Structure-controlled solventless thermolytic synthesis of uniform silver nanodisks

Article abstract of DOI:10.1021/ic051246d

Monodisperse silver nanodisks are synthesized on the gram scale from a well-characterized layered silver thiolate precursor via thermolysis at 180-225°C under a N₂ atmosphere. XRD, TEM, HRTEM, and AFM analyses indicate that the nanodisks generated at 180°C over 2 h have an average diameter of about 16.1 nm (σ = ±12%) and a thickness of 2.3 nm (σ = ±14%), and they lie on their (111) faces. The disk shape is considered to be predestined by the crystal structure of the precursor. Important aspects regarding the stability of the precursor, the thermolysis temperature, and the annealing time, as well as a possible conversion mechanism, are discussed.

Full text of DOI:10.1021/ic051246d

Inorg. Chem. 2005, 44, 9817−9822
Structure-Controlled Solventless Thermolytic Synthesis of Uniform
Silver Nanodisks
Yu-Biao Chen,†,‡ Ling Chen,† and Li-Ming Wu*,†
State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of
Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, P. R. China, and Graduate School
of the Chinese Academy of Sciences, Beijing 100039, P. R. China
Received July 26, 2005
Monodisperse silver nanodisks are synthesized on the gram scale from a well-characterized layered silver thiolate
precursor via thermolysis at 180 225 C under a N atmosphere. XRD, TEM, HRTEM, and AFM analyses indicate
that the nanodisks generated at 180 C over 2 h have an average diameter of about 16.1 nm (σ ) ±12%) and
−
°
2
°
a thickness of 2.3 nm (σ ) ±14%), and they lie on their (111) faces. The disk shape is considered to be predestined
by the crystal structure of the precursor. Important aspects regarding the stability of the precursor, the thermolysis
temperature, and the annealing time, as well as a possible conversion mechanism, are discussed.
Introduction
controlled via the structural state of the precursor used in
this method. For example, the viscosity of the colloidal
thiolate precursor proved to be a key parameter in controlling
the shape of the nanoproducts. Uniform nanowires, nanorods,
or nanospheres could be made from the corresponding
precursors that came from solutions with different viscosities
and thus characteristics of the precursor polymerization. In
this paper, we present further developments in this mild
conversion to nanoparticles at relatively low temperatures.
Under such conditions, the primary distribution of product
nuclei and the interparticle aggregations are thought to be
influenced largely by the structure of the precursor. There-
fore, a structurally anisotropic precursor is very likely to
restrict both the initial nuclei concentration and the conse-
quent atom diffusion path and speed and to lead to the
formation of an anisotropic nanoproduct. That is, the control
Research in the most interesting field of nanomaterials has
been active since late in the last century motivated by the
unique properties associated with the nanoscale applications
as optical, catalytic, and electronic devices and the funda-
mental curiosity of scientists. The physical properties of
nanomaterials are usually closely related to their shape and
size, for example, shape-related anisotropic optical properties,
luminescence, conductivity and catalytic activity. Hence, the
syntheses of special morphologies have become the primary
challenge, and diverse methods have been explored to gain
control over particle size and shape. However, attempts to
control particle shape have met with only limited success.
The newly established solventless thermolytic method has
proven to be successful in producing various nanomaterials,
2 2 3
such as Cu S, NiS, and Bi S rods, trigonal prisms, wires,
and fabrics. Our previous report demonstrated that the
morphology of the nanoproducts could be significantly
1
2
3
4
5
6
7
8
(3) (a) Morales, A. M.; Lieber, C. M. Science 1998, 279, 208-211. (b)
Trentler, T. J.; Hichman, K. M.; Geol, S. C.; Viano, A. M.; Gibbons,
P. C.; Buhro, W. E. Science 1995, 270, 1791-1794. (c) Cheon, J.;
Kang, N. J.; Lee, S. M.; Lee, J. H.; Yoon, J. H.; Oh, S. J. J. Am.
Chem. Soc. 2004, 126, 1950-1951.
(4) (a) Xia, Y.; Yang, P.; Sun, Y.; Wu, Y.; Mayers, B.; Gates, B.; Yin,
Y.; Kim, F.; Yan, H. AdV. Mater. 2003, 15, 353-389. (b) Jin, R.;
Cao, Y.; Mirkin, A. C.; Kelly, K. L.; Schatz, G.; Zheng, J. G. Science
2001, 294, 1901-1903.
(5) (a) Larsen, T. H.; Sigman, M.; Ghezelbash, A.; Doty, R. C.; Korgel,
B. A. J. Am. Chem. Soc. 2003, 125, 5638-5639. (b) Sigman, M. B.;
Ghezelbash, A.; Hanrath, T.; Saunders, A. E.; Lee, F.; Korgel, B. A.
J. Am. Chem. Soc. 2003, 125, 16050-16057.
*
To whom correspondence should be addressed. E-mail:
Liming_Wu@fjirsm.ac.cn. Phone: (011)86-591-83705401. Fax: (011)86-
5
91-83704947.
†
Fujian Institute of Research on the Structure of Matter.
‡
Graduate School of the Chinese Academy of Sciences.
(
1) (a) Duan, X.; Niu, C.; Sahi, V.; Chen, J.; Parce, J. W.; Empedocles,
S.; Goldman, J. L. Nature 2003, 425, 274-278. (b) Bruchez, M.;
Moronne, M.; Gin, P.; Weiss, S.; Alivisatos, A. P. Science 1998, 281,
2013-2016. (c) Sun, S.; Murray, C. B.; Weller, D.; Folks, L.; Moser,
A. Science 2000, 287, 1989-1992. (d) Wang, J. F.; Gudiksen, M. S.;
Duan, X. F.; Cui, Y.; Lieber, C. M. Science 2001, 293, 1455-1457.
2) (a) Jin, R.; Cao, Y. C.; Hao, E.; M e´ traux, G. S.; Schatz, G. C.; Mirkin,
C. A. Nature 2003, 425, 487-490. (b) Murphy, C. J.; Jana, N. R.
AdV. Mater. 2002, 14, 80-82.
(6) Ghezelbash, A.; Sigman, M. B.; Korgel, B. A. Nano Lett. 2004, 4,
537-542.
(7) Sigman, M. B.; Korgel, B. A. Chem. Mater. 2005, 17, 1655-1660.
(8) Chen, L.; Chen, Y.-B.; Wu, L.-M. J. Am. Chem. Soc. 2004, 126,
16334-16335.
(
1
0.1021/ic051246d CCC: $30.25
© 2005 American Chemical Society
Inorganic Chemistry, Vol. 44, No. 26, 2005 9817
Published on Web 11/24/2005

Chen et al.
over the shape of the product is achievable through control
of the structural character of the precursor. Thus, we have
successfully synthesized remarkably uniform silver nanodisks
Table 1. Experimental Conditions for Preparation of Silver Nanodisks
of Different Sizes from AgSC12H25
annealing
annealing
time (h)
description of products
and phase analysis
temp (°C)a
b
(
∼16 × 2.3 nm) by this conversion of a layered silver thiolate
1
1
1
65
80
80
4
0.75
2
black, mainly precursor
black, mainly precursor
black, fcc Ag nanodisk
(16.1 nm (σ ) ( 12%))
black, fcc Ag nanodisk
with a large interlayer spacing of 34.6 Å.
Silver nanoparticles are of particular interest because of
the unusual properties and applications presumably associated
9
200
25
2
2
with their shape and size. A number of methods exhibit
(24.5 nm (σ ) ( 10%))
excellent control over shape and lead to silver nanocubes,
2
black, fcc Ag nanodisk
3
a,10
nanowires, nanospheres, nanoprisms, and nanorods.
In
(40.6 nm (σ ) ( 15%))
+
monoclinic Ag2S (5 nm)
contrast, layered nanoparticles are less well-known even
though such a structural motif is highly desired for advanced
applications in light-emitting diodes and biological diagnos-
a
Heating from room temperature to the desired temperature was finished
within 2 h. b Phase analysis judged from the XRD pattern and the average
diameter.
9
tics, for example. To date, flat silver nanodisks have come
1
1
12a
12b
from template, soft colloidal,
solution-phase,
and
photoreduction methods.1 However, these products show
different degrees of coexistence with other shapes, such as
triangles and prisms.12
2c
Experimental Section
Chemicals. Dodecanethiol (C12
ethylamine ((C N) (A.R. > 99.5%), silver nitrate grains
AgNO ) (Shanghai, A.R. >99.8%), acetonitrile (CH CN), (A.R.),
ethanol (A.R.), and chloroform (A.R.) were used as purchased
H25SH) (Labcaster, 98%), tri-
2 5 3
H )
(
3
3
without further purification. N
Fuzhou Xinhang Gas Co.
2
gas (99.99%) was purchased from
Synthesis of Ag Thiolate Precursor. Silver nitrate (AgNO
3
, 1.36
g, 8 mmol) was dissolved in 70 mL acetonitrile, and 1.92 mL (16
mmol) of dodecanethiol was added with vigorous stirring, resulting
in a white powder precipitate. After the dropwise addition of 1.16
mL (16 mmol) triethylamine to the mixture and another 30 min of
stirring, the precipitate was collected by filtration, washed two to
three times with acetonitrile to ensure the removal of all soluble
materials, and then pumped in a vacuum desiccator to remove
residual solvent. The light yellow powder precursor was determined
Figure 1. Polycrystalline diffraction pattern (Cu KR radiation) of the as-
synthesized Ag thiolate precursor with the indexes of reflections.
2
ends, purged with N gas for 5 min, heated in a programmed tube
furnace at 180 °C for 2 h, and cooled to room temperature radiantly
in the furnace. The product was dispersed in a chloroform/ethanol
mixture (v/v ratio about 1:10) and centrifuged at 4,000 rpm for 5
min to remove molecular byproducts. The nanodisk yield was
to be a pure layered silver thiolate (see details below), and the yield
∼
52% based on number of moles of AgSR converted to elemental
+
is about 100% based on AgNO
3
, indicating that the Ag ions are
Ag. The reaction conditions for the Ag nanodisks are summarized
in Table 1, and more XRD patterns are shown in Supporting
Information. Detailed XRD and TEM studies are described below.
Sample Characterization. Powder X-ray diffraction (XRD),
transmission electron microscopy (TEM), high-resolution TEM
completely precipitated. Elemental analysis on the dry powder
assumed formula AgSC12 25) found (calcd): C, 46.69 (46.74);
(
H
H, 8.12 (8.18); N, < 0.3 (0); S, 10.40 (10.38). This is reinforced
by its presumed stoichiometric synthesis from a 1:1:1 mole ratio
of AgNO /thiol/triethylamine as above which resulted in a structur-
3
(HRTEM), and atomic force microscopy (AFM) were used to
ally identical product judged from the X-ray powder diffraction
patterns. The weak base triethylamine used in the synthesis serves
characterize the structure, composition, size, and shape of the
synthesized materials. TEM and HRTEM images were collected
using JEOL 2010 TEM equipped with a field emission gun
operating at a 200 kV. Images were acquired digitally using a Gatan
multipole scanning CCD camera with an imaging software system.
All TEM samples were prepared by depositing a drop of dilute
nanodisks dispersion in chloroform onto 200 mesh carbon-film-
coated Cu grids. Chemical elemental analysis performed by Vario
EL III (Elementar Co.). XRD was obtained using a Rigaku DMAX
+
to bind protons and accelerate the coordination between Ag and
thiols.
Synthesis of Ag Nanodisks. In a representative reaction, the
light yellow powdered AgSC12
H25 precursor in a Pyrex boat was
transferred into a long Pyrex tube (6 cm × 1m), capped on both
(
9) (a) Sun, Y.; Xia, Y. Science 2002, 298, 2176-2179. (b) Dumestre,
F.; Chaudret, B.; Amiens, C.; Renaud, P.; Fejes, P. Science 2004, 303,
2500 powder diffractometer with ultra 18 KW Cu radiation. UV-
8
21-823.
10) (a) Yu, D.; Yam, V. W. J. Am. Chem. Soc. 2004, 126, 13200-13201.
b) Sun, Y.; Mayers, B.; Herricks, T.; Xia, Y. Nano Lett. 2003, 3,
55-960. (c) Sun, Y.; Xia, Y. AdV. Mater. 2003, 15, 695-699. (d)
Jana, N. R.; Gearheart, L.; Murphy, C. J. Chem. Commun. 2001, 617-
18.
11) Hao, E.; Kelly, K. L.; Hupp, J. T.; Schatz, G. C. J. Am. Chem. Soc.
002, 124, 15182-15183.
(
vis spectroscopy was measured on a PerkinElmer Lambda-900
spectrophotometer.
(
9
Results and Discussion
6
(
(
Structural Description of AgSC12
X-ray powder diffraction pattern of the as-synthesized
25 precursor in Figure 1 shows intense narrow
reflections corresponding to successive orders of diffraction
H25 Precursor. The
2
12) (a) Maillard, M.; Giorgio, S.; Pileni, M.-P. AdV. Mater. 2002, 14,
1084-1086. (b) Maillard, M.; Huang, P.; Brus, L. Nano Lett. 2003,
3, 1611-1615. (c) Chen, S.; Fan, Z.; Carroll, D. L. J. Phys. Chem. B
2002, 106, 10777-10781.
AgSC12
H
9818 Inorganic Chemistry, Vol. 44, No. 26, 2005

Uniform SilWer Nanodisks
from a layered structure with large d spacing and preferred
orientation. This precursor is structurally analogous to the
shorter silver alkylthiolates,13 AgSR (R ) (CH
CH
, n )
2
)
n
3
2
, 3, 5, 7), which have {AgSR} layers with substituents
∞
extending normal to both sides of a central slab of Ag and
S atoms. Each central slab is a quasi-hexagonal network
constructed of [Ag (SR) ] six-rings. Such geometry gives
3 3
in-plane Ag-Ag distances of around 4.5 Å. The interlayer
distance is found to be in proportion to the length (Ln+1) of
the substituent, wherein the central Ag/S slab contributes a
constant ∼1.5 Å. To be consistent with ref 13, we define b
as the axial direction normal to the layers. The progressions
of interlayer reflections (0k0) of our AgSC12H25 precursor
are presented in SI Table 1. There is excellent agreement
between the calculated axial lengths (kd) for reflections with
Figure 2. XRD pattern of Ag nanodisks produced at 180 °C for 2 h. All
peaks are indexed as face-centered-cubic silver.
3
e k e 18 with an average of 34.6 Å. The proposed formula
for the thickness of the complete layers is to be (2Ln+1
.5 Å), and the lengths of some alkylthiol chains (Ln+1) from
crystal structure data on AgS(CH CH , are 5.7, 6.9, 9.5,
and 11.9 Å for n ) 2, 3, 5, and 7, respectively, increasing
roughly 1.2 Å per CH group. In our case, (2Ln+1 + 1.5 Å)
centered-cubic silver (ICSD #64706) by XRD (Figure 2),
and its TEM images (Figure 3) show a remarkably mono-
disperse nanodisk morphology. To gain insight into the
mechanistic basis behind this unusually efficient conversion,
we investigated the importance of two reaction conditions:
reaction temperature and time. Several reactions carried out
at 140 °C for 8 h, 165 °C for 2 h, and 180 °C for 0.75 h
produce dark yellow powders. Their XRD patterns (SI Figure
1) contain all the axial reflections of the layered precursor
and no other detectable phases, although the color change
does imply the formation of small amounts of silver.
However, the absence of XRD signals and the invisibility
of crystals by TEM observation indicate that the silver in
these three reactions is still poorly crystalline or amorphous.
An optimum synthesis condition is heating the precursor for
2 h at 180 °C, but uniform Ag nanodisks are repeatedly
produced by firing for 2 h in the temperature range between
180 °C and 225 °C (Table 1). As expected, the diameters of
the nanodisks increase (from 16.1 to 40.6 nm) (SI Figures
2-5) with the temperature increase, but the morphology
remains strikingly uniform. An efficient mechanism for this
one-to-one (layered precursor to nanodisk) conversion will
be discussed below. We also found that at g225 °C, a second
+
1
2
)
n
3
13
2
for dodecanethiolate would be 34.9 Å, consistent with the
observed value (SI Table 1). The small discrepancy may
come from a nonzero tilt angle of the long chain with respect
to the central slab and no interpenetration at the interface
between layers. Such monolayer structural motifs have been
observed for thiols on clean gold surfaces but differ
significantly in that the Ag-SR bond contrasts with the Au-
HSR absorption. A common observation with layered
AgSR compounds is that the {0k0} reflections get more
pronounced with the increase of alkyl chain length, together
with the fact that the layered compounds have a high
orientation preference (SI Figure 1). The {h0l} reflections
1
4
of polycrystalline AgSC12H25 are too weak to allow inves-
tigation of the intralayer structural details. However, similar
bonding patterns and geometry for the Ag/S central slab
relative to those of bulk layered silver-thiolates are reason-
able.
Ag Nanodisks Converted from a Layered Precursor.
Uniform Ag nanodisks are obtained by heating light yellow
major phase, Ag S (acanthite, ICSD#30445), is formed.
Above 250 °C, no silver is formed.
2
AgSC12
H
25 powder at 180 °C for 2 h under N
2
+
flow; the
Characterization. TEM images for the as-synthesized
nanodisks prepared at 180 °C for 2 h (Figure 3) reveal a
strikingly uniform morphology with an average diameter of
16.1 nm (σ ) ( 12%) nm (SI Figure 3). The disk shapes
product turned black during the firing. The Ag is thought
to be reduced by the thiolate (SR ) through the electron
transfer from the thiolate (SR ) to silver cation; then two
SR radicals yield the disulfide shown in the following
-
-
have been obtained before under different experimental
1
5
11,12
equations.
conditions,
but not with such monodispersity in shape
and size. The EDX from a nanodisk shown in Figure 3 on
a Cu grid indicates only pure silver (SI Figure 7), and the
single-phase purity is confirmed by the XRD result (Figure
∆
•
AgSR 98 Ag + SR
•
2
SR f RSSR
2
). The HRTEM image of Ag nanodisks in Figure 4b shows
Ag atoms with close-packed hexagonal symmetry and an
interlayer distance of 2.37 Å, corresponding to the (111) layer
spacing of fcc silver. Figure 4c shows a model (111) image
of fcc silver. The Fourier transform (FFT) of the image in
Figure 4a gives a decent description of the crystal orientation,
and the 6-fold {111} and 4-fold {002} reciprocal points are
marked in Figure 4d. The measured values of d111 and
After it was washed with a chloroform/ethanol mixture,
the black powder was identified as single-phase face-
(
(
(
13) Dance, I. G.; Fisher, K. J.; Banda, R. M. H.; Scudder, M. L. Inorg.
Chem. 1991, 30, 183-187.
14) Porter, M. D.; Bright, T. B.; Allara, D. L.; Chidesey, C. E. D. J. Am.
Chem. Soc. 1987, 109, 3559-3568.
15) Oae, S. Organic Sulfur Chemistry: Structure and Mechanism; CRC
Press: Boca Raton, FL, 1991; Chapter 6, pp 204-206.
d
002(2.37 and 2.04 Å, respectively) are in agreement with
Inorganic Chemistry, Vol. 44, No. 26, 2005 9819

Chen et al.
Figure 3. Ag nanodisks converted from the layered AgSC12H25 precursor at 180 °C for 2 h.
Figure 4. (a) HRTEM image of Ag nanodisks produced at 180 °C for 2
h. (b) An enlarged image of the selected part of panel a. The hexagonally
arranged spots correspond to the close-packed (111) layers of face-centered-
cubic silver. (c) A [111] projection of the cubic silver structure with the
unit cell marked, and a (d) FFT of the imaged nanodisk in panel a
demonstrating crystal orientation.
bulk crystallographic data (a ) 4.08 Å, ICSD #64706). The
lattice parameter is calculated to be 4.12 Å from this pattern,
which is similar to the value of 4.17 Å in ref 12a and that of
4
.08 Å for bulk silver. All nanodisks appear as layered and
lying on their (111) faces. The average diameter by TEM is
6.1 nm (Figure 3). The TEM images indicate that all of
1
Figure 5. (top) AFM images of the Ag nanodisks produced at 180 °C for
the nanoparticles are nummular, which suggests only two
possibilities: they are either perfect spheres or have large
diameter/height (D/H) ratios, disklike morphologies, and lie
on their faces. AFM is further used to define the morphology
of nanoparticles (Figure 5). The line analysis at the bottom
indicates that this disk has a thickness 2.2 nm and diameter
of 18 nm, consistent with the TEM observations. The
thickness and diameter value for the individual disks give a
large D/H ratio of about 7, diameter(av) ) 16.1 nm (σ ) (
2
h, and (bottom) the height profile along the line in the top figure. The
height is about 2.2 nm.
4b
significantly different than the flatness of the Ag nanoprisms
12a
and other nanodisks. The aspect ratio of the last are 4-5.5
for the truncated hexagonal or pseudo-hexagonal Ag disk.1
The average diameter of the as-made Ag nanodisks increases
to 24.5 nm at 200 °C and to 40.6 nm at 225 °C for 2 h (SI
Figures 4 and 5). The nanodisks show an absorption band
at ca. 413 nm (Figure 6), typical of the plasmon resonance
of the spherical silver nanoparticles, since the nanodisks
assumed a rounded rather than sharply angular surfaces as
2a
12%) and height(av) ) 2.3 nm (σ ) ( 14%) (SI Figures 3
and 6); therefore, we define the as-made Ag particles as
nanodisks. Of course, with such large D/H ratios, it is difficult
for the nanodisks to stand on their edges. It is important to
notice the curved top surfaces of these nanodisks, which are
4
b,12
do triangles or prisms.
This is similar to the phenomenon
1
0a
found with silver nanocubes.
9820 Inorganic Chemistry, Vol. 44, No. 26, 2005

Uniform SilWer Nanodisks
is fulfilled by atom diffusion which is guided by the
concentration gradient of the Ag atoms. The Ag atom
distribution, constrained by the structure motif of the
precursor, has a layered pattern, and the in-plane Ag atoms
diffuse isotropically; naturally, the intraplane silver atom
aggregation is identical in two directions. In contrast, the
interplane silver atom diffusion is hindered by the organic
chains, and this diffusion path (34.6 Å initially, Figure 1) is
much longer than the intraplane one. Thus, the interplane
aggregation is much slower, leading to the formation of a
disklike morphology. This mechanism explains the mono-
disperse morphology of the nanodisk product (Figure 3) well
because the Ag atom concentration is self-controlled by the
structure of the AgSR precursor, and it is evenly distributed
on a atomic level under the mild reaction conditions.
Structure-Controlled Solventless Method. We present
here some experimental facts to illustrate our structure-
controlled solventless method for converting a layered
precursor to the layered nanoproduct. The key character of
this approach is that it is a mild conversion, and the reactions
can be regarded as a quasi-solid-state process. As is usual
Figure 6. Room-temperature UV-vis absorption spectrum of the chlo-
roform suspension of Ag nanodisks produced at 180 °C for 2 h.
Possible Conversion Mechanism. The Ag nanodisks are
successfully formed from the thiolate precursor by thermoly-
sis between 180 and 225 °C for an appropriate period of
time. A lower temperature or a shorter time regularly
produces a dark-yellow powder that possesses an identical
XRD pattern to that of the precursor (SI Figure 1).
17
in solid-state reactions, the nucleation of the desired product
may be relatively easy, and the subsequent growth or
thickening of the product is more difficult and mainly
determined by atomic diffusion. The molecular structure of
the precursor influences the diffusion speed and path of atoms
as described above. A structure determination for the solid-
state precursor in this method is practical, baring any
intervening processes, and we are able to chose/design a
precursor structurally to rationally achieve the desired
morphology of the nanoproduct. Furthermore, other motifs
would be expected if other pronouncedly anisotropic mor-
phologies could be formed for the precursor giving nanobelts,
nanorings, etc. Control of the structure of the precursor on
the basis of traditional coordination chemistry is more
governable and advantageous, and the diversity of known
AgSC12H25 has been reported to exhibit a columnar rather
than a lamellar structure from 130 to 180 °C in air without
any decomposition, and the different heating rates or
preparation procedures were found to have noticeable influ-
ences on the temperatures at which the different mesophases
of AgSC12
structure under our heating conditions, another reaction was
carried out in which crystalline AgSC12 25 was heated in
air at 155 °C for 2 h, and then immediately quenched in
liquid N to freeze the precursor structure. The XRD pattern
H H
25 appeared.16 To examine the AgSC12
25
H
2
taken right after quenching (SI Figure 8a) showed a layered
structure with an interlayer spacing of 34.6 Å consisted with
the room-temperature structure (Figure 1) and the results in
SI Figure 1. Thereafter, the dark-red synthesized product was
dispersed and washed in a chloroform/ethanol mixture to get
rid of most of the organic components. The XRD pattern of
the precipitate (SI Figure 8b) make it clear that Ag has
formed under such conditions which indicates that decom-
18
coordination structure types is prominent. Our discoveries
of a dependence of the nanoproduct morphology on the
precursor structure should also be effective in the preparation
of nanoparticles of main group elements with special shapes,
such as Bi nanocubes, nanofibers, and nanodisks. And this
novel method is also expected to give nanoparticles with
heterometal mixing on an atomic scale.
Conclusions. Monodisperse Ag nanodisks with an aspect
ratio of 7 have been successfully synthesized giving convinc-
ing experimental support for our new structure-controlled
solventless method. Silver clusters formed during the in situ
reduction of layered silver thiolate are nuclei for the nanodisk
formation, which involves anisotropic growth perpendicular
to (111) face of fcc silver. One of the key points of this
process is that the nanoproduct morphology is self-controlled
on the atomic level by the structure of the precursor during
the mild conversion. This method for the synthesis of layered
silver nanodisks is simple, inexpensive, and suitable for
production on a gram scale. It is also applicable to the
postion of AgSC12
.
H25 occurred In other words, the experi-
mental conditions in ref 16 led to different results from ours
in that they only found a crystal-to-micellar transformation.
This suggests that the experimental conditions are crucial to
the chemical behavior of the Ag thiolate, especially, under
thermolysis condition. On the basis of these facts, it is
reasonable to regard the structure of the AgSC12H25 precursor
under our firing conditions to still be a layered structure while
its decomposition occures.
We thus hypothesize that the conversion mechanism
contains two processes: nucleation and growth. On the first
heating, the AgSR partly decomposes to small metallic silver
clusters that serve as nuclei for the further reaction stages,
and their distribution inherits the layered pattern of the
mother structure. Second, the subsequent nanoparticle growth
(
17) West, A. R. Basic Solid State Chemistry; Wiley: New York, 1999;
(
16) Baena, M. J.; Espinet, P.; Lequerica, M. C.; Levelut, A. M. J. Am.
Chapter 9, pp 408-411.
Chem. Soc. 1992, 114, 4182-4185.
(18) Henkel, G.; Krebs, B. Chem. ReV. 2004, 104, 801-824.
Inorganic Chemistry, Vol. 44, No. 26, 2005 9821

Chen et al.
synthesis of other layered metallic nanoparticles such as Bi
or Au and for salts such as Bi , Cu
S, etc.19 In addition,
the method opens up new possibilities and considerations
for the shape control of nanoparticles. More experiments are
ongoing to extend the application of this method and to
deepen our understanding of the method.
National Natural Science Foundation of China under Projects
20401014 and 20401013 and the State Key Laboratory
Science Foundation under Projects 050086 and 050097. We
also thank F. Bao and C.-P. Yang for the assistance with
the TEM and AFM measurements.
S
2 3
2
Supporting Information Available: Additional XRD patterns,
size distributions, and EDX results. This material is available free
of charge via the Internet at http://pubs.acs.org.
Acknowledgment. We thank Professor John D. Corbett
for proof reading. This research was supported by the
(19) Chen, J.; Chen, L.; Wu, L.-M. Unpublished results.
IC051246D
9822 Inorganic Chemistry, Vol. 44, No. 26, 2005