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Microwave-Assisted Synthesis of Silver Nanoparticles
Using Chitosan: A Novel Approach
a

b

a

a

c

Ngoan Thi Nguyen , Binh Hai Nguyen , Duong Thi Ba , Dien Gia Pham , Tran Van Khai ,
b

Loc Thai Nguyen & Lam Dai Tran
a

b

Institute of Chemistry, Vietnam Academy of Science and Technology , Ha Noi , Viet Nam

b

Institute of Materials Science, Vietnam Academy of Science and Technology , Ha Noi , Viet
Nam
c

Faculty of Materials Technology , Ho Chi Minh City University of Technology , Ho Chi Minh
City , Viet Nam
Accepted author version posted online: 20 Feb 2014.Published online: 01 Apr 2014.

To cite this article: Ngoan Thi Nguyen , Binh Hai Nguyen , Duong Thi Ba , Dien Gia Pham , Tran Van Khai , Loc Thai Nguyen
& Lam Dai Tran (2014) Microwave-Assisted Synthesis of Silver Nanoparticles Using Chitosan: A Novel Approach, Materials and
Manufacturing Processes, 29:4, 418-421, DOI: 10.1080/10426914.2014.892982
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Materials and Manufacturing Processes, 29: 418–421, 2014
Copyright # Taylor & Francis Group, LLC
ISSN: 1042-6914 print=1532-2475 online
DOI: 10.1080/10426914.2014.892982

Microwave-Assisted Synthesis of Silver Nanoparticles Using
Chitosan: A Novel Approach
Ngoan Thi Nguyen1, Binh Hai Nguyen2, Duong Thi Ba1, Dien Gia Pham1, Tran Van Khai3,
Loc Thai Nguyen2, and Lam Dai Tran2
1

Institute of Chemistry, Vietnam Academy of Science and Technology, Ha Noi, Viet Nam
Institute of Materials Science, Vietnam Academy of Science and Technology, Ha Noi, Viet Nam
3
Faculty of Materials Technology, Ho Chi Minh City University of Technology, Ho Chi Minh City, Viet Nam

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2

In this work, microwave-assisted (MwH) synthesis of silver nanoparticles (AgNPs) using chitosan was investigated. The new method was
compared against chemical reduction (CRed) by NaBH4 and conventional thermal method (CvH). The as-synthesized AgNPs were characterized by UV–Visible spectroscopy, transmission electron microscopy (TEM) and infrared spectroscopy. The MwH method was found to
effectively synthesize AgNPs of which properties were comparable CRed and CvH. The average particle sizes of AgNPs produced by CRed,
CvH and MwH were approximately 20, 5 and 7 nm, respectively. The proposed approach can provide a viable green route for synthesizing
AgNPs with high potential applicability.
Keywords Biodegradable; Chitosan; Green; Heating; Microwave; Nanoparticles; Reduction; Silver.

INTRODUCTION
In recent years, metal nanoparticles (NPs) have
attracted increasing attention due to their unique physical, chemical properties and numerous prospective

applications [1, 2]. In general, metal NPs can be synthesized by chemical or physical pathways. The chemical
method in which NPs are formed by reduction of metal
ions in the solution is most widely used [2–6] due to its
cost effectiveness, simple equipment and capability of
large-scale production. However, strong reducing agents
such as NaBH4, citrate or ascorbate could be sources of
environmental toxics or biological hazards [6]. Therefore, alternative ‘‘green’’ agents derived from naturally
occurring substances are desirable. Natural polymers
such as starch and chitosan (CS) are highly preferred
due to their non-toxic properties and biocompatibility
[7]. Chitosan, N-deacethylated derivative of chitin, is a
viable option since it is cheap, easily available [8], biocompatible, biodegradable and environmental-friendly
[9]. Various studies demonstrate that chitosan could be
successfully used as a reducing and stabilizing agent in
the synthesis of metal NPs [1, 2, 6]. Despite the fact that
chemical reducing reactions can generally take place at
ambient conditions [10, 11], they require the input of
additional thermal energy to achieve high reaction rate.
Traditional heating method in which the heat transfer is
mainly driven by conduction and convection takes long

time and can result in nonuniform temperature distribution. Since morphology and properties of metal NPs
strongly depend on experimental conditions [2], selection
of an appropriate heating method would be essential to
reproducibly synthesize metal NPs of desired properties.
Microwave-assisted (MwH) heating received considerable interests in organic synthesis [12, 13] and inorganic
materials preparation [14, 15] due to its ability to generate the fast reaction times, high-throughput capabilities
and beneficial crystallization effects [15]. Rapid and uniform heating effects of microwave heating were reported
to be conducive to synthesis of metal nanoclusters of
small size and uniform dispersity [16]. MwH heating

was also shown to have marked effects on nucleation
and growth mechanisms of NPs [17]. In this study, a
novel pathway to synthesize silver nanoparticles
(AgNPs) using chitosan and MwH heating was investigated. Properties of AgNPs produced were characterized
by transmission electron microscopy (TEM), UV–vis
and (infrared) IR spectroscopy and compared against
those obtained by traditional chemical synthesis and
conventional heating.
EXPERIMENTAL
Chitosan was purchased from Tokyo Chemical Co.
Ltd. Other reagents were of analytical grades. In this
research, MwH synthesis of AgNPs was studied and
compared against chemical reduction (CRed) and conventional thermal (CvH) methods. The schematic
diagram of experimental procedures used is given in
Fig. 1.
Chitosan suspension in acetic acid solution was prepared by dissolving 0.5 g of chitosan in 100 mL of 2%
acetic acid solution. The mixture was vortexed until a

Received December 12, 2013; Accepted January 9, 2014
Address correspondence to Lam Dai Tran, Institute of Materials
Science, Vietnam Academy of Science and Technology, 18 Hoang
Quoc Viet Road, Ha Noi, Viet Nam; E-mail:
Color versions of one or more of the figures in the article can be
found online at www.tandfonline.com/lmmp.

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MICROWAVE-ASSISTED SYNTHESIS OF SILVER NANOPARTICLES

FIGURE 1.—Schematic diagram of experimental procedures for synthesizing silver nanoparticles (AgNPs) via different pathways.

homogeneous product was obtained. Then, 20 mL of
0.1 M AgNO3 solution was added to 100 mL of chitosan
suspension and the mixture was vigorously agitated by a
magnetic stirrer for 30 min. Chemical reduction was conducted at room temperature by adding 2 M NaBH4 solution (10 mL) to AgNO3=chitosan suspension with the
initial molar ratio of NaBH4 to AgNO3 fixed at 1:1.
The reaction was allowed to take place for 15 min during
which the suspension turned to dark brown color. With
respect to the production of AgNPs by conventional
heating, 100 mL of AgNO3=chitosan suspension was
heated on a hot-plate at 70 C and the sample was mixed
by a magnetic stirrer. In previous study [2], it was found
that optimal reaction time for conventional heating
method was about 6 hr. Therefore, the same holding
time was used for this study. Upon completion of the
reaction, the suspension was observed to change from
light-yellowish to light-brown color. The MwH synthesis
of AgNPs was conducted at 70 C for 2 min in a microwave oven (model MW-ER-01, Lab-kits) with output
power fixed at 200 W. The suspension obtained had a
light-brown color.
The AgNPs were characterized using UV–visible spectroscopy, IR spectroscopy and TEM. Prior to spectroscopy analysis, colloidal suspension of AgNPs was
diluted by water to concentration of 200 ppm. UV–visible spectra were recorded using a Beckman DU 520
UV–Vis spectrophotometer. IR spectra were collected
from 500 to 4000 cmÀ1 by Impact 410 (Nicolet) spectrophotometer (Carl Zeiss Jena). The morphology of the
NPs was examined by Hitachi H7600 transmission electron microscope at 120 kV.
RESULTS AND DISCUSSION
UV–Vis Absorption Spectra of Synthesized AgNPs

In Fig. 2, UV–Vis spectra of AgNPs obtained by
CRed, CvH and MwH are comparatively presented.
The spectra exhibit surface plasmon resonance (SPR)

419

FIGURE 2.—The UV–visible spectra of silver nanoparticles produced by
reducing with NaBH4 at room temperature (AgNPs1), conventional thermal method (AgNPs2) and microwave-assisted method (AgNPs3).

peaks from 400 to 420 nm which clearly evidenced the
formation of AgNPs. The change in color of the suspensions (inset) further confirmed the UV–Vis data. It was
worth noting that AgNPs produced by CRed and
MwH had significantly higher SPR band intensity than
that of AgNPs obtained from CvH. Since the intensity
of SPR band depends on AgNPs concentration, it was
obvious from UV–Vis spectra that the syntheses of
AgNPs by MwH and CRed were more effective than
CvH. Similar trends were also noticed for the color
intensity of the CRed, CvH and MwH suspensions.
The influence of MwH in the synthesis of noble metal
NPs was previously investigated and compared to CvH
[16, 17]. Enhanced effectiveness was attributed to rapid
and uniform heating of MwH [16] or alternately, marked
effects of MwH on nucleation and growth mechanism of
NPs [17].
Analysis of TEM Images
Figure 3 shows the TEM images (Fig. 3(a)–(c)) and
particle size histograms (Fig. 3(d)–(f)) of AgNPs
obtained by CRed, CvH and MwH, respectively. As illustrated in images, three methods produced AgNPs with
approximate spherical shape. Average diameters were

estimated to be 20, 5 and 7 nm for AgNPs prepared by
CRed, CvH and MwH, respectively. Particle sizes varied
from 5.0 to 27.0 nm for AgNPs1; 1.0–9.0 nm for AgNPs2
and 1.0–12.0 nm for AgNPs3.
Analysis of IR Spectra
Figure 4 presents IR spectra of chitosan and AgNPs
synthesized by CvH and MwH. Broad peaks at
3440 cmÀ1 overlap –OH and –NH stretching vibrations.
Changes in intensity of peaks from 3300 to 3500 cmÀ1
were reportedly attributed to attachment of silver which
affected N–H vibrations [18]. Other authors suggested


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N. T. NGUYEN ET AL.

FIGURE 3.—Transmission electron microscopy (TEM) images and particle size histograms of silver nanoparticles produced by chemical reduction (a, d),
conventional heating (b, e) and microwave-assisted synthesis (c, f). Scale bar corresponds to 20 nm.

FIGURE 4.—Infrared spectra of chitosan (CS), silver nanoparticles synthesized by conventional heating (AgNPs2) and microwave-assisted method
(AgNPs3).

that variations of shape and intensity of peaks in this
region resulted from contribution to reduction and
stabilizing process [19]. The bands from 1350 to
1390 cmÀ1 correspond to absorption of C–N vibrations
and residual NO3 À1 [20]; hence change of peak intensity

could indicate the presence of NO3 À1 after reaction of
chitosan with AgNO3. The spectra of AgNPs produced
by CvH and MwH exhibit blue shift of CS peak at
1646 cmÀ1 and 1560 cmÀ1 to 1634 cmÀ1 and 1544 cmÀ1,
respectively. Since these bands are associated with
amines groups of chitosan, the shift of the peaks probably indicates attachment of AgNPs to amine groups
which leads to change in molecular weight and subsequently, vibration intensity.
To verify if the reducing reaction was completed,
AgNPs suspensions (AgNPs1, AgNPs3) were tested with
solution of NaCl 1 M (Fig. 5). The results were negative
which meant AgNPs suspensions were completely free
from Agþ1.


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MICROWAVE-ASSISTED SYNTHESIS OF SILVER NANOPARTICLES

FIGURE 5.—Testing of residual Agþ1 in AgNPs1 and AgNPs3 using 1 M
NaCl solution.

CONCLUSION
In summary, the proposed MwH synthesis of AgNPs
could successfully produce NPs with properties comparable to those obtained by traditional chemical reduction. The formation of AgNPs was validated by TEM,
UV–Vis and IR spectroscopic analysis. The AgNPs
synthesized by MwH had relatively uniform sizes with
average diameter of approximately 7 nm. The findings
revealed that the MwH method could serve as an alternative to traditional chemical reduction for green synthesis of AgNPs.
FUNDING
This work was financially supported by the National

Foundation for Science and Technology Development
(NAFOSTED), project number 103.02-2011.57. Financial
support was also provided in part by IFS grant (No
F=5022-1).
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