C.P. Shah et al. / Materials Research Bulletin 45 (2010) 56–62
57
2
. Experimental details
nitrogen, as a carrier gas. NMR spectra of the samples were taken
on Bruker machine.
High purity polyvinyl alcohol (PVA) of molecular weight
1
25,000 and AR grade acrylamide (AM) obtained from S.D. Fine
3. Results and discussion
0
chemical, laboratory grade N,N -dimethylene bis acrylamide
(
BisAM) from sigma, methyl methacrylate (MMA) from R.
In an attempt to synthesize polymer–selenium nanoparticle
composites by radiation-induced method, it was observed that
sodium selenosulphate reacts with vinyl monomers, precipitating
elemental selenium, under ambient conditions. The simplicity and
environmental friendly nature of the reaction drove us to study it
in detail, and to develop it as a new method for production of
selenium nanoparticles. A detailed study of the reaction was first
carried out with acrylamide monomer, in the presence of PVA
stabilizer, to produce selenium nanoparticles. Then, it was
extended to other vinyl monomers, such as sodium acrylate,
Johnson, acrylic acid from Ferak Berlin and selenium powder
from Aldrich, were used as received. All the other chemicals
used were of GR grade, procured from the local market. Sodium
acrylate (NaA) was prepared by neutralizing acrylic acid
monomer with sodium hydroxide, and the final pH of the
solution was adjusted to ꢀ8. Aqueous solutions were prepared,
using water obtained from Millipore-Q water purification
system. Sodium selenosulphate was prepared by the method
reported earlier, using reaction between aqueous Na
solution and Se powder [16]
2 3
SO
0
N,N -dimethylene bis acrylamide, methyl methacrylate,
a-methyl
styrene, etc. PVA was found to be an efficient stabilizer for
selenium, as its presence in the reaction mixture resulted in the
formation of orange/red coloured selenium nanoparticle sols,
while in its absence, black elemental selenium powder precipi-
tated out from the reaction mixture. Kinetics of the formation
reaction and particle size of synthesized selenium nanoparticles,
by reaction of sodium selenosulphate with different monomers,
have been investigated.
Na
2
SO3ðaqÞ þ SeðsÞ ! Na
2
SeSO3ðaqÞ
(1)
Briefly, a mixture of selenium powder (2 g) and solution of
SO (20 g) in 100 ml water was refluxed at 70 8C, for about 7 h.
Na
2
3
After completion of the refluxing process, the reaction mixture was
filtered, and the solution obtained was kept in dark to prevent
photo-oxidation. This sodium selenosulphate solution (ꢀ0.25 M),
containing unreacted Na
2
SO
3
, was used as a stock for Se precursor.
The intensity of the selenium nanoparticle sols was found to be
dependent on the concentration of sodium selenosulphate taken in
the reaction mixture. A typical selenium nanoparticle sol formed
1
% PVA stock solution was prepared by the addition of 1.0 g of PVA
into 100 ml water, while stirring at 80 8C. Both these stock
solutions were diluted with water, to the required concentrations,
for different experiments.
ꢂ3
ꢂ3
by the reaction of 1.0 ꢁ 10 mol dm
sodium selenosulphate
ꢂ2
ꢂ3
with 1.6 ꢁ 10 mol dm acrylamide, in the presence of 0.05%
PVA-stabilized Se nanoparticles were synthesized by reaction
PVA is shown in Fig. 1.
ꢂ4
of sodium selenosulphate (concentration 5 ꢁ 10
to 1.5 ꢁ
Selenium nanoparticles are known to exhibit a regular
ꢂ3
ꢂ3
)
1
0
mol dm
with different vinyl monomers in aqueous
absorption maximum, in the wavelength region above 350 nm,
only when particles size is 150 nm, or more. Both the absorption
maximum and the peak intensity are reported to change with the
particle size. The absorption maximum generally shifts towards
red, and the peak intensity decreases with increase in the size of
the nanoparticles [7,17]. Fig. 2 shows the effect of concentration of
medium, in the presence of PVA as a stabilizer, in the concentration
range 0.05–0.15%. The formation of selenium nanoparticles was
studied for different time periods, depending on the nature and the
concentration of the monomer used. Completion of the reaction,
during the study of the reaction kinetics, was checked by
spectrophotometric method as well as by the addition of dilute
nitric acid in a small volume of the reaction mixture, after
separating the selenium nanoparticles, using high-speed centri-
fuge (acid test). The presence of unreacted sodium selenosulphate
was indicated by almost instantaneous development of red colour
due to the acid-induced formation of selenium nanoparticles [7].
UV–vis optical absorption spectra of the selenium nanoparticle
sols were recorded, using a double beam spectrophotometer,
model Spectroscan 2600 from Chemito. XRD patterns of the
nanoparticles were recorded with a Phillips X-ray diffractometer,
model PW 1710, using a Cu Ka source (l = 0.15406 nm). DSC
measurements were carried out, using a Mettler TA 3000 thermal
analysis system. About 5–10 mg of the synthesized selenium
nanoparticles and standard selenium powder were weighed into
aluminum crucibles separately, and DSC measurements of both the
samples were carried out in N
0 8C/min., from 50 to 250 8C (model DSC-30). Selenium nano-
particles, separated from aqueous sols, using high-speed
2
atmosphere, at a heating rate of
1
a
centrifuge, at about 15,000 rpm, washed with water and dried
at room temperature, were used for XRD and thermal analysis
measurements. AFM analysis of the synthesized selenium nano-
particles was carried out, using a Solver P47 model from NT-MDT,
Russia. SEM of the synthesized selenium nanoparticle was
recorded, using a TESCAN VEGA MV 2300 T/A digital microscope.
TEM characterization was carried out with a JEOL-2000 FX electron
microscope, using the sample on a copper grid coated with a thin
amorphous carbon film. Gas chromatography experiments were
carried out on GC 8610 model from Chemito, using a Porapak-Q
column of length of 6 ft and diameter of 1/8 in., at 230 8C, and
Fig. 1. Aqueous selenium nanoparticles sol obtained by the reaction of 1.0 ꢁ
10ꢂ3 mol dmꢂ3 sodium selenosulphate with 1.6 ꢁ 10ꢂ2 mol dmꢂ3 acrylamide in the
presence of 0.05% PVA.