Formation and characterization of silver nanoparticle composite with poly(p-Br/F-phenylsilane)

Article abstract of DOI:10.1166/jnn.2015.9329

The one-pot production and structural characterization of composites of silver nanoparticles with poly(p-Br/F-phenylsilane), Br/F-PPS, have been performed. The conversion of Ag⁺ ions to stable Ag⁰ nanoparticles is mediated by the cop

Full text of DOI:10.1166/jnn.2015.9329

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Nanoscience and Nanotechnology
Vol. 15, 1760–1763, 2015
Copyright © 2015 American Scientific Publishers
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Formation and Characterization of Silver Nanoparticle
Composite with Poly(p-Br/F-phenylsilane)
Sung-Hee Roh1ꢀ∗, Ji Eun Noh2, Hee-Gweon Woo2ꢀ∗, Myong-Shik Cho3, and Honglae Sohn4
1Department of Chemical and Biochemical Engineering, Chosun University, Gwangju 501-759, Korea
2Department of Chemistry, Chonnam National University, Gwangju 500-757, Korea
3Gwangu Regional Food and Drug Administration, Gwangju 500-480, Korea
4Department of Chemistry, Chosun University, Gwangju 501-759, Korea
The one-pot production and structural characterization of composites of silver nanoparticles with
poly(p-Br/F-phenylsilane), Br/F-PPS, have been performed. The conversion of Ag+ ions to stable
Ag0 nanoparticles is mediated by the copolymer Br/F-PPS having both possibly reactive Si
H
bonds in the polymer backbone and C Br bonds in the substituents along with relatively inert
F bonds. Transmission electron microscopy and field emission scanning electron microscopy
C
analyses show the formation of the composites where silver nanoparticles (less than 30 nm of
size) are well dispersed over the Br/F-PPS matrix. X-ray diffraction patterns are consistent with that
for face-centered-cubic typed silver. The polymer solubility in toluene implys that the cleavage of
C
Br bond and the Si F dative bonding may not be occurred appreciably at ambient temperature.
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Nonetheless, thermogravimetric analysis data suggest that some sort of cross-linking could take
place at high temperature. Most of the silver particles undergo macroscopic aggregation without
Br/F-PPS, which indicates that the polysilane is necessary for stabilizing the silver nanoparticles.
IP: 137.189.170.231 On: Fri, 13 Feb 2015 08:07:14
Copyright: American Scientific Publishers
Keywords: Composite, Cross-Linking, Polymeric Reducing Agent, Polymeric Stabilizer,
Dehydrocoupling, Silver Nanoparticles, Copolysilane.
1. INTRODUCTION
have some disadvantages, i.e., the high inclinations of
oxidative deterioration and aggregation when compared
to the nanoparticles of gold and platinum metals. Thus,
the protection of silver nanoparticles with proper poly-
mer matrix should be absolutely necessary for proper
applications.
An inorganic polymer with Si Si bonding in the back-
bone, poly(p-Br/F-phenylsilane), (Br/F-PPS) was chosen
as a stabilizer in this study. Inorganic polymers are gen-
erally known to have better optoelectronic and mechan-
ical properties than organic polymers with main group
element C in the backbone.11 Hydrostannanes (or tin
hydrides) and hydrogermanes (or germanium hydrides)
in spite of their low bond energy (bond energy: 66
and 75 kcal/mol, respectively)12 are not suitable because
hydrostannanes are well known as toxic materials and
hydrogermanes are quite expensive. In contrast, hydrosi-
lanes (or silicon hydrides) are cheap and are reason-
ably not toxic. Thus, hydrosilanes (Si H bond energy:
88 kcal/mol)12 or polysilanes might be proper choice for
Metals (Lewis acid) can be stabilized by the coordina-
tion of ligands (Lewis base) to form a complex. Polymer-
protected, colloidal noble metal particles (i.e., Ag, Au, Pt)
have received great attention because of their diverse appli-
cations in industry: e.g., in catalysis, electronics, green
commodity, etc.1–5 In particular, suitable silver nanopar-
ticles is important because bulk silver metal reveals the
highest electrical and thermal conductivity among all met-
als, and the performance of silver metal in many appli-
cations may be significantly enhanced by processing bulk
silver into nanosized silver.6 A few methods have been
devoted to prepare different shaped silver nanostructures:
(1) silver nanodisks, synthesized by using polystyrene
mesospheres as templates7 and (2) silver nanowires pre-
pared by using physical templates (e.g., carbon nanotubes,8
mesoporous materials,9 organic nanotubes arrays,10 etc.).
Nonetheless, the high surface area of silver nanoparticles
∗Authors to whom correspondence should be addressed.
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doi:10.1166/jnn.2015.9329

Roh et al.
Formation and Characterization of Silver Nanoparticle Composite with Poly(p-Br/F-phenylsilane)
this experiment. In particular, Br/F-PPS is well suited
for hosting noble metal nanoparticles for the following
reasons:
(1) Hydrosilanes with backbone Si H bonds, well-
known reducing agents, have been successfully used for
the generation of Pt, Pd, and Rh nanoparticles in the con-
text of metal-catalyzed hydrosilylation of alkenes.13 Br/F-
PPS with Si H functionalities in the backbone can act as
a reducing agent and thus can eliminate the need for an
extra reducing agent.
(2) The Si Si and C Br bond (bond energy: 53 and
68 kcal/mol, respectively)12 may have chance of being
homolytically cleaved during the composite formation for
inducing a chemical cross-linking of polymer matrix.
(3) Furthermore, although C F bond may not be cleaved
because of high bond energy (116 kcal/mol), F-PPS could
undergo a physical cross-linking by a weak dative inter-
action between empty 3d orbitals of Si atoms (in back-
bone) and filled p orbitals of F (in substituent). In our
approach, well-defined polyhydrosilanes are expected to
act as reducing agents, as well as templates to control the
size, stability, and solubility of nanoparticles ranging in
diameter from less than 1 up to 30 nm.
on a Perkin Elmer 7 Series Thermal Analysis System
under a nitrogen flow. Polymer sample was heated from
25 ꢀC to 700 ꢀC at a speed of 20 ꢀC/min. Ceramic
residue yield is reported as the percentage of the sam-
ple remaining after completion of the heating cycle.
UV-Vis absorption spectra of samples were taken using
a Hitachi U-3501 spectrometer. The transmission electron
microscopy (TEM) images of the nanocomposites were
obtained using a Tecnai F20 transmission electron micro-
scope. Samples for TEM analysis were prepared by dip-
coating a solution of a sample on formvar/carbon-film Cu
grids (20 mesh, 3 mm). The average particle size and dis-
tribution were determined based on the measurement of
at least 100 particles. The SEM image of the nanocompos-
ite was obtained on a JSM-7500F field emission scanning
electron microscopy (FE-SEM). X-ray diffraction (XRD)
measurements were obtained with a D-Max-2400 diffrac-
tometer, equipped with graphite monochromatized Cu Kꢀ
radiation (ꢁ = 0ꢂ154 nm). The total diameter (includ-
ing the polysilane shell) of the silver nanoparticles was
determined using dynamic light scattering (DLS) on a
particle size analyzer (Malyern Zetasizer Nano) analy-
ꢀ
sis. All the measurements were done at 25 C. For the
test, three replicate samples were used, and the aver-
age values were quoted. LiAlH4, zirconocene (Cp2ZrCl2),
Red-Al (Na[H2Al(OCH2CH2OCH3ꢃ2]), and silver nitrate
(AgNO3ꢃ were purchased from Aldrich Chemical Co. and
(4) The glass-transition temperature (Tg) of Br/F-PPS is
relatively lower than that of industrial organic polymer,
such as polyvinyl chloride (PVC), polycarbonate (PC) or
acrylonitrile-butadiene-styrene (ABS). This physical prop-
erty has the advantage of making it easier to investigate the
morphology of nanosilver/PPS composites as a function
of their thermal treatment conditions at relatively lower
fabrication temperatures.
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were used as received without further purification. (p-X-
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C6H4)Si(OEt)3 (X = F, Br) was prepared by the controlled
Copyright: American Scientific Publishers
Grignard reaction of 1,4-dibromobenzene (and 1-fluoro-
4-bromobenzene) with Si(OEt)4. (p-X-C6H4)Si(OEt)3 was
then converted to (p-X-C6H4)SiH3 with LiAlH4 in diethyl
ether solvent in good yield.
Here we report the one-step preparation and structural
characterization of silver nanoparticles/PPS composites.
We also will discuss the synthesis parameters (including
Br/F-PPS concentrations) influence the size and/or shape.
2.2. Dehydrocoupling of (p-Br/F-C6H4)SiH3 Catalyzed
by Cp2ZrCl2/Red-Al Combination
In a typical dehydrocoupling synthesis, (p-Br-C6H4)SiH3
(1.55 g, 8.30 mM) and (p-F-C6H4)SiH3 (0.12 g, 0.92 mM)
were slowly added to a Schlenk flask containing Cp2ZrCl2
(54.0 mg, 0.18 mM) and Red-Al (56.0 ꢄL, 0.18 mM;
3.40 M solution in toluene). The reaction mixture immedi-
ately turned light yellow, and the reaction medium became
rapidly viscous with the vigorous evolution of hydrogen
gas. The reaction mixture was allowed to stir under a
stream of nitrogen for 24 hrs to reach the steady state
of polymer molecular weight distribution. The catalyst
was allowed to oxidize by exposure to the air, and then
the mixture was dissolved in toluene. The solution was
then passed rapidly through a Florisil column (100–200
mesh, 20 cm × 2 cm) under air atmosphere. The col-
umn was rinsed with 200 mL of toluene. The removal
of volatiles at reduced pressure gave clear tacky product.
2. EXPERIMENTAL DETAILS
2.1. General Considerations
All reactions and manipulations were performed under
ambient air atmosphere unless specified. Fourier-transform
infrared (FT-IR) spectra of Br/F-PPS were acquired with
a Nicolet 520P FT-IR spectrometer. Proton nuclear mag-
netic resonance (1H NMR) spectra of Br/F-PPS were
recorded on a Varian Gemini 300 spectrometer (oper-
ating at 300 MHz) using CDCl3/CHCl3 as a reference
at 7.24 ppm downfield from tetramethylsilane (TMS).
Gel permeation chromatography (GPC) was carried out
on a Waters Millipore GPC liquid chromatograph. The
calibrant (monodisperse polystyrene standard) and the
sample were dissolved in tetrahydrofuran (THF) and
separately eluted from an Ultrastyragel GPC column
series (sequence 500, 103, 104 Å columns). Molecu-
lar weights were extrapolated from the calibration curve
derived from the polystyrene standard. Thermogravimet-
ric analysis (TGA) of polymer sample was performed
1
The product was identified as Br/F-PPS by H NMR, FT-
IR, and GPC. FT-IR (film, KBr, cm−1): 2111 (ꢅSi H).
1H NMR (CDCl3, 300 MHz, ꢆ ppm): 3.50–4.50 (br,
SiH), 6.30–7.70 (br, C6H4). GPC Mw = 2650, Mn = 2220,
J. Nanosci. Nanotechnol. 15, 1760–1763, 2015
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Formation and Characterization of Silver Nanoparticle Composite with Poly(p-Br/F-phenylsilane)
PDI (Mw/Mnꢃ = 1ꢂ19. TGA residue yield = 45% (at
Roh et al.
ꢀ
700 C).
p-Br/F-C6H4
Cp2ZrCl2/Red-Al
Si
H
(p-Br/F-C6H4)SiH3
neat, R.T.
-H2
n
2.3. Synthesis of the Nanosilver/Br/F-PPS Composites
Br/F-PPS composite with silver nanoparticles were syn-
thesized by reducing AgNO3 in the presence of Br/F-PPS
in toluene. Br/F-PPS (0.81 g, 4.60 mM) was dissolved in
50 mL of toluene, and AgNO3 (0.131 g, 0.77 mM) was
added (thus maintaining the weight ratio between AgNO3
and Br/F-PPS approximately equal to 1:6) while stirring
gently at room temperature under ambient atmosphere.
The color of the reaction mixtures changed rapidly from
light yellow to dark brown, indicating the formation of sil-
ver nanoparticles. Finally, the mixture was separated by
ultracentrifugation. After collecting the deposit, washing
with THF several times and vacuum-drying, the Ag/Br/F-
PPS composite was acquired. TGA residue yield = 83%
Figure 1. XRD pattern of the Ag/Br/F-PPS nanocomposites prepared
by reacting AgNO3 with Br/F-PPS.
silver nanoparticles well dispersed over Br/F-PPS matrix.
Corresponding selected area electron diffraction (SAED)
of the silver nanostructure shown in inset of Figure 2(d).
The clear spots in Figure 2(d) (SAED of the silver nano-
structures) indicate that these Ag nanoparticles are sin-
gle crystals and can be indexed to (1ꢇ1ꢇ1). (2ꢇ2ꢇ2), and
(3ꢇ3ꢇ1) reflections from fcc silver, and the zone axis pro-
jection is along.14
The ceramic reside yield of Br/F-PPS was enhanced
from 45% to 85% after treating with AgNO3 while that
of PPS is 39%, indicating C Br and C F contribute to
the increase of TGA ceramic yield by the small degree of
cross-linking with C Br bond hemolysis and F Si dative
bonding at high temperature, respectively. This fact sug-
gests that the thermal stability of the polymer is improved
due to the presence of silver as a nanofiller and a cross-
linking agent at high temperature.
If decreasing the concentration of Br/F-PPS to one-
third of the original one (thus maintaining the weight
ratio between AgNO3 and Br/F-PPS approximately equal
to 1:2) and keeping other conditions constant, the big-
ger spherical nanoparticles are mainly obtained because
of the increase of aggregation of silver nanoparticles. The
TEM images (Fig. 3) of the sample show that they are of
ꢀ
(at 700 C). XRD, FE-SEM, and TEM analyses were per-
formed on the composite sample.
3. RESULTS AND DISCUSSION
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When a mixture of AgNO3 in toluene is reduced in the
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presence of Br/F-PPS (Scheme 1), the color of the solu-
tion changes from pale yellow to dark brown due to the
reduction of Ag+ ions to Ag0 nanoparticles. UV-Vis spec-
tra (operating range 180–1000 nm; cuvette path length:
10 mm) were obtained to confirm the formation of silver
nanoparticles.
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Figure 1 shows the XRD patterns of the samples pre-
pared by the reaction AgNO3 with Br/F-PPS where Br/F-
PPS serves as both structure-directing (stabilizing) agent
and reducing agent. All diffraction peaks can be readily
indexed to fcc (face-centered-cubic) silver with a calcu-
lated parameter a = 4ꢂ09 Å, which is in good agreement
with the literature values (JCPDS 4-0783). The sharp-
ness of the peaks indicates that the products are well
crystallized.
TEM images (Figs. 2(a) and (b)) of the nanosilver/Br-
PPS composites in Figure 2 show that they are of
the randomly ramified nanostructure, composed of near-
spherical nanoparticles with about 10–20 nm in diame-
ter. The total diameter including the Br/F-PPS shell of
the silver nanoparticle was 131.3 8.4 nm. SEM image
(Fig. 2(c)) of the nanosilver/Br/F-PPS composite exhibits
reduction
Ag+
Ag0
[Ag0/Br/F-PPS]
+
Br/F-PPS
toluene
Figure 2. TEM images ((a) and (b)) and SEM image (c) of nano/Br/F-
PPS nanocomosites. Inset of (d) shows the selected area electron diffrac-
tion patterns of the silver nanostructures.
Scheme 1. Preparation of nanosilver/Br/F-PPS composite.
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Roh et al.
Formation and Characterization of Silver Nanoparticle Composite with Poly(p-Br/F-phenylsilane)
formation of the silver nanostructures, namely it provides
lots of active sites for the coordination, nucleation, growth
and serves as backbones for the assembly of the nanopar-
ticles formed. Poly(p-Br/F-phenylsilane)s, Br/F-PPSs with
Si H functionalities also can act as a reducing agent
and thus can eliminate the need for extra reducing agents
which will be problematic to remove after reaction. The
inorganic polymer, Br/F-PPS, apparently stabilizes the sil-
ver nanoparticles by preventing them from aggregating.
The amount of Br/F-PPS added to the solution can affect
the growth process of the silver nanoparticles. SEM and
TEM analyses revealed that the particle dimension is
nanometer scale.
Figure 3. TEM images ((a) and (b)) of the bigger spherical silver
nanoparticles. Inset of (a) shows the selected area electron diffraction
patterns of the silver nanostructures.
the randomly ramified nanostructure, composed of near-
spherical nanoparticles with about 15–30 nm in diameter.
The hydrophobic backbone and Si H bonds of
the polymers apparently induce the stabilization of the
hydrophobic silver colloid particles, but also promote the
agglutination of the primary polymer chains to a more
complex, three-dimensionally functionalized structure. The
reaction scheme for producing spherical nanoparticles
involves the reduction of the soluble silver (+ 1) complex
species, nucleation of metallic particles, and growth of the
individual nuclei in the presence of a suitable reducing and
stabilizing agent. The presence of Br/F-PPS is essential for
preventing the coalescence of the nuclei during the growth
Acknowledgment: This research was supported by the
Global Research Laboratory (Grant Nos. K20903002024-
12E0100-04010) through the National Research Founda-
tion of Korea (NRF) funded by the Ministry of Science.
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Copyright: American Scientific Publishers
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4. CONCLUSION
A one-step conversion of Ag+ ions to stable Ag0 nanopar-
ticles is made rapidly by a simple and mild Br/F-PPS-
mediated reduction. PPS plays an important role in the
Received: 19 June 2013. Accepted: 13 November 2013.
J. Nanosci. Nanotechnol. 15, 1760–1763, 2015
1763