBD
Enterprises) through the AugerScan 3.21 software. Binding energies
were calibrated by using the containment carbon (C1s = 284.6 eV).
The data analysis was carried out by using the RBD AugerScan 3.21
software provided by RBD Enterprises or XPSPeak4.1 provided by
Raymund W. M. Kwok (The Chinese University of Hongkong,
China). Vibration sample magnetometry (VSM) was used to examine
the magnetic properties of as-obtained NiCo nanocrystals on
Lakeshore7312.
Further oxidation gives
2CO32 (aq) + 2H O(l) + 2e =
−
−
2
2
−
−
C O (aq) + 4OH (aq)
2 4
ϕθ
2−
2− = −1.05 (V)
CO3 /C O
4
(4)
2
1
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Inorganic Chemistry
Article
When pH = 11.5
1a. The average size of icosahedral NiCo NCs was ∼450 nm
with a yield of ∼65%. A high magnification SEM image of
icosahedral NiCo NCs oriented along the 5-fold axes is
presented in inset I of Figure 1a. The icosahedral shape is
bounded by 20 regular triangle facets and 12 vertices, in which
each vertex was formed by five triangle planes with two
4
2− + 0. 02 59 log
⎡ 1 ⎤
ϕCO32−
2− =ϕθ
2−
/C O
CO3 /C O
2 4
⎢
⎣
⎥
⎦
2
4
OH
=
=
=
−1.05 + 0.118(14 − pH)
−1.05 + 0.118(14 − 11.5)
−0.755 (V)
18
adjecent facets angles of 138.19°. In some cases, shown in
inset II of Figure 1a, imperfection can be introduced at vertices,
which is not caused by the {220} truncation of icosahedral NC
but rather because crystal facets of different sizes are produced
by substrate effects. TEM analysis in bright-field (Figure 1c)
and dark-field (Figure 1d) indicates that such structure clearly
reveals three-dimensional (3D) structure of the NCs. The
regular hexagon with observed inner angle of 120° for a single
icosahedral NiCo NC in Figure 1c under TEM confirms the 3D
icosohedron shape. The facets of the icosahedral NiCo NCs
were determined by HRTEM and selected-area electron
diffraction (SAED) pattern. Figure 1b presents HRTEM
image recorded from a boxed area I marked in Figure 1c.
The dominant exposed facets of the NiCo icosahedral NCs are
{112}, which are the only plane normal to both the plane of
(111) with a lattice space of 0.21 nm and the plane of (220)
with a crossing lattice space of 0.13 nm. The SAED recorded
from boxed areas I and II marked in Figure 1c are given in the
insets of Figure 1e,f, respectively. The 3-fold symmetry of the
SAED pattern confirms that the icosahedral NiCo NC is a
single crystal, and can be indexed as (111) and (220) planes.
Figure 2a−c shows representative STEM images and the
So
ϕ
, ϕ
Co(OH) /Co
Ni(OH) /Ni
2
2
>
>
ϕ
ϕ
2−
C O /C H O
2
4
2
6
2
2−
C O /C H O
2
4
2 6
2
Thus, the reaction is carried out following reaction (4).
2
3
‑
Ethylene glycol finally completely is oxidized forming CO .
Therefore, Co2 and Ni can be completely reduced by
ethylene glycol under present conditions. The total reaction
function is given as follows:
+
2+
−
C H O (1) + 5Ni(OH) (s) + 4OH
2
6
2
2
2
−
=
2CO3 + 5Ni(s) + 10H O(1)
2
−
3
C H O (1) + 10Co(OH) (s) + 12OH
2
6
2
3
−
=
6CO32 + 10Co(s) + 30H O(1)
2
The morphology of as-synthesized NiCo alloy icosahedral
NCs was determined initially by FE-SEM, and shown in Figure
Figure 2. (a) BF-STEM image of a icosahedral NiCo NC. (b) XRD
pattern of icosahedral NiCo NCs. (c) EDXS of NiCo icosahedral NCs.
(d, e) The elemental maps of Ni and Co in a icosahedral NiCo NC,
respectively.
Figure 1. (a) SEM image of icosahedral NiCo NCs with inset high-
magnification images of a perfect (I) and an imperfect (II) icosahedral
NC. (b) HRTEM image recorded from the boxed area I marked in
part f. (c) Bright-field and (d) dark-field TEM image of a single
icosahedral NiCo NC. (e, f) Corresponding SAED pattern recordered
from the boxed area I and II marked in part f, respectively.
corresponding EDXS maps for Ni and Co in a single
icosahedral NC, indicating icosahedral NC is a NiCo alloy.
EDXS performed on NiCo alloy icosahedral NCs undoubtedly
indicates that they contain Ni and Co with the ratio of ∼1/1 in
Figure 2d. The composition analysis for other NiCo NCs are
1
497
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Inorganic Chemistry
Article
confirmed by AAS and EDXS (Supporting Information, Table
S1 and Figure S1). In Figure 3, the XRD pattern of NiCo
Figure 4. (a) XPS spectra for NiCo icosohedral nanocrystals. (b)
Detailed spectra of Co2p. (c) Detailed spectra of Ni2p. All the
horizontal axes represent the binding energy corrected by that of C1s.
Figure 3. XRD patterns of NiCo nanocrystals in different
compositions: (a) Ni, (b) Ni Co , (c) Ni Co , (d) Ni Co , (e)
82
18
76
24
48
52
Ni Co , (f) Ni Co , (g) Co.
25
75
16
84
Owing to the different environments, the signals of metallic
bonding energy in as-obtained NiCo alloy NCs are slightly
shifted compared with the pure nickel and cobalt bulk metals.
The shape of NiCo NCs could be controlled by varying the
composition and the reaction conditions based on the growth
habit (which is leaded by the underlying crystal structure). In
Figure 5, owing to the influence of the growth habits of Ni and
Co, with increasing Co content, the shape changes from
icosahedral NCs is similar to those of either Ni or Co with an
fcc structure (JCPDS 01-1260 and 15-0806) and corresponding
to (111) and (220) in SAED pattern in Figure 1e,f, while the
content of Co over 84 at. % in NiCo NCs results in the mixed
1
9,20
structures of hcp and fcc.
The growth process of NiCo alloy
icosahedral NCs was monitored by withdrawing samples at
different growth periods in Figure S2 in Supporting
Information. During the early stages, Ni2+ and Co were
reduced by propylene glycol and alloyed to the aggregation of
NiCo alloy nucleus. In the current reaction system, the
nanocrystal morphology tends to be dictated by underlying
crystal structure, and the NiCo alloy nucleus then formed small
icosahedral NCs because Ni−Co alloy clusters have an
2+
multihorn-sphere in Ni and Ni Co to icosahedral NCs in
82
18
Ni Co , and then to hexagonal plate in Ni Co . In addition,
48
52
16
2+
84
2+
the molar ratio of NaOH:M and PVP:M in the reaction
system is the important effect factor of the shape of NiCo
nanoalloys. The clear icosohedral shape with uniform size of
about ∼450 nm can be observed when the molar ratio of
NaOH:M2+ is 1:10 (Surpporting Information, Figure S3) and
2
1,22
icosahedral morphology.
The further growth gives large
perfect icosahedral NCs with edge-shapening and size-focusing
2
3,24
2+
of PVP:M is 1:2 (Surpporting Information, Figure S4). The
by Ostwald ripening.
presentation of bounded facets of {112} as the time prolongs to
h. After 10 h, the morphology remained similar to that at 6 h
Finally, the growth leads to the
size of the icosahedral NiCo NCs can be adjusted by the
concentration of the metal precursor at the above optimized
concentration of NaOH and PVP. The SEM images of NiCo
6
with relatively larger size. Thus, the formation of icosahedral
NCs can be completed at ∼6 h. Scheme S1 in Supporting
Information shows the representative surface atom arrange-
ment of the fcc NiCo icosahedral NCs with different crystal
planes. The area of adjacent four atoms of the {111} (b), {220}
2
+
icosahedral NCs obtained in the concentration of M at 4, 6, 8,
and 10 mM are shown in Figure 6. The corresponding average
sizes are ∼200, ∼ 300, ∼ 450, and ∼850 nm, respectively.
3.2. Magnetic Properties of NiCo Nanoalloys. Hyste-
resis measurement results show that the magnetic behavior is
dependent on the size and component. Figure 7a shows the
magnetic behavior of the icosahedral NCs in different sizes
measured at 300 K, and the detailed data are summarized in
Table S2 in Supporting Information. Generally, as the particle
2
2
(
2
c), and {112} (d) facets is (√3/2)α , (√2/2)α , and (√6/
2
)α , respectively, suggesting the {112} planes are more open
than the {111} and {220} planes. Of the three planes, the most
densely packed {111} planes have the lowest surface energy
based on its surface atoms having the smallest number of
missing nearest neighbors per unit area. Therefore, the {112}
planes have a more reactive surface.
In Figure 4, X-ray photoelectron spectroscopy (XPS) shows
five photoemission peaks for Ni2p, Co2p, C1s, and O1s.
Magnified Ni2p peaks, consisting of two peaks at 851.8 and
size increases, the coercivity (H ) increases rapidly upon the
c
size exceeding the superparamagnetic limit, saturates when the
size approaches the single-domain limit, and gradually decreases
to the bulk value upon passing the multidomain region
25
(Supporting Information, Figure S5). Because the reported
single-domain limit of 20 and 32 nm was estimated for Co and
8
70.7 eV, are due to the spin−orbit splitting of 2p and 2p1/2,
3
/2
2
6
indicating dominant Ni(0). For Co2p, two peaks resulting from
the 2p electron multiplet-splitting are 2p3/2 and 2p1/2 with the
binding energy of 779.15 and 794.18 eV, implying Co(0). In
Binding Energy Lookup Table for Signals from Elements and
Common Chemical Species, C1s = 285.0, Co2p3/2 = 778.3,
Co2p1/2 = 793.7, Ni2p3/2 = 852.6, Ni2p1/2 = 869.9, respectively.
Ni nanoparticles, our icosahedral NiCo NCs show Hc
decreases from 189.02 to 147.95 Oe with the size increase
from 200 to 850 nm because of their size all over the single-
domain limit. This variation trend of H over size can be clearly
c
observed in the inset of Figure 7a. The different components of
NiCo nanoalloys within the different shapes from multihorn-
1
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Inorganic Chemistry
Article
Figure 5. SEM images of NiCo NCs in different compositions: (a, b) Ni and Ni Co multihorn-sphere, (c) Ni Co irregular polyhedral NCs, (d)
82
18
76
24
Ni Co icosahedral NCs, (e) Ni Co truncation icosahedral NCs, (f) Ni Co nanoplates.
48
52
25
75
16
84
Figure 6. SEM images of icosahedral NiCo NCs within different sizes: (a) ∼200 nm, (b) ∼300 nm, (c) ∼450 nm, (d) ∼850 nm. (e) Size
distributions of icosahedral NiCo NCs in parts a−d, respectively, after counting more than 200 particles for each sample.
and together with the effect of shape anisotropy lead to the
variation trend in Figure 7b. The detailed data are summarized
in Table S1 in Supporting Information.
4
. CONCLUSION
In conclusion, we have reported here new dimensional NiCo
alloy icosahedral NCs with controllable size and magnetism
synthesized through an Ostwald Ripening process. The as-
synthesized icosahedral NCs of NiCo nanoalloys are bounded
by the active predominantly exposed planes of {112}. The
magnetic properties of NiCo alloy NCs indicated that the
magnetic behavior is dependent on size, shape, and
Figure 7. Magnetic behavior of icosahedral NiCo NCs measured at
3
00 K: (a) M−H curves for 200, 300, 450, and 850 nm sized
icosahedral NCs with inset curve of H over the particle size. (b) The
c
variation of M and H for NiCo NCs within different compositions.
s
c
composition. H decreases with the increase of icosahedral
NC size. In addition, the Co content increase can increase the
c
sphere to icosahedron and then to plate exhibit different
magnetic properties; the values of M and H over the content
s
c
M and H of as-obtained NiCo nanoalloys. This approach can
s
c
of Co are plotted in Figure 7b. The increase of Co content
be readily extended to the synthesis of polyhedron NCs of
other related magnetic transition metal alloys without noble
metals. The preparation of these magnetic alloy polyhedron
NCs with uniform reactive crystal facets is expected to bring up
a new way to design and control physical and chemical
specificity, suggesting the applications in magnetic carriers,
sensors, and other devices.
resulted in an increase of M from 42 to 139 emu/g, induced by
s
the difference of atomic magnetic dipole moment between Ni
2
7
(
0.6 μ ) and Co atoms (1.75 μ ). However, H depends on
B B c
effective anisotropy which is decided by both the magneto-
crystalline and shape anisotropy. For fcc structure, the
magnetocrystalline anisotropy constant K of Co is higher
1
than that of Ni. So, H increases with increasing Co content,
c
1
499
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Inorganic Chemistry
Article
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22) Robert, W. G. Encyclopedia Polyhedra: ICOSAHEDRON 2007,
ASSOCIATED CONTENT
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(
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, 28.
23) Seo, D.; Park, J. C.; Song, H. J. Am. Chem. Soc. 2006, 128 (46),
4863−14870.
(24) Hoang, T. K. N.; Deriemaeker, L.; La, V. B.; Finsy, R. Langmuir
*
S
Supporting Information
SEM and TEM images, EDX spectroscopy, and the detailed
data of alloy composition and magnetic parameters. This
material is available free of charge via the Internet at http://
pubs.acs.org.
2004, 20 (21), 8966−8969.
(25) Klabunde, K. J. Nanoscale Materials in Chemistry; Wiley-
Interscience: New York, 2001; Vol. 3, pp 263−277.
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AUTHOR INFORMATION
■
*
(
5
(
119−5121.
27) Dinega, D. P.; Bawendi, M. G. Angew. Chem., Int. Ed. 1999, 38,
1788−1791.
Corresponding Author
E-mail: m_wen@tongji.edu.cn (M.W.); qswu@tongji.edu.cn
Q.W.). Phone: +86-21-65982653 ext 8544. Fax: +86-21-
5981097.
6
ACKNOWLEDGMENTS
■
This work was financially supported by the National Natural
Science Foundation of China (Nos. 21171130, 51072134, and
9
1122025), Innovation Program of SECF (10ZZ21), and 973
Project of China (No. 2011CB932404).
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