Metal nano particles are one of the most attractive aspects of nano materials in recent years. The reason
for this growing attraction is because of their special physical and chemical properties, which are more enhanced
from bulk material. Hence they find wide application in various fields like catalysis, photonics, optoelectronics,
information storage, antibacterial applications, etc. While considering metal nano particles,
electrical conductivity is one of the most important properties that can be used for humans’ benefit and
should be enhanced. Silver nano particles can be used in the electronics industry as conductive fillers because
of their unique properties such as high electrical and thermal conductivity, high resistance to oxidation.
It is impressive that eco friendly methods are being developed for synthesizing these nano particles,
using different kinds of plant extracts and water soluble component as capping agents, which results in different
forms of particle morphologies.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3523

Bayat, M.

Khatibzadeh, M.

Electronic Sumy State University Institutional Repository

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE  NANOMATERIALS: APPLICATIONS AND PROPERTIES Vol. 2 No 2, 02PCN36(6pp) (2013)   2304-1862/2013/2(2)02PCN36(6) 02PCN36-1  2013 Sumy State University A Review On Green Methods for Synthesis of Silver Nano Particles   Mehrnaz Bayat*, Marziyeh Khatibzadeh†  Department of Polymer Engineering and Color Technology, Amirkabir University of Technology P.O. Box 15875, Hafez Street, Tehran, Iran  (Received 15 June 2013; published online 01 September 2013)  Metal nano particles are one of the most attractive aspects of nano materials in recent years. The reason for this growing attraction is because of their special physical and chemical properties, which are more en-hanced from bulk material. Hence they find wide application in various fields like catalysis, photonics, op-toelectronics, information storage, antibacterial applications, etc. While considering metal nano particles, electrical conductivity is one of the most important properties that can be used for humans’ benefit and should be enhanced. Silver nano particles can be used in the electronics industry as conductive fillers be-cause of their unique properties such as high electrical and thermal conductivity, high resistance to oxida-tion. It is impressive that eco friendly methods are being developed for synthesizing these nano particles, using different kinds of plant extracts and water soluble component as capping agents, which results in dif-ferent forms of particle morphologies.  Keywords: Silver nano particles, Green synthesis.   PACS numbers: 61.82.Rx, 61.46.Bc                                                  * bayatmehrnaz@yahoo.com † khatib@aut.ac.ir 1. INTRODUCTION  Electronic industry is currently one of the most practical industries and advancements in order to make the process of assembling a circuit board easier has become very attractive. Nano-particle metal inks are being developed for printed electronics, particularly on flexible plastic substrates, driving the need to un-derstand their electrical performance [1].  Silver as the best conductor among metals is studied most intensively.  Metal nano-inks consist of a colloidal suspension of nano-sized metal particles which was coated with a thin stabilizer shell. Very small particle sizes of silver, has the ability to sinter at exceptionally low temperatures due to their high surface area to vol-ume ratio, so when the ink is exposed to heat, the nano-particles diffuse in each other and form a continuous film (Fig.1) [1]. Changing the concentration ratio of the components used in synthesizing silver nano particles, such as sil-ver nitrate, reducing agents, stabilizers and capping agents can cause the formation of a variety of morphol-ogies for silver nano particles such as nano spheres, wires, plates and etc.   2. EXPERIMENTAL  2.1 Chemical Approach  The most common approach for synthesis of silver nanoparticles is chemical reduction by organic and inorganic reducing agents. In general, different reducing agents such as sodium citrate, ascorbate, sodium borohydride (NaBH4), elemental hydrogen, polyol process, tollens reagent, N, N-dimethylformamide (DMF), and poly (ethylene glycol)-block copolymers are used for reduction of silver ions (Ag+) in aqueous or non-aqueous solutions.       Fig. 1– SEM images of 100 nm silver nanoparticle film in as-dried condition (a), followed by curing at 150 for 5 min (b) and for 3 h (c) resulting in a continuous porous film [1]  a b c  MEHRNAZ BAYAT, MARZIYEH KHATIBZADEH PROC. NAP 2, 02PCN36 (2013)   02PCN36-2 The aforementioned reducing agents reduce silver ions (Ag+) and lead to the formation of metallic silver (Ag0), which is followed by agglomeration into oligomeric clusters. These clusters eventually lead to formation of metallic colloidal silver particles [2].(Fig. 2)    Fig. 2 – The schematic illustration of chemical reduction pro-cess for silver nitrate molecules, trapped among capping agents in water  2.2 Different Morphologies  Sintering temperature is one of the most important properties of silver nano particles. Different morpholo-gies will result in different sintering temperatures, due to the amount of particles bulk that should be melted into each other during sintering process. The more the nano particles shapes becomes spherical, the more the particles become 3dimensional in nano scale. As illus-trated in Fig.3 for spherical particles more energy and time is needed in sintering process than for planar parti-cles that have 1dimension in nano scale.     Fig. 3 – Illustration of  nano particles sintering process for (a) 3dimensional nano particles and (b) 1dimensional nano particles  3. RESULT AND DISCUSSION  3.1 Articles on Green Synthesis  In 2009 Sharma et al. mentioned in their review ar-ticle that Nanomaterials often show unique and consid-erably changed physical, chemical and biological prop-erties compared to their macro scaled counterparts [3]. They also mentioned that synthesis of noble metal na-noparticles for applications such as catalysis, electron-ics, optics, and biotechnology is an area of constant in-terest for scientists. Sharma et al. studied several synthetic methods for silver nano particles using inexpensive and nontoxic compounds in water environment. Rapid and green synthetic methods using extracts of bio-organisms have shown a great potential in synthesis of silver nano par-ticles.It is also said that silver nano particles have ad-vantages in antibacterial activities. Green synthetic methods include mixed-valence polyoxometallates, pol-ysaccharide, Tollens, irradiation, and biological. The mixed-valence polyoxometallates method was carried out in water, an environmentally-friendly solvent [4]. In 2009 Rao et al. synthesized silver nano particles using silver nitrate, glucose, diethyl amine, sodium carbonate and sodium hydroxide. The different concen-trations of aqueous solutions of silver nitrate and glu-cose solutions were mixed together and stirred to ob-tain a homogeneous solution. The result of this work was an eco friendly wet chemistry rout that produced spherical silver nano particles in suspension and as shown in Fig.4 [5].    Fig. 4 – Spherical silver nano particles synthesized by using glucose and diethyl amine [5].  In 2010 Khan et al. synthesized silver nanoparticles were by a simple chemical reduction method using ascorbic acid and starch as reducing and stabilizing agents, respectively. The advantage of this green meth-od was its simplicity, and room temperature conditions.  nanoparticles which acted as a probable stabilizer and/or capping agent. The hydrophilic poly –OH groups were mainly responsible for the adsorption of amylose onto the surface of nanoparticles through electrostatic interactions. The size dispersity of quasi-spherical, tri-angular nano-plates and nano-rods of pure crystalline metallic silver could be synthesized in presence of starch [6] (Fig.5). In 2011 Yi et al. synthesized silver nano plates, in room temperature, using tannic acid solution via chem-ical reduction method. The synthesis was a seedless process in which tannic acid was used as a reducing as well as a capping agent, and did not need any other surfactant or capping agent. The reason for this im-provement lies in the structure of tannic acid (Fig.6), which has OH groups that participate in reduction re-action and also the branches in its structure that keep the Ag atoms from accumulation and growth [7]. a b  A REVIEW ON GREEN METHODS FOR SYNTHESIS … PROC. NAP 2, 02PCN36 (2013)   02PCN36-3   Fig. 5 – TEM image of silver nano crystals synthesized using ascorbic acid and starch [6]    Fig. 6 – Chemical structure of tannic acid [7]  The result of this work was green synthesis of pla-nar nano particles without introducing any surfactant or seed to direct the two-dimensional growth. The syn-thetic strategy presented was simple and environmen-tally friendly. Fig. 7 shows the TEM image of these planar particles.    Fig. 7 – TEM image of silver nano plates synthesized using tannic acid [7] In 2011 Zhang et al. stated that the main problem in preparing stable nanoparticles for inkjet printing is to overcome the strong agglomeration of the particles in dispersion medium. Good dispersion of metal particles in the ink with a low viscosity is essential to achieve. Nanoparticles tend to cluster and agglomerate if they are not prevented to do so. Particle agglomeration causes the system to change to the one with fewer but larger particles. Hence, it is necessary to modify the surface of the particles so that the agglomeration or clustering can be delayed [8].  The result of this work was eco friendly method for synthesis of sphere shaped nano particles. Fig.8 shows the SEM image of these particles.    Fig. 8 – SEM image of silver nano particles [8]  printable fluid and assure its performance. Due to ag-glomeration of particles, the viscosity tends to increase during storage.One of the advantages coming from the nano-size of material is a dramatic reduction in melting point. Films printed using such small particles can be annealed at lower temperatures to form conductive films of low resistance [8]. In 2011 Philip et al. developed a green synthesis of noble metal nanoparticles. This method contained us-ing aqueous seed extract of Macrotyloma uniflorum [9].  Before that many other methods were employed to en-hance the green preparation of nanosized silver nano particles using plant extracts including honey [10], mangifera indica [11], hibiscus leaf extract [12], Cash-ew leaf [13], murraya koenigii leaf [14], glucose in the presence of soluble starch as a stabilizing agent [15–16], sucrose and maltose [17], aloevera plant extracts [18] and etc.  In their research, Philip et al. used plant extract from Macrotyloma uniflorum, which is an herbaceous plant with lots of medicinal properties. The plant ex-tract was used as capping agent for synthesizing silver nano particles (Fig.9). It was concluded in this work, that several factors influence the formation of silver nanoparticles such as plant source, organic compound in plant extract. Organic compounds like alkaloids, polyphenols, proteins and even some natural pigments are present in plant extracts [9].   MEHRNAZ BAYAT, MARZIYEH KHATIBZADEH PROC. NAP 2, 02PCN36 (2013)   02PCN36-4   Fig. 9 – TEM image of silver nano particles, using Ma-crotyloma uniflorum extract as capping agent [9]  In 2012 Vijayaraghavan et al. stated that nanopar-ticles can be synthesized intracellularly or extracellu-larly using bacteria, yeast, fungi and plant materials [18]. These green synthesizing methods can also find wide applications [20].  In their research Vijayaraghavan et al. used the ex-tract of Syzygium aromaticum plant as reducing and capping agent and the reduction reaction was per-formed in the presence of different bacteria. The result of their work was colloidal silver nano particles as illus-trated in Fig. 10 [19].    Fig. 10 – SEM image of silver nano particles, using Syzygium aromaticum extract as reducing and capping agent [19]  In 2012 Yi et al. developed a chemical reduction meth-od by seed-mediated method in the presence of trisodium citrate and poly (vinyl pyrrolidone) at room temperature.  In this work PVP molecules were used as capping agent and the result was formation of silver nano particles with plate shape morphology (Fig. 11) [21]. The difference approach in this method of green syn-thesizing was that, with preparing the silver seeds before adding all the components, the 2dimentional particles were produced conveniently [21]. (Fig.12) In 2013 Bapat et al. introduced Artocarpus heterophyl-lus Lam. seed extract as a reducing agent for green syn-thesis of silver nano particles in water medium. The result of this eco-friendly method was nano particles that had irregular shapes and morphologies with semi wide distri-bution in particle diameters [22].   Fig. 11 – TEM image of silver nano plates [21]    Fig. 12 – TEM image of Silver nanoplates, with average thickness about 5 nm and average tunable size from 40 to 500 nm [21]  This research indicates that the variety of natural compounds that are present in plant extracts can cause a wide distribution in particle diameters and irregularity in particle morphologies as illustrated in Fig.13 [22].    Fig. 13 – TEM image of Silver nano particles, synthesized  using Artocarpus heterophyllus Lam. seed extract as a reduc-ing agent, and their diameters [22]  A REVIEW ON GREEN METHODS FOR SYNTHESIS … PROC. NAP 2, 02PCN36 (2013)   02PCN36-5 In 2013 Saravanan et al. produced silver nanoparti-cles with another green synthesizing method by using leaf extract of Mimusops elengi, Linn. at room temper-ature. The reason for using this plant extract was be-cause leaf of Mimusops elengi, L. appeared  to be a po-tential source of hydrocarbons. It has been reported that the leaves contain various organic compounds such as alkaloids, flavonoids, tannins, terpenoids, steroids, glycosides and benzenoids, which are water soluble compounds present in the aqueous extract. As a result these compounds act as efficient stabilizing agents dur-ing reduction of silver ions [23]. Fig.14 shows the SEM image of the spherical silver nano particles that were produced by this leaf extract.    Fig. 14 – SEM image of Silver nano particles, synthesized  using leaf extract of Mimusops elengi, Linn. as an stabilizer [23].  In 2013 Kannan et al. reported an inexpensive and reproducible method for the large scale synthesis of silver nano particles by reduction process using flower extract of Millingtonia hortensis. This flower extract, which can act both as reducing and stabilizing agent [24]. Silver nano particles with diameters in the range of 10–40nm using the broth of flower as reducing agent and capping agent, were synthesized (Fig.15). It was understood that the flower extract can reduce the silver salt solution and also hindering the particle growth. This green chemistry approach toward the synthesis of silver nano particles has many advantages such as, ease with which the process can be scaled up, economic viability, etc. The reduction of silver ions and stabiliza-tion of the silver nano particles happened through the participation of flower compounds like proteins and metabolites [24].     Fig. 15 – sEM image of Silver nano particles, synthesized  using Millingtonia hortensis [24].  4. CONCLUSION  Both chemical and physical methods have been used to prepare metal nano particles. Chemical reduction is the most common method because of its convenience. Control over the growth of metal nano particles is required to obtain nano particles of small size with different shapes. It is well known that silver nano particles can be produced by chemical reaction at low cost and in high yield [25].  Natural sources have the potential to reduce metal ion into metal nanoparticles [26]. Silver nano particles were used in various applications such as catalytic, electrical conducting [27–30] and antimicrobialactivity [31-32].  The size, shape and surface morphology of nanoparticles plays a vital role in controlling the physical and chemical properties. The synthesis of metal nanoparticles by chemical reduction method was often performed in the presence of stabilizing agent to prevent the unwanted agglomeration of colloids. Furthermore, the chemically synthesized metal nanoparticles are expensive, hazardous to environment and require high energy consumption. Biological approaches using plant extracts for metal nanoparticles synthesis have been suggested as valuable alternative tool towards chemical methods. It is understood that the variety of natural compounds that are present in plant extracts can cause irregularity in particle morphologies and shapes and in case of spherical particles wide distributions in particle diameters.   REFERENCES  1. J.R. Greer and R.A. Street, Acta Mat. 55, 6345 (2007). 2. B. Wiley, Y. Sun, B. Mayers and Y. Xi, Chem. Eur. J. 11, 454 (2005). 3. N. Hideyuki, J.M.B. Kyle and K. Bartlomiej, Nature 460, 371, (2009). 4. V.K. Sharma, R.A. Yngard, and Y. Lin, Adv. Colloid Inter. Sci. 145, 83 (2009). 5. R. Janardhanan, M. Karuppaiah, N. Hebalkar, and  T.N. Rao, Polyhedron 28, 2522 (2009). 6. Z. Khan, T. Singh, J.I. Hussain, A.Y. Obaid, S.A. al Thabaiti, E.H. El-Mossalamy, Colloids Surf. B (2010). 7. Z. Yi, X. Li, X. Xu, B. Luo, J. Luo, W. Wu and Y.Yi, Col-loids Surf. A 392, 131 (2011). 8. A. Kosmala, R. Wright, Q. Zhang and P. Kirby, Mat. Chem. Phys. 129, 1075 (2011). 9. V.K. Vidhu, S. Aswathy Aromal, and D. Philip, Spectro-chim. Acta A 83, 392 (2011). 10. D. Philip, Spectrochim. Acta A 75, 1078 (2010). 11. D. Philip, Spectrochim. Acta A 78, 327 (2011). 12. D. Philip, Phys. E 42, 1417 (2010). 13. D.S. Sheny, J. Mathew, D. Philip, Spectrochim. Acta A 79, 254 (2011). 14. D. Philip, C. Unni, S.A. Aromal and V.K. Vidhu, Spectro-chim. Acta A 78, 899 (2011).  MEHRNAZ BAYAT, MARZIYEH KHATIBZADEH PROC. NAP 2, 02PCN36 (2013)   02PCN36-6 15. P. Raveendran, J. Fu, S.L. Wallen, and J. Am. Chem. Soc. 125, 13940 (2003). 16. V.K. Sharma, R.A. Yngard and Y. Lin, Adv. Colloid Inter-face Sci. 145, 83 (2009). 17. E. Filippo, A. Serra, A. Buccolieri and D. Manno, J. Non-Cryst. Solids 356, 344 (2010). 18. P. Chandran, M. Chaudhary, R. Pasricha, A. Ahmad and M. Sastry, Biotechnol. Prog. 22, 577 (2006). 19. K. Vijayaraghavan, S.P. Kamala Nalini, N. Udaya Pra-kash and D. Madhankumar, Mat. Lett. 75, 33 (2012). 20. V.K. Sharma, R.A. Yngard and Y.Lin, Adv. Colloid Inter-face Sci. 145, 345 (2009). 21. Y.G. Yi, Z.Yi, J.B. Zhang, and H. He, Trans. Nonferrous Met. Soc. China 22, 865 (2012). 22. U.B. Jagtap, V.A. Bapat, Ind. Crops Prod. 46, 132 (2013). 23. P. Prakash, P. Gnanaprakasam, R. Emmanuel, S. Aroki-yaraj and M. Saravanan, Colloid Surf. B 108, 255 (2013). 24. G. Gnanajobitha, M. Vanaja, K. Paulkumar, S. Rajeshku-mar, C. Malarkodi, G. Annadurai and C. Kannan, J. Na-nomat. Biostruct. (not yet published). 25. J. Natsuki and T. Abe, J. Colloid Inter. Sci. 359, 19 (2011). 26. A.R. Vilchis-Nestor, V. Sanchez-Mendieta, M.A. Camacho-Lopez, R.M. Gomez-Espinosa and J.A. Arenas-Alatorre, Mat. Lett. 62, 3103 (2008). 27. A.R. Shahverdi, A. Fakhmi, H.R. Shahverdi and S. Min-ian, Nanomed. 3, 168 (2007). 28. B.R. Cuenya, Thin Solid Films 518, 3127 (2010). 29. A. Tripathy, A.M. Raichur, N. Chandrasekaran, T.C. Prathna and A. Mukherjee, J. Nanopart. Res. 12, 237 (2010). 30. V. Kumar and S.K. Yadav, J. Chem. Technol. Biotechnol. 842, 151 (2009). 31. M. Saravanan, A.K. Vemu and S.K. Barik, Colloid Surf. B 88, 325 (2011). 32. V. Kumar, S.C. Yadav and S.K. Yadav, J. Chem, Technol. Biotechnol. 85, 1301 (2010).  

A Review On Green Methods for Synthesis of Silver Nano Particles

SocioEconomic Challenges Journal (Sumy State University)

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE  
NANOMATERIALS: APPLICATIONS AND PROPERTIES 
Vol. 2 No 2, 02PCN36(6pp) (2013) 
 
 
2304-1862/2013/2(2)02PCN36(6) 02PCN36-1  2013 Sumy State University 
A Review On Green Methods for Synthesis of Silver Nano Particles  
 
Mehrnaz Bayat*, Marziyeh Khatibzadeh† 
 
Department of Polymer Engineering and Color Technology, Amirkabir University of Technology P.O. Box 15875, 
Hafez Street, Tehran, Iran 
 
(Received 15 June 2013; published online 01 September 2013) 
 
Metal nano particles are one of the most attractive aspects of nano materials in recent years. The reason 
for this growing attraction is because of their special physical and chemical properties, which are more en-
hanced from bulk material. Hence they find wide application in various fields like catalysis, photonics, op-
toelectronics, information storage, antibacterial applications, etc. While considering metal nano particles, 
electrical conductivity is one of the most important properties that can be used for humans’ benefit and 
should be enhanced. Silver nano particles can be used in the electronics industry as conductive fillers be-
cause of their unique properties such as high electrical and thermal conductivity, high resistance to oxida-
tion. It is impressive that eco friendly methods are being developed for synthesizing these nano particles, 
using different kinds of plant extracts and water soluble component as capping agents, which results in dif-
ferent forms of particle morphologies. 
 
Keywords: Silver nano particles, Green synthesis. 
 
 PACS numbers: 61.82.Rx, 61.46.Bc 
 
 
                                               
* bayatmehrnaz@yahoo.com 
† khatib@aut.ac.ir 
1. INTRODUCTION  
Electronic industry is currently one of the most 
practical industries and advancements in order to 
make the process of assembling a circuit board easier 
has become very attractive. Nano-particle metal inks 
are being developed for printed electronics, particularly 
on flexible plastic substrates, driving the need to un-
derstand their electrical performance [1].  
Silver as the best conductor among metals is studied 
most intensively.  Metal nano-inks consist of a colloidal 
suspension of nano-sized metal particles which was 
coated with a thin stabilizer shell. Very small particle 
sizes of silver, has the ability to sinter at exceptionally 
low temperatures due to their high surface area to vol-
ume ratio, so when the ink is exposed to heat, the nano-
particles diffuse in each other and form a continuous 
film (Fig.1) [1]. 
Changing the concentration ratio of the components 
used in synthesizing silver nano particles, such as sil-
ver nitrate, reducing agents, stabilizers and capping 
agents can cause the formation of a variety of morphol-
ogies for silver nano particles such as nano spheres, 
wires, plates and etc.  
 
2. EXPERIMENTAL 
 
2.1 Chemical Approach 
 
The most common approach for synthesis of silver 
nanoparticles is chemical reduction by organic and 
inorganic reducing agents. In general, different reducing 
agents such as sodium citrate, ascorbate, sodium 
borohydride (NaBH4), elemental hydrogen, polyol process, 
tollens reagent, N, N-dimethylformamide (DMF), and poly 
(ethylene glycol)-block copolymers are used for reduction 
of silver ions (Ag+) in aqueous or non-aqueous solutions. 
 
 
 
 
 
 
Fig. 1– SEM images of 100 nm silver nanoparticle film in as-
dried condition (a), followed by curing at 150 for 5 min (b) and 
for 3 h (c) resulting in a continuous porous film [1]  
a 
b 
c 
 MEHRNAZ BAYAT, MARZIYEH KHATIBZADEH PROC. NAP 2, 02PCN36 (2013) 
 
 
02PCN36-2 
The aforementioned reducing agents reduce silver 
ions (Ag+) and lead to the formation of metallic silver 
(Ag0), which is followed by agglomeration into oligomeric 
clusters. These clusters eventually lead to formation of 
metallic colloidal silver particles [2].(Fig. 2) 
 
 
 
Fig. 2 – The schematic illustration of chemical reduction pro-
cess for silver nitrate molecules, trapped among capping agents 
in water 
 
2.2 Different Morphologies 
 
Sintering temperature is one of the most important 
properties of silver nano particles. Different morpholo-
gies will result in different sintering temperatures, due 
to the amount of particles bulk that should be melted 
into each other during sintering process. The more the 
nano particles shapes becomes spherical, the more the 
particles become 3dimensional in nano scale. As illus-
trated in Fig.3 for spherical particles more energy and 
time is needed in sintering process than for planar parti-
cles that have 1dimension in nano scale. 
 
 
 
 
Fig. 3 – Illustration of  nano particles sintering process for (a) 
3dimensional nano particles and (b) 1dimensional nano particles 
 
3. RESULT AND DISCUSSION 
 
3.1 Articles on Green Synthesis 
 
In 2009 Sharma et al. mentioned in their review ar-
ticle that Nanomaterials often show unique and consid-
erably changed physical, chemical and biological prop-
erties compared to their macro scaled counterparts [3]. 
They also mentioned that synthesis of noble metal na-
noparticles for applications such as catalysis, electron-
ics, optics, and biotechnology is an area of constant in-
terest for scientists. 
Sharma et al. studied several synthetic methods for 
silver nano particles using inexpensive and nontoxic 
compounds in water environment. Rapid and green 
synthetic methods using extracts of bio-organisms have 
shown a great potential in synthesis of silver nano par-
ticles.It is also said that silver nano particles have ad-
vantages in antibacterial activities. Green synthetic 
methods include mixed-valence polyoxometallates, pol-
ysaccharide, Tollens, irradiation, and biological. The 
mixed-valence polyoxometallates method was carried 
out in water, an environmentally-friendly solvent [4]. 
In 2009 Rao et al. synthesized silver nano particles 
using silver nitrate, glucose, diethyl amine, sodium 
carbonate and sodium hydroxide. The different concen-
trations of aqueous solutions of silver nitrate and glu-
cose solutions were mixed together and stirred to ob-
tain a homogeneous solution. The result of this work 
was an eco friendly wet chemistry rout that produced 
spherical silver nano particles in suspension and as 
shown in Fig.4 [5]. 
 
 
 
Fig. 4 – Spherical silver nano particles synthesized by using 
glucose and diethyl amine [5]. 
 
In 2010 Khan et al. synthesized silver nanoparticles 
were by a simple chemical reduction method using 
ascorbic acid and starch as reducing and stabilizing 
agents, respectively. The advantage of this green meth-
od was its simplicity, and room temperature conditions.  
nanoparticles which acted as a probable stabilizer 
and/or capping agent. The hydrophilic poly –OH groups 
were mainly responsible for the adsorption of amylose 
onto the surface of nanoparticles through electrostatic 
interactions. The size dispersity of quasi-spherical, tri-
angular nano-plates and nano-rods of pure crystalline 
metallic silver could be synthesized in presence of 
starch [6] (Fig.5). 
In 2011 Yi et al. synthesized silver nano plates, in 
room temperature, using tannic acid solution via chem-
ical reduction method. The synthesis was a seedless 
process in which tannic acid was used as a reducing as 
well as a capping agent, and did not need any other 
surfactant or capping agent. The reason for this im-
provement lies in the structure of tannic acid (Fig.6), 
which has OH groups that participate in reduction re-
action and also the branches in its structure that keep 
the Ag atoms from accumulation and growth [7]. 
a 
b 
 A REVIEW ON GREEN METHODS FOR SYNTHESIS … PROC. NAP 2, 02PCN36 (2013) 
 
 
02PCN36-3 
 
 
Fig. 5 – TEM image of silver nano crystals synthesized using 
ascorbic acid and starch [6] 
 
 
 
Fig. 6 – Chemical structure of tannic acid [7] 
 
The result of this work was green synthesis of pla-
nar nano particles without introducing any surfactant 
or seed to direct the two-dimensional growth. The syn-
thetic strategy presented was simple and environmen-
tally friendly. Fig. 7 shows the TEM image of these 
planar particles. 
 
 
 
Fig. 7 – TEM image of silver nano plates synthesized using 
tannic acid [7] 
In 2011 Zhang et al. stated that the main problem 
in preparing stable nanoparticles for inkjet printing is 
to overcome the strong agglomeration of the particles in 
dispersion medium. Good dispersion of metal particles 
in the ink with a low viscosity is essential to achieve. 
Nanoparticles tend to cluster and agglomerate if they 
are not prevented to do so. Particle agglomeration 
causes the system to change to the one with fewer but 
larger particles. Hence, it is necessary to modify the 
surface of the particles so that the agglomeration or 
clustering can be delayed [8]. 
 The result of this work was eco friendly method for 
synthesis of sphere shaped nano particles. Fig.8 shows 
the SEM image of these particles. 
 
 
 
Fig. 8 – SEM image of silver nano particles [8] 
 
printable fluid and assure its performance. Due to ag-
glomeration of particles, the viscosity tends to increase 
during storage.One of the advantages coming from the 
nano-size of material is a dramatic reduction in melting 
point. Films printed using such small particles can be 
annealed at lower temperatures to form conductive 
films of low resistance [8]. 
In 2011 Philip et al. developed a green synthesis of 
noble metal nanoparticles. This method contained us-
ing aqueous seed extract of Macrotyloma uniflorum [9].  
Before that many other methods were employed to en-
hance the green preparation of nanosized silver nano 
particles using plant extracts including honey [10], 
mangifera indica [11], hibiscus leaf extract [12], Cash-
ew leaf [13], murraya koenigii leaf [14], glucose in the 
presence of soluble starch as a stabilizing agent [15–
16], sucrose and maltose [17], aloevera plant extracts 
[18] and etc.  
In their research, Philip et al. used plant extract 
from Macrotyloma uniflorum, which is an herbaceous 
plant with lots of medicinal properties. The plant ex-
tract was used as capping agent for synthesizing silver 
nano particles (Fig.9). It was concluded in this work, 
that several factors influence the formation of silver 
nanoparticles such as plant source, organic compound 
in plant extract. Organic compounds like alkaloids, 
polyphenols, proteins and even some natural pigments 
are present in plant extracts [9]. 
 
 MEHRNAZ BAYAT, MARZIYEH KHATIBZADEH PROC. NAP 2, 02PCN36 (2013) 
 
 
02PCN36-4 
 
 
Fig. 9 – TEM image of silver nano particles, using Ma-
crotyloma uniflorum extract as capping agent [9] 
 
In 2012 Vijayaraghavan et al. stated that nanopar-
ticles can be synthesized intracellularly or extracellu-
larly using bacteria, yeast, fungi and plant materials 
[18]. These green synthesizing methods can also find 
wide applications [20].  
In their research Vijayaraghavan et al. used the ex-
tract of Syzygium aromaticum plant as reducing and 
capping agent and the reduction reaction was per-
formed in the presence of different bacteria. The result 
of their work was colloidal silver nano particles as illus-
trated in Fig. 10 [19]. 
 
 
 
Fig. 10 – SEM image of silver nano particles, using Syzygium 
aromaticum extract as reducing and capping agent [19] 
 
In 2012 Yi et al. developed a chemical reduction meth-
od by seed-mediated method in the presence of trisodium 
citrate and poly (vinyl pyrrolidone) at room temperature.  
In this work PVP molecules were used as capping agent 
and the result was formation of silver nano particles with 
plate shape morphology (Fig. 11) [21]. 
The difference approach in this method of green syn-
thesizing was that, with preparing the silver seeds before 
adding all the components, the 2dimentional particles 
were produced conveniently [21]. (Fig.12) 
In 2013 Bapat et al. introduced Artocarpus heterophyl-
lus Lam. seed extract as a reducing agent for green syn-
thesis of silver nano particles in water medium. The result 
of this eco-friendly method was nano particles that had 
irregular shapes and morphologies with semi wide distri-
bution in particle diameters [22]. 
 
 
Fig. 11 – TEM image of silver nano plates [21] 
 
 
 
Fig. 12 – TEM image of Silver nanoplates, with average 
thickness about 5 nm and average tunable size from 40 to 500 
nm [21] 
 
This research indicates that the variety of natural 
compounds that are present in plant extracts can cause a 
wide distribution in particle diameters and irregularity 
in particle morphologies as illustrated in Fig.13 [22]. 
 
 
 
Fig. 13 – TEM image of Silver nano particles, synthesized  
using Artocarpus heterophyllus Lam. seed extract as a reduc-
ing agent, and their diameters [22] 
 A REVIEW ON GREEN METHODS FOR SYNTHESIS … PROC. NAP 2, 02PCN36 (2013) 
 
 
02PCN36-5 
In 2013 Saravanan et al. produced silver nanoparti-
cles with another green synthesizing method by using 
leaf extract of Mimusops elengi, Linn. at room temper-
ature. The reason for using this plant extract was be-
cause leaf of Mimusops elengi, L. appeared  to be a po-
tential source of hydrocarbons. It has been reported 
that the leaves contain various organic compounds such 
as alkaloids, flavonoids, tannins, terpenoids, steroids, 
glycosides and benzenoids, which are water soluble 
compounds present in the aqueous extract. As a result 
these compounds act as efficient stabilizing agents dur-
ing reduction of silver ions [23]. 
Fig.14 shows the SEM image of the spherical silver 
nano particles that were produced by this leaf extract. 
 
 
 Fig. 14 – SEM image of Silver nano particles, synthesized  
using leaf extract of Mimusops elengi, Linn. as an stabilizer 
[23]. 
 
In 2013 Kannan et al. reported an inexpensive and 
reproducible method for the large scale synthesis of silver 
nano particles by reduction process using flower extract 
of Millingtonia hortensis. This flower extract, which can 
act both as reducing and stabilizing agent [24]. 
Silver nano particles with diameters in the range of 
10–40nm using the broth of flower as reducing agent 
and capping agent, were synthesized (Fig.15). It was 
understood that the flower extract can reduce the silver 
salt solution and also hindering the particle growth. 
This green chemistry approach toward the synthesis of 
silver nano particles has many advantages such as, 
ease with which the process can be scaled up, economic 
viability, etc. The reduction of silver ions and stabiliza-
tion of the silver nano particles happened through the 
participation of flower compounds like proteins and 
metabolites [24].  
 
 
 
Fig. 15 – sEM image of Silver nano particles, synthesized  
using Millingtonia hortensis [24]. 
 
4. CONCLUSION 
 
Both chemical and physical methods have been used 
to prepare metal nano particles. Chemical reduction is 
the most common method because of its convenience. 
Control over the growth of metal nano particles is 
required to obtain nano particles of small size with 
different shapes. It is well known that silver nano 
particles can be produced by chemical reaction at low 
cost and in high yield [25].  
Natural sources have the potential to reduce metal 
ion into metal nanoparticles [26]. Silver nano particles 
were used in various applications such as catalytic, 
electrical conducting [27–30] and antimicrobialactivity 
[31-32].  
The size, shape and surface morphology of 
nanoparticles plays a vital role in controlling the 
physical and chemical properties. The synthesis of 
metal nanoparticles by chemical reduction method was 
often performed in the presence of stabilizing agent to 
prevent the unwanted agglomeration of colloids. 
Furthermore, the chemically synthesized metal 
nanoparticles are expensive, hazardous to environment 
and require high energy consumption. Biological 
approaches using plant extracts for metal nanoparticles 
synthesis have been suggested as valuable alternative 
tool towards chemical methods. 
It is understood that the variety of natural 
compounds that are present in plant extracts can cause 
irregularity in particle morphologies and shapes and in 
case of spherical particles wide distributions in particle 
diameters. 
 
 
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A Review On Green Methods for Synthesis of Silver Nano Particles

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