Riley oxidation: A forgotten name reaction for synthesis of selenium nanoparticles

Article abstract of DOI:10.1016/j.materresbull.2010.05.013

A simple wet chemical method, involving reaction of acetone with selenium dioxide, has been developed, to synthesize polyvinyl alcohol-stabilized selenium nanoparticles. The method is capable of producing nanoparticles in the size range of about 100-300 nm, under ambient conditions. The synthesized nanoparticles can be separated easily from the aqueous sols by a high-speed centrifuge, and can be re-dispersed in aqueous medium by a sonicator. The effect of concentrations of selenium dioxide, acetone and PVA on the size of the selenium nanoparticles has been studied. The size of the selenium nanoparticles has been found to increase with increase in the reaction time as well as the concentration of selenium dioxide, while it decreases with increase in the concentration of the stabilizer, PVA. The synthesized selenium nanoparticles have been characterized by UV-visible optical absorption spectroscopy, X-ray diffraction, energy dispersive X-ray analysis, differential scanning calorimetry, atomic force microscopy, scanning electron microscopy and transmission electron microscopy techniques.

Full text of DOI:10.1016/j.materresbull.2010.05.013

Materials Research Bulletin 45 (2010) 1213–1217
Contents lists available at ScienceDirect
Materials Research Bulletin
journal homepage: www.elsevier.com/locate/matresbu
Riley oxidation: A forgotten name reaction for synthesis of selenium nanoparticles
*
Chetan P. Shah, Charu Dwivedi, Krishan K. Singh, Manmohan Kumar , Parma N. Bajaj
Radiation and Photochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085, India
A R T I C L E I N F O
A B S T R A C T
Article history:
A simple wet chemical method, involving reaction of acetone with selenium dioxide, has been
developed, to synthesize polyvinyl alcohol-stabilized selenium nanoparticles. The method is capable of
producing nanoparticles in the size range of about 100–300 nm, under ambient conditions. The
synthesized nanoparticles can be separated easily from the aqueous sols by a high-speed centrifuge, and
can be re-dispersed in aqueous medium by a sonicator. The effect of concentrations of selenium dioxide,
acetone and PVA on the size of the selenium nanoparticles has been studied. The size of the selenium
nanoparticles has been found to increase with increase in the reaction time as well as the concentration
of selenium dioxide, while it decreases with increase in the concentration of the stabilizer, PVA. The
synthesized selenium nanoparticles have been characterized by UV–visible optical absorption
spectroscopy, X-ray diffraction, energy dispersive X-ray analysis, differential scanning calorimetry,
atomic force microscopy, scanning electron microscopy and transmission electron microscopy
techniques.
Received 26 October 2009
Received in revised form 29 March 2010
Accepted 18 May 2010
Available online 25 May 2010
Keywords:
A. Nanostructure
A. Semiconductor
B. Chemical synthesis
C. Differential scanning calorimetry (DSC)
C. Electron microscopy
ß 2010 Elsevier Ltd. All rights reserved.
1. Introduction
Both reduction and oxidation techniques can be employed to
prepare selenium nanoparticles, starting with suitable precursors.
The research on synthesis of nanostructured materials has great
interest because of their unique optoelectronic, magnetic and
mechanical properties, which differ largely from that of the bulk
materials, as well as their applications in the fields of catalysis,
sensors, nanodevices, etc. [1]. Though a lot of research work has
been carried out on semiconductors and metals, the studies on
metalloids, like selenium, etc., are scanty. The high reactivity of
selenium towards a large number of chemicals has stimulated
researchers recently, to convert selenium into various important
nano-materials of selenium, such as ZnSe, CdSe, etc. [2]. These
selenium containing nano-materials have excellent photoelectri-
cal characteristics, semiconductor properties and high biological
activity [3]. Nano-selenium has been widely used in electrical
rectifiers, photocells, photographic exposure meter, xerography,
etc. [4]. In nature, selenium is present in igneous rocks and fossil
fuels. It is a metalloid, and exists as toxic water soluble selenate
(SeO42À) and selenite (SeO32À) forms, and also as insoluble
nontoxic elemental selenium (Se0) form [5]. It is an essential
micronutrient, required at low concentrations, for most of the
living organisms, including human beings, but it is toxic at high
concentration. The whole body content of selenium is about 2–
10 mg. Human liver and kidney have the highest concentration of
selenium [6].
Most of the work on production of selenium nanoparticles has
been reported by the reduction method. Mostly, selenate, selenite
and selenium dioxide precursors, along with reducing agents, like
glycol, hydrazine, etc., which are quite toxic chemicals, and high
temperature have been used in the reduction method [7]. Bacterial
reduction of selenite (SeO32À) to Se0 has also been studied [5].
Some researchers have reported synthesis of nano-selenium by
oxidation of its precursors as well [8]. We have also reported acid
as well as acrylonitrile-induced synthesis of selenium nanopar-
ticles by oxidation of sodium selenosulphate as a precursor of
selenium [9,10].
In the present study, we have used a very simple and well-
known organic name reaction, ‘‘Riley Oxidation’’ [11], for the
synthesis of selenium nanoparticles, by the reaction of selenium
dioxide with acetone, under ambient conditions. Conversion of
ketone, or aldehyde (with
a-methylene –CH2– group), into 1,2-
dicarbonyl compound is an important reaction, and has been
studied by many researchers [12]. This reaction is carried out by
oxidation of a suitable carbonyl compound, such as acetone, with
selenium dioxide, forming 1,2-dicarbonyl compound, and the
latter getting reduced. The formation of elemental selenium as a
by-product in the reaction can be utilized to produce selenium
nanoparticles, in the presence of a suitable stabilizer. However,
there is not even a single report on the synthesis of nano-selenium
by using the same name reaction, to the best of our knowledge.
Taking advantage of efficient stabilizing property of PVA [9,10], we
have synthesized selenium nanoparticles by the above reaction, in
* Corresponding author. Tel.: +91 22 25593994; fax: +91 22 25505151.
E-mail address: manmoku@barc.gov.in (M. Kumar).
0025-5408/$ – see front matter ß 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.materresbull.2010.05.013

1214
C.P. Shah et al. / Materials Research Bulletin 45 (2010) 1213–1217
the presence of PVA stabilizer. The synthesized selenium
nanoparticles were characterized by UV–visible optical absorption
spectroscopy, X-ray diffraction (XRD), energy dispersive X-ray
analysis (EDAX), differential scanning calorimetry (DSC), atomic
force microscopy (AFM), scanning electron microscopy (SEM) and
transmission electron microscopy (TEM) techniques.
nanoparticles and the standard selenium powder were weighed
into aluminum crucibles separately, and DSC measurements of
both the samples were carried out in N2 atmosphere, at a heating
rate of 10 8C/min, from 45 to 250 8C (model DSC-30). Selenium
nanoparticles, separated from aqueous sols, using high-speed
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 Solver P47 model from NT-MDT,
Russia. SEM and EDAX images of the synthesized selenium
nanoparticles were recorded, using 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. Samples for XRD,
EDAX, AFM, SEM and TEM analysis were prepared by re-dispersing
the synthesized selenium nanoparticles in aqueous medium, using
a sonicator, and drying it on a suitable substrate.
2. Experimental details
High purity polyvinyl alcohol (PVA) of molecular weight
125,000, obtained from s.d. fine chemicals, selenium dioxide
powder from Central Drug House (CDH), New Delhi, and AR grade
acetone from Chemco Fine Chemicals, were used as received. All
the other chemicals used were of GR grade, procured from the local
market. Aqueous solutions were prepared, using water obtained
from Millipore-Q water purification system (with conductivity of
0.6
m
S cmÀ1, or lower).
5% PVA stock solution was prepared by dissolving of 5.0 g of
PVA in 100 ml water, while stirring at 80 8C. An aqueous
0.1 mol dmÀ3 selenium dioxide solution was used as a selenium
precursor. Both these stock solutions were diluted with water, to
the required concentrations, for different experiments.
PVA-stabilized Se nanoparticles were synthesized by mixing
known concentration of aqueous selenium dioxide solution
(5.0 Â 10À3 to 25 Â 10À3 mol dmÀ3), containing the required
concentration of PVA stabilizer (0.5–3.0%), and acetone (2.0–
5.4 mol dmÀ3). The mixture was stirred at room temperature, to
produce beautiful orange/red-coloured sols, containing selenium
nanoparticles. However, in the absence of PVA, a dark reddish-
black-coloured precipitate of selenium was formed.
3. Result and discussion
The simplicity and the environmental friendly nature of this old
well-known organic name reaction drove us to study it in detail,
and to develop it as a new method for the production of selenium
nanoparticles. During the reaction, acetone gets converted to
methyl glyoxal, and elemental selenium is formed. 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, reddish-black
elemental selenium powder precipitated out from the reaction
mixture. Kinetics of nanoparticle formation, by the reaction of
selenium dioxide with acetone under different experimental
conditions, and the size of the synthesized selenium nanoparticles
have been investigated.
UV–visible optical absorption spectra of the selenium nanopar-
ticle sols were recorded, using double beam spectrophotometer,
model Spectroscan 2600 from Chemito. X-ray diffraction patterns
(XRD) of the nanoparticles were recorded with a Phillips X-ray
The mechanism of the reaction was proposed by the H.L. Riley
et al., in 1932 [11]. The necessary condition for the reaction between
selenium dioxide and aldehyde/ketone to occur is that, the latter
diffractometer, model PW 1710 system, using a Cu K source
a
(l = 0.15406 nm). Differential scanning calorimetry (DSC) mea-
surements were carried out, using Mettler TA 3000 thermal
analysis system. About 10 mg of the synthesized selenium
[(Scheme_1)TD$FIG]
reactant must have an active methylene group at
general reaction and the mechanism are given in Scheme 1.
a-position. The
Scheme 1. General reaction and its mechanism.

[
C.P. Shah et al. / Materials Research Bulletin 45 (2010) 1213–1217
1215
Fig. 1. Effect of (a) reaction time, (b) selenium dioxide concentration and (c) PVA concentration, on the UV–visible absorption spectra of the aqueous selenium sols formed by
the reaction of selenium dioxide with acetone, in the presence of PVA.
In the aqueous solution of 5.0 Â 10À3 mol dmÀ3 selenium
dioxide, containing 5.4 mol dmÀ3 acetone and 1% PVA, the reaction
was not observed at room temperature, even up to 24 h. However,
at higher selenium dioxide concentrations, the reaction was
observed, and the reaction time decreased with increase in
selenium dioxide concentration, for the same concentration of
acetone and PVA. Thus, the rate of formation of selenium
nanoparticles was found to increase, with increase in selenium
dioxide concentration. A minimum acetone concentration of about
2.0 mol dmÀ3 was found to be necessary to observe the formation
of selenium nanoparticles at room temperature. However, at
higher temperatures, selenium nanoparticles were formed even at
lower concentration of acetone.
maximum of the selenium nanoparticle sols shifts towards blue,
along with decrease in absorbance at higher PVA concentrations of
2.0 and 2.5%, as shown in Fig. 1c. This may be due to restricted
agglomeration of the particles, in the presence of higher PVA
concentration, resulting in smaller selenium nanoparticles.
Phase composition and crystal structure of the selenium
nanoparticles were determined by XRD technique. XRD patterns
of the synthesized selenium nanoparticles, as a function of
annealing temperature, are displayed in Fig. 2. The XRD pattern
of the un-annealed sample suggests that the synthesized selenium
is probably nano-crystalline/amorphous in nature, and its crystal-
linity increases, on annealing at higher temperatures, as shown in
Fig. 2a–d. The Kaur et al. have also reported that, no peaks can be
seen in the XRD pattern of the amorphous selenium [15]. The XRD
pattern of the sample annealed at the highest temperature
matches very well with that of the standard selenium powder,
confirming the formation of selenium nanoparticles. All the
diffraction peaks are indexed, assuming a trigonal phase, with
Fig. 1a shows UV–visible absorption spectra of the selenium
nanoparticle sols at different reaction times. With increase in the
reaction time, the absorption maximum shifts towards the longer
wavelength due to increase in the size of the particles. This
behavior is observed at all the studied concentrations of selenium
dioxide. Fig. 1b shows the effect of the concentration of selenium
dioxide on the UV–visible absorption spectrum of the sols, after
about 4 days of reaction time. It can be seen that, with increase in
the concentration of selenium dioxide, the absorption maximum
shifts to longer wavelength. This may be due to increase in the size
of selenium nanoparticles with increase in the concentration of
selenium dioxide. Thus, it is clear that, with increase in the
concentration of selenium dioxide, in the studied range, as well as
with the reaction time, the size of the selenium nanoparticles
increases. Selenium nanoparticles are known to exhibit a regular
absorption maximum, in the wavelength region above 300 nm,
only when the particle size is 100 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. The nature and evolution of the present spectra
match very well with that reported by Lin and Wang [13], and
comparison of the wavelength maxima indicates that spherical
particles of size 100–300 nm are formed, depending on the
employed experimental conditions. However, Kaur et al. have
observed absorption spectra of nano-selenium in aqueous micellar
phase, with peak at greater than 550 nm, due to bigger size non-
spherical particles (large petals), in the case of reaction of sodium
selenite, at lower concentration of hydrazine, and absorption
spectra with peak at around 400 nm, due to smaller size particles,
at higher concentration of hydrazine [14]. Further, there is not
much effect of acetone concentration on the UV–visible spectra
and the size of the selenium nanoparticles. However, with increase
in the concentration of PVA from 0.5 to 2.5%, the absorption
˚
˚
calculated lattice constants, a = 4.363 A and c = 4.952 A, which are
˚
in agreement with the literature values of a = 4.360 A and
˚
c = 4.956 A (JCPDS FILE No. 06-362) [7].
[F(ig._2)TD$FIG]
Fig. 2. XRD pattern of the selenium nanoparticles synthesized by the reaction of
1.5 Â 10À2 mol dmÀ3 selenium dioxide with 5.4 mol dmÀ3 acetone, in the presence
of 1% PVA (a) without heating the nanoparticles, (b) after annealing at 70 8C for 2 h,
(c) after annealing at 85 8C for 2 h and (d) after annealing at 120 8C for 30 min.

[
C.P. Shah et al. / Materials Research Bulletin 45 (2010) 1213–1217
Fig. 3. EDAX pattern of the selenium nanoparticles synthesized by the reaction of 1.5 Â 10À2 mol dmÀ3 selenium dioxide with 5.4 mol dmÀ3 acetone, in the presence of 1%
PVA.
[(Fig._4)TD$FIG]
Fig. 4. DSC thermograms of (a) the selenium nanoparticles synthesized by the reaction of 1.2 Â 10À2 mol dmÀ3 selenium dioxide with 5.4 mol dmÀ3 acetone, in the presence
of 1% PVA, (b) the synthesized selenium nanoparticles brought to ambient temperature after the first run and (c) inset: standard commercial selenium powder.
Furthermore, chemical composition of the synthesized seleni-
um nanoparticles was also confirmed with EDAX technique. The
EDAX spectrum of the selenium nanoparticles, shown in Fig. 3, also
confirms that the nanoparticles are of pure selenium only, and no
other element is present.
DSC thermogram of the synthesized selenium nanoparticles,
recorded up to 250 8C, is shown in Fig. 4a. It shows an exothermic
transition at 81 8C, in addition to endothermic melting peak at
higher temperature. Enthalpy of the exothermic transition has
been found to be 48.4 J/g. The initial small endothermic peak (up to
ꢀ70 8C) may be due to the presence of a small amount of moisture
in the sample. The repeat DSC thermogram of the same selenium
sample, recorded after bringing it to ambient temperature, did not
show any exothermic peak at the mentioned temperature (Fig. 4b).
This clearly indicates that the selenium nanoparticles loose their
nano-crystalline nature in the first run itself, and the exothermic
transition is assigned to the increase in crystallinity of the
selenium nanoparticles. This observation is in corroboration with
the XRD results obtained with the synthesized sample (before and
after annealing). Whereas, DSC thermogram of the standard
[(Fig._5)TD$FIG]
Fig. 5. AFM images of selenium nanoparticles formed by the reaction of 1.2 Â 10À2 mol dmÀ3 selenium dioxide with 2.7 mol dmÀ3 acetone, in the presence of 1% PVA, (a) 2D
image and (b) 3D image.

[
C.P. Shah et al. / Materials Research Bulletin 45 (2010) 1213–1217
1217
Typical 2D and 3D AFM images are shown in Fig. 5. Both individual
particles and aggregates are seen in the 2D image. The maximum
height of ꢀ120 nm in the 3D image indicates that particles smaller
than 120 nm can be produced by this method.
Scanning electron microscope and transmission electron
microscope images of the synthesized selenium nanoparticles
are shown in Figs. 6 and 7, respectively. Spherical shape of the
individual nanoparticles is visible in the SEM image, with size in
the range of 100–300 nm. Majority of the particles are of size
ꢀ200 nm, which is also reflected in the TEM image. The conclusion
drawn from AFM, SEM and TEM studies are more or less in
corroboration with each other. Thus, the method is capable of
producing nanospheres of selenium, in the presence of PVA
stabilizer. The somewhat larger size in the SEM image as compared
to that in the AFM image is probably due to more aging (ꢀ4 days) of
the selenium sol, before preparing the sample for SEM imaging.
4. Conclusions
Fig. 6. SEM image of selenium nanoparticles (after aging for ꢀ4 days), formed by the
reaction of 1.2 Â 10À2 mol dmÀ3 selenium dioxide with 2.7 mol dmÀ3 acetone, in
the presence of 1% PVA.
Selenium dioxide-induced oxidation of acetone, ‘‘Riley Oxida-
tion’’ reaction, has been used, for the first time, to synthesize
selenium nanoparticles. The new method is found to be simple, and
can be carried out under ambient condition, using easily available
low-cost laboratory chemicals. The method is capable of producing
selenium nanoparticles, with size about 100–300 nm, depending
on the employed experimental conditions. Further, PVA is
observed to be an efficient stabilizer for the produced nanopar-
ticles. Concentrations of selenium dioxide and PVA, as well as the
reaction time, can be efficiently utilized to control the size of the
synthesized selenium nanoparticles. The formation of the nano-
crystalline selenium particles, and an increase in the crystallinity
on annealing, were concluded from both XRD and DSC results. The
selenium nanoparticles may serve as a template, to generate other
important nano-materials, and find applications in fabrication of
nanoscale optoelectronic devices.
[(Fig._7)TD$FIG]
Acknowledgements
The author Chetan P. Shah is grateful to Department of Atomic
Energy, for awarding research fellowship. The authors are thankful
to Dr. P.A. Hassan, BARC, for AFM; Dr. S.K. Gupta, BARC, for SEM; Dr.
D. Shrivastava, BARC, for TEM; and Dr. L. Varshney, BARC, for DSC
experiments. The authors also wish to acknowledge Dr. S.K. Sarkar
and Dr. T. Mukherjee, for their encouragement during the course of
the study.
References
[1] Y. Haoyong, X. Zhude, B. Huahui, B. Jingyi, Z. Yifan, Chem. Lett. 34 (2005) 122.
[2] S. Nath, S.K. Ghosh, T. Pal, Chem. Commun. (2004) 966.
[3] A. Jagminas, I. Gailiute, G. Niaura, R. Giraitis, Chemija 16 (2005) 15.
[4] X. Cao, Y. Xie, S. Zhang, F. Li, Adv. Mater. 16 (2004) 6490.
[5] R.S. Oremland, M.J. Herbel, J.S. Blum, S. Langley, T. Beveridge, P.M. Ajayan, T. Sutto,
A.V. Ellis, S. Curran, Appl. Environ. Microbiol. 70 (2004) 52.
[6] M.A. Bakir, G. Alya, A. Mohammad, R. Azroony, F. Kasies, J. Radioanal. Nucl. Chem.
266 (2005) 165.
[7] B. Zhang, X. Ye, W. Dai, W. Hou, F. Zuo, Y. Xie, Nanotechnology 17 (2006) 385.
[8] B. Mishra, P.A. Hassan, K.I. Priyadarsini, H. Mohan, J. Phys. Chem. B 109 (2005)
12718.
Fig. 7. TEM image of selenium nanoparticles formed by the reaction of
1.2 Â 10À2 mol dmÀ3 selenium dioxide with 2.7 mol dmÀ3 acetone, in the
presence of 1% PVA.
[9] C.P. Shah, M. Kumar, P.N. Bajaj, Nanotechnology 18 (2007) 385607.
[10] C.P. Shah, K.K. Puspa, M. Kumar, P.N. Bajaj, Cryst. Growth Des. 8 (2008) 4159.
[11] H.L. Riley, J.F. Morley, N.A.C. Friend, J. Chem. Soc. (1932) 1875.
[12] V.S. Dalavoy, V.B. Deodhar, U.R. Nayak, Ind. J. Chem. 26B (1987) 1.
[13] Z.H. Lin, C.R.C. Wang, Mater. Chem. Phys. 92 (2005) 591.
[14] G. Kaur, M.S. Bakshi, J. Phys. Chem. C 114 (2010) 143.
selenium powder sample did not show any such exothermic peak
(inset Fig. 4c). All the three DSC thermograms showed selenium
melting peak at 217 8C.
Morphology and structure of the synthesized selenium
nanoparticles were determined by AFM and SEM techniques.
[15] G. Kaur, M. Iqbal, M.S. Bakshi, J. Phys. Chem. C 113 (2009) 13670.