ГОДИШНИК НА МИННО-ГЕОЛОЖКИЯ УНИВЕРСИТЕТ “СВ. ИВАН РИЛСКИ”, Том 57, Св. II, Добив и преработка на минерални суровини, 2014
ANNUAL OF THE UNIVERSITY OF MINING AND GEOLOGY “ST. IVAN RILSKI”, Vol. 57, Part ІI, Mining and Mineral processing, 2014
LOW TEMPERATURE SYNTHESIS OF SILVER NANOPARTICLES
Georgi Nikolov, Maria Manastirli, Gospodinka Gicheva
University of Mining and Geology “St. Ivan Rilski”, 1700 Sofia, e_gospodinka@yahoo.com
ABSTRACT. Metal nanoparticles are of great importance for modern science. With their numerous applications in many different areas of technology they have
attracted a great deal of interest in their direction. Nobel metals nanoparticles such as silver (Ag NP) and gold (Au NP) in particular have been intensively studied due
to their stability and interesting and unique physical and optical properties. Due to them they have been engaged in wide areas of research including photocatalysis
and biotechnology. This fact is pushing scientists into developing new and cost effective methods for metal nanoparticle synthesis. The key component here is “cost
effective”. If metal nanoparticles are to be applied in large scale production their preparation have to be relatively cheap. Here we present a low temperature synthesis
of silver nanoparticles which is a precondition for their potential large scale production.
Keywords: nanotechnology, metal nanoparticles, synthesis.
НИСКОТЕМПЕРАТУРЕН СИНТЕЗ НА СРЕБЪРНИ НАНОЧАСТЦИ
Георги Николов, Мария Манастирли, Господинка Гичева
Минно-геоложки университет “Св. Иван Рилски”, 1700 София, e_gospodinka@yahoo.com
РЕЗЮМЕ. Металните наночастици са от излючително значение за съвременнта наука. Наночастиците от благородни метали, в частност сребро и злато,
биват изследвани интензивно поради тяхната стабилност и уникални физични и оптични свойства. Именно заради тези си свойства те биват прилагани в
различни области на науката, като фотокатализа и биотехнологии. Именно този широк спектър на приложение на наночастиците кара учените да
разработват нови и икономически изгодни методи за синтез с оглед потенциалното им промишлено производство. Ако искаме да разработим метод за
производство на метални наночастици в индустриален мащаб, то тяхната цена трябва да е относително ниска. В настоящото изследване се предлага
такъв евтив нискотемпературен синтез на сребърни наночастици, което е необходима предпоставка за тяхното производство в промишлени мащаби.
Ключови думи: нанотехнологии, метални наночастици, синтез
some of the physical properties of the silver nanoparticles
(AgNPs) like their conductivity. They are used in production of
inkjet inks for fabrication of flexible electronic displays via inkjet
printing technology (Abe et al, 2011).
Introduction
Metal nanoparticles have attracted the attention of
researchers due to their unique optical and electronic
properties (Liz-Marzán, 2006). Their applications vary in
different areas of modern technology – optics and electronics
(Azizi-Toupkanloo H et al, 2013; Saion et al, 2014), catalysis
(Philip et al., 2014; Ehsani et al., 2014; Janani, 2014), biology
(Abdel-Wahhab M., 2014), medicine (Bandara et al., 2013,
Çeliköz et al., 2005) and etc. Large part of the interest in them
stems from the fact that they possess an antimicrobial activity.
In the recent years due to the extensive overuse of antibiotics
a generation of antibiotic resistant strains (and infections)
emerged that can’t be easily treated by standard procedures.
In response to the growing concern people have turned to an
age-old cure – silver. Its antibacterial properties have been
long known. They are attributed to the silver ions (Ag+) but with
the development of nanotechnology and the production of
silver nanoparticles (Ag0) it was established that they also
possess such activity. There are even commercially available
pharmaceutical products containing silver nanoparticles
(Colargol®, Chemax Pharma), presently. So incorporating
silver nanoparticles gives us an opportunity to produce
materials and devices with antibacterial activity such as
antibacterial textile, antibacterial wound bandages, vials and
containers with antibacterial surfaces as well as water
treatment devices. Other major field of application exploits
Having said that, it becomes apparent that low cost and
environmental friendly (“green”) method for silver nanoparticles
synthesis is key component for their mass production. Some of
the most common methods for AgNPs production involve
chemical reduction of silver salt (silver nitrate AgNO3 for
example) by various reductors such as sodium borhydride
(NaBH4), sodium citrate (Na3Cit), formaldehyde and some
saccharides – glucose, galactose, lactose and maltose (Zboril
et al, 2006). The chemical reaction that takes place results in
formation of silver nanoparticles (AgNPs). Even though the
process itself is easily conducted with high yield, a control over
the size of the obtained nanoparticles remains elusive. It
should be pointed out that size control for this kind of material
is of great importance since all properties of nanomaterials are
size dependent. It was found that the antimicrobial activity of
silver nanoparticles strongly depends on their size and size
distribution. So one can see how important is to come up with
a synthesis method which could allow us a control over the
size of the AgNPs.
Other methods involve reduction of silver ions in the
presence of amines (Abe et al, 2011). These methods have
their merits based on the low temperature of the synthesis
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process and control over the size of the obtained AgNPs.
Following that examples a low temperature method for silver
nanoparticles has been investigated. It has the benefit of being
cost effective using relatively inexpensive reagents, nontoxic
organic solvents and lacking the need of heating the reaction
mixture thus saving additional expenses for production. These
features allow the method to be potentially applied for industrial
production of AgNPs.
Effect of PVP
In the series of conducted experiments we altered the
amount of polyvinylpyrrolidone (PVP) in order to establish its
effect on the formation of silver nanoparticles. From the data
presented in Table 1 becomes apparent that changing the
amount of PVP (from 0 g in sample “2” to 0.5 g in sample “1”)
does not greatly affect the final size of the obtained
nanoparticles, but not is not the case of samples marked as
“3”, “4”, “5” and “6”. We observed that in the cases where the
concentration of TEA is higher (“3”, “4”, “5” and “6”) there is
distinction between the samples with and without PVP. We can
see that where PVP is present in the reaction mixture the final
size of the AgNPs is bigger. Some literature sources claim that
a coordinative bond between silver ions (Ag+) and N and/or O
atoms form PVP molecule is formed resulting in the formation
of a complex (Abe et al, 2011) with increased reactivity
compared to silver ions alone. That could explain why in the
series with higher concentration of TEA, which acts as a
catalyst, the more active PVP-Ag+ complex will give AgNPs
with bigger size.
Experimental part
Materials
Silver nitrate (AgNO3) and trisodium citrate (Na3Cit.2H2O)
were purchased by Merck KGaA, triethanolamine (TEA; ≥98%)
by Sigma-Aldrich and polyvinylpyrrolidone (PVP K30; Mw ~40
000) by Fluka. All reagents were used without any further
purification or modification.
Synthesis of silver nanoparticles (AgNPs)
Other important distinction between the reaction mixtures
containing PVP is the fact that the obtained dispersions of
AgNPs in water are much more stable throughout the time
compared to the ones without PVP. PVP acts as surfactant
stabilizing the dispersion most likely by coordinating to the
surface of the obtained AgNPs as some sources indicate (Abe
et al, 2011).
A definite amount of PVP (0.5 g) was dissolved in distilled
water under magnetic stirring at room temperature until a clear
solution was obtained. A silver nitrate salt (0.25 g) was then
added to this solution under constant stirring to its total
dissolve. After 10 min an aqueous solution of sodium citrate
(0.44 g) was added dropwise to the mixed solution of PVP and
AgNO3. After the gradual addition of sodium citrate (Na3Cit) the
solution slowly turns opaque. We proceeded by adding a
solution of triethanolamine (TEA) to the reaction mixture and
then the colour turned from white to light brown signifying the
formation of silver nanoparticles.
Materials characterization
UV-VIS absorbance spectra of the AgNPs dispersed in water
were taken on UV-VIS spectrophotometer Shimadzu UV160U.
Atomic force microscopy analysis of selected samples was
performed.
Results and discussion
The AgNPs synthesis method presented in this research is
conducted at room temperature. It allows us to obtain
nanoparticles without heating the reaction mixture. In order to
gain some insight on the process of formation and the factors
affecting it we have conducted series of experiments varying
some of the reagents concentration (Table 1). As an indication
of the size of the AgNPs we take into account the wavelength
of the maximum in the absorbance spectrum (Liz-Marzán,
2006). It is considered to be indicative for the silver
nanoparticles’ size at same other conditions, so AgNPs with
longer wavelength maximum are generally considered larger.
Fig. 1. Absorbance spectra of silver nanoparticles AgNPs obtained at
different reaction conditions (Table 1)
The absorbance spectra of AgNPs dispersions were taken
(Fig. 1). The spectra exhibit a maximum in the region 405-420
nm characteristic for them and in good agreement with the
literature data for silver nanoparticles. The position of
absorbance maximum in spectrum of the different samples
depicts the difference in their size.
Table 1
№
1
2
3
4
5
6
AgNO3, g
0.25
0.25
0.25
0.25
0.25
0.25
PVP, g
0.5
0
0.5
0
0.5
0
Na3Cit, g
0.44
0.44
0.44
0.44
0.44
0.44
TEA, ml
0.020
0.020
0.060
0.060
0.180
0.180
The effect of PVP on AgNPs morphology will be further
investigated by transmission electron microscopy (TEM) to see
if there is any difference in the shape of the resulting silver
nanoparticles.
Λmax, nm
420
420
415
410
410
405
Effect of TEA
One factor that significantly affects the formation of AgNPs is
the amount of the added amine. Looking at Table 1 one can
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clearly see that increasing the amount of the amine (TEA) in
reaction mixture leads to the formation of smaller AgNPs. That
bodes well with the literature data (Abe et al, 2011) of other
authors that have observed the same effect. It is proposed that
TEA act as some sort of catalyst of the process of reduction of
silver ions to silver nanoparticles by Na3Cit thus increasing its
rate. When AgNPs are produced by reduction of silver ions by
citrate alone (“citrate method”) the reaction mixture needs to
heat up to 1000C in order for reaction to take place. When
adding amine (TEA) reaction proceeds at room temperature.
Since it was suggested that TEA takes part in the reaction,
increasing its concentration will lead to faster reaction rate and
smaller size of the resulting AgNPs. This assumption is
supported by the fact that the size of the obtained AgNPs is
smaller indeed (Figure 1).
Anbazhagan V., Ahmed K.B.A, Janani S. 2014, Synthesis of
catalytically active silver nanoparticles using lipid derived
signaling molecule, N-steroylethanolamine: Promising
antibacterial agent and selective colorimetric sensor for
mercury ion. – In: Sensor Actuat B-Chem, 200, 92-100.
Faraji N., Yunus W.M.M, Kharazmi A., Saion E. 2014, Thirdorder nonlinear optical properties of silver nanoparticles
mediated by chitosan. – In: Optik - International Journal for
Light and Electron Optics, 125(12), 2809-2812.
Goharshadi E.K., Azizi-Toupkanloo H. 2013, Silver colloid
nanoparticles: Ultrasound-assisted synthesis, electrical and
rheological properties. – In: Powder Technol, 237, 97-101.
Liz-Marzán L.M. 2006, Tailoring surface plasmons through the
morphology and assembly of metal nanoparticles. – In:
Langmuir, 22(1), 32-41.
Nasrollahzadeh M., Babaei F., Sajadi S.M., Ehsani A. 2013,
Green synthesis, optical properties and catalytic activity of
silver nanoparticles in the synthesis of N-monosubstituted
ureas in water. – In: Spectrochim Acta A, 132, 423-429.
Natsuki J., Abe T. 2011, Synthesis of pure colloidal silver
nanoparticles with high electroconductivity for printed
electronic circuits- The effect of amines on their formation
in aqueous media. – In: J Colloid Interf Sci, 359, 19-23.
Panacek A., Kvitek L., Prucek R., Kolar M., Vecerova R.,
Pizurova N., Sharma V.K., Nevecna T., Zboril R. 2006,
Silver nanoparticles: Synthesis, characterization, and their
antibacterial activity. – In: J. Phys. Chem. B, 110, 1624816253.
Perera S., Bhushan B., Bandara R., Rajapakse G., Rajapakse
S., Bandara C. 2013, Morphological, antimicrobial,
durability, and physical properties of untreated and treated
textiles using silver-nanoparticles. – In: Colloid Surface A,
436, 975-989.
Ülküra E., Oncul O., Karagoz H., Yeniz E., Çeliköz B. 2005,
Comparison of silver-coated dressing (Acticoat™),
chlorhexidine acetate 0.5% (Bactigrass®), and fusidic acid
2% (Fucidin®) for topical antibacterial effect in methicillinresistant Staphylococci-contaminated, full-skin thickness
rat burn wounds. – In: Burns, 31(7), 874-877.
Vidhu V.K., Philip D. 2014, Spectroscopic, microscopic and
catalytic properties of silver nanoparticles synthesized
using Saraca indica flower. – In: Spectrochim Acta A, 117,
102-108.
The effect of amine (TEA) concentration on AgNPs
morphology and size distribution is yet to be thoroughly
investigated by transmission electron microscopy (TEM) and
dynamic light scattering (DLS) to confirm the results obtained
by UV-VIS spectrophotometry. The additional results will
broaden our view in the process of AgNPs formation and to
give us a clearer perspective about the nature of the process.
Conclusions
In this study a method for low temperature synthesis of
AgNPs is discussed. In involves addition of amines to the
“citrate method” which allows the reaction to take place at
room temperature. Some of the main advantages of the
method include the use of low cost reagents, omitting usage of
toxic organic solvents and lacking the need of heating up the
reaction mixture. It was shown that by varying the amount of
amine the size of the obtained AgNPs can be controlled. All of
the above mentioned facts suggest that this method could be
employed in industrial production of AgNPs.
Acknowledgements
This research was funded by project MTF-133/ 09.05.2014 of
UMG “St. Ivan Rilski”.
References
Abdel-Aziz M.S., Shaheen M.S., El-Nekeety A.A., AbdelWahhab M.A. 2014, Antioxidant and antibacterial activity of
silver nanoparticles biosynthesized using Chenopodium
murale leaf extract. – In: Journal of Saudi Chemical
Society, 18(4), 356-363.
The article has been reviewed by assoc. prof. N. Mincheva-Peneva and
recommended for publication by department “Chemistry”.
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