World Journal of Nano Science and Engineering, 2012, 2, 47-52
http://dx.doi.org/10.4236/wjnse.2012.22008 Published Online June 2012 (http://www.SciRP.org/journal/wjnse)
Switchgrass (Panicum virgatum) Extract Mediated Green
Synthesis of Silver Nanoparticles
Cynthia Mason1,2, Singaravelu Vivekanandhan1,2, Manjusri Misra1,2*, Amar Kumar Mohanty1,2
1School of Engineering, Thornborough Building, University of Guelph, Guelph, Canada
2Bioproducts Discovery and Development Centre, Department of Pla nt Agricultu re,
University of Guelph, Guelph, Canada
Received January 25, 2012; revised February 16, 2012; accepted February 28, 2012
ABSTRACT
A novel switchgrass (Panicum virgatum) extract mediated green process was demonstrated for the synthesis of silver
nanoparticles from silver nitrate solution at ambient temperature. UV-visible spectroscopic analysis indicates the rapid
reduction of silver (Ag+) ions by swithgrass extract. The silver nanoparticles began to form at 15 min and the reduction
reaction was completed within 2 hours. Synthesized silver nanoparticles were subjected to x-ray diffraction (XRD) for
structural characterization, which confirms the FCC symmetry of silver nanoparticles with the lattice parameter of
4.0962 Å. The particle size of bio-synthesized silver nanoparticles was identified through transmission electron
microscopic (TEM) analysis and found to be in the range of 20 - 40 nm.
Keywords: Panicum virgatum; Biosynthesis; Silver Nanoparticles
1. Introduction
Silver nanoparticles receive enormous scientific, techno-
logical, and commercial attention due to their unique size
and shape dependent properties [1,2]. Extensive research
has been devoted to explore the applications of silver
nanoparticles in diversified fields including healthcare/
biomedical [3-5], sensors [6], spectroscopy [7] and cata-
lysis [8]. One of the challengin g tasks in the synthesis of
nanostructured materials is the precise control of size and
shape [9]. Especially, silver nanoparticles exhibit drastic
variation in their physicochemical properties with the
size, shape, and their conjugation with other organic/
biological substances [10-12]. The synthesis processes of
silver nanoparticles play a major role in the control of
their size and shape, thus wide range of physical, chemi-
cal, as well as biological methods have been established
and reported [13-15]. Among them, biological processes
that are based on bacteria, fungus, bio-derived chemicals,
and plant extracts are extensively investigated due their
eco-friendly protocol and better morphological control
[16-18]. Using “green” methods in the synthesis of silver
nanoparticles has increasingly become a topic of interests
as conventional chemical methods are expensive and re-
quire the use of chemical compounds/organic solvents as
reducing agents.
Recently, plant (leaf, flower, seed, tuber, and bark) ex-
tract mediated biological process for the synthesis of
silver nanoparticles has been extensively explored and
compared to other bio-inspired processes [19-26]. A
range of plant extracts have been investigated for their
ability to efficiently synthesize silver nanoparticles, and
are mentioned as follows. Shankar et al., demonstrated a
geranium (Pelargonium graueolens) leaf extract based
biological process for the synthesis of silver nanoparticles
[21]. Song et al., used persimmon (Diopyros kaki) leaf
extract for the synthesis of bimetallic gold/silver
nanoparticles [22]. Sathishkumar et al. has synthesised
silver nanoparticles using Cinnamon zeylanicum bark
extract and reported their bactericidal activity [23]. An-
anda Babu et al. reported the synthesis of silver nanopar-
ticles using Calotropis procera flower extract at room
temperature [24]. In addition, we have also explored the
synthesis of silver nanoparticles using soy (Glycine max)
and curry (Murraya Koengii) leaf extracts [25,26]. Simi-
larly, neem (Azadirachta indica) and mango (Mangifera
indica) leaf extracts were effectively utilized for the syn-
thesis of silver nanoparticles [27,28]. Apart from silver
nanoparticles, plant ex tract mediated biological processes
are also explored for the synthesis of gold and palladium
nanoparticles [29,30]. Detailed literature work on the
plant extract mediated biological synthesis of metal
nanoparticles has been performed by Rai et al. and Ira-
vani [31,32]. Recent accomplishments in the plant leaf
extract mediated biological process include the impreg-
nation of silver nanopartic l e s into carbon nanotubes, which
*Corresponding author.
C
opyright © 2012 SciRes. WJNSE

C. MASON ET AL.
48
indicates new opportunities for this process in the
development of novel multifunctional materials [33,34].
Present research has prompted for further exploration in
the use of plant extracts for the synthesis of silver nano-
particles from switchgrass extract. Switchgrass is a war m-
season perennial plant that requires minimal agriculture in-
puts (including pesticides, energy, and fertilizer), with the
ability to survive on marginal lands, providing economic
and envi r onm ent al a dv ant a ges. S witc h gr ass ha s be e n wi del y
used as fuel for generating energy and is currently used as
feedstock for bio-ethanol production. Despite these devel-
opments in its ma ny u ses, th ere are currently no r eports that
show the bio-reduction mechanism of switchgrass extract
for the synthesis of silver nanoparticles. This report outlines
the use of switchgrass extract as the reducing agent in the
reaction that converts silver ions into silver nanoparticles.
Bioreduction mechanism of switchgrass extract for the syn-
thesis of silver nanoparticles was investigated trough UV-
visible, XRD, TEM, and XRD techniques.
2. Experimental
2.1. Preparation of Switchgrass Extract
The switchgrass extract was made using 20 g of fresh
switchgrass, which was obtained from the Elora Research
Station, University of Guelph, Ontario. A photograph of
switchgrass is shown in Figure 1. Prior to extract pre-
paration, the switchgrass was cleaned thoroughly using
deionized water and then cut into small pieces. The swit-
chgrass sample was then added into 125 mL of boiling
deionized water, and left to boil for 3 minutes. The so lu-
tion was then removed from the heat source and left to
cool to ambient temperature (approximately 23˚C). Fol-
lowing this step, the extract was then filtered through a
course sieve to remove any leaf matter and the resultant
filtrate was then refrigerated.
2.2. Synthesis of Silver Nanoparticles
The silver nitrate (AgNO3) used in this experiment was
Figure 1. Photograph of switchgrass.
obtained from Sigma Aldrich. 3 mL of switchgrass ex-
tract was added to 60 mL of 10–3 M AgNO3 solution and
the reaction was left to take place at ambient conditions.
The observed change in color from colorless to transpar-
ent yellow and finally to a dark brown with time, indi-
cating the formation of silver nanoparticles. Reduction of
the Ag+ ions was monitored with respect to time using
UV-visible spectral analysis. Once the reaction mixture
had reached a dark brown color, it was then centrifuged
in order to collect the silver nanoparticles. The nanoparticles
were washed an additional two times using deionized
water, and were then re-suspended in 95% ethanol (Fisher
Scientific) prior to characterization.
2.3. Characterization
Optical absorbance of the synthesized silver nanoparticles
was performed using a UV-visible spectrophotometer
(Varian Cary 300 Bio) between the wavelengths of 300
and 700 nm at a resolution of 1 nm. The reaction mixture
was first diluted 15 times with distilled water and used
for UV-visible analysis. Transmission electron micro-
scopy (TEM) was performed on the silver nanoparticles
us in g a LE O mo d el 912 AB instrument at the acceleratin g
voltage of 100 k. A drop of the silver nanoparticle-ethanol
dispersion was placed on a carbon coated copper grid,
which allowed the ethanol to evaporate before analysis
began. The phase purity and the crystalline structure of
bio-systhesized silver nanoparticles were investigated
through x-ray diffraction technique using a Rigaku
Mul-tiflex x-ray powder diffractometer employing CuKα
radiation. The silver nanoparticle dispersion was placed
on a glass slide and the solution (ethanol) was allowed to
evaporate such that a thin film of silver nanoparticles
remained. This thin silver film was subjected to x-ray
diffraction operating between 10˚ and 80˚, with a scan-
ning rate of 2˚ per minute. The average crystallite size of
the silver nanoparticles was calculated using a line
broadening profile of (111) peak at 38˚ and Sherrer’s
formula as follows,
d = 0.9 (λ)/β Cos θ
where λ is the wavelength (1.5418 Å), β is the full width
half maximum (FWHM) of corresponding peek, and θ is
the angle of the diffra ction pe ek .
3. Results and Discussion
Figure 2 shows the color change of reaction mixture
( silver n itrate solu tion and switchg rass extr act) with respect
to time. Color change can be observed at 15 minutes from
colorless to faint yellow, indicating the formation of sil-
ver nanoparticles. As time elapsed, the yellow colored
solution eventually became dark brown at 120 minutes,
which is due to the increasing concentration of silver
nanoparticles as well as the particles’ growth in size. Ther e

C. MASON ET AL. 49
0 15 30 60 75 90 120 180
(In minutes)
Figure 2. Photograph of reaction mixture (switchgrass extract
and silver nitrate solution) as a function of time.
is no significant change beyond 180 minutes, therefore
indicating the completion of the reduction reaction. This
was further confirmed by UV-vis spectroscopic analysis.
This physical appearance of the reaction mixture turning
from yellow to brown is due to the surface plasmon reso-
nance (SPR) of the silver nanoparticles, which is consid-
ered to be the primary signature of nanoparticle formation.
UV-vis spectroscopy is a versatile technique to understand
the bioreduction mechanism of silver ions into silver
nanoparticles by switchgrass extract. The UV-vis spectra
of the reaction mixture recorded as a function of time, is
are shown in Figure 3(a). An observed peak at 435 nm is
assigned to the surface plasmon resonance band (longitu-
dinal vibration) of the silver nanoparticles, which is com-
parable with the literature values and exhibits continuous
rise in intensity without any ch ange in the peak position as
a function of time. During 15 - 60 minutes intervals the
absorption peak was weak and broad, which indicates the
smaller size of silver nanoparticles. Nucleation occurs
between 60 - 90 minutes, which appeared as strong a ab-
sorption peak, as shown in Figure 3(a). Figure 3(b) shows
the absorbance at λmax (i.e. at 435 nm) as a function of time.
From Figure 3(b) it is indentified that the reduction of
silver ions to silver nanoparticles occurs quite rapidly, as
more than 90% of the bioreduction reaction completes
within 90 minutes. Th is is faster than earlier stud ies of the
synthesis of silver nanoparticles usi ng biol ogical sources.
The crystalline structure of the bio-syntheized silver
nanoparticles was investigated by XRD analysis and the
obtained x-ray diffraction pattern is shown in Figure 4.
The obtained diffraction peaks at 38˚, 44˚, 64˚ and 77˚
are respectively assigned to (111), (200), (311) and (222)
plans, which indicates that the synthesized silver nanop ar-
ticles are crystallized in face centered cubic (fcc) sym-
metry. No additional diffraction peaks were observed
other than the characteristic peak of the silver structure
that reflects the purity of synthesized silver nanoparticles.
The lattice parameter (A) of the bio-synthesized silver
nanoparticles was calculated from the diffraction data
and was found to be A = 4.0962 Å, which is comparab le
with the JCPDS value. Th e calculated crystallite size has
been found to be ~10 nm, which is comparable with the
particle size as obtained from TEM analysis.
(a)
(b)
Figure 3. (a) UV-vis absorption spectra of reaction mixture
(switchgrass and silver nitrate) and (b) Absorbance at λmax
(i.e., at 435 nm) as a function of time.
Figure 4. XRD pattern of silver nanoparticles synthesized
using switchgrass extract.
The microscopic structure of the switchgrass extract
mediated bio-synthesized silver nanoparticles was inves-
tigated by TEM analysis. The obtained TEM images are
shown in Figure 5. TEM images confirm the formation
of silver nanoparticles with the size range between 20
and 40 nm. In addition, the TEM images show th e shape
of the nanoparticles are highly diversified, which includes

C. MASON ET AL.
50
(a) (b)
(c) (d)
Figure 5. (a)-(d) TEM images of silver nanoparticles synthesized using switchgrass extract.
5. Acknowledgements
spherical, rod-like, triangular, pentagonal, and hexagonal.
It was found that the synthesized silver nanoparticles have
the tendency to aggregate and form the agglomerations. The authors would lik e to acknowledge the 2009, Ontario
Ministry of Agriculture, Food and Rural Affairs (OMA-
FRA)—New Directions & Alternative Renewable Fuels
Research Program Project number SR9225 and NSERC
NCE AUTO21 project for the financial support to carry
out this research.
The agglomerated silver nanoparticles assemble to-
gether without much physical contact. Thus they can be
separated by physical agitation for the further utilization.
4. Conclusion
Silver nanoparticles were successfully synthesized using
switchgrass extract used at room temperature. Synthesis
of silver nanoparticles through this process was fairly
rapid, with 90% of silver ion reduction completed within
90 minutes. TEM analysis confirms that the synthesized
silver nanoparticles exist between 20 and 40 nm and ex-
hibit the tendency to aggregate. XRD analysis indicates
the formation of phase pure silver nanoparticles with
FCC symmetry. The calculated av erage crystallite size is
found to be of 10 nm, which is consistent with TEM
analysis. The fundamental understanding of switchgrass
mediated biological process for the synthesis of silver
nanoparticles will allow the expansion of this p rocess for
the synthesis of gold and palladium nanoparticles and
their applications.
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