This document summarizes research characterizing nano-Ag/PVP composites synthesized via ultra-violet irradiation. Nano-silver/polyvinylpyrrolidone composites were prepared by reducing silver nitrate and polymerizing N-vinyl pyrrolidone simultaneously under UV light, without additional reagents. Characterization using FT-IR, XRD, TEM and XPS showed that spherical silver nanoparticles around 5 nm were homogenously dispersed in the PVP polymer matrix. Spectroscopy indicated interactions between nano silver and carbonyl oxygen as well as nitrogen groups in PVP through pi-conjugation effects.

1. JOURNAL OF COAL SCIENCE & ENGINEERING
(CHINA) DOI 10.1007/s12404-010-0214-6
pp 188–192 Vol.16 No.2 June 2010
Characterization of nano-Ag/PVP composites synthesized via
ultra-violet irradiation
HUANG Wen-yao, XU Guo-cai
( School of Chemical Engineering, Anhui University of Science and Technology, Huainan 232001, China )
© The Editorial Office of Journal of Coal Science and Engineering (China) and Springer-Verlag Berlin Heidelberg 2010
Abstract Nano-silver/polyvinylpyrrolidone(PVP)composite materials were successfully
synthesized bi-insitu from silver nitrate solution with N-vinyl pyrrolidone (NVP) monomer,
containing neither initiator nor reductant, in ultraviolet irradiation conditions. The resultant
Ag/PVP nanocomposites were characterized by infrared spectroscopy (FT-IR), high reso-
lution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy
(XPS), and X-ray diffraction (XRD). TEM show that nano silver particles are homogene-
ously dispersed in PVP polymer matrix, and the mean size of spherical silver particles is
about 5 nm. The spectroscopy of XPS and FTIR showed that there is an interaction be-
tween nano silver not only with carbonyl oxygen but also with the nitrogen group within the
NVP molecule through the p-π conjugation effect in the nano-silver/PVP composites sys-
tem.
Keywords nano-Ag, NVP, nanocomposites, ultraviolet irradiation
development of the nanotechnology. Silver nanocom-
Introduction
posites have their unique physical and chemical prop-
With the rapid development of polymer-based erties, including reversible metal/insulator electronic
nanocomposites in recent years, researches on poly- transition, nonlinear optical effect, the effect of light
mer-based metal nanocomposite materials have energy conversion, catalytic effect, and so on (Yao et
aroused considerable interest because of their exten- al., 2003). Generally, nanometal-polymer composites
sive application in catalysis, magnetic recording, mi- are prepared by following method: the metal ions are
croelectronics, etc. (Khanna et al., 2007). Metal reduced to nanoclusters in polymer solution, such as
nanoparticles, particularly gold, silver, and copper par- nano Gold/PVP (polyvinylpyrrolidone) (Liu et al.,
ticles, have been the focus of great interest because of 2006) and nano Ag/polymethacrylic acid (Quaroni and
their unique properties. For instance, nanometer-sized Chumanov, 1999). In this case, nanometal particles
particles containing a gold core and poly (methyl me- congregate probably in the polymer matrix because
thacrylate) shells as protector were prepared by sur- polymerization and reduction of metal ions occurred
face-confined living radical polymerization on gold separately. Certainly the homogeneous dispersion sys-
nanoparticles (Li et al., 2009). Based on their advan- tem of polymer-based nanometallic composites was
tageous properties and many new characteristics com- obtained since the synthesis technique was improved,
pared with corresponding single-phase metal or poly- such as polymer solution containing nano Ag (Han
mer, the synthetic technique for polymer-based nano- et al., 2007).
metal composites has been renewed quickly with the To avoid effecting the congregational phenome-
Received: 7 August 2009
Tel: 86-554-6668485, E-mail: wyhuang@aust.edu.cn

2. HUANG Wenyao, et al. Characterization of nano-Ag/PVP composites synthesized via 189
non of the nanometal particles, the bi-insitu synthetic color changes of the reaction system were observed,
technique is put forward, whereby a kind of poly- which were from colorless to canary, saffron yellow,
merizable monomer and metallic ions coexisting in the even to hypermelanic brown with the reduction of Ag
same system are simultaneously transformed into ions to Ag atoms, even to Ag clusters. When the reac-
composites with polymer as continuous phase and tion system was put into ethanol in the right propor-
nano metallic particles as disperse phase, respectively. tional volume of the reaction system, nano-Ag/PVP
Thus, the bi-insitu synthetic technique is a new tech- composites as powder were obtained after precipita-
nique in which polymer as continuous phase and nano tion, washed with methanol, and finally subjected to
metallic clusters as disperse phase are simultaneously vacuum drying at 80 ℃ for 12 h for subsequent test-
formed in one system. The advantage of this method is ing.
that nanoparticles can be homogeneously dispersed in Characterization of Ag/PVP nanocomposites was
the polymer and the preparation process can be sim- done as follows: The size and morphology of nano-
plified (Kim et al., 2007). Up to now, some typical silver particles in Ag/PVP Nanocomposites was ob-
methods used in bi-insitu synthetic technique include served by high-resolution transmission electron mi-
ultraviolet, γ-ray (Choi et al., 2005), microwave (Jiang croscopy (HRTEM) of the JEM-2010 (JEOL Ltd.)
et al., 2006), ultrasound (Xu et al., 2007), and so on. when a little of the powder samples was dispersed in
The photochemical method has received extensive acetone to form a dispersion system and the suspen-
attention because this method has some advantages, sion was dropped to a copper grid. The brown samples
such as, without other components, homogeneous nu- were pressed into a pellet together with potassium
cleation. Some research (Liao et al., 2009) on poly- bromide for testing of Fourier transform infrared spec-
mer-based nano Cu or nano Pd composites has been troscopy (FTIR). All infrared spectra were recorded on
reported, but the preparation and characterization of a VECTOR-33 FT-IR spectrometer (Germany Bruker
nano silver-organic polymer prepared bi-insitu by ul- Corporation), with the wave number ranging from 500
to 4 000 cm 1 at a resolution of 2 cm 1. The X-ray
- -
traviolet irradiating technique have not been reported.
PVP is a common dispersant, and possesses a powder diffraction (XRD) patterns of the samples
greater coordination with the transition metal ions were determined at a scanning rate of 0.02°/s in 2θ
such as gold, silver, and platinum ion, and so on. ranging from 10° to 90°, using XD-3 X-ray dif-
What’s more, PVP has a strong affinity interaction fract-meter (XD-3 X-ray powder diffract meter, Bei-
with reduced metal atoms and metal clusters (Ma et al., jing General Instrument Co., Ltd.). XPS measurements
2004). In this paper, nano-silver/polyvinylpyrrolidone were performed using a VG-Scientific ESCALAB 250
(PVP)composite materials were prepared from the spectrometer (XPS USA Thermo Corporation).
silver nitrate solution containing NVP at room tem-
2 Results and discussion
perature bi-insitu by ultraviolet irradiating technique,
and the interaction between nano silver and PVP is The infrared spectra of PVP and nano-Ag/PVP
discussed. composites are shown in Fig.1. It was found that all
peaks were identical in both Ag/PVP composite and
1 Experimental
pure PVP, which confirmed the formation of PVP in
To prepare the Ag/PVP Nanocomposites, a nanocomposites. Some special peaks were shown as
known quantity of silver nitrate (3 mL, 8%) (A.P. follows: the stretching vibration peak of C═O at
1 673 cm 1, that of —C—N— at 1 290 cm 1. The
- -
Huainan City Chemistry Reagent Factory, China) was
amplifying spectrum from 1 550 cm to 1 820 cm 1 is
-1 -
added to 100 mL distilled water containing a quantity
of NVP (7 mL) (N-vinyl pyrrolidinone, A.P., Jiaozuo presented in Fig.1(b). The stretching vibration absorp-
tion peak of carboxyl (1 661 cm 1) of the nano-Ag/
-
Media Fine Chemicals Co., Ltd, China), and the solu-
PVP composite was shifted 12 cm 1 to the right in
-
tion was irradiated by UV (under UV lamps of 125A
UV Curing Machine, Beijing Aishi Bo Printing Tech- comparison with the stretching vibration absorption
peak of carboxyl (1 673 cm 1) of pure PVP, which was
-
nology Development Center) after stirring. The reac-
tion was finished after about 40 min, so nano-Ag/PVP because of the carboxyl in nano-Ag/PVP composites
composites were formed when NVP was polymeri- probably gaining part electrons cloud of the silver at-
zated and Ag ions were reduced simultaneously under oms. Therefore, there was a certain chemical action
UV irradiating. During the reaction procedure, the between silver nanoparticles and the carboxyl of the

3. 190 Journal of Coal Science & Engineering (China)
PVP in nano-Ag/PVP composites. It was consistent surface of the nano Ag sticks have obvious dark stripes.
with the result reported by the Yang (Yang and Yun, It was suggested that nano-silver particles in the
2005). growth process acquired stacking faults (Wu et al.,
2007) due to the interactions between nano silver and
PVP. These features might make nano-silver particles
have some special properties. The corresponding se-
lected area electron diffraction is shown in the up-
per-right corner of Fig.3. The diffractive cycles of the
pattern are observed, which indicate that the nano sil-
ver particles were face-centered cubic crystal accord-
ing to the electron diffraction formula (d=K/R,
K=20.08).
Fig.1 FT-IR spectra of PVP and nano-Ag/PVP composites Fig.3 TEM images of nano-Ag/PVP composites
The XRD pattern of Ag/PVP nanocomposites is To gain more information on the surface of na-
shown in Fig.2. The XRD pattern reveals that silver no-Ag/PVP composites, XPS techniques were em-
nanoparticles possessed the diffraction peaks with 2θ ployed to detect the composition of the examples.
values of 37.986, 44.128, 64.438 and 77.392°, corre- Fig.4 shows the XPS spectrum of the surface of nano-
sponding to the (111), (200), (220) and (311) of the Ag/PVP composites. The elements of C, O, N, and Ag
crystalline silver (PDFWIN#87-0597) respectively. of the samples were detected, as shown in Fig.4(a), in
There was one diffraction peak at 2θ=20° with the correspondence with the component of Ag/PVP com-
broad peak for PVP polymer (Bai et al., 2005). posites. The XPS spectrum of Ag3d is shown in Fig.
4(b); the binding energy of Ag3d3/2(374.2 eV) increased
1.2 eV in contrast to the standard binding energy of
Ag3d3/2 (373.0 eV), and the energy spectrum peaks of
Ag3d3/2 moved to the high binding energy region,
which indicates that the chemical environment of
nano-Ag was changed because of nano silvers losing
part electronics cloud by the coordination action be-
tween nano-Ag and the other atom. Moreover, valence
electron density and the shielding effects of domestic
electronic shell of nano-Ag were decreased, so the
Fig.2 XRD pattern of nano-Ag/PVP composites
binding energy within the electronic shell of nano-Ag
The TEM image of the nano-Ag/PVP composites was increased, which was consistent with other reports
is shown in Fig.3. It was found that the nano silver (Jiang et al., 2004).
particles were homogeneously dispersed in polymer Fig.4(c) shows C1s fitting spectra that were fitted
matrix, and the mean size of spherical particles was by OriginPro7.5 downloaded from the net. Curve 1
about 5 nm. The results suggest that the uniform and was the C1s fitting spectrum of C—N, curve 2 for the
stability system of nano-Ag with PVP coating was C1s fitting spectrum of C═O, curve 3 for the C1s fit-
conveniently obtained by means of bi-insitu technol- ting spectrum of —CH2—CH2—, and curve 4 was the
ogy. A careful observation of the TEM image shows a superposition peak of C1s fitting spectrum in the three
few nano Ag sticks among the nanoparticles, and the chemical environments. From Fig.4(c), the C1s binding

4. HUANG Wenyao, et al. Characterization of nano-Ag/PVP composites synthesized via 191
conjugation is concerned, it was a kind of p-π conju-
gation system, that was π3, which consisted of two
electrons of N, one electron of C and O atoms, respec-
tively, as shown in Fig.5. It was documented that car-
bonyl oxygen obtained part electronic cloud from nano
silver cluster; conversely, the electron cloud of the
carbonyl oxygen was delocalized to the carbonyl car-
bon atom and nitrogen atom. Finally, the comprehen-
sive result shows that the electron cloud density of
nitrogen, carbonyl oxygen, and carbonyl carbon were
toward average distribution through the conjugation
effect. Thus, one important phenomenon was that
there was not only an interaction between nano silver
and carbonyl oxygen (Li et al., 2008), but also an in-
teraction with nitrogen and carbonyl carbon through
the p-π conjugation effect in the nano-silver/ PVP.
Fig.5 Schematic diagram of the interaction between
nano-Ag and PVP
3 Conclusions
Nano-silver/polyvinylpyrrolidone composites we-
re successfully prepared bi-insitu under ultraviolet
irradiation. The resultant Ag/PVP nanocomposites
were characterized by means of FT-IR, XRD, HRTEM,
and XPS. FT-IR improved the existence of polyvi-
nylpyrrolidone and the interaction of nano-silver with
polyvinylpyrrolidone. XRD interpreted the existence
of nano Ag crystal. HRTEM showed that nano silver
particles were homogeneously dispersed in PVP
polymer matrix, and the mean size of spherical silver
particles was about 5 nm. XPS showed that there was
an interaction between nano silver not only with car-
Fig.4 XPS of nano-Ag/PVP composites powder bonyl oxygen but also with nitrogen atom within NVP
molecule through the p-π conjugation effect in the
energy (285.61 eV) of C═O reduced 2.18 eV com- nano-silver/PVP composites system.
pared with the standard C1s binding energy (287.79
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