- Email: [email protected]
Instant green synthesis of silver nanoparticles using Terminalia chebula fruit extract and evaluation of their catalytic activity on reduction of methylene blue
Process Biochemistry 47 (2012) 1351–1357
Contents lists available at SciVerse ScienceDirect
Process Biochemistry journal homepage: www.elsevier.com/locate/procbio
Instant green synthesis of silver nanoparticles using Terminalia chebula fruit extract and evaluation of their catalytic activity on reduction of methylene blue T. Jebakumar Immanuel Edison, M.G. Sethuraman ∗ Department of Chemistry, Gandhigram Rural Institute – Deemed University, Gandhigram – 624 302, Dindigul District, Tamil Nadu, India
a r t i c l e
i n f o
Article history: Received 19 December 2011 Received in revised form 26 March 2012 Accepted 28 April 2012 Available online 5 May 2012 Keywords: Instant green synthesis Colloidal silver nanoparticles HR-TEM Reduction of methylene blue Electron relay effect
a b s t r a c t A novel green approach for the synthesis and stabilization of silver nanoparticles (AgNPs) using water extract of Terminalia chebula (T. chebula) fruit under ambient conditions is reported in this article. The instant formation of AgNPs was analyzed by visual observation and UV–visible spectrophotometer. Further the effect of pH on the formation of AgNPs was also studied. The synthesized AgNPs were characterized by FT-IR, XRD, HR-TEM with EDS and DLS with zeta potential. Appearance of brownish yellow color confirmed the formation of AgNPs. In the neutral pH, the stability of AgNPs was found to be high. The stability of AgNPs is due to the high negative values of zeta potential and capping of phytoconstituents present in the T. chebula fruit extract which is evident from zeta potential and FT-IR studies. The XRD and EDS pattern of synthesized AgNPs showed their crystalline structure, with face centered cubic geometry oriented in (1 1 1) plane. HR-TEM and DLS studies revealed that the diameter of stable AgNPs was approximately 25 nm. Moreover the catalytic activity of synthesized AgNPs in the reduction of methylene blue was studied by UV–visible spectrophotometer. The synthesized AgNPs are observed to have a good catalytic activity on the reduction of methylene blue by T. chebula which is confirmed by the decrease in absorbance maximum values of methylene blue with respect to time using UV–visible spectrophotometer and is attributed to the electron relay effect. © 2012 Elsevier Ltd. All rights reserved.
1. Introduction In the recent past, there has been an increasing demand for nanoparticles due to their applications in various areas like medicine, catalysis, energy and materials [1–4]. The size, shape, and surface morphology of nanoparticles play a key role in controlling the physical, chemical, optical, and electronic properties of these nanomaterials. Metallic nanoparticles are synthesized by various methods such as, physical vapor deposition, chemical vapor deposition, sol–gel method, microwave-assisted synthesis, ultrasonication method, electrochemical synthesis and chemical reduction of metallic ions [5–11]. The chemicals used for these syntheses are often toxic, costly and non-ecofriendly. Nowadays bioreduction methods based on fungi, microorganisms, plant extracts are being attempted due to the ease of synthesis, environmentally benign nature and greater stability of nanoparticles [12–16]. AgNPs have received attention due to the surface plasmon resonance (strong absorption in the visible region), which can be easily monitored by UV–visible spectrophotometer. The applications of
∗ Corresponding author. Tel.: +91 0 451 2452371. E-mail address: [email protected] (M.G. Sethuraman). 1359-5113/$ – see front matter © 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.procbio.2012.04.025
AgNPs in the field of medicine, optoelectronics, optics, catalysis, sensors are well known [1–4]. Yadav and co-workers [17] had reviewed the synthesis of plant mediated silver and gold nanoparticles. Plant extracts, like Magnolia kobus, Diopyros kaki, Ficus benghalensis and Citrus limon extracts, have been shown to produce nanoparticles with good stability [18–20] due to the presence of reducing agents like alkaloids, polyphenols and flavonoids which are the major phytoconstituents. Terminalia chebula fruit (belonging to the family Combretaceae) is commonly known as myrobalan. It is mainly used in the Ayurvedic preparations as laxative, diuretic and cardiotonic [21]. Moreover, it is a good reducing agent for hazardous hexavalent chromium ions to trivalent chromium ions [22]. The major phytoconstituents present in the fruit are hydrolysable tannins, gallic acid, chebulic acid, chebulic ellagitannins and gallate esters [23]. In the present study, the instant synthesis of AgNPs using water extract of T. chebula fruit by the reduction of Ag+ ions is reported. The effect of pH on the formation of AgNPs was also studied using UV–visible spectrophotometer. AgNPs were further characterized by FT-IR, XRD, HR-TEM with EDS and DLS with zeta potential. Moreover, its catalytic activity on reduction of methylene blue (MB) in the presence of T. chebula fruit extract was also studied. MB is a thiazine dye, used in the analysis of trace levels of sulphide ions in aquatic samples. The cationic form of MB is used as
1352
T.J.I. Edison, M.G. Sethuraman / Process Biochemistry 47 (2012) 1351–1357
Fig. 1. Schematic representations of the reactions for evaluation of the effect of synthesized AgNPs on the reduction of methylene blue by T. chebula.
an anti-malarial agent and chemotherapeutic agent in the aqua culture industry. Moreover, it is used in microbiology, surgery and diagnostic field [24–26].
diffractometer, with the following working conditions: CuK␣ Ni-filtered radiation; 40 kV, 30 mA; divergence slit 0.47◦ . 2.6. HR-TEM with EDS analysis
2. Materials and methods 2.1. Preparation of aqueous fruit extract The fruits of T. chebula were cleaned, dried and powdered. The aqueous extract was prepared by the addition of 0.4 g of powdered fruit with 100 ml of distilled water at 50 ◦ C for 2 min. Further, the extract was filtered using Whatman 40 filter paper and the filtrate was preserved in a refrigerator (10 ◦ C).
The stable biogenic AgNPs were washed and diluted by distilled water to attain the absorbance range of 0.5. Further, one drop of diluted AgNPs sample was placed on Cu grid with Ultrathin Cu on holey carbon disc and was allowed to dry in vacuo. After drying, the nanoparticles were visualized using JEOL JEM 2100 High Resolution Transmission Electron Microscope operating in the range of 200 kV of acceleration. Simultaneously the energy dispersive spectrum (EDS) was also recorded.
2.2. Synthesis of AgNPs About 1 ml of the extract was added separately to 25 ml of 0.01 M AgNO3 (CDH Chemicals, Mumbai, India) solution at room temperature. 2.3. UV–visible spectroscopic characterization of AgNPs The synthesis of AgNPs and the effect of variation of pH from 4 to 9 on the formation of AgNPs were studied using PerkinElmer Lamda 35 UV–visible spectrophotometer. The pH was varied by the addition of 0.1 M sulfuric acid in the acidic region and 0.1 M sodium hydroxide solution in the basic region. For the analysis, 0.3 ml of AgNPs was taken in a cuvette and diluted by 2 ml of distilled water. 2.4. FT-IR spectroscopic studies The functional groups present in the phytoconstituents on the fruit extract of T. chebula and their involvement in the synthesis of AgNPs was determined by the FT-IR studies. The dried aqueous extract and synthesized AgNPs were mixed with KBr to make pellet and the FT-IR analysis was carried out by JASCO FT-IR 400. 2.5. XRD studies The phytoreduced silver colloidal solution was drop-coated onto a glass substrate and the XRD measurements were carried out using a Philips X’Pert Pro X-Ray
Fig. 2. Visual observation and UV–visible absorption spectra of instantly synthesized AgNPs.
T.J.I. Edison, M.G. Sethuraman / Process Biochemistry 47 (2012) 1351–1357
0.75
100
412 nm
T. chebula extract Absorbance
0.70 0.65 0.60 0.55 0.50
80
424 nm Wavelength (λ (nm))
0.45 426 nm
-- pH 8
60
A
-- pH 4
0.15 488 nm
40
300
400
500
600
700
1383
0.00 200
-NO 3
3380
0.10 0.05
1208
-- pH 5
1344
-- pH 6
454 nm
3377
0.25 0.20
B
1032
-- pH 7
0.30
%T
-- pH 9
1448
0.40 0.35
1615 1714
Absorbance
1353
800
Wavelength (λ (nm))
4000
3500
3000
2500
2000
1500
1000
500
Wavenumber (cm-1)
Fig. 3. UV–visible absorption spectra of AgNPs at various pH ranges.
Fig. 5. FT-IR spectra of aqueous fruit extract of T. chebula (A) and synthesized AgNPs with capping of phytoconstituents (B).
2.7. Dynamic light scattering (DLS) and zeta potential measurements In order to find out the stability and size distribution of AgNPs, the DLS and zeta potential measurements were carried out using Zetasizer Nano S90 (Malvern). 2.8. Evaluation of the effect of synthesized AgNPs on the reduction of methylene blue by T. chebula Methylene blue purchased from CDH chemicals, India was used for this study. In order to assess the catalytic activity of synthesized AgNPs, two reactions were carried out in a 3.5 ml capacity quartz cuvette and absorbance values were monitored using UV–visible spectrophotometer. In the first reaction, 1 ml of methylene blue (1 × 10−4 M) was mixed with 0.2 ml of aqueous fruit extract and 1.8 ml of water, this reaction was monitored after 30 min (I). In second reaction, 1 ml of methylene blue (1 × 10−4 M) was mixed with 0.2 ml extract and 2 ml of synthesized AgNPs and this reaction was monitored at three different time intervals viz., 30 min, 45 min and 60 min (II). In all the reactions total volume of the mixture was made up to 3 ml. The values of absorption maxima (max ) were compared, with that of methylene blue. The schematic representations of the two reactions are depicted in Fig. 1.
3. Results and discussion 3.1. UV–visible spectroscopy The formation of nanoparticles was easily detected and characterized by UV–visible spectroscopy owing to the surface plasmon resonance (SPR), i.e., the interaction of electromagnetic radiation
and the electrons in the conduction band around the nanoparticles [27]. AgNPs were observed strongly in the range of 400–450 nm in visible region. In the present work, the AgNPs are rapidly formed (pH 6.8) after the addition of T. chebula extract, evident from the appearance of brownish yellow color and the max appeared at 440 nm is depicted in Fig. 2. The effect of pH on the formation of AgNPs was evaluated by UV–visible spectroscopic studies and is given in Fig. 3. From the figure, it is evident that the formation of AgNPs mainly depends on the pH of the reaction medium. The absorbance value was increased gradually with increasing of pH range from 4 to 9, suggesting the rate of formation of AgNPs is high in basic pH than in acidic pH. The formation of AgNPs occurs rapidly, in neutral and basic pH which is evident from visual observation and may be due to the ionization of the phenolic group present in the extract [28]. The slow rate of formation and aggregation of AgNPs at acidic pH could be related to electrostatic repulsion of anions present in the solution [29]. At basic pH range there is a possibility of Ag+ precipitating as AgOH also. On the basis of the results, it could be concluded that the
120 38.175 (111)
434 nm
0.8
100
0.7
80
0.5 -- 10 days
0.4
-- 10 hr
Counts
Absorbance
0.6
44.175 (200) 63.525 (220)
60 78.325 (311)
-- 100 min
0.3 0.2
270 nm 420 nm
0.1
--
80 min
--
60 min
--
40 min
--
20 min
--
1 sec
0.0 200
40
20
0
300
400
500
600
700
800
Wavelength (λ (nm)) Fig. 4. UV–visible absorption spectra of time dependent formation of AgNPs (pH 7).
0
10
20
30
40
50
60
2θ° Fig. 6. XRD patterns of synthesized AgNPs.
70
80
90
1354
T.J.I. Edison, M.G. Sethuraman / Process Biochemistry 47 (2012) 1351–1357
Fig. 7. HR-TEM and SAED images of synthesized AgNPs (pH 7) under different magnifications.
optimum condition for the preparation of AgNPs using T. chebula can be taken as the neutral pH and hence the UV–visible spectroscopic studies were carried out at various time intervals at this pH. The effect of reaction time at pH 7 was shown in Fig. 4. From the figure, it can be observed that the absorbance of AgNPs increased with increase of reaction time, indicating more reduction of Ag+ with respect to time. The synthesized AgNPs are stable for 10 days at 5 ◦ C evident from, the max value.
3.2. FT-IR studies FT-IR spectroscopy measurements were carried out to identify the biomolecules that capped on silver nanoparticles. FT-IR spectrum of dried aqueous extract and synthesized AgNPs are shown in Fig. 5. The major phytoconstituents present in the myroblan fruit are hydrolysable tannins, gallic acid, chebulic acid, chebulic ellagitannins and gallate esters. The IR-spectrum of fruit extract showed an absorption band at 3380 cm−1 which is characteristic of the OH
Fig. 8. EDS pattern of synthesized AgNPs.
T.J.I. Edison, M.G. Sethuraman / Process Biochemistry 47 (2012) 1351–1357
1355
Fig. 9. DLS and zeta potential of AgNPs synthesized at pH 7.
stretching of phenolic group. The absorption bands at 1714 and 1615 cm−1 correspond to carbonyl group present in the extract. The sharp band at 1032 cm−1 indicated C O group of ester and the band at 1448 cm−1 is due to aromatic CH stretching vibrations. The absorption bands that appear in the IR spectrum of the aqueous extract could also be seen in the IR spectra of phytocapped AgNPs. This shows that the phytoconstituents (mostly tannins) protect the AgNPs from aggregation.
3.3. XRD studies The XRD patterns of synthesized AgNPs are shown in Fig. 6. From the figure it can be seen that four major peaks appeared with 2 values of 38.175◦ , 44.175◦ , 63.525◦ and 78.325◦ . These peaks correspond to the (1 1 1), (2 0 0), (2 2 0) and (3 1 1) planes of facecentered-cubic (fcc) geometry of AgNPs, which is in agreement with the JCPDS file No. 42-0783. The ratio between the intensities of (1 1 1) and (2 0 0) diffraction peaks is relatively higher than the usual values which indicate that the experimental system has AgNPs oriented in (1 1 1) plane [30]. XRD pattern thus reveals that
the AgNPs have fcc geometry with the nanoparticles oriented in (1 1 1) plane.
3.4. HR-TEM with EDS studies The application of TEM in nanosciences is significant to view the particles in nanoscale. The HR-TEM images of synthesized AgNPs (pH 7) and SAED pattern obtained from HR-TEM studies are depicted in Fig. 7, which give clear indications regarding size, shape and size distribution of nanoparticles. From the images, it can be seen that the AgNPs are capped with phytoconstituents of myrobalan. The SAED pattern of AgNPs reveals its crystalline nature (white dots in Fig. 11). The result of EDS gives a clear idea about the elements present in the nanoparticles. The EDS profile of phytocapped AgNPs is presented in Fig. 8. The strong signal of the Ag atoms indicates the crystalline property. The presence O peaks along with the Ag signals, suggest that the AgNPs are capped by phytoconstituents through oxygen atom. The Cu peak comes from the TEM grid. The size of the synthesized AgNPs are approximately 25 nm.
Fig. 10. Mechanism involved in the formation of AgNPs.
1356
T.J.I. Edison, M.G. Sethuraman / Process Biochemistry 47 (2012) 1351–1357
3.5. DLS with zeta potential Methylene blue (MB)
0.4
MB+Extract (After 30 mins)
The DLS size distribution image of AgNPs (pH 7) is shown in Fig. 9. From the results, the calculated average particle size distribution of AgNPs is 25 nm and the corresponding average zeta potential value is −35.6 mV (Fig. 9), suggesting higher stability of AgNPs. The large negative potential value could be due to the capping of polyphenolic constituents present in the extract [31].
MB+Extract+Ag nps (After 30 mins) MB+Extract+Ag nps (After 45 mins) MB+Extract+Ag nps (After 60 mins)
Absorbance
0.3
0.2 3.6. Mechanism of reduction of AgNO3 to AgNPs by the phytoconstituents of T. chebulla
0.1
0.0 400
500
600
700
Wavelength ( λ (nm)) Fig. 11. UV–visible spectra of methylene blue reduction by T. chebula in the presence of AgNPs.
The major phytoconstituents present in the myroblan fruit are hydrolysable tannins, polyphenols, gallic acid, chebulagic acid and chebulinic acid. The possible mechanism for the reduction of Ag+ is proposed and presented in Fig. 10. In this scheme, Ag+ ions can form intermediate complexes with phenolic OH groups present in hydrolysable tannins which subsequently undergo oxidation to quinone forms with consequent reduction of Ag+ to AgNPs [32].
Fig. 12. Catalytic action of AgNPs between T. chebula extract and methylene blue (electron relay effect).
T.J.I. Edison, M.G. Sethuraman / Process Biochemistry 47 (2012) 1351–1357
3.7. Catalytic activity of AgNPs on reduction of methylene blue by T. chebula extract It is a well known fact that AgNPs and their composites show greater catalytic activity in the area of dye reduction and removal. Pal et al. studied the reduction of methylene blue by arsine in the presence of silver nano [33], while Witcomb et al. studied the catalytic activity of AgNPs on the reduction of phenosaffarin dye [34]. The present study aims at the reduction of methylene blue by the natural green aqueous extract of myrobalan containing AgNPs. Pure methylene blue has a max value of 664 nm. Thirty minutes after the addition of the extract to the dye, the absorbance is gradually decreased and is shifted to higher wavelength. The decrease of absorbance is indicative of the ability of phytoextract to degrade methylene blue. System containing dye, AgNPs and the extract at the end of 30 min time interval showed a marked decrease in the absorbance of methylene blue and increase of SPR peak of AgNPs (Fig. 11). This reveals that AgNPs act as an electron transfer mediator between the extract and methylene blue by acting as a redox catalyst, which is often termed as electron relay effect [35] (Fig. 12). 4. Conclusions The study has demonstrated that AgNPs could be prepared instantly by making use of aqueous extract of myrobalan. The phytoconstituents such as hydrolysable tannins, gallic acid, chebulic acid, chebulic ellagitannins and gallate esters act as reducing agents for the preparation of AgNPs and the capping of AgNPs by the phytoconstituents provide stability to AgNPs as evident from FT-IR and EDS studies. The synthesized AgNPs were found to have a crystalline structure with face centered cubic geometry as studied by XRD method. The HR-TEM images and DLS studies had shown that the synthesized AgNPs are having the size around 25 nm. The synthesized AgNPs act through the electron relay effect and influence the degradation of methylene blue by myrobalan extract. References [1] Nam J, Won N, Jin H, Chung H, Kim S. pH-induced aggregation of gold nanoparticles for photothermal cancer therapy. J Am Chem Soc 2009;131: 13639–45. [2] Narayanan KB, Sakthivel N. Synthesis and characterization of nano-gold composite using Cylindrocladium floridanum and its heterogeneous catalysis in the degradation of 4-nitrophenol. J Hazard Mater 2011;189:519–25. [3] Li J, Chen X, Ai N, Hao J, Chen Q, Strauf S, et al. Silver nanoparticle doped TiO2 nanofiber dye sensitized solar cells. Chem Phys Lett 2011;514:141–5. [4] Fayaza AM, Girilal M, Mahdy SA, Somsundar SS, Venkatesan R, Kalaichelvan PT. Vancomycin bound biogenic gold nanoparticles: a different perspective for development of anti VRSA agents. Process Biochem 2011;46:636–41. [5] Horwat D, Zakharov DI, Endrino JL, Soldera F, Anders A, Migot S, et al. Chemistry, phase formation, and catalytic activity of thin palladium-containing oxide films synthesized by plasma-assisted physical vapor deposition. Surf Coat Technol 2011;205:S171–7. [6] Dillon AC, Mahan AH, Deshpande R, Alleman JL, Blackburn JL, Parillia PA, et al. Hot-wire chemical vapor synthesis for a variety of nano-materials with novel applications. Thin Solid Films 2006;501:216–20. [7] Sobhani M, Rezaie HR, Naghizadeh R. Sol–gel synthesis of aluminum titanate (Al2 TiO5 ) nano-particles. J Mater Process Technol 2008;206:282–5. [8] Nadagouda MN, Speth TF, Varma RS. Microwave-assisted green synthesis of silver nanostructures. Acc Chem Res 2011;44:469–78. [9] Wani IA, Ganguly A, Ahmed J, Ahmad T. Silver nanoparticles: ultrasonic wave assisted synthesis, optical characterization and surface area studies. Mater Lett 2011;65:520–2.
1357
[10] Starowicz M, Stypula B, Banas J. Electrochemical synthesis of silver nanoparticles. Electrochem Commun 2006;8:227–30. [11] Kima KD, Hanb DN, Kim HT. Optimization of experimental conditions based on the Taguchi robust design for the formation of nano-sized silver particles by chemical reduction method. Chem Eng J 2004;104:55–61. [12] Balaji DS, Basavaraja S, Deshpandeb R, Mahesh DB, Prabhakara BK, Venkataraman A. Extracellular biosynthesis of functionalized silver nanoparticles by strains of Cladosporium cladosporioides fungus. Colloids Surf B: Biointerfaces 2009;68:88–92. [13] Shahverdi AR, Minaeian S, Shahverdi HR, Jamalifar H, Nohi AA. Rapid synthesis of silver nanoparticles using culture supernatants of Enterobacteria: a novel biological approach. Process Biochem 2007;42:919–23. [14] Kumar KP, Paul W, Sharma CP. Green synthesis of gold nanoparticles with Zingiber officinale extract: characterization and blood compatibility. Process Biochem 2011;46:2007–13. [15] Dubey SP, Lahtinen M, Sillanpaa M. Tansy fruit mediated greener synthesis of silver and gold nanoparticles. Process Biochem 2010;45:1065–71. [16] Sukirtha R, Priyanka KM, Antony JJ, Kamalakkannan S, Thangam R, Gunasekaran P, et al. Cytotoxic effect of Green synthesized silver nanoparticles using Melia azedarach against in vitro HeLa cell lines and lymphoma mice model. Process Biochem 2012;47:273–9. [17] Mohanpuria P, Rana NK, Yadav SK. Biosynthesis of nanoparticles: technological concepts and future applications. J Nanopart Res 2008;10:507–17. [18] Song JY, Jang HK, Kim BS. Biological synthesis of gold nanoparticles using Magnolia kobus and Diopyros kaki leaf extracts. Process Biochem 2009;44:1133–8. [19] Saxena A, Tripathi RM, Zafar F, Singh P. Green synthesis of silver nanoparticles using aqueous solution of Ficus benghalensis leaf extract and characterization of their antibacterial activity. Mater Lett 2012;67:91–4. [20] Prathnaa TC, Chandrasekarana N, Raichurb AM, Mukherjee A. Biomimetic synthesis of silver nanoparticles by Citrus limon (lemon) aqueous extract and theoretical prediction of particle size. Colloids Surf B: Biointerfaces 2011;82:152–9. [21] Saleem A, Husheem M, Harkonen P, Pihlaj K. Inhibition of cancer cell growth by crude extract and the phenolics of Terminalia chebula retz fruit. J Ethnopharm 2002;81:327–36. [22] Kapure G, Rao SM. Application of Terminalia chebula for removal of hexavalent chromium in chromite concentrates. ISIJ Int 2008;48:868–74. [23] Pfundstein B, El Desouky SK, Hull WE, Haubner R, Erben G, Owen RW. Polyphenolic compounds in the fruits of Egyptian medicinal plants (Terminalia bellerica Terminalia chebula and Terminalia horrida): characterization, quantitation and determination of antioxidant capacities. Phytochemistry 2010;71:1132–48. [24] Small JM, Hintelmann H. Methylene blue derivatization then LC-MS analysis for measurement of trace levels of sulfide in aquatic samples. Anal Bioanal Chem 2007;387:2881–6. [25] Burhenne J, Riedl KD, Rengelshausen J, Meissner P, Muller O, Mikus G, et al. Quantification of cationic anti-malaria agent methylene blue in different human biological matrices using cation exchange chromatography coupled to tandem mass spectrometry. J Chromatogr B 2008;863:273–82. [26] Xu JZ, Dai L, Wu B, Ding T, Zhu JJ, Lin H, et al. Determination of methylene blue residues in aquatic products by liquid chromatography-tandem mass spectrometry. J Sep Sci 2009;32:4193–9. [27] Park J, Kim Y. Effect of shape of silver nanoplates on the enhancement of surface plasmon resonance (SPR) signals. J Nanosci Nanotech 2008;8:1–4. [28] Martinez-Castanon GA, Nino-Martinez N, Martinez-Gutierrez F, MartinezMendoza JR. Synthesis and antibacterial activity of silver nanoparticles with different sizes. J Nanopart Res 2008;10:1343–8. [29] Sun L, Wang L, Yonghai Song, Guo C, Sun Y, Peng C, et al. Aggregationbased growth of silver nanowires at room temperature. App Surf Sci 2008;254:2581–7. [30] Zhu Y, Wang X, Guo W, Wang J, Zhu CW, Wang X, et al. Sonochemical synthesis of silver nanorods by reduction of sliver nitrate in aqueous solution. Ultrason Sonochem 2010;17:675–9. [31] Sathishkumar M, Sneha K, Won SW, Cho C-W, Kim S, Yun Y-S. Cinnamon zeylanicum bark extract and powder mediated green synthesis of nano-crystalline silver particles and its bactericidal activity 2009;73:332–8. [32] Bulut E, Rapid Ozacar M. Facile synthesis of silver nanostructure using hydrolyzable tannin. Ind Eng Chem Res 2009;48:5686–90. [33] Kundu S, Ghosh SK, Mandal M, Pal T. Silver and gold nanocluster catalyzed reduction of methylene blue by arsine in micellar medium. Bull Mater Sci 2002;25:577–9. [34] Mallick K, Witcomb M, Scurrell M. Silver nanoparticle catalysed redox reaction: an electron relay effect. Mater Chem Phys 2006;97:283–7. [35] Gupta N, Singh HP, Sharma RK. Metal nanoparticles with high catalytic activity in degradation of methyl orange: an electron relay effect. J Mol Catal A: Chem 2011;335:248–52.
Contents lists available at SciVerse ScienceDirect
Process Biochemistry journal homepage: www.elsevier.com/locate/procbio
Instant green synthesis of silver nanoparticles using Terminalia chebula fruit extract and evaluation of their catalytic activity on reduction of methylene blue T. Jebakumar Immanuel Edison, M.G. Sethuraman ∗ Department of Chemistry, Gandhigram Rural Institute – Deemed University, Gandhigram – 624 302, Dindigul District, Tamil Nadu, India
a r t i c l e
i n f o
Article history: Received 19 December 2011 Received in revised form 26 March 2012 Accepted 28 April 2012 Available online 5 May 2012 Keywords: Instant green synthesis Colloidal silver nanoparticles HR-TEM Reduction of methylene blue Electron relay effect
a b s t r a c t A novel green approach for the synthesis and stabilization of silver nanoparticles (AgNPs) using water extract of Terminalia chebula (T. chebula) fruit under ambient conditions is reported in this article. The instant formation of AgNPs was analyzed by visual observation and UV–visible spectrophotometer. Further the effect of pH on the formation of AgNPs was also studied. The synthesized AgNPs were characterized by FT-IR, XRD, HR-TEM with EDS and DLS with zeta potential. Appearance of brownish yellow color confirmed the formation of AgNPs. In the neutral pH, the stability of AgNPs was found to be high. The stability of AgNPs is due to the high negative values of zeta potential and capping of phytoconstituents present in the T. chebula fruit extract which is evident from zeta potential and FT-IR studies. The XRD and EDS pattern of synthesized AgNPs showed their crystalline structure, with face centered cubic geometry oriented in (1 1 1) plane. HR-TEM and DLS studies revealed that the diameter of stable AgNPs was approximately 25 nm. Moreover the catalytic activity of synthesized AgNPs in the reduction of methylene blue was studied by UV–visible spectrophotometer. The synthesized AgNPs are observed to have a good catalytic activity on the reduction of methylene blue by T. chebula which is confirmed by the decrease in absorbance maximum values of methylene blue with respect to time using UV–visible spectrophotometer and is attributed to the electron relay effect. © 2012 Elsevier Ltd. All rights reserved.
1. Introduction In the recent past, there has been an increasing demand for nanoparticles due to their applications in various areas like medicine, catalysis, energy and materials [1–4]. The size, shape, and surface morphology of nanoparticles play a key role in controlling the physical, chemical, optical, and electronic properties of these nanomaterials. Metallic nanoparticles are synthesized by various methods such as, physical vapor deposition, chemical vapor deposition, sol–gel method, microwave-assisted synthesis, ultrasonication method, electrochemical synthesis and chemical reduction of metallic ions [5–11]. The chemicals used for these syntheses are often toxic, costly and non-ecofriendly. Nowadays bioreduction methods based on fungi, microorganisms, plant extracts are being attempted due to the ease of synthesis, environmentally benign nature and greater stability of nanoparticles [12–16]. AgNPs have received attention due to the surface plasmon resonance (strong absorption in the visible region), which can be easily monitored by UV–visible spectrophotometer. The applications of
∗ Corresponding author. Tel.: +91 0 451 2452371. E-mail address: [email protected] (M.G. Sethuraman). 1359-5113/$ – see front matter © 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.procbio.2012.04.025
AgNPs in the field of medicine, optoelectronics, optics, catalysis, sensors are well known [1–4]. Yadav and co-workers [17] had reviewed the synthesis of plant mediated silver and gold nanoparticles. Plant extracts, like Magnolia kobus, Diopyros kaki, Ficus benghalensis and Citrus limon extracts, have been shown to produce nanoparticles with good stability [18–20] due to the presence of reducing agents like alkaloids, polyphenols and flavonoids which are the major phytoconstituents. Terminalia chebula fruit (belonging to the family Combretaceae) is commonly known as myrobalan. It is mainly used in the Ayurvedic preparations as laxative, diuretic and cardiotonic [21]. Moreover, it is a good reducing agent for hazardous hexavalent chromium ions to trivalent chromium ions [22]. The major phytoconstituents present in the fruit are hydrolysable tannins, gallic acid, chebulic acid, chebulic ellagitannins and gallate esters [23]. In the present study, the instant synthesis of AgNPs using water extract of T. chebula fruit by the reduction of Ag+ ions is reported. The effect of pH on the formation of AgNPs was also studied using UV–visible spectrophotometer. AgNPs were further characterized by FT-IR, XRD, HR-TEM with EDS and DLS with zeta potential. Moreover, its catalytic activity on reduction of methylene blue (MB) in the presence of T. chebula fruit extract was also studied. MB is a thiazine dye, used in the analysis of trace levels of sulphide ions in aquatic samples. The cationic form of MB is used as
1352
T.J.I. Edison, M.G. Sethuraman / Process Biochemistry 47 (2012) 1351–1357
Fig. 1. Schematic representations of the reactions for evaluation of the effect of synthesized AgNPs on the reduction of methylene blue by T. chebula.
an anti-malarial agent and chemotherapeutic agent in the aqua culture industry. Moreover, it is used in microbiology, surgery and diagnostic field [24–26].
diffractometer, with the following working conditions: CuK␣ Ni-filtered radiation; 40 kV, 30 mA; divergence slit 0.47◦ . 2.6. HR-TEM with EDS analysis
2. Materials and methods 2.1. Preparation of aqueous fruit extract The fruits of T. chebula were cleaned, dried and powdered. The aqueous extract was prepared by the addition of 0.4 g of powdered fruit with 100 ml of distilled water at 50 ◦ C for 2 min. Further, the extract was filtered using Whatman 40 filter paper and the filtrate was preserved in a refrigerator (10 ◦ C).
The stable biogenic AgNPs were washed and diluted by distilled water to attain the absorbance range of 0.5. Further, one drop of diluted AgNPs sample was placed on Cu grid with Ultrathin Cu on holey carbon disc and was allowed to dry in vacuo. After drying, the nanoparticles were visualized using JEOL JEM 2100 High Resolution Transmission Electron Microscope operating in the range of 200 kV of acceleration. Simultaneously the energy dispersive spectrum (EDS) was also recorded.
2.2. Synthesis of AgNPs About 1 ml of the extract was added separately to 25 ml of 0.01 M AgNO3 (CDH Chemicals, Mumbai, India) solution at room temperature. 2.3. UV–visible spectroscopic characterization of AgNPs The synthesis of AgNPs and the effect of variation of pH from 4 to 9 on the formation of AgNPs were studied using PerkinElmer Lamda 35 UV–visible spectrophotometer. The pH was varied by the addition of 0.1 M sulfuric acid in the acidic region and 0.1 M sodium hydroxide solution in the basic region. For the analysis, 0.3 ml of AgNPs was taken in a cuvette and diluted by 2 ml of distilled water. 2.4. FT-IR spectroscopic studies The functional groups present in the phytoconstituents on the fruit extract of T. chebula and their involvement in the synthesis of AgNPs was determined by the FT-IR studies. The dried aqueous extract and synthesized AgNPs were mixed with KBr to make pellet and the FT-IR analysis was carried out by JASCO FT-IR 400. 2.5. XRD studies The phytoreduced silver colloidal solution was drop-coated onto a glass substrate and the XRD measurements were carried out using a Philips X’Pert Pro X-Ray
Fig. 2. Visual observation and UV–visible absorption spectra of instantly synthesized AgNPs.
T.J.I. Edison, M.G. Sethuraman / Process Biochemistry 47 (2012) 1351–1357
0.75
100
412 nm
T. chebula extract Absorbance
0.70 0.65 0.60 0.55 0.50
80
424 nm Wavelength (λ (nm))
0.45 426 nm
-- pH 8
60
A
-- pH 4
0.15 488 nm
40
300
400
500
600
700
1383
0.00 200
-NO 3
3380
0.10 0.05
1208
-- pH 5
1344
-- pH 6
454 nm
3377
0.25 0.20
B
1032
-- pH 7
0.30
%T
-- pH 9
1448
0.40 0.35
1615 1714
Absorbance
1353
800
Wavelength (λ (nm))
4000
3500
3000
2500
2000
1500
1000
500
Wavenumber (cm-1)
Fig. 3. UV–visible absorption spectra of AgNPs at various pH ranges.
Fig. 5. FT-IR spectra of aqueous fruit extract of T. chebula (A) and synthesized AgNPs with capping of phytoconstituents (B).
2.7. Dynamic light scattering (DLS) and zeta potential measurements In order to find out the stability and size distribution of AgNPs, the DLS and zeta potential measurements were carried out using Zetasizer Nano S90 (Malvern). 2.8. Evaluation of the effect of synthesized AgNPs on the reduction of methylene blue by T. chebula Methylene blue purchased from CDH chemicals, India was used for this study. In order to assess the catalytic activity of synthesized AgNPs, two reactions were carried out in a 3.5 ml capacity quartz cuvette and absorbance values were monitored using UV–visible spectrophotometer. In the first reaction, 1 ml of methylene blue (1 × 10−4 M) was mixed with 0.2 ml of aqueous fruit extract and 1.8 ml of water, this reaction was monitored after 30 min (I). In second reaction, 1 ml of methylene blue (1 × 10−4 M) was mixed with 0.2 ml extract and 2 ml of synthesized AgNPs and this reaction was monitored at three different time intervals viz., 30 min, 45 min and 60 min (II). In all the reactions total volume of the mixture was made up to 3 ml. The values of absorption maxima (max ) were compared, with that of methylene blue. The schematic representations of the two reactions are depicted in Fig. 1.
3. Results and discussion 3.1. UV–visible spectroscopy The formation of nanoparticles was easily detected and characterized by UV–visible spectroscopy owing to the surface plasmon resonance (SPR), i.e., the interaction of electromagnetic radiation
and the electrons in the conduction band around the nanoparticles [27]. AgNPs were observed strongly in the range of 400–450 nm in visible region. In the present work, the AgNPs are rapidly formed (pH 6.8) after the addition of T. chebula extract, evident from the appearance of brownish yellow color and the max appeared at 440 nm is depicted in Fig. 2. The effect of pH on the formation of AgNPs was evaluated by UV–visible spectroscopic studies and is given in Fig. 3. From the figure, it is evident that the formation of AgNPs mainly depends on the pH of the reaction medium. The absorbance value was increased gradually with increasing of pH range from 4 to 9, suggesting the rate of formation of AgNPs is high in basic pH than in acidic pH. The formation of AgNPs occurs rapidly, in neutral and basic pH which is evident from visual observation and may be due to the ionization of the phenolic group present in the extract [28]. The slow rate of formation and aggregation of AgNPs at acidic pH could be related to electrostatic repulsion of anions present in the solution [29]. At basic pH range there is a possibility of Ag+ precipitating as AgOH also. On the basis of the results, it could be concluded that the
120 38.175 (111)
434 nm
0.8
100
0.7
80
0.5 -- 10 days
0.4
-- 10 hr
Counts
Absorbance
0.6
44.175 (200) 63.525 (220)
60 78.325 (311)
-- 100 min
0.3 0.2
270 nm 420 nm
0.1
--
80 min
--
60 min
--
40 min
--
20 min
--
1 sec
0.0 200
40
20
0
300
400
500
600
700
800
Wavelength (λ (nm)) Fig. 4. UV–visible absorption spectra of time dependent formation of AgNPs (pH 7).
0
10
20
30
40
50
60
2θ° Fig. 6. XRD patterns of synthesized AgNPs.
70
80
90
1354
T.J.I. Edison, M.G. Sethuraman / Process Biochemistry 47 (2012) 1351–1357
Fig. 7. HR-TEM and SAED images of synthesized AgNPs (pH 7) under different magnifications.
optimum condition for the preparation of AgNPs using T. chebula can be taken as the neutral pH and hence the UV–visible spectroscopic studies were carried out at various time intervals at this pH. The effect of reaction time at pH 7 was shown in Fig. 4. From the figure, it can be observed that the absorbance of AgNPs increased with increase of reaction time, indicating more reduction of Ag+ with respect to time. The synthesized AgNPs are stable for 10 days at 5 ◦ C evident from, the max value.
3.2. FT-IR studies FT-IR spectroscopy measurements were carried out to identify the biomolecules that capped on silver nanoparticles. FT-IR spectrum of dried aqueous extract and synthesized AgNPs are shown in Fig. 5. The major phytoconstituents present in the myroblan fruit are hydrolysable tannins, gallic acid, chebulic acid, chebulic ellagitannins and gallate esters. The IR-spectrum of fruit extract showed an absorption band at 3380 cm−1 which is characteristic of the OH
Fig. 8. EDS pattern of synthesized AgNPs.
T.J.I. Edison, M.G. Sethuraman / Process Biochemistry 47 (2012) 1351–1357
1355
Fig. 9. DLS and zeta potential of AgNPs synthesized at pH 7.
stretching of phenolic group. The absorption bands at 1714 and 1615 cm−1 correspond to carbonyl group present in the extract. The sharp band at 1032 cm−1 indicated C O group of ester and the band at 1448 cm−1 is due to aromatic CH stretching vibrations. The absorption bands that appear in the IR spectrum of the aqueous extract could also be seen in the IR spectra of phytocapped AgNPs. This shows that the phytoconstituents (mostly tannins) protect the AgNPs from aggregation.
3.3. XRD studies The XRD patterns of synthesized AgNPs are shown in Fig. 6. From the figure it can be seen that four major peaks appeared with 2 values of 38.175◦ , 44.175◦ , 63.525◦ and 78.325◦ . These peaks correspond to the (1 1 1), (2 0 0), (2 2 0) and (3 1 1) planes of facecentered-cubic (fcc) geometry of AgNPs, which is in agreement with the JCPDS file No. 42-0783. The ratio between the intensities of (1 1 1) and (2 0 0) diffraction peaks is relatively higher than the usual values which indicate that the experimental system has AgNPs oriented in (1 1 1) plane [30]. XRD pattern thus reveals that
the AgNPs have fcc geometry with the nanoparticles oriented in (1 1 1) plane.
3.4. HR-TEM with EDS studies The application of TEM in nanosciences is significant to view the particles in nanoscale. The HR-TEM images of synthesized AgNPs (pH 7) and SAED pattern obtained from HR-TEM studies are depicted in Fig. 7, which give clear indications regarding size, shape and size distribution of nanoparticles. From the images, it can be seen that the AgNPs are capped with phytoconstituents of myrobalan. The SAED pattern of AgNPs reveals its crystalline nature (white dots in Fig. 11). The result of EDS gives a clear idea about the elements present in the nanoparticles. The EDS profile of phytocapped AgNPs is presented in Fig. 8. The strong signal of the Ag atoms indicates the crystalline property. The presence O peaks along with the Ag signals, suggest that the AgNPs are capped by phytoconstituents through oxygen atom. The Cu peak comes from the TEM grid. The size of the synthesized AgNPs are approximately 25 nm.
Fig. 10. Mechanism involved in the formation of AgNPs.
1356
T.J.I. Edison, M.G. Sethuraman / Process Biochemistry 47 (2012) 1351–1357
3.5. DLS with zeta potential Methylene blue (MB)
0.4
MB+Extract (After 30 mins)
The DLS size distribution image of AgNPs (pH 7) is shown in Fig. 9. From the results, the calculated average particle size distribution of AgNPs is 25 nm and the corresponding average zeta potential value is −35.6 mV (Fig. 9), suggesting higher stability of AgNPs. The large negative potential value could be due to the capping of polyphenolic constituents present in the extract [31].
MB+Extract+Ag nps (After 30 mins) MB+Extract+Ag nps (After 45 mins) MB+Extract+Ag nps (After 60 mins)
Absorbance
0.3
0.2 3.6. Mechanism of reduction of AgNO3 to AgNPs by the phytoconstituents of T. chebulla
0.1
0.0 400
500
600
700
Wavelength ( λ (nm)) Fig. 11. UV–visible spectra of methylene blue reduction by T. chebula in the presence of AgNPs.
The major phytoconstituents present in the myroblan fruit are hydrolysable tannins, polyphenols, gallic acid, chebulagic acid and chebulinic acid. The possible mechanism for the reduction of Ag+ is proposed and presented in Fig. 10. In this scheme, Ag+ ions can form intermediate complexes with phenolic OH groups present in hydrolysable tannins which subsequently undergo oxidation to quinone forms with consequent reduction of Ag+ to AgNPs [32].
Fig. 12. Catalytic action of AgNPs between T. chebula extract and methylene blue (electron relay effect).
T.J.I. Edison, M.G. Sethuraman / Process Biochemistry 47 (2012) 1351–1357
3.7. Catalytic activity of AgNPs on reduction of methylene blue by T. chebula extract It is a well known fact that AgNPs and their composites show greater catalytic activity in the area of dye reduction and removal. Pal et al. studied the reduction of methylene blue by arsine in the presence of silver nano [33], while Witcomb et al. studied the catalytic activity of AgNPs on the reduction of phenosaffarin dye [34]. The present study aims at the reduction of methylene blue by the natural green aqueous extract of myrobalan containing AgNPs. Pure methylene blue has a max value of 664 nm. Thirty minutes after the addition of the extract to the dye, the absorbance is gradually decreased and is shifted to higher wavelength. The decrease of absorbance is indicative of the ability of phytoextract to degrade methylene blue. System containing dye, AgNPs and the extract at the end of 30 min time interval showed a marked decrease in the absorbance of methylene blue and increase of SPR peak of AgNPs (Fig. 11). This reveals that AgNPs act as an electron transfer mediator between the extract and methylene blue by acting as a redox catalyst, which is often termed as electron relay effect [35] (Fig. 12). 4. Conclusions The study has demonstrated that AgNPs could be prepared instantly by making use of aqueous extract of myrobalan. The phytoconstituents such as hydrolysable tannins, gallic acid, chebulic acid, chebulic ellagitannins and gallate esters act as reducing agents for the preparation of AgNPs and the capping of AgNPs by the phytoconstituents provide stability to AgNPs as evident from FT-IR and EDS studies. The synthesized AgNPs were found to have a crystalline structure with face centered cubic geometry as studied by XRD method. The HR-TEM images and DLS studies had shown that the synthesized AgNPs are having the size around 25 nm. The synthesized AgNPs act through the electron relay effect and influence the degradation of methylene blue by myrobalan extract. References [1] Nam J, Won N, Jin H, Chung H, Kim S. pH-induced aggregation of gold nanoparticles for photothermal cancer therapy. J Am Chem Soc 2009;131: 13639–45. [2] Narayanan KB, Sakthivel N. Synthesis and characterization of nano-gold composite using Cylindrocladium floridanum and its heterogeneous catalysis in the degradation of 4-nitrophenol. J Hazard Mater 2011;189:519–25. [3] Li J, Chen X, Ai N, Hao J, Chen Q, Strauf S, et al. Silver nanoparticle doped TiO2 nanofiber dye sensitized solar cells. Chem Phys Lett 2011;514:141–5. [4] Fayaza AM, Girilal M, Mahdy SA, Somsundar SS, Venkatesan R, Kalaichelvan PT. Vancomycin bound biogenic gold nanoparticles: a different perspective for development of anti VRSA agents. Process Biochem 2011;46:636–41. [5] Horwat D, Zakharov DI, Endrino JL, Soldera F, Anders A, Migot S, et al. Chemistry, phase formation, and catalytic activity of thin palladium-containing oxide films synthesized by plasma-assisted physical vapor deposition. Surf Coat Technol 2011;205:S171–7. [6] Dillon AC, Mahan AH, Deshpande R, Alleman JL, Blackburn JL, Parillia PA, et al. Hot-wire chemical vapor synthesis for a variety of nano-materials with novel applications. Thin Solid Films 2006;501:216–20. [7] Sobhani M, Rezaie HR, Naghizadeh R. Sol–gel synthesis of aluminum titanate (Al2 TiO5 ) nano-particles. J Mater Process Technol 2008;206:282–5. [8] Nadagouda MN, Speth TF, Varma RS. Microwave-assisted green synthesis of silver nanostructures. Acc Chem Res 2011;44:469–78. [9] Wani IA, Ganguly A, Ahmed J, Ahmad T. Silver nanoparticles: ultrasonic wave assisted synthesis, optical characterization and surface area studies. Mater Lett 2011;65:520–2.
1357
[10] Starowicz M, Stypula B, Banas J. Electrochemical synthesis of silver nanoparticles. Electrochem Commun 2006;8:227–30. [11] Kima KD, Hanb DN, Kim HT. Optimization of experimental conditions based on the Taguchi robust design for the formation of nano-sized silver particles by chemical reduction method. Chem Eng J 2004;104:55–61. [12] Balaji DS, Basavaraja S, Deshpandeb R, Mahesh DB, Prabhakara BK, Venkataraman A. Extracellular biosynthesis of functionalized silver nanoparticles by strains of Cladosporium cladosporioides fungus. Colloids Surf B: Biointerfaces 2009;68:88–92. [13] Shahverdi AR, Minaeian S, Shahverdi HR, Jamalifar H, Nohi AA. Rapid synthesis of silver nanoparticles using culture supernatants of Enterobacteria: a novel biological approach. Process Biochem 2007;42:919–23. [14] Kumar KP, Paul W, Sharma CP. Green synthesis of gold nanoparticles with Zingiber officinale extract: characterization and blood compatibility. Process Biochem 2011;46:2007–13. [15] Dubey SP, Lahtinen M, Sillanpaa M. Tansy fruit mediated greener synthesis of silver and gold nanoparticles. Process Biochem 2010;45:1065–71. [16] Sukirtha R, Priyanka KM, Antony JJ, Kamalakkannan S, Thangam R, Gunasekaran P, et al. Cytotoxic effect of Green synthesized silver nanoparticles using Melia azedarach against in vitro HeLa cell lines and lymphoma mice model. Process Biochem 2012;47:273–9. [17] Mohanpuria P, Rana NK, Yadav SK. Biosynthesis of nanoparticles: technological concepts and future applications. J Nanopart Res 2008;10:507–17. [18] Song JY, Jang HK, Kim BS. Biological synthesis of gold nanoparticles using Magnolia kobus and Diopyros kaki leaf extracts. Process Biochem 2009;44:1133–8. [19] Saxena A, Tripathi RM, Zafar F, Singh P. Green synthesis of silver nanoparticles using aqueous solution of Ficus benghalensis leaf extract and characterization of their antibacterial activity. Mater Lett 2012;67:91–4. [20] Prathnaa TC, Chandrasekarana N, Raichurb AM, Mukherjee A. Biomimetic synthesis of silver nanoparticles by Citrus limon (lemon) aqueous extract and theoretical prediction of particle size. Colloids Surf B: Biointerfaces 2011;82:152–9. [21] Saleem A, Husheem M, Harkonen P, Pihlaj K. Inhibition of cancer cell growth by crude extract and the phenolics of Terminalia chebula retz fruit. J Ethnopharm 2002;81:327–36. [22] Kapure G, Rao SM. Application of Terminalia chebula for removal of hexavalent chromium in chromite concentrates. ISIJ Int 2008;48:868–74. [23] Pfundstein B, El Desouky SK, Hull WE, Haubner R, Erben G, Owen RW. Polyphenolic compounds in the fruits of Egyptian medicinal plants (Terminalia bellerica Terminalia chebula and Terminalia horrida): characterization, quantitation and determination of antioxidant capacities. Phytochemistry 2010;71:1132–48. [24] Small JM, Hintelmann H. Methylene blue derivatization then LC-MS analysis for measurement of trace levels of sulfide in aquatic samples. Anal Bioanal Chem 2007;387:2881–6. [25] Burhenne J, Riedl KD, Rengelshausen J, Meissner P, Muller O, Mikus G, et al. Quantification of cationic anti-malaria agent methylene blue in different human biological matrices using cation exchange chromatography coupled to tandem mass spectrometry. J Chromatogr B 2008;863:273–82. [26] Xu JZ, Dai L, Wu B, Ding T, Zhu JJ, Lin H, et al. Determination of methylene blue residues in aquatic products by liquid chromatography-tandem mass spectrometry. J Sep Sci 2009;32:4193–9. [27] Park J, Kim Y. Effect of shape of silver nanoplates on the enhancement of surface plasmon resonance (SPR) signals. J Nanosci Nanotech 2008;8:1–4. [28] Martinez-Castanon GA, Nino-Martinez N, Martinez-Gutierrez F, MartinezMendoza JR. Synthesis and antibacterial activity of silver nanoparticles with different sizes. J Nanopart Res 2008;10:1343–8. [29] Sun L, Wang L, Yonghai Song, Guo C, Sun Y, Peng C, et al. Aggregationbased growth of silver nanowires at room temperature. App Surf Sci 2008;254:2581–7. [30] Zhu Y, Wang X, Guo W, Wang J, Zhu CW, Wang X, et al. Sonochemical synthesis of silver nanorods by reduction of sliver nitrate in aqueous solution. Ultrason Sonochem 2010;17:675–9. [31] Sathishkumar M, Sneha K, Won SW, Cho C-W, Kim S, Yun Y-S. Cinnamon zeylanicum bark extract and powder mediated green synthesis of nano-crystalline silver particles and its bactericidal activity 2009;73:332–8. [32] Bulut E, Rapid Ozacar M. Facile synthesis of silver nanostructure using hydrolyzable tannin. Ind Eng Chem Res 2009;48:5686–90. [33] Kundu S, Ghosh SK, Mandal M, Pal T. Silver and gold nanocluster catalyzed reduction of methylene blue by arsine in micellar medium. Bull Mater Sci 2002;25:577–9. [34] Mallick K, Witcomb M, Scurrell M. Silver nanoparticle catalysed redox reaction: an electron relay effect. Mater Chem Phys 2006;97:283–7. [35] Gupta N, Singh HP, Sharma RK. Metal nanoparticles with high catalytic activity in degradation of methyl orange: an electron relay effect. J Mol Catal A: Chem 2011;335:248–52.