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Green synthesis of silver nanoparticles using seed extract of Jatropha curcas
Colloids and Surfaces A: Physicochem. Eng. Aspects 348 (2009) 212–216
Contents lists available at ScienceDirect
Colloids and Surfaces A: Physicochemical and Engineering Aspects journal homepage: www.elsevier.com/locate/colsurfa
Green synthesis of silver nanoparticles using seed extract of Jatropha curcas Harekrishna Bar, Dipak Kr. Bhui, Gobinda P. Sahoo, Priyanka Sarkar, Santanu Pyne, Ajay Misra ∗ Department of Chemistry and Chemical Technology, Vidyasagar University, Midnapore 721102, West Bengal, India
a r t i c l e
i n f o
Article history: Received 23 March 2009 Received in revised form 2 July 2009 Accepted 13 July 2009 Available online 21 July 2009 Keywords: Silver nanoparticles Jatropha curcas Green synthesis HRTEM
a b s t r a c t An eco-friendly process for rapid synthesis of silver nanoparticles has been reported using aqueous seed extract of Jatropha curcas. Formation of stable silver nanoparticles at different concentration of AgNO3 gives mostly spherical particles with diameter ranging from 15 to 50 nm. The resulting silver particles are characterized using HRTEM, XRD and UV–vis spectroscopic techniques. XRD study shows that the particles are crystalline in nature with face centered cubic geometry. © 2009 Elsevier B.V. All rights reserved.
1. Introduction During the last two decades, research on inorganic nanoparticles has been developing rapidly due to their exceptional electronic, catalytic, optical, magnetic and other physical and chemical properties that are quite different from the bulk one [1]. Among the noble metal nanoparticles silver is perhaps the most widely recognized for its application in photonics [2–4], micro-electronics [5,6], photocatalysis [7,8], lithography [9,10] etc. Various techniques including chemical and physical mean were developed to prepare metal nanoparticles such as chemical reduction [11–15], electrochemical reduction [16,17], photochemical reduction [18,19], heat evaporation [20,21] and so on. In most cases, the surface passivator reagents are needed to prevent nanoparticles from aggregation. Unfortunately many organic passivators such as thiophenol [22], thiourea [23], marcapto acetate [24] etc. are toxic enough to pollute the environment if large scale nanoparticles are produced. Biosynthesis of nanoparticles has received considerable attention due to the growing need to develop environmentally benign technologies in material synthesis. For instance, a great deal of effort has been put into the biosynthesis of inorganic materials, especially metal nanoparticles using microorganisms [25–31]. While microorganisms such as bacteria, actinomycetes and fungi continue to be investigated in metal nanoparticles synthesis, the use of parts of whole plants in similar nanoparticles synthesis methodologies is an exciting possibility that is relatively unexplored and under exploited. Even though gold nanoparticles are considered bio-compatible, chemical synthesis methods may still
∗ Corresponding author. Tel.: +91 9433 220206; fax: +91 3222 275329. E-mail address: [email protected] (A. Misra). 0927-7757/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.colsurfa.2009.07.021
lead to the presence of some toxic chemical species absorbed on the surface that may have adverse effects in medical applications [32]. Synthesis of nanoparticles using microorganisms or plants can potentially eliminate this problem by making the nanoparticles more bio-compatible. Use of plant extract for the synthesis of nanoparticles could be advantageous over other environmentally benign biological processes by eliminating the elaborate process of maintaining cell cultures. Jose-Yacaman and co-workers first reported the formation of gold and silver nanoparticles by living plants [33,34]. The above synthetic protocol by plant extract or biomass exemplifies the promising application of the green synthesis of metal nanoparticles. Very recently green silver nanoparticles have been synthesized using various natural products like green tea (Camellia sinensis) [35], neem (Azadirachta indica) leaf broth [36], natural rubber [37], starch [38], aloe vera plant extract [39], lemongrass leaves extract [40,41] leguminous shrub (Sesbania drummondii) [42], latex of Jatropha curcas [43] etc. In this present investigation we are going to report a green method for the synthesis of silver nanoparticles using aqueous seed extract of J. curcas and no toxic chemicals are used as reducing and stabilizing agent during the synthesis. J. curcas is a tree of significant economic importance. It has been identified as potential biodiesel crop for the presence of 40–50% oil from seed called biocrude which can be converted into biodiesel by chemical or lipid mediated esterification process [44]. Kernel of the Jatropha seed gives 40–60% oil as valuable end product. In Indian sub-continents the kernel to shell ratio of J. curcas seed is 62:38 [45]. It contains approximately 47% crude fat, 25% crude protein, 10% crude fiber, 5% moisture and 8% carbohydrate [46]. Saturated fatty acids constitute 20% of crude fat and those remaining are unsaturated one. Oleic acid is the most abundant (44.8%) followed by linoleic acid (34%), palmitic acid (12.8%), and stearic acid (7.3%) [47]. Biomolecules with
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carbonyl, hydroxyl, and amine functional groups have the potential for metal ion reduction and capping the newly formed particles during their growth processes [48]. In a recent communication, we reported that the latex of J. curcas could be used to reduce Ag+ to Ag and latex components also act as capping agent to stabilize Ag nanoparticles [43]. Our present study shows that the aqueous seed extract of J. curcas can be used for both reducing Ag+ to Ag and stabilizing the particles during the growth process. It has also been shown that size of the particles can be controlled within certain range by just varying the concentration of AgNO3 . 2. Materials and methods 2.1. Materials Jatropha seeds were obtained from local source. 50 g of seeds were milled using an ordinary coffee grinder and ground kernel were boiled with 500 ml triply distilled deionized water for 2 h. After filtration clear seed extract was obtained for further use. Silver nitrate (AgNO3 ) analytical grade was purchased from Sigma–Aldrich. All the aqueous solutions were prepared using triply distilled deionized water. 2.2. Synthesis of silver nanoparticles In a typical reaction procedure, 5 ml of seed extract was added to 20 ml of 10−3 (M) aqueous silver nitrate solution, the mixture was heated at 80 ◦ C and the resulting solution became reddish in colour after 15 min of heating. UV–vis spectra showed strong SPR band at 425 nm and thus indicating the formation of silver nanoparticles. Colour intensity increases with the increase of silver nitrate concentrations at a fixed volume fraction (f = 0.2) of seed extract. 2.3. Apparatus UV–vis spectroscopic studies were carried out using Shimadzu UV-1601 spectrophotometer. Crystalline metallic silver was examined by X-ray diffraction analysis using X’Pert PRO PAnalytical-PW 3040/60 X-ray diffractometer with a Cu K␣ radiation monochromatic filter in the range 35–80◦ . The morphology and size of silver nanoparticles were characterized by JEOL-JEM-2100 higher resolution transmission electron microscope (HRTEM). Photoluminescence measurements were carried out using Hitachi F 2500 fluorescence spectrophotometer. For FTIR spectrum analysis, the silver nanoparticles synthesized using seed extract of J. curcas were centrifuged at 10,000 rpm for 20 min to remove free proteins or other components present in the solution. The centrifuged, collected and vacuum dried powder sample was placed in ATR sample holder of FTIR instrument (JASCO FT/IR-6200) for measurement. 3. Results and discussion 3.1. UV–vis spectral study Formation and stability of silver nanoparticles in aqueous colloidal solution are confirmed using UV–vis spectral analysis. Extinctions spectra of silver hydrosol synthesized from different concentrations of AgNO3 are shown in Fig. 1. Characteristic surface plasmon absorption bands are observed at 425 nm for the reddish yellow coloured silver nanoparticles synthesized from 10−3 (M) AgNO3 and the fixed volume fraction (f = 0.2) of aqueous seed extract. SPR band shifted to the red with increasing concentration of silver nitrate from 10−3 to 10−2 (M) and the corresponding colour changes are observed from reddish yellow to deep red.
Fig. 1. (a) UV–vis absorption spectra of silver nanoparticles synthesized from Jatropha seed extract (f = 0.2) at different AgNO3 concentration (i) 10−3 (M); (ii) 2 × 10−3 (M); (iii) 4 × 10−3 (M); (iv) 6 × 10−3 (M); (v) 8 × 10−3 (M); (vi) 10−2 (M).
The surface plasmon resonance (SPR) derived extinction spectra of silver hydrosols can be compared to the extinction spectra theoretically calculated using modified Mie’s Scattering theory. Recently, a modified equation has been proposed by Bohren et al. [49] using the real part of the dielectric function at the peak position (εpeak ). According to the modification, the dipolar absorption efficiency (Qabs ) of a metal sphere with radius ‘R’ is given by, Qabs =
24R εm 3/2 ε (ω) · 2 2 ε (ω) + ε (ω) + 2εm + 482 R2 εm 2 /52
(1)
where εm is the medium dielectric constant, ε (ω) and ε (ω) are the real and imaginary part of the dielectric constant of the metal at wavelength . Thus, the absorption efficiency of a metallic sphere is a function of dielectric constant of the metal, that of medium and the size of the particle. The absorption spectra of colloidal silver particles differing by their size are simulated by using Eq. (1), with parameters typical of silver. Fig. 2 shows that the increase in particle size induces shifting of the SPR band and increase in the bandwidth. On the other hand, UV–vis spectral measurement illustrates (Fig. 1), shifting of SPR band from 425 to 452 nm and the simultaneous broadening of the band. The above features of extinction spectra along with HRTEM micrograph of our synthesized silver hydrosol indicates that with the increase of particle size SPR band broadened and also shifted to the red. Since the SPR extinction spectra is a complex function of SPR absorption and scattering, heterogeneous size distribution of our present synthesize silver hydrosol making it more difficult to fit with Eq. (1). We rather did a qualitative comparison between our experimentally observed SPR extinction spectra and the simulated one obtained from Eq. (1). Both the results are in agreement i.e., with increasing particle size SPR band shows broadening and red shift. 3.2. HRTEM study HRTEM image of silver colloidal solution synthesized by treating 10−3 (M) AgNO3 solution with 0.2 volume fraction of aqueous
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Fig. 2. Simulated surface plasmon resonance band of silver nanoparticles of two different sizes. (a) 2R = 25 nm and (b) 2R = 50 nm.
seed extract is shown in Fig. 3a. Fig. 3a illustrates that the particles are predominantly spherical in shape with diameter ranging from 15 to 25 nm. Larger and uneven shaped particles with diameter 30–50 nm are obtained from 10−2 (M) aqueous AgNO3 solution are shown in Fig. 3b. Sizes of the particle at two different AgNO3 concentrations are in agreement with the observed surface plasmon resonance (SPR) band i.e., at 425 and 452 nm respectively. Insets of HRTEM images show the selected area electron diffraction (SAED) pattern and it suggests the polycrystalline nature of the present synthesized silver nanoparticles.
3.3. XRD study Fig. 4 shows the XRD patterns of silver nanoparticles synthesized from seed extract of J. curcas. A number of Bragg reflections with 2 values of 38.03◦ , 46.18◦ , 63.43◦ and 77.18◦ correspond to the (1 1 1 ), (2 0 0 ), (2 2 0 ) and (3 1 1 ) sets of lattice planes are observed which may be indexed as the band for face centered cubic structures of silver. The XRD pattern thus clearly illustrates that the silver nanoparticles synthesized by the present green method are crystalline in nature.
Fig. 4. XRD patterns of silver nanoparticles synthesized by treating Jatropha seed extract (f = 0.2) with aqueous 10−2 (M) AgNO3 solution.
3.4. FTIR study It is observed that the silver nanoparticles solution is extremely stable for nearly 65 days with only a little aggregation of particles in solution. It has been reported that proteins can provide a good protecting environment for metal hydrosol during their growth processes [50]. FTIR spectroscopy measurements are carried out to identify the biomolecules that bound specifically on the silver surface. Fig. 5 shows the presence of three bands 1744, 1650, 1550 and 1454 cm−1 . The strong absorption at 1744 cm−1 is due carbonyl stretching vibration of the acid groups of different fatty acids present in the extract. The bands at 1650 and 1550 cm−1 are characteristic of amide I and II band [51] respectively. The amide band I is assigned to the stretch mode of the carbonyl group coupled to the amide linkage while the amide II band arises as a result of the N–H stretching modes of vibration in the amide linkage. The band at 1454 cm−1 is assigned to the methylene scissoring vibrations from the proteins. It is well known that proteins can bind to silver nanoparticle through either free amine groups or cystein residues in the proteins [52] and therefore stabilization of silver nanoparti-
Fig. 3. (a) HRTEM micrograph of silver nanoparticles synthesized from 10−3 (M) AgNO3 and Jatropha seed extract (f = 0.2), (b) HRTEM image of larger particles synthesized from 10−2 (M) AgNO3 solution and Jatropha seed extract (f = 0.2) (inset shows the SAED pattern of nanocrystalline silver).
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the other words this emission behavior supports the involvement of J. curcas seed extract in stabilizing the silver nanohydrosol. 4. Conclusion We have developed a green method to synthesize silver nanoparticles using the aqueous seed extract of J. curcas. Here Jatropha seed extract which is environmentally benign and renewable, act as both reducing and stabilizing agent. Particles are mostly spherical in shape. Size of the particles can be controlled by varying the concentration of AgNO3 . Ag nanoparticles prepared in this process are quiet stable and remain intact for nearly two months if it protected under light proof conditions. Acknowledgements Fig. 5. FTIR spectrum of vacuum dried powder of silver nanoparticles synthesized from 10−3 (M) AgNO3 and Jatropha seed extract (f = 0.2).
cles by the surface bound proteins is possible in the present green synthesis. 3.5. Fluorescence study The fluorescent spectra of the colloidal nanoparticles synthesized from different AgNO3 concentration with fixed volume fraction (f = 0.2) of seed extract are shown in Fig. 6. A broad emission band having prominent peak centered at ∼500 nm is observed for the seed extract as it is excited at 420 nm. We anticipate that the emission is due to several saturated and unsaturated organic fatty acid present in J. curcas seed extract. Similar type broad and shifted emission peaks are observed from our bio-synthesized silver nanoparticles after excitation at 420 nm. But the emission intensity gradually decreases with the increasing concentration of AgNO3 or so to say increasing concentration and increasing size of silver nanoparticles. This decreasing intensity suggest that due to the close proximity of emissive species with nanoparticles, quenching of emission take takes place through energy transfer process. In
Fig. 6. Fluorescence emission spectra (excitation at 420 nm) of (i) Jatropha seed extract (f = 0.2) and Jatropha seed extract in presence of silver nanoparticles synthesized from (ii) 2 × 10−3 (M); (iii) 4 × 10−3 (M); (iv) 6 × 10−3 (M); (v) 8 × 10−3 (M) AgNO3 solutions.
The support rendered by the Sophisticated Central Research Facility at IIT Kharagpur, India for sample analysis using XRD and HRTEM is gratefully acknowledged. We are also grateful to DST (Ref. No. SR/FTP/PS-60/2003) and UGC, New Delhi for financial support. P.S. and S.P. thank to CSIR, Govt. of India, for providing individual fellowship during this research work. References [1] G.A. Ozin, Nanochemistry: synthesis in diminishing dimensions, Adv. Mater. 4 (1992) 612–649. [2] Y. Wang, N. Toshima, Preparation of Pd–Pt bimetallic colloids with controllable core/shell structures, J. Phys. Chem. B 101 (1997) 5301–5306. [3] J.C. Lin, C.Y. Wang, Effects of surfactant treatment of silver powder on the rheology of its thick-film paste, Mater. Chem. Phys. 45 (1996) 136–144. [4] I.R. Gould, J.R. Lenhard, A.A. Muenter, S.A. Godleski, S. Farid, Two-electron sensitization: a new concept for silver halide photography, J. Am. Chem. Soc. 122 (2000) 11934–11943. [5] G. Schimd, Large clusters and colloids. Metals in the embryonic state, Chem. Rev. 92 (1992) 1709–1727. [6] W.A. Deheer, The physics of simple metal clusters: experimental aspects and simple models, Rev. Mod. Phys. 65 (1993) 611–676. [7] M.G. Bawendi, M.L. Steigerwald, L.E. Brus, The quantum mechanics of larger semiconductor clusters (“Quantum Dots”), Annu. Rev. Phys. Chem. 41 (1990) 477–496. [8] Y. Kayanuma, Quantum-size effects of interacting electrons and holes in semiconductor microcrystals with spherical shape, Phys. Rev. B 38 (1988) 9797–9805. [9] Y. Xia, J.A. Rogers, K.E. Paul, G.M. Whitesides, Unconventional methods for fabricating and patterning nanostructures, Chem. Rev. 99 (7) (1999) 1823–1848. [10] A.N. Shipway, M. Lahav, I. Willner, Nanostructured gold colloid electrodes, Adv. Mater. 12 (13) (2000) 993–998. [11] X. Devaux, Ch. Laurent, A. Rousset, Chemical synthesis of metal nanoparticles dispersed in alumina, Nanostruct. Mater. 2 (1993) 339–346. [12] Y. Tan, Y. Wang, L. Jiang, et al., Thiosalicylic acid-functionalized silver nanoparticles synthesized in one-phase system, J. Colloid Interf. Sci. 249 (2002) 336–345. [13] P. Christophe, L. Patricia, P. Marie-Paule, In situ synthesis of silver nanocluster in AOT reverse micelles, J. Phys. Chem. 97 (1993) 12974–12983. [14] S.A. Vorobyova, A.I. Lesnikovich, N.S. Sobal, Preparation of silver nanoparticles by interphase reduction, Colloid Surf. A 152 (1999) 375–379. [15] D.K. Bhui, H. Bar, P. Sarkar, G.P. Sahoo, S.P. De, A. Misra, Synthesis and UV–vis spectroscopic study of silver nanoparticles in aqueous SDS solution, J. Mol. Liq. 145 (2009) 33–37. [16] Y.C. Liu, L.H. Lin, New pathway for the synthesis of ultrafine silver nanoparticles from bulk silver substrates in aqueous solutions by sonoelectrochemical methods, Electrochem. Commun. 6 (2004) 1163–1168. [17] G. Sandmann, H. Dietz, W. Plieth, Preparation of silver nanoparticles on ITO surfaces by a double-pulse method, J. Electroanal. Chem. 491 (2000) 78–86. [18] K. Mallick, M.J. Witcombb, M.S. Scurrella, Self-assembly of silver nanoparticles in a polymer solvent: formation of a nanochain through nanoscale soldering, Mater. Chem. Phys. 90 (2005) 221–224. [19] S. Keki, J. Torok, G. Deak, et al., Silver nanoparticles by PAMAM-assisted photochemical reduction of Ag+ , J. Colloid Interf. Sci. 229 (2000) 550–553. [20] C.H. Bae, S.H. Nam, S.M. Park, Formation of silver nanoparticles by laser ablation of a silver target in NaCl solution, Appl. Surf. Sci. 197 (2002) 628–634. [21] A.B. Smetana, K.J. Klabunde, C.M. Sorensen, Synthesis of spherical silver nanoparticles by digestive ripening, stabilization with various agents, and their 3-D and 2-D superlattice formation, J. Colloid Interf. Sci. 284 (2005) 521–526. [22] T.R. Ravindran, A.K. Arora, B. Balamuragan, B.R. Mehta, Inhomogeneous broadening in the photoluminescence spectrum of CdS nanoparticles, Nanostruct. Mater. 11 (1999) 603–609.
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Contents lists available at ScienceDirect
Colloids and Surfaces A: Physicochemical and Engineering Aspects journal homepage: www.elsevier.com/locate/colsurfa
Green synthesis of silver nanoparticles using seed extract of Jatropha curcas Harekrishna Bar, Dipak Kr. Bhui, Gobinda P. Sahoo, Priyanka Sarkar, Santanu Pyne, Ajay Misra ∗ Department of Chemistry and Chemical Technology, Vidyasagar University, Midnapore 721102, West Bengal, India
a r t i c l e
i n f o
Article history: Received 23 March 2009 Received in revised form 2 July 2009 Accepted 13 July 2009 Available online 21 July 2009 Keywords: Silver nanoparticles Jatropha curcas Green synthesis HRTEM
a b s t r a c t An eco-friendly process for rapid synthesis of silver nanoparticles has been reported using aqueous seed extract of Jatropha curcas. Formation of stable silver nanoparticles at different concentration of AgNO3 gives mostly spherical particles with diameter ranging from 15 to 50 nm. The resulting silver particles are characterized using HRTEM, XRD and UV–vis spectroscopic techniques. XRD study shows that the particles are crystalline in nature with face centered cubic geometry. © 2009 Elsevier B.V. All rights reserved.
1. Introduction During the last two decades, research on inorganic nanoparticles has been developing rapidly due to their exceptional electronic, catalytic, optical, magnetic and other physical and chemical properties that are quite different from the bulk one [1]. Among the noble metal nanoparticles silver is perhaps the most widely recognized for its application in photonics [2–4], micro-electronics [5,6], photocatalysis [7,8], lithography [9,10] etc. Various techniques including chemical and physical mean were developed to prepare metal nanoparticles such as chemical reduction [11–15], electrochemical reduction [16,17], photochemical reduction [18,19], heat evaporation [20,21] and so on. In most cases, the surface passivator reagents are needed to prevent nanoparticles from aggregation. Unfortunately many organic passivators such as thiophenol [22], thiourea [23], marcapto acetate [24] etc. are toxic enough to pollute the environment if large scale nanoparticles are produced. Biosynthesis of nanoparticles has received considerable attention due to the growing need to develop environmentally benign technologies in material synthesis. For instance, a great deal of effort has been put into the biosynthesis of inorganic materials, especially metal nanoparticles using microorganisms [25–31]. While microorganisms such as bacteria, actinomycetes and fungi continue to be investigated in metal nanoparticles synthesis, the use of parts of whole plants in similar nanoparticles synthesis methodologies is an exciting possibility that is relatively unexplored and under exploited. Even though gold nanoparticles are considered bio-compatible, chemical synthesis methods may still
∗ Corresponding author. Tel.: +91 9433 220206; fax: +91 3222 275329. E-mail address: [email protected] (A. Misra). 0927-7757/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.colsurfa.2009.07.021
lead to the presence of some toxic chemical species absorbed on the surface that may have adverse effects in medical applications [32]. Synthesis of nanoparticles using microorganisms or plants can potentially eliminate this problem by making the nanoparticles more bio-compatible. Use of plant extract for the synthesis of nanoparticles could be advantageous over other environmentally benign biological processes by eliminating the elaborate process of maintaining cell cultures. Jose-Yacaman and co-workers first reported the formation of gold and silver nanoparticles by living plants [33,34]. The above synthetic protocol by plant extract or biomass exemplifies the promising application of the green synthesis of metal nanoparticles. Very recently green silver nanoparticles have been synthesized using various natural products like green tea (Camellia sinensis) [35], neem (Azadirachta indica) leaf broth [36], natural rubber [37], starch [38], aloe vera plant extract [39], lemongrass leaves extract [40,41] leguminous shrub (Sesbania drummondii) [42], latex of Jatropha curcas [43] etc. In this present investigation we are going to report a green method for the synthesis of silver nanoparticles using aqueous seed extract of J. curcas and no toxic chemicals are used as reducing and stabilizing agent during the synthesis. J. curcas is a tree of significant economic importance. It has been identified as potential biodiesel crop for the presence of 40–50% oil from seed called biocrude which can be converted into biodiesel by chemical or lipid mediated esterification process [44]. Kernel of the Jatropha seed gives 40–60% oil as valuable end product. In Indian sub-continents the kernel to shell ratio of J. curcas seed is 62:38 [45]. It contains approximately 47% crude fat, 25% crude protein, 10% crude fiber, 5% moisture and 8% carbohydrate [46]. Saturated fatty acids constitute 20% of crude fat and those remaining are unsaturated one. Oleic acid is the most abundant (44.8%) followed by linoleic acid (34%), palmitic acid (12.8%), and stearic acid (7.3%) [47]. Biomolecules with
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carbonyl, hydroxyl, and amine functional groups have the potential for metal ion reduction and capping the newly formed particles during their growth processes [48]. In a recent communication, we reported that the latex of J. curcas could be used to reduce Ag+ to Ag and latex components also act as capping agent to stabilize Ag nanoparticles [43]. Our present study shows that the aqueous seed extract of J. curcas can be used for both reducing Ag+ to Ag and stabilizing the particles during the growth process. It has also been shown that size of the particles can be controlled within certain range by just varying the concentration of AgNO3 . 2. Materials and methods 2.1. Materials Jatropha seeds were obtained from local source. 50 g of seeds were milled using an ordinary coffee grinder and ground kernel were boiled with 500 ml triply distilled deionized water for 2 h. After filtration clear seed extract was obtained for further use. Silver nitrate (AgNO3 ) analytical grade was purchased from Sigma–Aldrich. All the aqueous solutions were prepared using triply distilled deionized water. 2.2. Synthesis of silver nanoparticles In a typical reaction procedure, 5 ml of seed extract was added to 20 ml of 10−3 (M) aqueous silver nitrate solution, the mixture was heated at 80 ◦ C and the resulting solution became reddish in colour after 15 min of heating. UV–vis spectra showed strong SPR band at 425 nm and thus indicating the formation of silver nanoparticles. Colour intensity increases with the increase of silver nitrate concentrations at a fixed volume fraction (f = 0.2) of seed extract. 2.3. Apparatus UV–vis spectroscopic studies were carried out using Shimadzu UV-1601 spectrophotometer. Crystalline metallic silver was examined by X-ray diffraction analysis using X’Pert PRO PAnalytical-PW 3040/60 X-ray diffractometer with a Cu K␣ radiation monochromatic filter in the range 35–80◦ . The morphology and size of silver nanoparticles were characterized by JEOL-JEM-2100 higher resolution transmission electron microscope (HRTEM). Photoluminescence measurements were carried out using Hitachi F 2500 fluorescence spectrophotometer. For FTIR spectrum analysis, the silver nanoparticles synthesized using seed extract of J. curcas were centrifuged at 10,000 rpm for 20 min to remove free proteins or other components present in the solution. The centrifuged, collected and vacuum dried powder sample was placed in ATR sample holder of FTIR instrument (JASCO FT/IR-6200) for measurement. 3. Results and discussion 3.1. UV–vis spectral study Formation and stability of silver nanoparticles in aqueous colloidal solution are confirmed using UV–vis spectral analysis. Extinctions spectra of silver hydrosol synthesized from different concentrations of AgNO3 are shown in Fig. 1. Characteristic surface plasmon absorption bands are observed at 425 nm for the reddish yellow coloured silver nanoparticles synthesized from 10−3 (M) AgNO3 and the fixed volume fraction (f = 0.2) of aqueous seed extract. SPR band shifted to the red with increasing concentration of silver nitrate from 10−3 to 10−2 (M) and the corresponding colour changes are observed from reddish yellow to deep red.
Fig. 1. (a) UV–vis absorption spectra of silver nanoparticles synthesized from Jatropha seed extract (f = 0.2) at different AgNO3 concentration (i) 10−3 (M); (ii) 2 × 10−3 (M); (iii) 4 × 10−3 (M); (iv) 6 × 10−3 (M); (v) 8 × 10−3 (M); (vi) 10−2 (M).
The surface plasmon resonance (SPR) derived extinction spectra of silver hydrosols can be compared to the extinction spectra theoretically calculated using modified Mie’s Scattering theory. Recently, a modified equation has been proposed by Bohren et al. [49] using the real part of the dielectric function at the peak position (εpeak ). According to the modification, the dipolar absorption efficiency (Qabs ) of a metal sphere with radius ‘R’ is given by, Qabs =
24R εm 3/2 ε (ω) · 2 2 ε (ω) + ε (ω) + 2εm + 482 R2 εm 2 /52
(1)
where εm is the medium dielectric constant, ε (ω) and ε (ω) are the real and imaginary part of the dielectric constant of the metal at wavelength . Thus, the absorption efficiency of a metallic sphere is a function of dielectric constant of the metal, that of medium and the size of the particle. The absorption spectra of colloidal silver particles differing by their size are simulated by using Eq. (1), with parameters typical of silver. Fig. 2 shows that the increase in particle size induces shifting of the SPR band and increase in the bandwidth. On the other hand, UV–vis spectral measurement illustrates (Fig. 1), shifting of SPR band from 425 to 452 nm and the simultaneous broadening of the band. The above features of extinction spectra along with HRTEM micrograph of our synthesized silver hydrosol indicates that with the increase of particle size SPR band broadened and also shifted to the red. Since the SPR extinction spectra is a complex function of SPR absorption and scattering, heterogeneous size distribution of our present synthesize silver hydrosol making it more difficult to fit with Eq. (1). We rather did a qualitative comparison between our experimentally observed SPR extinction spectra and the simulated one obtained from Eq. (1). Both the results are in agreement i.e., with increasing particle size SPR band shows broadening and red shift. 3.2. HRTEM study HRTEM image of silver colloidal solution synthesized by treating 10−3 (M) AgNO3 solution with 0.2 volume fraction of aqueous
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Fig. 2. Simulated surface plasmon resonance band of silver nanoparticles of two different sizes. (a) 2R = 25 nm and (b) 2R = 50 nm.
seed extract is shown in Fig. 3a. Fig. 3a illustrates that the particles are predominantly spherical in shape with diameter ranging from 15 to 25 nm. Larger and uneven shaped particles with diameter 30–50 nm are obtained from 10−2 (M) aqueous AgNO3 solution are shown in Fig. 3b. Sizes of the particle at two different AgNO3 concentrations are in agreement with the observed surface plasmon resonance (SPR) band i.e., at 425 and 452 nm respectively. Insets of HRTEM images show the selected area electron diffraction (SAED) pattern and it suggests the polycrystalline nature of the present synthesized silver nanoparticles.
3.3. XRD study Fig. 4 shows the XRD patterns of silver nanoparticles synthesized from seed extract of J. curcas. A number of Bragg reflections with 2 values of 38.03◦ , 46.18◦ , 63.43◦ and 77.18◦ correspond to the (1 1 1 ), (2 0 0 ), (2 2 0 ) and (3 1 1 ) sets of lattice planes are observed which may be indexed as the band for face centered cubic structures of silver. The XRD pattern thus clearly illustrates that the silver nanoparticles synthesized by the present green method are crystalline in nature.
Fig. 4. XRD patterns of silver nanoparticles synthesized by treating Jatropha seed extract (f = 0.2) with aqueous 10−2 (M) AgNO3 solution.
3.4. FTIR study It is observed that the silver nanoparticles solution is extremely stable for nearly 65 days with only a little aggregation of particles in solution. It has been reported that proteins can provide a good protecting environment for metal hydrosol during their growth processes [50]. FTIR spectroscopy measurements are carried out to identify the biomolecules that bound specifically on the silver surface. Fig. 5 shows the presence of three bands 1744, 1650, 1550 and 1454 cm−1 . The strong absorption at 1744 cm−1 is due carbonyl stretching vibration of the acid groups of different fatty acids present in the extract. The bands at 1650 and 1550 cm−1 are characteristic of amide I and II band [51] respectively. The amide band I is assigned to the stretch mode of the carbonyl group coupled to the amide linkage while the amide II band arises as a result of the N–H stretching modes of vibration in the amide linkage. The band at 1454 cm−1 is assigned to the methylene scissoring vibrations from the proteins. It is well known that proteins can bind to silver nanoparticle through either free amine groups or cystein residues in the proteins [52] and therefore stabilization of silver nanoparti-
Fig. 3. (a) HRTEM micrograph of silver nanoparticles synthesized from 10−3 (M) AgNO3 and Jatropha seed extract (f = 0.2), (b) HRTEM image of larger particles synthesized from 10−2 (M) AgNO3 solution and Jatropha seed extract (f = 0.2) (inset shows the SAED pattern of nanocrystalline silver).
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the other words this emission behavior supports the involvement of J. curcas seed extract in stabilizing the silver nanohydrosol. 4. Conclusion We have developed a green method to synthesize silver nanoparticles using the aqueous seed extract of J. curcas. Here Jatropha seed extract which is environmentally benign and renewable, act as both reducing and stabilizing agent. Particles are mostly spherical in shape. Size of the particles can be controlled by varying the concentration of AgNO3 . Ag nanoparticles prepared in this process are quiet stable and remain intact for nearly two months if it protected under light proof conditions. Acknowledgements Fig. 5. FTIR spectrum of vacuum dried powder of silver nanoparticles synthesized from 10−3 (M) AgNO3 and Jatropha seed extract (f = 0.2).
cles by the surface bound proteins is possible in the present green synthesis. 3.5. Fluorescence study The fluorescent spectra of the colloidal nanoparticles synthesized from different AgNO3 concentration with fixed volume fraction (f = 0.2) of seed extract are shown in Fig. 6. A broad emission band having prominent peak centered at ∼500 nm is observed for the seed extract as it is excited at 420 nm. We anticipate that the emission is due to several saturated and unsaturated organic fatty acid present in J. curcas seed extract. Similar type broad and shifted emission peaks are observed from our bio-synthesized silver nanoparticles after excitation at 420 nm. But the emission intensity gradually decreases with the increasing concentration of AgNO3 or so to say increasing concentration and increasing size of silver nanoparticles. This decreasing intensity suggest that due to the close proximity of emissive species with nanoparticles, quenching of emission take takes place through energy transfer process. In
Fig. 6. Fluorescence emission spectra (excitation at 420 nm) of (i) Jatropha seed extract (f = 0.2) and Jatropha seed extract in presence of silver nanoparticles synthesized from (ii) 2 × 10−3 (M); (iii) 4 × 10−3 (M); (iv) 6 × 10−3 (M); (v) 8 × 10−3 (M) AgNO3 solutions.
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