H. K. CHITTE ET AL.
20
adopted was to coat the pre-formed Ag nanoparticles
with the polymers in suspension. The nanocomposites
thus formed were characterized using UV-Vis spectros-
copy (UV-Vis), X-ray diffraction (XRD) and Scanning
electron Microscopy (SEM). The advantages of these
nanocomposites over the control polymer and industrial
applications will be reported in a separate communica-
tion.
2. Experimental
2.1. Preparation of Silver Nanoparticles
AgNO3 was dissolved in double distilled water to give a
solution of 0.001 M solution. Trisodium citrate (0.02 M)
was used as reducing agent. To 100 ml of silver nitrate
solution was added to trisodium citrate solution drop by
drop, over a period of 30 min and maintained at 80˚C.
The stirring was continued for 1 hr. It was found that
solution turns yellow. The yellow colour confirms the
formation of silver nanoparticles [3]. A large quantity of
such solution was made and served as the stock solution
for other e xp erim en t s.
2.2. Coating of Ag Nanoparticles by Polymers
The coating of silver nanoparticle by polypyrrole was
performed by addition of 4 ml of pyrrole to 600 ml of
silver nanoparticle solution. The solution was stirred con-
tinuously during and after addition and it was observed
that the conversion of pyrrole to polypyrrole takes place
within 15 min. However the stirring was continued for
another 1 hr so that the pyrrole fully polymerizes and
coats the Ag nanoparticle evenly. The color of the solu-
tion changes from yellow to steel grey to black. The ob-
tained solution was left in the ambient condition for an-
other 24 hr before the precipitated material was filtered
out and washed.
Polymeric composites of Polyvinyl alcohol and Car-
boxymethyl cellulose were prepared by mixing the aque-
ous solutions of the respective polymers and the colloidal
suspension of pre-formed silver nanoparticles. The solu-
tions of PVA and CMC were made in water using 4% of
powders (w/w) and stirring for one hour at 80˚C. To
these solutions were added the solution of AgNP to get
various compositions containing 1% to 5% of Ag. Thin
films of these solutions were casted on glass plates for
further analysis.
The results described in this paper are for composi-
tions all containing 1% w/w of Ag nanoparticles.
2.3. Methods of Characterization
All the preparations i.e. pure silver nanoparticles and the
composites were characterized by UV-Vis, XRD, SEM
and TEM. For this purpose UV-Vis Spectrometer of Var-
ian make Cary 5000 which could scan from 175 nm to
3300 nm was used. Diluted solution of nanop articles was
filled into the quartz cuv ette to obtain the spectrum. PAN
analytical Xpert pro X-ray diffractometer with Cu tube
was used for recording the XRD pattern. The specimen
in the form of thin coating on glass plate or PET film was
prepa red an d used for s canni ng in th e range of 10˚ to 80˚.
Scanning electron micrographs were obtained using JEOL
SEM model JSM 5400. The samples were mounted on the
stub and coated with a thin film of gold before observa-
tions. Transmission electron micrographs were obtained
by using Philips TEM CM200 operating at voltage of
200 kV. Structures of different polymers used for coating
of silver nanoparticles are shown in Figure 1.
3. Results and Discussions
3.1. Composite of Silver Nanoparticles with
Polypyrrole
3.1.1. U V-Vis Spectroscopy
The dispersions of silver nanoparticles display intense
colors due to the plasmon resonance absorption. The
surface of a metal is like plasma, having free electrons in
the conduction band and positively charged nuclei. Sur-
face plasmon resonance is a collective excitation of the
electrons in the conduction band near the surface of the
nanoparticles. Electrons are limited to specific vibrations
modes by the particle’s size and shape. Therefor e, metal-
lic nanoparticles have characteristic optical absorption
spectra in the UV-Vis region [3].
The UV-Vis absorption spectrum of pure silver nanopar-
ticle is shown in Figure 2. One can clearly see strong ab-
sorption at 417 nm, confirming the formation of silver
nanoparticles. The peak at 417 nm is attributed to the
surface plasmon reso nance.
UV-Vis Spectra for the solution in which pyrrole is
added is shown in Figure 3. Curve A of Figure 3 is UV-
Vis spectrum of silver nanoparticle solu tion. It shows the
strong absorption peak at 417 nm. Curve B of Figure 3
corresponds to Ag nanoparticle solution in which pyrro le
Figure 1. Molecular structures of Carboxy methyl cellulose,
Polypyrr o le and Polyvi nyl alcohol.
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