Preparation of silver nanoparticles from silver(I) nano-coordination polymer

Article abstract of DOI:10.1016/j.ica.2010.01.026

Nanorods of two-dimensional organometallic coordination polymer, [Ag(μ₄-DPOAc)]_n (1) [DPOAc^- = diphenylacetate], has been synthesized by the reaction of potassium diphenylacetate (DPOAcK) and AgNO₃ by sonochemic

Full text of DOI:10.1016/j.ica.2010.01.026

Inorganica Chimica Acta 363 (2010) 1435–1440
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Preparation of silver nanoparticles from silver(I) nano-coordination polymer
*
Kamran Akhbari, Ali Morsali
Department of Chemistry, Faculty of Sciences, Tarbiat Modares University, P.O. Box 14115-175, Tehran, Islamic Republic of Iran
a r t i c l e i n f o
a b s t r a c t
Nanorods of two-dimensional organometallic coordination polymer, [Ag(l =
4-DPOAc)]n (1) [DPOAcꢀ
Article history:
Received 11 November 2009
Received in revised form 12 January 2010
Accepted 22 January 2010
Available online 29 January 2010
diphenylacetate], has been synthesized by the reaction of potassium diphenylacetate (DPOAcK) and
AgNO3 by sonochemical process. Reaction conditions, such as the concentration of the initial reagents
played important roles in the size and growth process of the final product. Silver nanoparticles were syn-
thesized from nanorods of compound 1. These nano-coordination polymer and nanoparticles were char-
acterized by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). Thermal stability
of nano and crystal samples of compound 1 were studied and compared with each other.
Ó 2010 Elsevier B.V. All rights reserved.
Keywords:
Nano-coordination polymer
Silver nanoparticle
Sonochemical
Surfactant
Thermal analysis
1. Introduction
adsorbed onto the bacterial cellulose fibrils [13]. In recent years sil-
ver(I) complexes have found application as precursors for Chemical
Silver has been extensively used in a variety of applications
such as catalysis, electronics, photonics and photography due to
its unique properties. For example, silver has the highest electrical
conductivity, thermal conductivity and reflectivity of all metals [1].
Several methods can be applied to synthesize silver nanoparticles
with well-defined shapes. The majority of the more straightfor-
ward approaches are based on the reduction of silver nitrate by so-
dium borohydride [2] or sodium citrate [3]. Some of the more
diverse methods previously used include microwave plasma syn-
thesis [4], electrolysis of Ag salts [5], rapid expansion of supercrit-
ical solvents [6,7], microemulsion [8], and photoreduction of Ag
ions [9,10]. Recently in the last few years several methods for syn-
thesis of silver nano structures have been developed too, which
are: (a) synthesis of fine silver powder with a particle size range
of 50–1000 nm in a mechanochemical process by inducing a so-
lid-state displacement reaction between AgCl and sodium [11],
(b) synthesis of long silver nanowires with lengths of more than
50 mm, some even more than 100 mm, and average diameters of
about 80 nm at room temperature by a simple and fast process de-
rived from the development of photographic films [12], (c) synthe-
sis of metallic silver by direct hydrogen reduction of Ag2S in basic
slurry under hydrothermal conditions [1] and (d) in situ prepara-
tion of Ag nanoparticles from the hydrolytic decomposition of sil-
ver triethanolamine (TEA) complexes that lead to the formation of
spherical metallic silver particles with mean diameter of 8 nm well
Vapor Deposition (CVD) [14–17]. As mentioned above preparation
of silver nanoparticles from silver complexes reported by Barud
et al. [13], but the use of silver coordination polymers (CPs) or sil-
ver nano-coordination polymers (NCPs) to prepare silver nano
structures is sparse [18]. NCPs are generally synthesized by
exploiting the insolubility of the particles in a given solvent sys-
tem. Wang et al. reported the first synthesis of NCP in 2005 [19].
They isolated monodisperse spheres of approximately 420 nm in
diameter, taking advantage of the very low solubility in water of
the product from the reaction between the initial precursors. We
used this method to prepare NCPs by sonochemical process [20–
25]. Continuing our previous work on CPs [26–28,25,29–31], syn-
thesis of AgI NCP by sonochemical process and use this precursor
to fabricate silver nanoparticles with oleic acid as a surfactant were
reported.
2. Experimental
2.1. Materials and physical techniques
All reagents for the synthesis and analysis were commercially
available and used as received. Double distilled water was used
to prepare aqueous solutions. A multiwave ultrasonic generator
(Sonicator_3000; Misonix, Inc., Farmingdale, NY, USA), equipped
with
a converter/transducer and titanium oscillator (horn),
12.5 mm in diameter, operating at 20 kHz with a maximum power
output of 600 W, was used for the ultrasonic irradiation. Microa-
nalyses were carried out using a Heraeus CHN–O– Rapid analyzer.
* Corresponding author. Tel.: +98 21 8011001; fax: +98 21 8009730.
E-mail address: morsali_a@modares.ac.ir (A. Morsali).
0020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2010.01.026

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K. Akhbari, A. Morsali / Inorganica Chimica Acta 363 (2010) 1435–1440
Melting points were measured on an Electrothermal 9100 appara-
tus and are uncorrected. IR spectra were recorded using Perkin–El-
mer 597 and Nicolet 510P spectrophotometers. The thermal
behavior was measured with a PL-STA 1500 apparatus between
20 and 780 °C in a static atmosphere of nitrogen. Crystallographic
measurements were made using a Bruker APEX area-detector dif-
fractometer. The intensity data were collected using graphite
monochromated Mo Ka radiation. The structure was solved by di-
rect methods and refined by full-matrix least-squares techniques
on F2. Structure solution and refinement was accomplished using
SHELXL-97 program packages [32]. The molecular structure plot
and simulated XRD powder pattern based on single crystal data
were prepared using Mercury software [33]. X-ray powder diffrac-
tion (XRD) measurements were performed using a Philips X’pert
diffractometer with mono chromatized Cu ka radiation. The sam-
ples were characterized with a scanning electron microscope with
gold coating.
2.2. Synthesis of [Ag(l4-DPOAc)]n (1) and preparation
of its single crystals
In 20 ml CH3CN 0.212 g (1 mmol) 2,2-diphenylacetic acid were
mixed and stirred with a solution of 0.057 g (1 mmol) KOH in 3 ml
H2O to form a clear solution. Addition of 0.170 g (1 mmol) AgNO3
in 5 ml H2O produced a clear solution. The resulting solution was
stirred and then allowed to stand in darkness at room temperature
Fig. 1. (a) Molecular structure representations of 1, showing AgꢁꢁꢁAg and Ag–C
distances and Ag atom environment, (b)
a
fragment of the two-dimensional
Fig. 2. XRD patterns; (a) simulated pattern based on single crystal data of
compound 1, (b) nanorods of compound 1 prepared by sonochemical process, (c)
network in 1, (c) space filling representation of 1. (Ag = violet, O = red, C = gray). (For
interpretation of the references to color in this figure legend, the reader is referred
to the web version of this article.)
spongy silver prepared by calcinations of compound
nanoparticles prepared by OA at 453 K.
1 at 873 K, (d) silver

K. Akhbari, A. Morsali / Inorganica Chimica Acta 363 (2010) 1435–1440
1437
to evaporate for several days to obtain suitable crystals. The crys-
tals were washed with acetone and air dried, d.p. = 235 °C, Yield:
0.112 g (35% based on final product). IR (selected bands; in
cmꢀ1): 554m, 637m, 691s, 723s, 752m, 1023w, 1068w, 1267w,
1328w, 1374vs, 1437w, 1479m, 1531vs and 1589m. Anal. Calc.
for C14H11AgO2: C, 52.64; H, 3.45. Found: C, 52.50; H, 3.34%.
solution was degassed for 15 min and then heated to 180 °C for 1 h
under air atmosphere. At the end of the reaction, a black precipi-
tate was formed. A small amount of toluene and a large excess of
EtOH were added to the reaction solution, and metallic silver
was separated by centrifugation. The solid was washed with EtOH
and dried, neither d.p. and nor IR bands was observed.
2.3. Synthesis of [Ag(l4-DPOAc)]n (1) nanopowders
by sonochemical process
3. Results and discussion
The reaction between diphenylacetate (DPOAcꢀ) and Ag(NO3)
To prepare the nanorods of [Ag(l4-DPOAc)]n by sonochemical
provided a crystalline material of the general formula [Ag(l4
-
method, a high-density ultrasonic probe immersed directly into
the solution of DPOAcK (50 ml, 0.05 M) in double distilled water,
then into this solution, a proper volume of AgNO3 aqueous solution
(50 ml, 0.05 M) was added in drop wise manner. The solution was
ultrasonically irradiated with the power of 12 W for 1 h. The ob-
tained precipitates were filtered, subsequently washed with dou-
ble distilled water and then dried, d.p. = 200 °C, (Found C: 52.40,
H: 3.37%). IR (selected bands; in cmꢀ1): 555m, 635m, 690s, 727s,
755m, 1027w, 1069w, 1268w, 1327w, 1371vs, 1434w, 1479m,
1530vs and 1589m. Certainly we should mention that different
concentrations of metal and ligand solutions (0.0125, 0.025 and
0.125 M) with the power of 12 W for 1 h were tested but appropri-
ate nanorods of compound 1 with the best morphology and disper-
sion obtained under the mentioned conditions. In order to obtain
silver nanoparticles, precipitate of compound 1 nanorods which
obtained from 0.05 M solutions of initial reagents was calcinated
at 873 K in a furnace and static atmosphere of air for 5 h.
DPOAc)]n (1) [27]. The structure determination of 1 by X-ray crys-
tallography showed that the silver atoms can be considered to be
three-coordinate with AgO3 coordination sphere and Ag–O dis-
0
tance of 2.2063(17), 2.2519(17) and 2.4872(18) ÅA. Ag–O bonds in
similar compounds have distances in the range of 2.21–2.64 Å
[35–40]. The carboxylate group of the DPOAcꢀ ligand in compound
1 acts as a bridging group where each oxygen atom of the carbox-
ylate group coordinates to a silver(I) ion, and one of these oxygen
atoms also bridges to one other silver atom (Fig. 1a). A search was
made generally for AgꢁꢁꢁAg approaches and it appears that argent-
ophilic interactions could be observed in compound 1 with dis-
tance of 2.8463(4) Å between two Ag1 atoms. This Ag–Ag
interaction in compound 1 are longer than the Ag–Ag distances
in similar dinuclear complexes (i.e., 2.704(2), 2.669(1), and
0
2.726(1) ÅA) [41–46] and slightly shorter than those in the poly-
meric structure [47–50]. The relatively short Ag–Ag bonds found
here may thus be considered to be only d10ꢁꢁꢁd10 noncovalent inter-
actions [44–50]. A general search was also made for Ag–C ap-
proaches in compound 1 and it appears that the Ag atoms may
2.4. Synthesis of silver nanoparticles by surfactant
unexpectedly be involved in an g
1 interaction with the Cphenyl atom
To prepare silver nanoparticlas by surfactant [34], precipitates
of compound 1 nanorods (160 mg, 0.5 mmol) was dissolved in
oleic acid (OA), (8 mL, 25 mmol) and formed a yellow solution. This
of neighboring molecules with a Ag(1)–C(5) distance of 2.710(3) Å.
In compounds with similar bonds the Ag–C distances are in the
range of 2.40–2.70 Å [51–54], in [Ag(benzene)ClO4] for example
Fig. 3. SEM images of compound 1 nanorods obtained in various concentration of initial precursor; [Ag+] = [DPOAcꢀ] = (a) 0.125 M, (b) 0.05 M, (c) 0.025 M and (d) 0.0125 M.

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K. Akhbari, A. Morsali / Inorganica Chimica Acta 363 (2010) 1435–1440
they are 2.496 and 2.634 Å [45]. Some other Ag(I) polymeric com-
plexes with Ag–C (sp2) bonded polycyclic aromatic ligands have
been reported to have mean Ag–arene distances of 2.82–3.37 Å
[55–62]. Thus compound 1 can be considered to contain silver
atoms with fourfold coordination and an O3CAgꢁꢁꢁAgO3C environ-
ment (Fig. 1a). Thus, strong monohapto aromatic coordination of
Ag atoms in the compound 1 could be considered and appears to
be yet another factor which can make varying contributions to
the construction of an organometallic coordination polymer. The
structure of compound 1 may also be considered as a coordination
polymer of Ag(I) consisting of one-dimensional linear chains con-
structed of carboxylate group bridging, running parallel to the b
axis and the individual polymeric chains are almost parallel to each
other and further bridged by Ag–C bonds, resulting in a two-
dimensional framework as shown in Fig. 1b.
from this figure, concentration increase from 0.0125 M (Fig. 3d) to
0.05 M (Fig. 3b) results in monotonousness and non tenacity of the
nanorods, but the results of concentration increase from 0.05 M
(Fig. 3b) to 0.125 M (Fig. 3a) was not satisfactory. The best result
attributed to 0.05 M solution of Ag+ ion and DPOAcꢀ ligand that
shows the formation of silver nanorods with the diameter of about
80ꢀ250 nm (average diameter of 150 nm) and the length of about
0.5ꢀ3.0
lm (average length of 2 lm) as shown in Fig. 3b.
Thermal gravimetric (TG) and differential thermal analyses
(DTA) of compound 1 single crystals shows that the crystalline
form is very stable and does not decompose up to 235 °C
(Fig. 4a), at which temperature pyrolyze of compound 1 starts. In
Fig. 2a shows the simulated XRD pattern from single crystal X-
ray data of the above compound and Fig. 2b shows the XRD pattern
of a typical samples of [Ag(l4-DPOAc)]n (1) prepared by the sono-
chemical process. Acceptable matches, with slight different in 2h,
were observed between the simulated from single crystal X-ray
data patterns (Fig. 2a) and those from the experimental powder
X-ray diffraction patterns for nanopowders crystalline sample as
obtained from the synthesis by sonochemical process (Fig. 2b). Re-
sults of XRD powder patterns indicate that the experimental data
are in good agreement with the simulated XRD powder patterns
based on single crystal data, hence this compound obtained as a
mono-phase. The morphology, structure and size of the four sam-
ples which were prepared with different concentrations of AgNO3
and DPOAcK are investigated by Scanning Electron Microscopy
(SEM). Fig. 3a–d indicates that the original morphology of the
nanorods obtained by sonochemical process. As could be observed
Fig. 5. SEM images of silver spongy nano structure prepared by calcination of
compound 1 at 873 K (up), nanorods of compound 1 prepared by sonochemical
process (middle), silver nanoparticles prepared by OA at 453 K (down).
Fig. 4. Thermal behavior of compound 1 (a) single crystals and (b) nanorods.

K. Akhbari, A. Morsali / Inorganica Chimica Acta 363 (2010) 1435–1440
1439
this stage, exothermic removal of DPOAcꢀ occurs between 235 and
480 °C with mass loss of 63.0% (Calc. 63.6%). Mass loss
Acknowledgement
a
calculations and XRD pattern (Fig. 2c), shows that the final
decomposition product is metallic silver. Nanorods of compound
1 are much less stable at starts to decompose at 200 °C (Fig. 4b).
The TG curve exhibits a distinct decomposition stage between
200 and 430 °C with a mass loss of 64.2% (calcd 63.6%). Decompo-
sition of compound 1 nanorods starts at about 35° earlier than its
single crystals, probably due to different contact between crystals
and the pan, size, shape and compactness of the two samples or
due to more heat that needed to annihilate the lattices of single
crystal. This stabilization is annihilated approximately by produce
nanorods of this compound by sonochemical process.
Supporting of this investigation by Tarbiat Modares University
is gratefully acknowledged.
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