Green synthesis and characterization of silver nanoparticles produced using Arbutus Unedo leaf extract

Abstract

Metallic nanoparticles have received great attention from chemists, physicists, biologists and engineers who wish to use them for the development of a new generation of nanodevices. In the present study silver nanoparticles were synthesized from aqueous silver nitrate through a simple and eco-friendly route using leaf broth of Arbutus unedo, which acted as a reductant and stabilizer simultaneously. The aqueous silver ions when exposed to the leaf broth were reduced and stabilized over long periods of time resulting in the green synthesis of surface functionalized silver nanoparticles. The bio-reduced silver nanoparticles were appropriately characterized. The results revealed the formation of single crystalline Ag nanoparticles with a narrow size distribution for each sample. The particles, although discrete, were predominately coated with the organic leaf extract forming small aggregates, which makes them stable over long time periods and highly appropriate for coatings or biotechnology applications.

Full text

Green synthesis and characterization of silver nanoparticles produced using
Arbutus Unedo leaf extract
Pantelis Kouvaris
a
, Andreas Delimitis
b
, Vassilis Zaspalis
c
, Dimitrios Papadopoulos
a
,
Sofia A. Tsipas
d
, Nikolaos Michailidis
a,
⁎
a
Physical Metallurgy Laboratory (PML), Mechanical Engineering Department, Aristotle University of Thessaloniki, Thessaloniki 54124, Greece
b
Chemical Process Engineering Research Institute, CERTH, PO Box 60361, Thermi, 57001 Thessaloniki, Greece
c
Laboratory of Materials Technology, Chemical Engineering Department, Aristotle University of Thessaloniki, Thessaloniki 54124, Greece
d
Department of Materials Science & Engineering, IAAB, University Carlos III of Madrid, Avda Universidad 30, 28911, Leganes, Madrid, Spain
abstractarticle info
Article history:
Received 27 September 2011
Accepted 6 February 2012
Available online 15 February 2012
Keywords:
Green synthesis
Silver nanoparticles
Organic coating
Metallic nanoparticles have received great attention from chemists, physicists, biologists and engineers who
wish to use them for the development of a new generation of nanodevices. In the present study silver nano-
particles were synthesized from aqueous silver nitrate through a simple and eco-friendly route using leaf
broth of Arbutus unedo, which acted as a reductant and stabilizer simultaneously. The aqueous silver ions
when exposed to the leaf broth were reduced and stabilized over long periods of time resulting in the
green synthesis of surface functionalized silver nanoparticles. The bio-reduced silver nanoparticles were ap-
propriately characterized. The results revealed the formation of single crystalline Ag nanoparticles with a nar-
row size distribution for each sample. The particles, although discrete, were predominately coated with the
organic leaf extract forming small aggregates, which makes them stable over long time periods and highly
appropriate for coatings or biotechnology applications.
© 2012 Elsevier B.V. All rights reserved.
1. Introduction
In recent years nanomaterials fabrication and their uses is emerg-
ing as a critical technology with applications in many industrial sec-
tors. Nanoparticles, due to their specific electrical, optical, magnetic,
chemical and mechanical properties are currently used in many
high technology areas, such as the medical sector for diagnosis, anti-
microbial, drug delivery [1], as well as in the electronic and optoelec-
tronic industry [2] or in the chemical sector for catalysis [3], for
environmental protection [4] and energy conversion [5].
Nanoparticle synthesis is usually carried out by variousphysical and
chemical methods, such as laser ablation, pyrolysis, chemical or physi-
cal vapor deposition, sol gel, lithography electro-deposition most of
them being expensive, and/or requiring the use of toxic solvents [6]
Recently, great efforts are made to use environmentally friendly
methods for the synthesis of noble metal nanoparticles [7]. This is
achieved mostly by the use of plant or fruit extracts [8] and bio-
organisms [9]. These green methods are low cost, fast, efficient and
generally lead to the formation of crystalline nanoparticles with a va-
riety of shapes (spheres, rods, prisms, plates, needles, leafs or den-
drites), with sizes between 1 and 100 nm. These features mainly
depend on the process parameters, such as the nature of plant extract
and the relative concentrations of the extract and metal salt(s) react-
ing, pH, temperature, and time of reaction, as well as the rate of mix-
ing of plant extract and metal salt(s) [10]. The stability of produced
nanoparticles can in some cases change after a few days or the nano-
particles can remain stable over long periods [11].
In the present paper we present an environmentally friendly, one
step, ultra-fast, cost-efficient method for producing Ag nanoparticles
using readily available native Macedonian region Greek plant ex-
tracts. Some of the produced nanoparticles are covered by a stable or-
ganic coating, i.e. are surface functionalized, which makes them stable
over long periods and also suitable for a variety of medical applica-
tions such as drug delivery.
This type of surface functionalization of metal nanoparticles has
not been systematically reported for most if not all of the plant ex-
tracts previously used for the green synthesis of noble metal nanopar-
ticles, and may constitute a unique phenomenon observed only with
few specific plants.
2. Materials and methods
2.1. Preparation of Arbutus unedo leaf broth
Silver nitrate (AgNO
3
) was purchased from Sigma-Aldrich chemi-
cals and fresh Arbutus Unedo leaves were collected from surround-
ings of Thessaloniki region, Macedonia, Greece. The Arbutus unedo
Materials Letters 76 (2012) 18–20
⁎Corresponding author at: Physical Metallurgy Laboratory, Dept. of Mechanical
Engineering, Aristotle University of Thessaloniki, GR 54124 Thessaloniki, Greece.
Tel.: +30 2310 995891; fax: + 30 2310 996069.
E-mail address: nmichail@eng.auth.gr (N. Michailidis).
0167-577X/$ –see front matter © 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.matlet.2012.02.025
Contents lists available at SciVerse ScienceDirect
Materials Letters
journal homepage: www.elsevier.com/locate/matlet

fresh leaf extract used for the reduction of Ag
+
ions to Ag° was pre-
pared by placing 10 g of thoroughly washed finely cut leaves in
500 ml flask along with 100 ml of distilled water and then boiling
the mixture for 15 min before decanting it. The extract was filtered
and stored at room temperature in order to be used for further
experiments.
2.2. Synthesis of silver nanoparticles
An aqueous solution of silver nitrate was prepared by adding
1 mM of AgNO
3
to 50 ml of distilled water at room temperature.
The aqueous solution was mixed with 50 ml of leaf extracts at a tem-
perature of 80 °C while stirring magnetically at 1000 rpm for 30 s. The
bio-reduced aqueous component was used for the UV–vis spectrosco-
py characterization.
2.3. UV–vis spectral analysis
The UV–vis analysis was performed by sampling the aqueous
component at different time intervals and the absorption maxima
was scanned over the 300–800 nm wavelength range on a Perkin-
Elmer Lambda 25 spectrometer.
2.4. TEM analysis of silver nanoparticles
Samples for electron microscopy observations were prepared by
ultrasonically dissolving the aqueous solution in twice distilled
water. A drop of the solution was subsequently deposited onto a
lacey C film supported on a Cu grid and allowed to evaporate under
ambience conditions. Electron microscopy experiments were carried
out in a JEOL 2011 high resolution transmission electron microscope,
operating at 200 kV, with a point resolution of 0.23 nm and
C
s
=1.0 mm. The microscope is also fitted with an Oxford Instru-
ments INCAx-sight liquid nitrogen cooled energy-dispersive X-ray
analysis (EDS) detector with an ultrathin window for detailed ele-
mental analysis of the catalysts. Processing of the EDS spectra was ac-
complished using the INCA Microanalysis Suite software.
3. Results and discussion
Fig. 1 shows the UV–vis spectra of aqueous component as a func-
tion of time variation of leaf broth with 1 mM aqueous AgNO
3
solu-
tion. Metal nanoparticles have free electrons, which give surface
plasmon resonance (SPR) absorption band, due to the combined vi-
bration of electrons of metal nanoparticles in resonance with light
wave. The sharp bands of silver colloids were observed at 436 nm.
The intensity of absorption band increases with increasing time peri-
od of aqueous component and consequent color changes were ob-
served from colorless to reddish yellow. These characteristic color
variations is due to the excitation of the of the surface plasmon reso-
nance in the metal nanoparticles.
Transmission Electron Microscopy (TEM) experiments proved the
formation of nanocrystalline silver particles, as shown in Fig. 2. The
nanoparticles predominately adopt a spherical morphology and are
often agglomerated into small aggregates, comprising of 5–6 particles
each, as Fig. 2 illustrates. The obtained nanoparticles are quite uni-
form in size and up to 30 nm. In rare occasions, particles with higher
0
10
20
30
40
50
60
300 400 500 600 700 800
Counts
Wavelength [nm]
Fig. 1. The UV-absorption spectra obtained for Arbutus unedo plant. A characteristic
peak at 450 nm wavelength is clearly observed, which is indicative of the formation
of Ag nanoparticles.
Fig. 2. Typical TEM image of Ag nanoparticles, showing their spherical morphology and
agglomeration. The existence of a thin organic layer surrounding the Ag aggregates is
depicted with white arrows in the image.
Fig. 3. (a) SAD pattern (invert image) taken from the nanoparticles region. The discrete
spots in the ring is characteristic of the single crystalline structure of each individual
particle. (b) Higher magnification image of the same area of the Ag particles, illustrat-
ing the presence of three-fold twinning in one of them.
19P. Kouvaris et al. / Materials Letters 76 (2012) 18–20

sizes were also observed in the sample, but their population was rath-
er low. The TEM images revealed that the small particle aggregates
are coated with a thin organic layer, which acts as a capping organic
agent. This also may well explain that fact that the nanoparticles
showed a very good dispersion inside the bio-reduced aqueous solu-
tion, even in the macroscopic scale.
The crystallinity of the Ag nanoparticles was detected by selected
area diffraction (SAD) experiments and a typical SAD pattern is
depicted at Fig. 3a. The appearance of discrete spots in the ring pat-
tern proved that the majority of the particles are single crystalline
materials and they are predominately oriented along their [111] Ag
direction, as commonly found for the fcc silver crystal lattice. This
was also confirmed by higher magnification TEM images, such as
the one showed in Fig. 3b, where the formation of three-fold twinning
is demonstrated and further proves the single crystalline nature of
the particles. The twin planes are depicted with lines.
Chemical analysis of the produced nanoparticles was accom-
plished by means of EDS, which confirmed both the existence of Ag
and the organic component that covers the Ag aggregates; the latter
is implied by the presence of the C, O and Si peaks in the EDS SPEC-
TRA. The EDS analysis also proved that the Ag nanoparticles are in
metallic form, with no formation of Ag
2
O in them and free from any
other impurities.
4. Conclusions
The rapid biological synthesis of silver nanoparticles using leaf
broth of Arbutus Unedo provides an environmental friendly, simple
and efficient route for synthesis of benign nanoparticles. The size of
the silver nanoparticles was between 3 and 20 nm. The bioreduced
silver nanoparticles were characterized using UV-V and HRTEM tech-
niques. These reduced silver nanoparticles were surrounded by an
organic thin layer. From a technological point of view, these obtained
silver nanoparticles have potential applications in the biomedical
field and this simple procedure has several advantages such as cost-
effectiveness, compatibility for medical and pharmaceutical applica-
tions, as well as large scale commercial production.
References
[1] Parveen S, Misra R, Sahoo SK. Nanoparticles: a boom to drug delivery, therapeu-
tics, diagnostics and imaging. Nanomed-Nanotechnol 2012;8(2):147–66.
[2] Phillips J, Bowen W, Cagin E, Wang W. Electronic and optoelectronic devices
based on semiconducting zinc oxide. In: Pallab B, Roberto F, Hiroshi K, editors.
Comprehensive Semiconductor Science and Technology. Elsevier Science; 2011.
p. 101–27.
[3] Guliants VV, Shiju NR. Recent developments in catalysis using nanostructured ma-
terials. Appl Catal A Gen 2009;356:1–17.
[4] Lead JR, Ju-Nam Y. Manufactured nanoparticles: an overview of their chemistry,
interactions and potential environmental implications. Sci Total Environ
2008;400:396–414.
[5] Kim W, Kim K, Jung B, Kim J. Effects of embedding non-absorbing nanoparticles in
organic photovoltaics on power conversion efficiency. Sol Energy Mater Sol Cells
2010;94:1835–9.
[6] Park HH, Choi YJ. Direct patterning of SnO(2) composite films prepared with var-
ious contents of Pt nanoparticles by photochemical metal-organic deposition.
Thin Solid Films 2011;519:6214–8.
[7] Hubenthal F. Noble metal nanoparticles: synthesis and optical properties. In:
Andrews DL, Scholes GD, Wiederrecht GP, editors. Comprehensive Nanoscience
and Technology. Nanomaterials Elsevier Science; 2011. p. 375–435.
[8] Jin ES, Ghodake GS, Deshpande NG, Lee YP. Pear fruit extract-assisted room-
temperature biosynthesis of gold nanoplates. Colloids Surf B 2010;75:584–9.
[9] Sanghi R, Verma P. Biomimetic synthesis and characterisation of protein capped
silver nanoparticles. Bioresour Technol 2009;100:501–4.
[10] Noruzi M, Zare D, Khoshnevisan K, Davoodi D. Rapid green synthesis of gold nano-
particles using Rosa hybrida petal extract at room temperature. Spectrochim Acta
A 2011;79:1461–5.
[11] Pinto VV, Ferreira MJ, Silva R, Santos HA, Silva F, Pereira CM. Long time effect on
the stability of silver nanoparticles in aqueous medium: effect of the synthesis
and storage conditions. Colloids Surf A 2010;364:19–25.
20 P. Kouvaris et al. / Materials Letters 76 (2012) 18–20