# An Influence of Concentration of Polyvinylpyrrolidone on  the Morphology of Silver Metal Formed from

Authors: Junichi Nishino; Yoshinori Kanno
Journal: Journal of Nanomaterials
 (2008)

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## Abstract

Metal silver rods having a partly regular direction on the substrate are synthesized from the fine copper particles on acrylic plastic plate immersed in 50μM-PVP and 0.1 M-AgNO3 aqueous solution. An increase of PVP concentration in the AgNO3 aqueous solution inhibits the growth of the string-shaped silver and dendrite-shaped silver as well as polyol method. The absorbance of the plasmon peak around 410 nm immersed in 0.1 M-AgNO3 aqueous solution at 25∘C for 24 hours increased with an increase of the PVP concentration.


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## Body

## 1. Introduction

In the past years, as for the silver nanoparticles, a research on the particle diameter and the form is active in the application field of catalyst, optical material, nanodevice material, and so on. While the silver nanowire and
the nanorod play an important part as a machine for the mutual connection in
the electronic device of nanoscale, nanostructure silver has been synthesized
by polyol method [1–8], electron beam irradiation under
high vacuum [9], and template method [10–14]. When silver nanorod is synthesized by the polyol method, polyvinylpyrrolidone (PVP) is added as
a protecting agent in silver nitrate ethylene glycol solution [1–3, 5, 8]. However,
when we use it for catalysts and antibacterial materials, it is important to fix the
nanosilver on the substrate from the viewpoint of the environmental protection.This study concerns the
formation of nanostructure silver fromAgNO3 aqueous solution with
PVP and the substitution technique to change from copper fine particles to
silver on a substrate, based on the displacement plating and PVP reduction
effect [15].


## 2. Experimental Details

## 2.1. Materials and Methods

PVP-K30 ((C6H9NO)n molecular weight av. 40 000), AgNO3 (99.8%), and fine copper particles (99.99%, ca. 1 μm in size, protected from oxidation) were
purchased from Tokyo Chemical Industry Co., Ltd. (Japan), Nacalai Tesque Inc. (Japan),
and Kojundo Chemical Laboratory Co., Ltd. (Japan), respectively, and used as
received. Distilled and deionized water was used as the solvent. Acrylic, polystyrene, and polyethylene plates were used as a substrate.Plastic plates were ultrasonically cleaned in
distilled and deionized water for 5 minutes, and dried by air splay as a
substrate. Copper particles were daubed by pressing to be a support between the
plastic plates, and then the weak contact particles were brown off by gas
splaying. The plastic plate was hung by nylon yarn with sticking the side of
copper particles into the solution, and set on parallel to the bottom of
beaker. Then the silver was grown at 25°C on this plate in a 0.1 M-AgNO3 aqueous solution with 0 to
100 μM-PVP for 24 hours. The
electron transfer reaction from copper metal particle to silver metal is a
simple reduction-oxidation reaction of
(1)Cu+2Ag+→Cu++2Ag,where the reaction takes place at the surface of
copper metal and proceeds from the difference in the redox potential between
Cu/Cu2+and Ag/Ag+.


## 2.2. Evaluation Methods

The
morphology of the silver metal obtained from each sample was observed by
scanning electron microscope (SEM, JEOL-5310LVB). The absorbance of solution
containing nanoparticles silver was measured with a Shimadzu UV-3150
spectrometer at room temperature in the wave length ranging from 200 to 800 nm.


## 3. Results and Discussion

SEM images of the
silver metal obtained by ionic exchange from fine copper particles on acrylic
plastic plate in the various concentrations of PVP and 0.1 M-AgNO3 aqueous solutions are shown in Figure 1.When the silver was grown in the region from 1.0 μM to 10 μM PVP concentration
solution, the silver composed of needle-shaped, string-shaped, and board- shaped was grown on the acrylic
substrate. It is understood that the string-shaped silver being twisted has a
tendency to decrease in comparison with the case of no addition of PVP as shown
in Figure 2.
In this case, a growth direction was unified, because PVP
molecules had a coordination place around the silver [16].SEM images of the silver metal obtained by ionic exchange from fine copper particles on acrylic plastic plate in the various concentrations of PVP and 0.1 M-AgNO3 aqueous solutions at 25°C for 24 hours.
(a)(b)(c)(d)SEM image of the silver metal obtained by ionic exchange from fine copper particles on acrylic plastic plate in 0.1 M-AgNO3 aqueous solutions without PVP at 25°C for 24 hours.
(a)(b)Particle-shaped silvers were observed in theAgNO3 aqueous solution with PVP concentration of 100
μM. Even if the silver particles had been
aggregated, dendrite-shaped silver would not have been formed. We can consider
that the silver grows uniformly, because the reducing PVP molecules, which have
a reduction effect [15], are fully coordinated around the silver particles in
the region of high PVP concentration.Figure3 shows the SEM image of the silver rod, which was focused on the substrate, obtained from the fine copper particles on
acrylic plastic plate in
50 μM-PVP and 0.1 M-AgNO3 aqueous solution at 25°C for 24 hours. An average diameter of silver
rods was 119 ± 25 nm in size. As the angle of branching is 60 degrees between branch and trunk, we can consider that
the silver crystal growth direction is (211) direction.Figure 3
SEM image of the silver rod, which was focused on substrate, obtained from the fine copper particles on acrylic plastic plate in 50μM-PVP and 0.1 M-AgNO3 aqueous solution at 25°C for 24 hours.To see the influence of the substrate on the
grown particles, the copper particles supported by polystyrene and polyethylene were used as a substrate with the combination of 50μM-PVP
and 0.1 M-AgNO3. The SEM images of the
silver, on polystyrene and polyethylene substrates, which was synthesized by
being immersed in the aqueous solution at 25°C for 24 hours are
shown in Figure 4.SEM images of the silver on polystyrene (a) and polyethylene (b) substrates which were synthesized by being immersed in 50μM-PVP and 0.1 M-AgNO3 aqueous solution at 25°C for 24 hours.
(a)(b)Regular arranged needle-shaped silver was not formed on the polystyrene and the polyethylene
substrates. In the present work, we can assume that a strong electronegativity
of CN groups composed of acrylic substrate significantly affects the growth of
nanosize silver, that is, it contributes to attract the PVP molecules.The absorbance of UV-visible light for
various
concentrations of PVP and 0.1 M-AgNO3 aqueous solution, which is the samples after
24 hours, is shown in Figure 5. The absorbance of the plasmon peak around 410
nm increased with increasing the PVP concentration in 0.1 M-AgNO3 aqueous solution. The peak position means that the silver in nanoparticles size
is formed and the size is 20–30 nm [1]. The position of these plasmon peaks was
shifted to shorter wavelength with an increase of the PVP concentration. This
blue shift suggests that the size of silver particles decreased by protective
effect with increasing the PVP concentration.Figure 5
Absorbance spectra of various concentrations of PVP and 0.1 M-AgNO3 aqueous solutions after 24 hours at 25°C.Figure6 shows the SEM
images of the silver obtained by ionic exchange from copper plate for TEM
sample grid on in the various concentrations of the PVP and 0.1 M-AgNO3 aqueous solution. Dendrite-shaped silver was
observed at low concentration of PVP in 0.1 M-AgNO3 aqueous solution, but not observed in high PVP
concentration.
It suggests that PVP protective effect increases with increasing
the PVP concentration as well as fine copper particles as a reducer.SEM images of the silver obtained by ionic exchange from copper plate for TEM sample grid to silver metal in the various concentrations of PVP and 0.1 M-AgNO3 aqueous solution at 25°C for 5 minutes.
(a)(b)(c)(d)


## 4. Conclusions

The silver rods having
a partly regular direction on the substrate were obtained from the fine copper
particles on acrylic plastic plate immersed in 50μM-PVP and 0.1 M -AgNO3 aqueous
solution at 25°C for 24 hours.An increase of the PVP
concentration in theAgNO3   aqueous solution
inhibits the growth of the string-shaped silver and dendrite-shaped silver as
well as polyol method.



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*Source: 592838-2008-02-21.xml*