Time-dependent effect in green synthesis of silver nanoparticles.

Abstract

The application of "green" chemistry rules to nanoscience and nanotechnology is very important in the preparation of various nanomaterials. In this work, we successfully developed an eco-friendly chemistry method for preparing silver nanoparticles (Ag-NPs) in natural polymeric media. The colloidal Ag-NPs were synthesized in an aqueous solution using silver nitrate, gelatin, and glucose as a silver precursor, stabilizer, and reducing agent, respectively. The properties of synthesized colloidal Ag-NPs were studied at different reaction times. The ultraviolet-visible (UV-vis) spectra were in excellent agreement with the obtained nanostructure studies performed by transmission electron microscopy (TEM) and their size distributions. The prepared samples were also characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM). The use of eco-friendly reagents, such as gelatin and glucose, provides green and economic attributes to this work.

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Open Access Full Text Article
Time-dependent effect in green synthesis
of silver nanoparticles
DOI: 10.2147/IJN.S17669
Majid Darroudi1,2
Mansor Bin Ahmad3
reza Zamiri4
AK Zak5
Abdul halim Abdullah1,3
Nor Azowa Ibrahim3
1Advanced Materials and
Nanotechnology Laboratory, Institute
of Advanced Technology (ITMA),
Universiti Putra Malaysia, selangor,
Malaysia; 2Department of chemistry,
Faculty of science, Ferdowsi
University of Mashhad, Mashhad,
Iran; 3Department of chemistry,
4Department of Physics, Faculty of
science, Universiti Putra Malaysia,
selangor, Malaysia; 5Low Dimensional
Materials research center,
Department of Physics, Faculty of
science, University of Malaya, Kuala
Lumpur, Malaysia
correspondence: Majid Darroudi
Advanced Materials and Nanotechnology
Laboratory, Institute of Advanced
Technology (ITMA), Universiti Putra
Malaysia, 43400 UPM serdang,
selangor, Malaysia
Tel +60 3 89466044
Fax +60 3 89466043
email majiddarroudi@gmail.com
Abstract: The application of “green” chemistry rules to nanoscience and nanotechnology
is very important in the preparation of various nanomaterials. In this work, we successfully
developed an eco-friendly chemistry method for preparing silver nanoparticles (Ag-NPs)
in natural polymeric media. The colloidal Ag-NPs were synthesized in an aqueous solution
using silver nitrate, gelatin, and glucose as a silver precursor, stabilizer, and reducing agent,
respectively. The properties of synthesized colloidal Ag-NPs were studied at different reaction
times. The ultraviolet-visible (UV-vis) spectra were in excellent agreement with the obtained
nanostructure studies performed by transmission electron microscopy (TEM) and their size
distributions. The prepared samples were also characterized by X-ray diffraction (XRD) and
atomic force microscopy (AFM). The use of eco-friendly reagents, such as gelatin and glucose,
provides green and economic attributes to this work.
Keywords: silver nanoparticles, gelatin, green chemistry, time-dependent effect, ultraviolet-
visible spectra
Introduction
Nanomaterials have received much attention because their structure and properties
differ significantly from those of atoms, molecules, and bulk materials.1 The synthesis
of metal nanoparticles has been widely discussed in the literature due to their unique
physical and chemical properties, which have many potential applications.2–4 The use of
inexpensive chemicals and non-toxic solvents – environmentally friendly and renewable/
biodegradable – are central to materials synthesis and processing, considering the green
nature of these strategies. The reducing agent, reaction medium, and stabilizer are three
key factors in the synthesis and stabilization of metallic nanoparticles.5
Natural polymers such as gelatin, chitosan, proteins, and starch are all interesting
materials for medical applications because they are biodegradable and bioabsorb-
able with degradation products that are non-toxic.6 Gelatin is a natural biopolymer
extracted from the partial hydrolysis of collagen which has good biocompatibility
and biodegradability, and has been widely used in wound dressings, drug carriers,
and tissue scaffolds in recent years.7 There are many methods for synthesizing metal
nanoparticles, including photo reduction,8 laser ablation,9 chemical reduction in
aqueous media with different polymer surfactants,10,11 reduction of chemicals in soft
matrices,12–14 reduction of chemicals in solid matrices (eg, mesoporous silicate),15
and chemical vapor deposition.16 Silver nanoparticles (Ag-NPs) are widely used as
catalysts,17–19 photo-catalysts,20–22 and in surface-enhanced Raman spectroscopy24–26
as well as chemical analysis.27
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The use of gelatin as a capping agent and glucose as
a reducing agent to synthesize Ag-NPs in aqueous solutions
is attractive because organic solvents are not used and no
corresponding pollutants are made; moreover, the resulting
nanoparticles in gelatin matrix are biologically compatible.
The main objective of this work is to apply the principles
of green chemistry28 in the synthesis of Ag-NPs, such as
when using an eco-stabilizer and reducing agent. The syn-
thesis method presented could be useful in providing an
economic method for the industrial preparation of highly
monodispersed, biocompatible, and stable colloidal Ag-NPs.
The smallest nanoparticles of about 5 nm having totally
monodispersity could be obtained. Other advantages of this
approach include the physical conditions of the synthesis,
such as the moderate preparation temperature, the lack
of need for an additional flow of inert gas, and the use of
atmospheric pressure.
Experimental
All reagents in this work were analytical-grade and were
used as received without further purification. AgNO3
(99.98%) was used as a silver precursor, and was provided
by Merck, Germany. Gelatin (type B) was used as a sta-
bilizer for the preparation of Ag-NPs and was purchased
from Sigma-Aldrich, MO, USA. D-Glucose was used as a
reducing agent for the reduction of silver ions to Ag atoms
and was obtained from BDH Chemical Ltd., Poole, UK.
All solutions were freshly prepared using double distilled
water and kept in the dark to avoid any photochemical
reactions. All glassware used in experimental procedures
were cleaned in a fresh solution of HNO3/HCl (3:1, v/v),
washed thoroughly with double distilled water, and dried
before use.
For synthesis of Ag-NPs, 2.0 g gelatin was added to
190 mL H2O in a flask, and the solution was stirred and
heated at 40°C to obtain a clear solution. To obtain the Ag+/
gelatin solution, the silver solution (10 mL, 1M) was added
to the gelatin solution with continuous stirring. Then, 20 mL
of glucose solution (2 M) was added to the Ag+/gelatin solu-
tion. The solution obtained was distributed into 5 cuvettes,
and the prepared solutions were stirred and maintained for
different periods of time: 1 (S1), 3 (S2), 6 (S3), 24 (S4), and
48 hours (S5), respectively. Throughout the reduction process,
all solutions were kept at a temperature of 60°C in the dark
to avoid any photochemical reactions.
The prepared colloidal Ag-NPs were characterized
by using ultraviolet-visible (UV-vis) spectroscopy, X-ray
diffraction (XRD), transmission electron microscopy
(TEM), and atomic force microscopy (AFM). To ensure
the formation of nanosilver, the particles were tested for
their optical absorption property using a Lambda 35-Perkin
Elmer UV-vis spectrophotometer over the range of 300 to
700 nm. The crystalline structure of Ag-NPs was charac-
terized with an XRD (Philips, X’pert, Cu Kα). The XRD
patterns were scanned at a speed of 2°/min. The AFM
experiments were carried out on an Ambios-Q scope
(SPM) machine. TEM observations were performed with a
Hitachi H-7100 electron microscopy, and the particle size
distributions were determined using UTHSCSA Image Tool
software (Ver. 3.00).
Glucose
Green
synthesis
Silver ions + Gelatin
Scheme 1 Photography scheme of the colloidal silver nanoparticles synthesized in
aqueous gelatin solution.
2.5
2
1.5
1
0.5
0
300350400450
Wavelength/nm
500550600650700
a
b
c
d
e
(b): 3 h
(c): 6 h
(d): 24 h
(e): 48 h
(a): 1 h
Increase of Ag plasmon peak
Absorbance/a.u.
Figure 1 The UV-vis absorption spectra of the colloidal Ag-NPs synthesized using
glucose at different reaction times.
Abbreviations: Ag-NPs, silver nanoparticles; UV-vis, ultraviolet visible.

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green synthesis of Ag-NPs
2530
20
10
0
20
15
10
5
0
010 2030 40500 10 2030 4050
Frequency (%) Frequency (%)
Particle diameter/nmParticle diameter/nm
Mean diameter: 9.62 nm
Std.dev: 2.46
Mean diameter: 5.28 nm
Std.dev: 1.71
AB
Figure 2 The typical TeM images and corresponding particles size distribution of Ag-NPs at different reaction times; A) s3 and B) s5.
Abbreviations: Ag-NPs, silver nanoparticles; TeM, transmission electron microscopy.
significant change in λmax value (430 nm), compared with the
24 hour reaction time. At the initial stage of the reaction, the
Ag-NPs formed with a broad size distribution, which led to
a SPR peak at about 440 nm. After this stage, the Ag-NPs
could dissociate due to heating to form smaller particles
stabilized by the amine pendant groups on the gelatin, which
leads to the formation of gelatin-stabilized stable Ag-NPs.31
The TEM images demonstrate the formation of Ag-NPs at
different periods of time. Figure 2 shows typical TEM images
and the corresponding particle size distribution of the pre-
pared Ag-NPs at different times. The TEM results indicate
that the samples obtained over a longer time period retained
a narrower particle size distribution; the average size of all
prepared Ag-NPs was ,20 nm; and a smaller average size
(about 5 nm) was obtained for S5.
Figure 3 shows the XRD patterns of Ag-NPs formed
in S5, which indicates the formation of the silver crystal-
line structure. The XRD peaks at 2θ degrees of 38.1, 44.3,
64.5, and 77.5 can be attributed to the (111), (200), (220),
and (311) crystalline planes of face-centered-cubic (fcc)
crystalline structure of metallic silver, respectively (JCPDS
file no. 00-004-0783). The AFM result shows the surface
Results and discussion
The color of Ag+/gel solutions over different periods of time
gradually changed from colorless to light brown, then to
brown, and finally dark brown, indicating the formation of
Ag-NPs in the gelatin solution (Scheme 1). Glucose, as an
aldehyde, was able to reduce Ag+ ions to Ag0, and through
this reaction, glucose can be oxidized to gluconic acid. The
gradual formation of Ag-NPs was investigated by UV-vis
spectroscopy, which has proven to be a useful spectroscopic
method for the detection of prepared NPs over time. In UV-vis
spectra, the Ag-NPs can be shown by a surface plasmon
resonance (SPR) peak at around 400 nm, but a small shift
(blue-shift or red-shift) in the wavelength of the peak could
be related to obtaining Ag-NPs in different shapes, sizes, or
solvent dependences of prepared Ag-NPs.
After reaction at 60°C for 1 hour, the Ag-NPs obtained
showed a UV-vis absorption peak, a characteristic SPR band
for Ag-NPs, centered at 400 nm (Figure 1A). As shown in
Figure 1, the intensity of the SPR peak increased as the
reaction time increased, which indicated the continued reduc-
tion of the silver ions, and the increase of the absorbance
with the reaction time indicates that the concentration of
Ag-NPs increases.29 When the reaction time reached 3 hours
(Figure 1B) the absorbance was increased, and the λmax value
was slightly blue-shifted to 438 nm. For reaction times of 6
(Figure 1C) and 24 hours (Figure 1D), the absorbance was
also increased and blue-shifted to 435 and 431 nm, respec-
tively. This phenomenon indicated that the size of particles
was decreased because the absorbance peak due to the SPR of
metal nanoparticles shows the blue-shift with decreasing par-
ticle size.30 At the end of the reaction (48 hours, Figure 1E),
the absorbance was considerably increased and there was no
1500
1000
500
0
3540 4550 55 6065 70 7580
2 θ/degrees
Intensity/Cps
(111)
(200)
(220)
(311)
Figure 3 The XrD pattern of prepared Ag-NPs (s5).
Abbreviation: Ag-NPs, silver nanoparticles; cps, counts per second; XrD, X-ray
diffraction

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Average height = 9.212 nmRMS deviation (variance) = 9.665 nm
Mean deviation (Ra) = 1.242 nm Image resolution = 600
Figure 4 The AFM image of prepared Ag-NPs (s5).
Abbreviations: AFM, atomic force microscopy; Ag-NPs, silver nanoparticles; ra, arithmetic mean of surface roughness; rMs, root mean square.
morphology of the well-dispersed Ag-NPs formed in gelatin
media. As observed in Figure 4, the value determined by
the AFM was close to the TEM determined, and the films
of gelatin containing Ag-NPs displayed a densely uniform
packed structure. Thus, the Ag-NPs–gelatin films could pro-
vide a biocompatible and rough surface for special biological
applications, such as cell immobilization.
Conclusion
We have described a simple and eco-friendly time-dependent
method to synthesize colloidal Ag-NPs in corresponding
metal solution using green agents, which requires no spe-
cial physical conditions. The Ag-NPs obtained in this work
are uniform and have a narrow particle size distribution,
with a small average particle diameter of about 5 nm. This
preparation method is general and may be extended to other
noble metals, such as Au, Pd, and Pt, and may possibly find
various additional medicinal, industrial, and technological
applications.
Disclosure
The authors disclose no conflicts of interest.
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