- Email: [email protected]
Phytosynthesis of Au, Ag and Au–Ag bimetallic nanoparticles using aqueous extract and dried leaf of Anacardium occidentale
Spectrochimica Acta Part A 79 (2011) 254–262
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
Phytosynthesis of Au, Ag and Au–Ag bimetallic nanoparticles using aqueous extract and dried leaf of Anacardium occidentale D.S. Sheny a , Joseph Mathew a , Daizy Philip b,∗ a b
Department of Chemistry, Mar Ivanios College, Thiruvananthapuram 695 015, Kerala, India Department of Physics, Mar Ivanios College, Nalanchira, Thiruvananthapuram 695 015, Kerala, India
a r t i c l e
i n f o
Article history: Received 18 January 2011 Received in revised form 20 February 2011 Accepted 25 February 2011 Keywords: Anacardium occidentale leaf Biosynthesis Gold nanoparticles Silver nanoparticles Au–Ag bimetallic nanoparticles Core–shell nanoparticles
a b s t r a c t Present study reports a green chemistry approach for the biosynthesis of Au, Ag, Au–Ag alloy and Au core–Ag shell nanoparticles using the aqueous extract and dried powder of Anacardium occidentale leaf. The effects of quantity of extract/powder, temperature and pH on the formation of nanoparticles are studied. The nanoparticles are characterized using UV–vis and FTIR spectroscopies, XRD, HRTEM and SAED analyses. XRD studies show that the particles are crystalline in the cubic phase. The formation of Au core–Ag shell nanoparticles is evidenced by the dark core and light shell images in TEM and is supported by the appearance of two SPR bands in the UV–vis spectrum. FTIR spectra of the leaf powder before and after the bioreduction of nanoparticles are used to identify possible functional groups responsible for the reduction and capping of nanoparticles. Water soluble biomolecules like polyols and proteins are expected to bring about the bio-reduction. © 2011 Elsevier B.V. All rights reserved.
1. Introduction A naturally motivated investigational practice for the biosynthesis of metal nanoparticles is now established as an emerging area of nanoscience research and development. As nature make optimum use of materials and space, many inorganic materials are produced in biological systems [1]. Similar to such natural processes, plants [2–5], fungi [6], and bacteria [7] are found to be of great success for the synthesis of metal nanoparticles [8]. The advances in the field of biotechnology and nanotechnology owes to the tremendous improvement in human life. In recent years, an increasing percentage of nanomaterials are emerging and making advancement in different fields. Unlike the bulk counterparts, nanoparticulate materials exhibit very interesting electrical, optical, magnetic and chemical properties [9]. Nanoparticles of noble metals are widely applied in common products like soaps, cosmetics, toothpaste, shampoos and medicines which make their synthesis vital [10]. Nanoparticle synthesis is usually carried out by various physical and chemical methods like laser ablation, pyrolysis, lithography, chemical vapour deposition, sol–gel technique and electro-deposition which are very expensive and hazardous. Therefore scientists are looking forward for greener methods [11,12]. In the present study, we report the green synthesis of gold and silver nanoparticles using both leaf extract
∗ Corresponding author. Tel.: +91 471 2530887; fax: +91 471 2530023. E-mail addresses: [email protected], [email protected] (D. Philip). 1386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2011.02.051
and powder of Anacardium occidentale. These metal nanoparticles have received attention due to their unique and tunable SPR and shape and size-dependent properties [13]. They find applications in scientific and technological fields like drug delivery [14], tissue/tumor imaging [15], photothermal therapy [15], catalysis [16,17], optoelectronics [18], water purification [19], SERS detection [20,21], and biosensing [22,23]. Silver nanoparticles have found to posses anti-fungal, anti-bacterial, anti-inflammatory, antiviral, anti-angiogenesis, and anti-platelet activity and cytotoxicity against cancer cells which makes them vital [24–27]. In recent years, synthesis of both Au and Ag NPs has been reported using the extracts of Chenopodium album [1], Coleus amboinicus Lour [13], Cinnamomum camphora [28], Sorbus aucuparia [29], Hibiscus rosa sinensis [30], Ocimum sanctum [31], Azadirachta indica [32] and Camellia sinensis [33]. There are also reports of using extracts of fruits like papaya [34], tansy [35], peer [36], lemon [37] and gooseberry [38] in the green synthesis of these nanoparticles. Shankar et al. [32] have shown that Au core–Ag shell NPs in solution can be synthesized using Neem leaf extracts. The Ag NPs prepared using Pelargonium graveolens leaves were found to be stabilized by an enzymatic process [39]. Importantly Huang et al. [28] have reported the synthesis of Au and Ag NPs by novel sundried biomass of Camphora leaf. Recently Ankamwar [40] has demonstrated the synthesis of stable Au NPs of size range 10–35 nm using Terminalia catappa leaf extract. Their group have also reported the synthesis of Au NPs using Indian goose berry fruit extract [38] and their phase transfer in to organic solution using a cationic surfactant. The transmetallation reaction between hydrophobised Ag
D.S. Sheny et al. / Spectrochimica Acta Part A 79 (2011) 254–262
255
were procured from Sigma–Aldrich chemicals. All glasswares were cleaned with aqua regia and rinsed several times with de-ionized water. 2.1. Synthesis of gold nanoparticles The leaf extract (1.25, 2.5, 5 and 10 ml) was added to 30 ml aqueous solution (2.5 × 10−4 M) of HAuCl4 ·3H2 O and stirred for 1 min to get colloids a1 , a2 , a3 and a4 . For a1 and a2 fast reduction occurred as indicated by a red solution and was complete within 10 min. They are stable for seven months. Seasonal changes may affect the composition of leaf constituents which can be avoided by using dried leaf power. 12 mg of the leaf powder was added to 30 ml of aqueous HAuCl4 ·3H2 O solution (2.5 × 10−4 M) and stirred for 1 min and filtered to obtain colloid b1 . The amount of leaf powder was varied as 9, 7, 5 and 3 mg to get to colloids b2 , b3 , b4 and b5 . The reduction was very slow in the case of b5 which has a light blue color developed after 1 h. 2.2. Synthesis of silver nanoparticles Fig. 1. Photograph of Anacadium occidentale.
NPs and hydrophobised chloroaurate ions in chloroform resulted in the formation of hollow-Au shells. A rapid synthesis of gold NPs having a mixture of plate and spherical structures using Magnolia kobus and Diopyros kaki leaf extracts were investigated by Song et al. [10]. Torresdey et al. [41] have reported the synthesis of Au and Ag NP within live Alfalfa plants. Wang et al. [42] used Skullcup herb for the extracellular synthesis of gold NPs. Chandran et al. had observed the formation of crystalline gold nano triangles using Aloe vera extract [43]. Ghodake et al. [36] have successfully biosynthesized triangular and hexagonal nanoplates, elegantly assembled with gold NPs using Peer fruit extract. Earlier reports from our lab include the green synthesis of Ag and Au NPs using Honey [44], H. rosa sinensis [30], O. sanctum [31], Mangifera indica [45,46] and Murraya Koenigii [47]. Au–Ag alloy nanoparticles were also synthesized using edible Mushroom extract [48]. In biosynthesis, plants are preferred to micro-organisms, as it does not involve any tedious process of maintaining cell cultures [15]. Beyond that, the seasonal effects of plants and variation boiling time can be eliminated by using dried biomass of plant material which can be used at any time anywhere. A. occidentale (Fig. 1) belonging to Anacardiaceae family, has great economic and medicinal value [49,50]. It is commonly called Cashew and is a multipurpose tree whose leaves, stem and bark extracts are used extensively for the treatment of diarrhea, hypertension, dysentery, toothache, sore gums, colonic pain etc. It has also been reported to possess anti-diabetic, anti-bacterial, antiinflammatory and anti-ulcerogenic properties [51–53]. India is the second largest producer of cashew nuts and it is widely cultivated in India. But the other parts of the plant have not been exploited. In this paper, rapid biosynthesis of Au, Ag and Au–Ag bimetallic NPs using cashew leaf extract and powder has been investigated which is an easiest, cost efficient, non-toxic, eco-friendly and efficient method for exploiting cashew leaves. 2. Materials and methods Fresh A. occidentale leaves were collected from rural areas of Thiruvananthapuram, India. Fresh leaves were washed thoroughly with de-ionized water. 10 g of the homogenized leaves were stirred with 100 ml de-ionized H2 O for 5 min and filtered to get the extract. For the preparation of leaf powder, the leaves were dried for two weeks, grounded and sieved to get fine powder. AgNO3 and HAuCl4
The leaf extract (2, 3, 4, 5 and 10 ml) was added to a vigorously stirred 30 ml solution of 5.9 × 10−4 M AgNO3 and stirring continued for 1 min to get the colloids c1 to c6 . Reduction was fast for c5 and c6 which is indicated by a reddish brown color. For the preparation of Ag NPs also seasonal effects of leaf extract can be avoided by using dried leaf powder. 30 ml of 5.9 × 10−4 M AgNO3 solution were added with 5 mg leaf powder, stirred for 5 min and filtered to get colloid d1 . The colloids d2 , d3 , d4 and d5 were obtained by increasing the amount of powder as 10, 15, 20 and 25 mg. The reduction occurred slowly and was complete within 2 h. 2.3. Synthesis of Au–Ag bimetallic nanoparticles The Au–Ag colloids were prepared in the gold to silver ratio, 1:2, 1:1, 2:1, 3:1, 4:1 and 9:1. The 1:2 bimetallic colloid (Y1 ) is obtained as follows: To a 30 ml of HAuCl4 ·3H2 O solution (2.5 × 10−4 M), 2.5 ml of extract were added and stirred for 2 min. To this solution, 60 ml of AgNO3 solution (5.9 × 10−4 M) was added and stirred vigorously followed by 8 ml extract. The stirring was continued for two more minutes and the formation of bimetallic nanoparticles was completed within 30 min. Similarly the 1:1, 2:1, 3:1, 4:1 and 9:1 colloids henceforth called Y2 , Y3 , Y4 , Y5 and Y6 , respectively were prepared in their corresponding ratios. These mixed colloids are very stable and their color changed from yellowish to red as the quantity of gold is increased. 3. Characterization The optical absorption spectra of the synthesized nanoparticles were observed by UV-2450 Shimadzu UV spectrometer. HRTEM images and electron diffraction patterns were obtained with a JEOL 3010 and Philips CM 200 transmission electron microscope. FTIR spectra of dried gold and silver nanoparticles, native and treated leaf power were recorded with an IR Pestige-21 Shimadzu spectrometer. X-ray diffraction pattern of dried nanoparticle powder were obtained using XPERT-PRO diffractometer using Cu K␣ radiation ( = 0.1542 nm). 4. Results and discussion 4.1. UV–vis spectral studies The optical absorption spectrum of metal nanoparticles is sensitive to several factors like particle size, shape, particle–particle
256
D.S. Sheny et al. / Spectrochimica Acta Part A 79 (2011) 254–262
Fig. 2. (a) UV–vis spectra of Au nanoparticles prepared using leaf extract: (a1 ) 1.25 ml, (a2 ) 2.5 ml, (a3 ) 5 ml and (a4 ) 10 ml. The inset shows the variation of SPR band wavelength with quantity of extract. (b) UV–vis spectra of Au nanoparticles prepared using leaf powder: (b1 ) 5 mg, (b2 ) 7 mg, (b3 ) 9 mg and (b4 ) 12 mg. The inset shows the variation of SPR band wavelength with mass of powder. (c) UV–vis spectra of Au nanoparticles at 300 K and 373 K. (d) UV–vis spectra of Au nanoparticles prepared at 373 K: (e1 ) 0.1 ml, (e2 ) 0.2 ml, (e3 ) 0.4 ml and (e4 ) 0.6 ml. The inset shows the variation of SPR band wavelength with quantity of extract. (e) Effect of pH on SPR of Au nanoparticles: (g1 ) pH-4, (g2 ) pH-5, (g3 ) pH-6, (g4 ) pH-7, and (g5 ) pH-8. The inset shows the variation of SPR band wavelength with pH.
interaction with the medium and local refractive index [54]. Fig. 2a and b show the UV–vis spectra of Au NPs prepared using leaf extract and dried leaf powder with SPR band around 529 nm and 526 nm respectively. The appearance of red color was due to the
excitation of surface Plasmon vibrations which is absent in bulk material [55,56]. From Fig. 2a, it is seen that as the quantity of the extract was increased, the SPR bands become broader and shift to higher wavelengths signifying an increase in particle size [57–59].
Table 1 Variation of FWHM with quantity of extract. Quantity of extract (ml)
FWHM (SPR of Au nanoparticles) (nm)
Quantity of extract (ml)
FWHM (SPR of nanoparticles Ag (ml)
1.25 2.5 5 10
136 163 204 216
2 3 4 5
236 268 304 312
D.S. Sheny et al. / Spectrochimica Acta Part A 79 (2011) 254–262
257
Fig. 3. (a) UV–vis spectra of Ag nanoparticles prepared using leaf extract: (c1 ) 2 ml, (c2 ) 3 ml, (c3 ) 4 ml, (c4 ) 5 ml and (c5 ) 10 ml. The inset shows the variation of SPR band wavelength with quantity of extract. (b) UV–vis spectra of Ag nanoparticles prepared using leaf powder: (d1 ) 2 mg, (d2 ) 3 mg, (d3 ) 4 mg, (d4 ) 5 mg and (d5 ) 10 mg. The inset shows the variation of SPR band wavelength with mass of powder. (c) UV–vis spectra of Ag nanoparticles at 300 K and 373 K. (d) UV–vis spectra of Ag nanoparticles prepared at 373 K: (f1 ) 0.2 ml, (f2 ) 0.4 ml, (f3 ) 0.6 ml, (f4 ) 0.8 ml and (f5 ) 1 ml. The inset shows the variation of the wavelength of SPR band with quantity of extract. (e) Effect of pH on SPR of Ag nanoparticles: (h1 ) pH-6, (h2 ) pH-7, (h3 ) pH-8, (h4 ) pH-9 and (h5 ) pH-10. The inset shows the variation of the wavelength of SPR band with pH.
With leaf powder, narrow and symmetric SPR band is obtained at larger amounts of powder. A similar result has been reported in the synthesis of Au and Ag NPs using the extracts of Mushroom [48], Coriander leaf [60] and H. rosa leaf [30]. With an increase in the quantity of extract, the full width at half maximum (FWHM) decreases supporting the reduction in particle size (Table 1). For silver nanoparticles prepared using extract and powder, the SPR band appears at 420 nm and 422 nm respectively (Fig. 3a and b). The SPR band became narrower at higher concentration of the extract. The broad SPR at lower concentrations of the extract is due to the formation of large anisotropic particles [28,32,48,61,62]. It is found that SPR wavelength has a small shift to shorter wavelength and consequently FWHM decreases showing decrease in particle size. Below 2 ml of the extract, no SPR band is observed due to insufficient quantity of reducing agent. More symmetrical SPR band is
observed with higher amounts of leaf powder. These results show that the quantity of plant material is a key factor determining the formation and size distribution of nanoparticles. The digital photograph and UV–vis spectra of Au–Ag colloids are shown in Fig. 4a and b, respectively. For 2:1 and 1:1 ratios, individual bands are observed for gold and silver at around 502 nm and 413 nm respectively. The core–shell NPs or a dispersion of separate Au and Ag NPs can give rise to two absorption bands and their intensities depends on their initial composition. Earlier reports reveal that phase separation at atomic scale leads to the formation of core–shell particles [63]. An ideal alloy system must have a single absorption which is in agreement with the colloids with ratio 1:2 onwards. A plot of absorption maximum of Au NPs against its percentage is shown in Fig. 4c. It shows a linear variation of max from 66% of gold. Therefore below that percentage of gold, Au core–Ag
258
D.S. Sheny et al. / Spectrochimica Acta Part A 79 (2011) 254–262
Fig. 4. (a) Photograph of colloids Y1 , Y2 , Y3 , Y4 , Y5 and Y6 . (b) UV–vis spectra of Au–Ag bimetallic nanoparticles. (c) Plot of max against percentage of Au present.
shell were present which is confirmed by HRTEM analysis (Section 4.2). The max of both Au and Ag NPs showed a red shift with increase in the percentage of Au and Ag, respectively indicating that a molar ratio of 1:2 with 66% of gold is required for the formation of Au–Ag alloy. 4.1.1. Effect of leaf quantity For gold NPs, with an increase in the extract quantity an increase in the peak absorbance was found in UV–vis spectrum (Fig. 2a). The solution showed a color change from wine red to violet indicating increase in particle size. For the generation of small NPs, lowest amount of leaf extract is preferred which is found to be lesser among previously reported ones [1,64,65]. Using dried leaf powder, 12 mg is found to be more suitable for the preparation of small and stable Au NPs. Below 12 mg, the color of the colloid changes from red to purple to violet with a decrease in UV–vis absorbance (Fig. 2b). The UV–vis spectra of Ag NPs (Fig. 3a) shows a linear relationship between absorbance and quantity of extract. A lower quantity of 5 mg of leaf powder gave high absorption in visible region which will be more suitable than their higher quantities (Fig. 3b).
(Fig. 2d). For silver nanoparticles 1 ml and 0.2 ml of extract were required for the reduction at 300 K and 373 K with SPR band at 429 nm and 418 nm, respectively (Fig. 3c). A blue shift occurred on increasing the concentration of extract at 373 K indicating reduction in the particle size. Ag NPs synthesized at 373 K were found to possess higher stability. The variations in the amount of extract at both temperatures have similar effects (Fig. 3a and d). 4.1.3. Effect of pH The UV–vis spectrum of Au NPs at different pH range from 4 to 8 is given in Fig. 2e. A sharp and symmetric peak is obtained at pH 6. It is stable for seven months. At pH 4, a broad peak indicates large sized particles. With the increase in pH, the SPR band shows a steep increase initially then becomes constant and finally decreases. In a range of pH from 5 to 6, SPR band reaches a maximum. For Ag NPs even though the position of SPR band does not show much variation, their absorbance increases with pH (Fig. 3e). At lower pH, broad peak is attributed to the large particle size. At higher pH 10, SPR band position has some deviation optimizing pH 8 or 9 for the above synthesis. 4.2. TEM studies
4.1.2. Effect of temperature Reductions occurred at 300 K and 373 K was compared for both Au and Ag nanoparticles. At 373 K even 0.1 ml of extract was sufficient to bring about the reduction of Au3+ . At 300 K a red colored stable colloid was obtained with 2.5 ml of extract whose SPR band appears at 529 nm while 0.6 ml was enough at 373 K with SPR band at 536 nm (Fig. 2c). Thus, reduction occurs at higher temperatures leading to large-sized and more stable nanoparticles. On increasing the concentration of extract, a blue shift is observed at 373 K
Transmission electron microscope images of Au NPs obtained at 300 K and 373 K are shown in Fig. 5a1 and a2 , respectively. Their particle size histograms (Fig. 5b) give an average size of 6.5 nm and 17 nm, respectively. The morphology of Au NPs was almost spherical. The images clearly show that higher temperatures during synthesis leads to an increase in particle size. The Au NPs are highly crystalline as shown by clear lattice fringe spacing of 0.21 nm and SAED pattern. The SAED pattern reveals diffraction rings from inner
D.S. Sheny et al. / Spectrochimica Acta Part A 79 (2011) 254–262
259
Fig. 5. (a1 ) TEM images and SAED pattern of Au NPs prepared using leaf extract at 300 K, (a)–(d) at different magnifications, (e) at high resolution and (f) SAED pattern. (a2 ) TEM images and SAED patterns of Au NPs prepared using leaf extract at 373 K, (a)–(d) at different magnifications, (e) at high resolution and (f) SAED pattern. (b) Histograms showing the particle sizes of NPs corresponding to the TEM images (a and b) a1 , a2 (c and d) c1 , c2 and (e and f) d1 and d2 . (c1 ) TEM images of Ag NPs prepared using leaf extract: (a), (b), (c) and (d) SAED pattern. (c2 ) TEM images of Ag NPs prepared using leaf powder: (a), (b), (c) under different magnification and (d) SAED pattern. (d1 ) TEM images of Au core–Ag shell NPs: (a)–(c) under different magnifications and (d) SAED pattern. (d2 ) TEM images of Au–Ag alloy NPs: (a)–(c) under different magnifications and (d) SAED pattern.
260
D.S. Sheny et al. / Spectrochimica Acta Part A 79 (2011) 254–262
Fig. 5. (Continued ).
to outer, which can be indexed as (1 1 1), (2 0 0), (2 2 0) and (3 1 1) reflections respectively confirming fcc structure. Fig. 5c1 and c2 shows TEM images of Ag NPs prepared using leaf extract and powder. In Fig. 5c2 well dispersed spherical nanoparticles of an average size 15.5 nm are seen. The fringe spacing is measured to be 0.21 nm, which corresponds to the spacing between the (1 1 1) plane of fcc gold. The SAED pattern revealed a highly crystalline lattice space. The histograms describing the dispersity in size distribution of the particles in both cases are shown in Fig. 5b. With leaf extract, smaller particles of an average size 5 nm were obtained. They have a SPR absorption 412 nm indicating smaller particle size. The TEM images and SAED pattern of Au–Ag bimetallic nanoparticles are shown in Fig. 5d1 and d2 corresponding to the Au to Ag ratio 1:2 and 9:1 respectively. At 1:2 ratios, TEM images show electron density banding with a dark gold core and a light silver shell indicating Au core–Ag shell NPs [66] which is clearly shown by the encircled portion in Fig. 5d1. This observation is in agreement with the UV–vis spectrum showing two Plasmon bands. Their particle size distribution histogram gives an average size 6.5 nm. Fig. 5d2 shows that the particles are almost uniform and homogeneous within the volume of the particle, suggesting the presence of Au–Ag alloy NPs supporting the observation of a single SPR band. Their particle size
histogram revealed an average size of 8 nm. In both case, SAED pattern clearly shows highly crystalline structure. These results show that it is possible to prepare stable Au–Ag core–shell NPs and alloy NPs of size below 10 nm by varying the ratio of HAuCl4 , AgNO3 and leaf extract solutions. 4.3. XRD studies The XRD patterns of Au and Ag NPs (Fig. 6a and b) show five intense peaks of (1 1 1), (2 0 0), (2 2 0), (3 1 1) and (2 2 2) facets of face centered cubic crystal structure with lattice parameter, a = 4.04 A˚ and 4.06 A˚ respectively. The broadening of Bragg’s peaks indicates the formation of nanoparticles. For both Au and Ag NPs the peak corresponding to the (1 1 1) plane was more intense than the other planes suggesting (1 1 1) is the predominant orientation [11,67,68]. The mean size of NPs were calculated using Scherrer formula, D=
K ˇs cos
where D is the size of the particles, K is the shape dependent Scherrer’s constant, is the wavelength of radiation and ˇs is the full peak width and is the diffraction angle [35,69]. Using the FWHM
D.S. Sheny et al. / Spectrochimica Acta Part A 79 (2011) 254–262
261
Fig. 7. FTIR spectra of dried (a) Au NPs and (b) Ag NPs.
Fig. 6. (a) XRD pattern of dried Au NPs. (b) XRD pattern of dried Ag NPs.
of (1 1 1) peak, the size of Au NP is found to be 8.5 nm and that of Ag NP is 19 nm which are in good agreement with the particle size obtained from TEM analysis. 4.4. FTIR studies In order to identify the possible molecules present in cashew leaf which are responsible for the reduction of Au3+ and Ag+ and their stabilization, FTIR measurement were carried out. A variety of secondary metabolites such as tannins, terpenoids, alkaloids, flavanols, phenols, glycosides are present in cashew leaf [65]. It has been also reported that Cashew contains gallic acid, anacardic acid, anacardol, hydroxyl benzoic acid, capryllic acid, gadoleic acid, lauric acid, leucine, leucocyanides, ocimene, limonene, caryophyllene and alpha cadinene [24,70]. The FTIR spectrum of Au NPs (Fig. 7a) shows bands due to the C–O–C and C–OH vibrations at 1024 cm−1 , C–N stretching mode of aromatic amine group at 1363 cm−1 , C–O–H bending vibrations at 1425 cm−1 , amide I band of proteins at 1624 cm−1 , C–H stretching vibration modes in hydrocarbon chains at 2904 cm−1 and hydroxyl functional groups in polyphenols and alcohols around 3381 and 1109 cm−1 [3,4,15,60,71–73]. All these reveal the presence of proteins, aromatic amines and polyphenols along with the Au NPs. In the case of Ag NPs, FTIR spectrum shows medium absorptions at 1026, 1099, 1448, 1622 cm−1 which are similar to the spectra of Au NPs. Additionally intense peaks were observed at 1205 cm−1 due to stretching vibrations of C–O in polyols, 1516 cm−1 due to stretching vibrations of –C–C– in aromatic rings, 1703 cm−1 due to C O stretching modes of carboxylic acid group and 3134, 3603 cm−1 due to –OH stretching vibrations [74]. The intense band at 1721 cm−1 in the IR spectra of Ag NPs shows the presence of –COOH group in the molecule bounded to Ag NPs. This band showed a shift from 1730 cm−1 confirming the above state-
ment. The bands at 1205 cm−1 and 1622 cm−1 reveal the presence of polyols and proteins along with Ag NPs. Therefore the capping agents are different for gold and silver nanoparticles. In Fig. 8, curves a–c represent the FTIR spectra of dried leaf powder before reduction, dried leaf powder after reduction of Au3+ and Ag+ respectively. In the first curve, the most intense peak occurred at 1641 cm−1 (amide I band) and in curve b the band at 1026 cm−1 (C–N stretching vibrations of aliphatic amines) appears as most intense one. The band at 1641 cm−1 due to amide I band in curve 1 (Fig. 8) has shown a shift to 1624 cm−1 in the IR spectrum of Au NPs (Fig. 7a) suggesting proteins as binding molecule [2,31]. Similarly band at 1033 cm−1 due to C–N stretching vibration of aliphatic amines shifted to 1024 cm−1 and the band at1328 cm−1 due to C–N stretching vibrations of aromatic amines shifted to 1363 cm−1 for gold nanoparticles. The bands at 1730 cm−1 (C O stretching vibrations of carboxylic acid), 1641 cm−1 (amide I), 1521 cm−1 (amide II) in curve 1 became comparatively weaker in curve b suggesting proteins as reducing agents for gold (Fig. 8). On comparing curve a and c, it is observed that the bands at 1219 cm−1 (polyols) and 1109 (phenols) became weaker in curve c indicating polyols as reducing agent for silver [23,75,76]. It is suggested that water soluble tannin, gallic acid present in Cashew leaf was responsible for the reduction of silver nitrate and leucine and glutamic acid from protein chains, again gallic acid are bounded to Ag NPs as capping agents. Simillarly for HAuCl4 , proteins acts as reducing agent and gallic acid, aliphatic amines, again proteins are present as capping agents with Au NPs.
Fig. 8. FTIR spectra of dried leaf powder (a) before reduction, (b) after reduction of Au. ions and (c) after reduction of Ag ions.
262
D.S. Sheny et al. / Spectrochimica Acta Part A 79 (2011) 254–262
5. Conclusion Biosynthesis of gold and silver nanoparticles using cashew leaf powder and extract were investigated. The amount of plant material was found to play a critical role in the size dispersity of NPs. It is found that lower amounts of plant material were sufficient to bring about reduction. Use of leaf powder is advantageous over leaf extract as it eliminates the seasonal effects and its concentration can be optimized. Similarly leaf powder is found to be useable at any time at any place. Au NPs were more stable at pH 6 while Ag NPs shows maximum stability at pH 8. Au–Ag alloy NPs were formed with 66% of Au. The biomolecules responsible for the reduction and stabilization of Au and Ag NPs are found to be different. Mainly proteins and polyols present in cashew leaves are responsible for the reduction. The plant material responsible for reduction and stabilization need further study including extraction and identification of compounds present in the leaf. Acknowledgements Sheny D S thanks the UGC for the Junior Research Fellowship. The authors are pleased to acknowledge Prof. T. Pradeep, DST unit of Nanoscience, IIT Madras and SAIF, IIT Bombay for TEM measurements. References [1] A.D. Dwivedi, K. Gopal, Colloids Surf. A 369 (2010) 27–33. [2] N. Ahmad, S. Sharma, V.N. Singh, S.F. Shamsi, A. Fatma, B.R. Mehta, Biotechnol. Res. Int. (2011). [3] R. Sarkar, P. Kumbhakar, A.K. Mitra, J. Digest, Nanomater. Biostruct. 5 (2010) 491–496. [4] S. Soisuwan, W. Warisnoicharoen, K. Lirdprapamongkol, J. Svasti, Am. J. Appl. Sci. 7 (2010) 1038–1042. [5] S.K. Nune, N. Chandra, R. Shukla, K. Katti, R.R. Kulkarni, S. Thilakavathy, S. Mekapothula, R. Kannan, K.V. Katti, J. Mater. Chem. 19 (2009) 2912–2920. [6] A.R. Binupriya, M. Sathishkumar, K. Vijayaraghavan, S. Yun, J. Hazard. Mater. 177 (2010) 539–545. [7] A.S. Reddy, C.Y. Chen, C.C. Chen, J.S. Jean, H.R. Chen, M.J. Tseng, C.W. Fan, J.C. Wang, J. Nanosci. Nanotechnol. 10 (2010) 6567–6574. [8] S. Sinha, I. Pan, P. Chanda, S.K. Sen, J. Appl. Biosci. 19 (2009) 1113–1130. [9] P.K. Sahoo, S.S.K. Kamal, T.J. Kumar, B. Sreedhar, A.K. Singh, S.K. Srivastava, Def. Sci. J. 59 (2009) 447–455. [10] J.Y. Song, H.K. Jang, B.S. Kim, Process Biochem. 44 (2009) 1133–1138. [11] B. Ankamwar, M. Chaudhary, M. Sastry, Synth. React. Inorg. Met. -Org. Chem. 35 (2005) 19–26. [12] N. Roy, A. Barik, Int. J. Nanotechnol. Appl. 4 (2010) 95–101. [13] K.B. Narayanan, N. Sakthivel, Mater. Charact. 61 (2010) 1232–1238. [14] R. Hu, SPIE Newsroom (2010), doi:10.1117/2.1201009.003119. [15] P.K. Jain, X. Huang, I.H. EI-Sayed, M.A. EI-Sayed, Acc. Chem. Res. 41 (2008) 1578–1586. [16] H. Xiao, Y. Xia, Society of Plastics Engineers (SPE) (2010), doi:10.1002/spepro.002978. [17] F.K. Alanazi, A.A. Radwan, I.A. Alsarra, Saudi Pharm. J. 18 (2010) 179–193. [18] P. Mohanpuria, N.K. Rana, S.K. Yadav, J. Nanopart. Res. 10 (2008) 507–517. [19] T. Pradeep, Anshup, Thin Solid Films 517 (2009) 6441–6478. [20] W. Cai, T. Gao, H. Hong, J. Sun, Nanotechnol. Sci. Appl. 1 (2008) 17–32. [21] D. Philip, K.G. Gopchandran, C. Unni, K.M. Nissamudeen, Spectrochim. Acta A 70 (2008) 780–784. [22] B. Zheng, L. Qian, H. Yuan, D. Xiao, X. Yang, M.C. Paau, Talanta 82 (2010) 177–183. [23] J. Hu, Z. Wang, J. Li, Sensors 7 (2007) 3299–3311. [24] M. Sathishkumar, K. Sneha, S.W. Won, C.W. Cho, S. Kim, Y.S. Yun, Colloids Surf. B 73 (2009) 332–338. [25] E.K. Elumalai, T.N.V.K.V. Prasad, J. Hemachandran, S.V. Therasa, T. Thirumalai, E. David, J. Pharm. Sci. Res. 2 (2010) 549–554. [26] M. Safaepour, A.R. Shahverdi, H.R. Shahverdi, M.R. Khorramizadeh, A.R. Gohari, Avicenna J. Med. Biotechnol. 1 (2009) 111–115. [27] K. Kalishwaralal, V. Deepak, S.R.K. Pandian, M. Kottaisamy, S.B. Manikanth, B. Kartikeyan, S. Gurunathan, Colloids Surf. B 77 (2010) 257–262.
[28] J. Huang, Q. Li, D. Sun, Y. Lu, Y. Su, X. Yang, H. Wang, Y. Wang, W. Shao, N. He, J. Hong, C. Chen, Nanotechnology 18 (2007) 105104. [29] S.P Dubey, M. Lahtinen, H. Sarkka, M. Sillanpaa, Colloids Surf. B 80 (2010) 26–33. [30] D. Philip, Phys. E 42 (2010) 1417–1424. [31] D. Philip, C. Unni, doi:10.1016/j.physe.2010.10.1006. [32] S.S. Shankar, A. Rai, A. Ahmad, M. Sastry, J. Colloid Interface Sci. 275 (2004) 496–502. [33] A.R. Vilchis-Nestor, V. Sanchez-Mendieta, M.A. Camacho-Lopez, R.M. GomezEspinosa, M.A. Camacho-Lopez, J.A. Arenas-Alatorre, Mater. Lett. 62 (2008) 3103–3305. [34] D. Jain, H.K. Daima, S. Kachhwaha, S.L. Kothari, Digest J. Nanomater. Biostruct. (2009) 723–727. [35] S.P. Dubey, M. Lahtinen, M. Sillanpaa, Process Biochem. 45 (2010) 1065–1071. [36] G.S. Ghodake, N.G. Deshpande, Y.P. Lee, E.S. Jin, Colloids Surf. B 75 (2010) 584–589. [37] T.C. Prathna, N. Chandrasekaran, A.M. Raichur, A. Mukherjee, Colloids Surf. B 82 (2011) 152–159. [38] B. Ankamwar, C. Damle, A. Ahmad, M. Sastry, J. Nanosci. Nanotechnol. 5 (2005) 1665–1671. [39] S.S. Shankar, A. Ahmad, M. Sastry, Biotechnol. Prog. 19 (2003) 1627–1631. [40] B. Ankamwar, E-J. Chem. 7 (2010) 1334–1339. [41] Gardea-Torresday, J.G. Parsons, E. Gomez, H.E. Peralta-Videa, P. Tronani, M.J. Santiago, Yacaman, Nano Lett. 2 (2002) 397–401. [42] Y. Wang, X. He, K. Wang, X. Zhang, W. Tan, Colloids Surf. B 73 (2009) 75–79. [43] S.P. Chandran, M. Chaudhary, R. Pasricha, A. Ahmad, M. Sastry, Biotechnol. Prog. 22 (2006) 577–583. [44] D. Philip, Spectrochim. Acta A 75 (2010) 1078–1081. [45] D. Philip, Spectrochim. Acta A 78 (2011) 327–331. [46] D. Philip, Spectrochim. Acta A 77 (2010) 807–810. [47] D. Philip, C. Unni, S.A. Aromal, V.K. Vidhu, Spectrochim. Acta A 78 (2011) 899–904. [48] D. Philip, Spectrochim. Acta A 73 (2009) 374–381. [49] V.R. Kannan, C.S. Sumathi, V. Balasubramanian, N. Ramesh, Bot. Res. Int. 2 (2009) 253–257. [50] J.G.S. Maia, E.H.A. Andrade, M.G.B. Zoghbi, J. Food Compos. Anal. 13 (2000) 227–232. [51] S. Yusuf, M. Aliyu, R. Ndanusa, J. Med. Plant Res. 3 (2009) 493–497. [52] L. Tedong, T. Dimo, P.D.D. Dzeufiet, A.E. Asongalem, D.S. Sokeng, P. Callard, J.F. Flejou, P. Kamtchouing, Afr. J. Trad. CAM 3 (2006) 23–35. [53] L. Tedong, P.D.D. Dzeufiet, T. Dimo, E.A. Asongalem, S.N. Sokeng, J.F. Flejou, P. Callard, P. Kamtchouing, Afr. J. Trad. CAM 4 (2007) 140–147. [54] D. Inbakandan, R. Venkatesan, S.A. Khan, Colloids Surf. B 81 (2010) 634–639. [55] R. Deshpande, M.D. Bedre, S. Basavaraja, B. Sawle, S.Y. Manjunath, A. Venkataraman, Colloids Surf. B 79 (2010) 235–240. [56] A.N. Mishra, S. Bhadauria, M.S. Gaur, R. Pasricha, B.S. Kushwah, Int. J. Green Nanotechnol. 1 (2010) 118–124. [57] A. Sugunan, J. Dutta, Mater. Res. Soc. Symp. Proc. 901E (2006). [58] D. Philip, Spectrochim. Acta A 71 (2008) 80–85. [59] S.L. Smitha, K.M. Nissamudeen, D. Philip, K.G. Gopchandran, Spectrochim. Acta A 71 (2008) 186–190. [60] K.B. Narayanan, N. Sakthivel, Mater. Lett. 62 (2008) 4588–4590. [61] C.E. Rayford II., G. Schatz, K. Shuford, Nanoscape 2 (2005). [62] E. Filippo, A. Serra, A. Buccolieri, D. Manno, J. Non-Cryst. Solids 356 (2010) 344–350. [63] P. Raveendran, J. Fu, S.L. Wallen, Green Chem. 8 (2006) 34–38. [64] S.L. Smitha, D. Philip, K.G. Gopchandran, Spectrochim. Acta A 74 (2009) 735–739. [65] H. Bar, D.K. Bhui, G.P. Sahoo, P. Sarkar, S.P. De, A. Misra, Colloids Surf. A339 (2009) 134–139. [66] D. Zheng, C. Hu, G. Tian, X. Dang, S. Hu, Sens. Actuators B148 (2010) 247–252. [67] N. Ahmad, S. Sharma, K. Alam, V.N. Singh, S.F. Shamsi, B.R. Mehta, A. Fatma, Colloids Surf. B81 (2010) 81–86. [68] A. Ingle, M. Rai, A. Gade, M. Bawaskar, J. Nanopart. Res. 11 (2009) 2079–2085. [69] M. Dubey, S. Bhadauria, B.S. Kushwah, Digest J. Nanomater. Biostruct. 4 (2009) 537–543. [70] D.A. Ofusori, B.U. Enaibe, A.E. Adelakun, O.A. Adesanya, R.A. Ude, K.A. Oluyemi, C.U. Okwuonu, O.A. Apantaku, Int. J. Altern. Med. 5 (2008) 1540–1584. [71] H. Schulz, M. Baranska, Vib. Spectrosc. 43 (2007) 13–25. [72] L. Castro, M.L. Blazquez, F. Gonzalez, J.A. Munyz, A. Ballester, Chem. Eng. J. 164 (2010) 92–97. [73] A. Bankar, B. Joshi, A.R. Kumar, S. Zinjarde, Colloids Surf. B 80 (2010) 45–50. [74] A.K. Singh, M. Talat, D.P. Singh, O.N. Srivastava, J. Nanopart. Res. 12 (2010) 1667–1675. [75] R.K. Das, B.B. Borthakur, U. Bora, Mater. Lett. 64 (2010) 1445–1447. [76] J. Kasthuri, K. Kathiravan, N. Rajendiran, J. Nanopart. Res. 11 (2009) 1075–1085.
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
Phytosynthesis of Au, Ag and Au–Ag bimetallic nanoparticles using aqueous extract and dried leaf of Anacardium occidentale D.S. Sheny a , Joseph Mathew a , Daizy Philip b,∗ a b
Department of Chemistry, Mar Ivanios College, Thiruvananthapuram 695 015, Kerala, India Department of Physics, Mar Ivanios College, Nalanchira, Thiruvananthapuram 695 015, Kerala, India
a r t i c l e
i n f o
Article history: Received 18 January 2011 Received in revised form 20 February 2011 Accepted 25 February 2011 Keywords: Anacardium occidentale leaf Biosynthesis Gold nanoparticles Silver nanoparticles Au–Ag bimetallic nanoparticles Core–shell nanoparticles
a b s t r a c t Present study reports a green chemistry approach for the biosynthesis of Au, Ag, Au–Ag alloy and Au core–Ag shell nanoparticles using the aqueous extract and dried powder of Anacardium occidentale leaf. The effects of quantity of extract/powder, temperature and pH on the formation of nanoparticles are studied. The nanoparticles are characterized using UV–vis and FTIR spectroscopies, XRD, HRTEM and SAED analyses. XRD studies show that the particles are crystalline in the cubic phase. The formation of Au core–Ag shell nanoparticles is evidenced by the dark core and light shell images in TEM and is supported by the appearance of two SPR bands in the UV–vis spectrum. FTIR spectra of the leaf powder before and after the bioreduction of nanoparticles are used to identify possible functional groups responsible for the reduction and capping of nanoparticles. Water soluble biomolecules like polyols and proteins are expected to bring about the bio-reduction. © 2011 Elsevier B.V. All rights reserved.
1. Introduction A naturally motivated investigational practice for the biosynthesis of metal nanoparticles is now established as an emerging area of nanoscience research and development. As nature make optimum use of materials and space, many inorganic materials are produced in biological systems [1]. Similar to such natural processes, plants [2–5], fungi [6], and bacteria [7] are found to be of great success for the synthesis of metal nanoparticles [8]. The advances in the field of biotechnology and nanotechnology owes to the tremendous improvement in human life. In recent years, an increasing percentage of nanomaterials are emerging and making advancement in different fields. Unlike the bulk counterparts, nanoparticulate materials exhibit very interesting electrical, optical, magnetic and chemical properties [9]. Nanoparticles of noble metals are widely applied in common products like soaps, cosmetics, toothpaste, shampoos and medicines which make their synthesis vital [10]. Nanoparticle synthesis is usually carried out by various physical and chemical methods like laser ablation, pyrolysis, lithography, chemical vapour deposition, sol–gel technique and electro-deposition which are very expensive and hazardous. Therefore scientists are looking forward for greener methods [11,12]. In the present study, we report the green synthesis of gold and silver nanoparticles using both leaf extract
∗ Corresponding author. Tel.: +91 471 2530887; fax: +91 471 2530023. E-mail addresses: [email protected], [email protected] (D. Philip). 1386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2011.02.051
and powder of Anacardium occidentale. These metal nanoparticles have received attention due to their unique and tunable SPR and shape and size-dependent properties [13]. They find applications in scientific and technological fields like drug delivery [14], tissue/tumor imaging [15], photothermal therapy [15], catalysis [16,17], optoelectronics [18], water purification [19], SERS detection [20,21], and biosensing [22,23]. Silver nanoparticles have found to posses anti-fungal, anti-bacterial, anti-inflammatory, antiviral, anti-angiogenesis, and anti-platelet activity and cytotoxicity against cancer cells which makes them vital [24–27]. In recent years, synthesis of both Au and Ag NPs has been reported using the extracts of Chenopodium album [1], Coleus amboinicus Lour [13], Cinnamomum camphora [28], Sorbus aucuparia [29], Hibiscus rosa sinensis [30], Ocimum sanctum [31], Azadirachta indica [32] and Camellia sinensis [33]. There are also reports of using extracts of fruits like papaya [34], tansy [35], peer [36], lemon [37] and gooseberry [38] in the green synthesis of these nanoparticles. Shankar et al. [32] have shown that Au core–Ag shell NPs in solution can be synthesized using Neem leaf extracts. The Ag NPs prepared using Pelargonium graveolens leaves were found to be stabilized by an enzymatic process [39]. Importantly Huang et al. [28] have reported the synthesis of Au and Ag NPs by novel sundried biomass of Camphora leaf. Recently Ankamwar [40] has demonstrated the synthesis of stable Au NPs of size range 10–35 nm using Terminalia catappa leaf extract. Their group have also reported the synthesis of Au NPs using Indian goose berry fruit extract [38] and their phase transfer in to organic solution using a cationic surfactant. The transmetallation reaction between hydrophobised Ag
D.S. Sheny et al. / Spectrochimica Acta Part A 79 (2011) 254–262
255
were procured from Sigma–Aldrich chemicals. All glasswares were cleaned with aqua regia and rinsed several times with de-ionized water. 2.1. Synthesis of gold nanoparticles The leaf extract (1.25, 2.5, 5 and 10 ml) was added to 30 ml aqueous solution (2.5 × 10−4 M) of HAuCl4 ·3H2 O and stirred for 1 min to get colloids a1 , a2 , a3 and a4 . For a1 and a2 fast reduction occurred as indicated by a red solution and was complete within 10 min. They are stable for seven months. Seasonal changes may affect the composition of leaf constituents which can be avoided by using dried leaf power. 12 mg of the leaf powder was added to 30 ml of aqueous HAuCl4 ·3H2 O solution (2.5 × 10−4 M) and stirred for 1 min and filtered to obtain colloid b1 . The amount of leaf powder was varied as 9, 7, 5 and 3 mg to get to colloids b2 , b3 , b4 and b5 . The reduction was very slow in the case of b5 which has a light blue color developed after 1 h. 2.2. Synthesis of silver nanoparticles Fig. 1. Photograph of Anacadium occidentale.
NPs and hydrophobised chloroaurate ions in chloroform resulted in the formation of hollow-Au shells. A rapid synthesis of gold NPs having a mixture of plate and spherical structures using Magnolia kobus and Diopyros kaki leaf extracts were investigated by Song et al. [10]. Torresdey et al. [41] have reported the synthesis of Au and Ag NP within live Alfalfa plants. Wang et al. [42] used Skullcup herb for the extracellular synthesis of gold NPs. Chandran et al. had observed the formation of crystalline gold nano triangles using Aloe vera extract [43]. Ghodake et al. [36] have successfully biosynthesized triangular and hexagonal nanoplates, elegantly assembled with gold NPs using Peer fruit extract. Earlier reports from our lab include the green synthesis of Ag and Au NPs using Honey [44], H. rosa sinensis [30], O. sanctum [31], Mangifera indica [45,46] and Murraya Koenigii [47]. Au–Ag alloy nanoparticles were also synthesized using edible Mushroom extract [48]. In biosynthesis, plants are preferred to micro-organisms, as it does not involve any tedious process of maintaining cell cultures [15]. Beyond that, the seasonal effects of plants and variation boiling time can be eliminated by using dried biomass of plant material which can be used at any time anywhere. A. occidentale (Fig. 1) belonging to Anacardiaceae family, has great economic and medicinal value [49,50]. It is commonly called Cashew and is a multipurpose tree whose leaves, stem and bark extracts are used extensively for the treatment of diarrhea, hypertension, dysentery, toothache, sore gums, colonic pain etc. It has also been reported to possess anti-diabetic, anti-bacterial, antiinflammatory and anti-ulcerogenic properties [51–53]. India is the second largest producer of cashew nuts and it is widely cultivated in India. But the other parts of the plant have not been exploited. In this paper, rapid biosynthesis of Au, Ag and Au–Ag bimetallic NPs using cashew leaf extract and powder has been investigated which is an easiest, cost efficient, non-toxic, eco-friendly and efficient method for exploiting cashew leaves. 2. Materials and methods Fresh A. occidentale leaves were collected from rural areas of Thiruvananthapuram, India. Fresh leaves were washed thoroughly with de-ionized water. 10 g of the homogenized leaves were stirred with 100 ml de-ionized H2 O for 5 min and filtered to get the extract. For the preparation of leaf powder, the leaves were dried for two weeks, grounded and sieved to get fine powder. AgNO3 and HAuCl4
The leaf extract (2, 3, 4, 5 and 10 ml) was added to a vigorously stirred 30 ml solution of 5.9 × 10−4 M AgNO3 and stirring continued for 1 min to get the colloids c1 to c6 . Reduction was fast for c5 and c6 which is indicated by a reddish brown color. For the preparation of Ag NPs also seasonal effects of leaf extract can be avoided by using dried leaf powder. 30 ml of 5.9 × 10−4 M AgNO3 solution were added with 5 mg leaf powder, stirred for 5 min and filtered to get colloid d1 . The colloids d2 , d3 , d4 and d5 were obtained by increasing the amount of powder as 10, 15, 20 and 25 mg. The reduction occurred slowly and was complete within 2 h. 2.3. Synthesis of Au–Ag bimetallic nanoparticles The Au–Ag colloids were prepared in the gold to silver ratio, 1:2, 1:1, 2:1, 3:1, 4:1 and 9:1. The 1:2 bimetallic colloid (Y1 ) is obtained as follows: To a 30 ml of HAuCl4 ·3H2 O solution (2.5 × 10−4 M), 2.5 ml of extract were added and stirred for 2 min. To this solution, 60 ml of AgNO3 solution (5.9 × 10−4 M) was added and stirred vigorously followed by 8 ml extract. The stirring was continued for two more minutes and the formation of bimetallic nanoparticles was completed within 30 min. Similarly the 1:1, 2:1, 3:1, 4:1 and 9:1 colloids henceforth called Y2 , Y3 , Y4 , Y5 and Y6 , respectively were prepared in their corresponding ratios. These mixed colloids are very stable and their color changed from yellowish to red as the quantity of gold is increased. 3. Characterization The optical absorption spectra of the synthesized nanoparticles were observed by UV-2450 Shimadzu UV spectrometer. HRTEM images and electron diffraction patterns were obtained with a JEOL 3010 and Philips CM 200 transmission electron microscope. FTIR spectra of dried gold and silver nanoparticles, native and treated leaf power were recorded with an IR Pestige-21 Shimadzu spectrometer. X-ray diffraction pattern of dried nanoparticle powder were obtained using XPERT-PRO diffractometer using Cu K␣ radiation ( = 0.1542 nm). 4. Results and discussion 4.1. UV–vis spectral studies The optical absorption spectrum of metal nanoparticles is sensitive to several factors like particle size, shape, particle–particle
256
D.S. Sheny et al. / Spectrochimica Acta Part A 79 (2011) 254–262
Fig. 2. (a) UV–vis spectra of Au nanoparticles prepared using leaf extract: (a1 ) 1.25 ml, (a2 ) 2.5 ml, (a3 ) 5 ml and (a4 ) 10 ml. The inset shows the variation of SPR band wavelength with quantity of extract. (b) UV–vis spectra of Au nanoparticles prepared using leaf powder: (b1 ) 5 mg, (b2 ) 7 mg, (b3 ) 9 mg and (b4 ) 12 mg. The inset shows the variation of SPR band wavelength with mass of powder. (c) UV–vis spectra of Au nanoparticles at 300 K and 373 K. (d) UV–vis spectra of Au nanoparticles prepared at 373 K: (e1 ) 0.1 ml, (e2 ) 0.2 ml, (e3 ) 0.4 ml and (e4 ) 0.6 ml. The inset shows the variation of SPR band wavelength with quantity of extract. (e) Effect of pH on SPR of Au nanoparticles: (g1 ) pH-4, (g2 ) pH-5, (g3 ) pH-6, (g4 ) pH-7, and (g5 ) pH-8. The inset shows the variation of SPR band wavelength with pH.
interaction with the medium and local refractive index [54]. Fig. 2a and b show the UV–vis spectra of Au NPs prepared using leaf extract and dried leaf powder with SPR band around 529 nm and 526 nm respectively. The appearance of red color was due to the
excitation of surface Plasmon vibrations which is absent in bulk material [55,56]. From Fig. 2a, it is seen that as the quantity of the extract was increased, the SPR bands become broader and shift to higher wavelengths signifying an increase in particle size [57–59].
Table 1 Variation of FWHM with quantity of extract. Quantity of extract (ml)
FWHM (SPR of Au nanoparticles) (nm)
Quantity of extract (ml)
FWHM (SPR of nanoparticles Ag (ml)
1.25 2.5 5 10
136 163 204 216
2 3 4 5
236 268 304 312
D.S. Sheny et al. / Spectrochimica Acta Part A 79 (2011) 254–262
257
Fig. 3. (a) UV–vis spectra of Ag nanoparticles prepared using leaf extract: (c1 ) 2 ml, (c2 ) 3 ml, (c3 ) 4 ml, (c4 ) 5 ml and (c5 ) 10 ml. The inset shows the variation of SPR band wavelength with quantity of extract. (b) UV–vis spectra of Ag nanoparticles prepared using leaf powder: (d1 ) 2 mg, (d2 ) 3 mg, (d3 ) 4 mg, (d4 ) 5 mg and (d5 ) 10 mg. The inset shows the variation of SPR band wavelength with mass of powder. (c) UV–vis spectra of Ag nanoparticles at 300 K and 373 K. (d) UV–vis spectra of Ag nanoparticles prepared at 373 K: (f1 ) 0.2 ml, (f2 ) 0.4 ml, (f3 ) 0.6 ml, (f4 ) 0.8 ml and (f5 ) 1 ml. The inset shows the variation of the wavelength of SPR band with quantity of extract. (e) Effect of pH on SPR of Ag nanoparticles: (h1 ) pH-6, (h2 ) pH-7, (h3 ) pH-8, (h4 ) pH-9 and (h5 ) pH-10. The inset shows the variation of the wavelength of SPR band with pH.
With leaf powder, narrow and symmetric SPR band is obtained at larger amounts of powder. A similar result has been reported in the synthesis of Au and Ag NPs using the extracts of Mushroom [48], Coriander leaf [60] and H. rosa leaf [30]. With an increase in the quantity of extract, the full width at half maximum (FWHM) decreases supporting the reduction in particle size (Table 1). For silver nanoparticles prepared using extract and powder, the SPR band appears at 420 nm and 422 nm respectively (Fig. 3a and b). The SPR band became narrower at higher concentration of the extract. The broad SPR at lower concentrations of the extract is due to the formation of large anisotropic particles [28,32,48,61,62]. It is found that SPR wavelength has a small shift to shorter wavelength and consequently FWHM decreases showing decrease in particle size. Below 2 ml of the extract, no SPR band is observed due to insufficient quantity of reducing agent. More symmetrical SPR band is
observed with higher amounts of leaf powder. These results show that the quantity of plant material is a key factor determining the formation and size distribution of nanoparticles. The digital photograph and UV–vis spectra of Au–Ag colloids are shown in Fig. 4a and b, respectively. For 2:1 and 1:1 ratios, individual bands are observed for gold and silver at around 502 nm and 413 nm respectively. The core–shell NPs or a dispersion of separate Au and Ag NPs can give rise to two absorption bands and their intensities depends on their initial composition. Earlier reports reveal that phase separation at atomic scale leads to the formation of core–shell particles [63]. An ideal alloy system must have a single absorption which is in agreement with the colloids with ratio 1:2 onwards. A plot of absorption maximum of Au NPs against its percentage is shown in Fig. 4c. It shows a linear variation of max from 66% of gold. Therefore below that percentage of gold, Au core–Ag
258
D.S. Sheny et al. / Spectrochimica Acta Part A 79 (2011) 254–262
Fig. 4. (a) Photograph of colloids Y1 , Y2 , Y3 , Y4 , Y5 and Y6 . (b) UV–vis spectra of Au–Ag bimetallic nanoparticles. (c) Plot of max against percentage of Au present.
shell were present which is confirmed by HRTEM analysis (Section 4.2). The max of both Au and Ag NPs showed a red shift with increase in the percentage of Au and Ag, respectively indicating that a molar ratio of 1:2 with 66% of gold is required for the formation of Au–Ag alloy. 4.1.1. Effect of leaf quantity For gold NPs, with an increase in the extract quantity an increase in the peak absorbance was found in UV–vis spectrum (Fig. 2a). The solution showed a color change from wine red to violet indicating increase in particle size. For the generation of small NPs, lowest amount of leaf extract is preferred which is found to be lesser among previously reported ones [1,64,65]. Using dried leaf powder, 12 mg is found to be more suitable for the preparation of small and stable Au NPs. Below 12 mg, the color of the colloid changes from red to purple to violet with a decrease in UV–vis absorbance (Fig. 2b). The UV–vis spectra of Ag NPs (Fig. 3a) shows a linear relationship between absorbance and quantity of extract. A lower quantity of 5 mg of leaf powder gave high absorption in visible region which will be more suitable than their higher quantities (Fig. 3b).
(Fig. 2d). For silver nanoparticles 1 ml and 0.2 ml of extract were required for the reduction at 300 K and 373 K with SPR band at 429 nm and 418 nm, respectively (Fig. 3c). A blue shift occurred on increasing the concentration of extract at 373 K indicating reduction in the particle size. Ag NPs synthesized at 373 K were found to possess higher stability. The variations in the amount of extract at both temperatures have similar effects (Fig. 3a and d). 4.1.3. Effect of pH The UV–vis spectrum of Au NPs at different pH range from 4 to 8 is given in Fig. 2e. A sharp and symmetric peak is obtained at pH 6. It is stable for seven months. At pH 4, a broad peak indicates large sized particles. With the increase in pH, the SPR band shows a steep increase initially then becomes constant and finally decreases. In a range of pH from 5 to 6, SPR band reaches a maximum. For Ag NPs even though the position of SPR band does not show much variation, their absorbance increases with pH (Fig. 3e). At lower pH, broad peak is attributed to the large particle size. At higher pH 10, SPR band position has some deviation optimizing pH 8 or 9 for the above synthesis. 4.2. TEM studies
4.1.2. Effect of temperature Reductions occurred at 300 K and 373 K was compared for both Au and Ag nanoparticles. At 373 K even 0.1 ml of extract was sufficient to bring about the reduction of Au3+ . At 300 K a red colored stable colloid was obtained with 2.5 ml of extract whose SPR band appears at 529 nm while 0.6 ml was enough at 373 K with SPR band at 536 nm (Fig. 2c). Thus, reduction occurs at higher temperatures leading to large-sized and more stable nanoparticles. On increasing the concentration of extract, a blue shift is observed at 373 K
Transmission electron microscope images of Au NPs obtained at 300 K and 373 K are shown in Fig. 5a1 and a2 , respectively. Their particle size histograms (Fig. 5b) give an average size of 6.5 nm and 17 nm, respectively. The morphology of Au NPs was almost spherical. The images clearly show that higher temperatures during synthesis leads to an increase in particle size. The Au NPs are highly crystalline as shown by clear lattice fringe spacing of 0.21 nm and SAED pattern. The SAED pattern reveals diffraction rings from inner
D.S. Sheny et al. / Spectrochimica Acta Part A 79 (2011) 254–262
259
Fig. 5. (a1 ) TEM images and SAED pattern of Au NPs prepared using leaf extract at 300 K, (a)–(d) at different magnifications, (e) at high resolution and (f) SAED pattern. (a2 ) TEM images and SAED patterns of Au NPs prepared using leaf extract at 373 K, (a)–(d) at different magnifications, (e) at high resolution and (f) SAED pattern. (b) Histograms showing the particle sizes of NPs corresponding to the TEM images (a and b) a1 , a2 (c and d) c1 , c2 and (e and f) d1 and d2 . (c1 ) TEM images of Ag NPs prepared using leaf extract: (a), (b), (c) and (d) SAED pattern. (c2 ) TEM images of Ag NPs prepared using leaf powder: (a), (b), (c) under different magnification and (d) SAED pattern. (d1 ) TEM images of Au core–Ag shell NPs: (a)–(c) under different magnifications and (d) SAED pattern. (d2 ) TEM images of Au–Ag alloy NPs: (a)–(c) under different magnifications and (d) SAED pattern.
260
D.S. Sheny et al. / Spectrochimica Acta Part A 79 (2011) 254–262
Fig. 5. (Continued ).
to outer, which can be indexed as (1 1 1), (2 0 0), (2 2 0) and (3 1 1) reflections respectively confirming fcc structure. Fig. 5c1 and c2 shows TEM images of Ag NPs prepared using leaf extract and powder. In Fig. 5c2 well dispersed spherical nanoparticles of an average size 15.5 nm are seen. The fringe spacing is measured to be 0.21 nm, which corresponds to the spacing between the (1 1 1) plane of fcc gold. The SAED pattern revealed a highly crystalline lattice space. The histograms describing the dispersity in size distribution of the particles in both cases are shown in Fig. 5b. With leaf extract, smaller particles of an average size 5 nm were obtained. They have a SPR absorption 412 nm indicating smaller particle size. The TEM images and SAED pattern of Au–Ag bimetallic nanoparticles are shown in Fig. 5d1 and d2 corresponding to the Au to Ag ratio 1:2 and 9:1 respectively. At 1:2 ratios, TEM images show electron density banding with a dark gold core and a light silver shell indicating Au core–Ag shell NPs [66] which is clearly shown by the encircled portion in Fig. 5d1. This observation is in agreement with the UV–vis spectrum showing two Plasmon bands. Their particle size distribution histogram gives an average size 6.5 nm. Fig. 5d2 shows that the particles are almost uniform and homogeneous within the volume of the particle, suggesting the presence of Au–Ag alloy NPs supporting the observation of a single SPR band. Their particle size
histogram revealed an average size of 8 nm. In both case, SAED pattern clearly shows highly crystalline structure. These results show that it is possible to prepare stable Au–Ag core–shell NPs and alloy NPs of size below 10 nm by varying the ratio of HAuCl4 , AgNO3 and leaf extract solutions. 4.3. XRD studies The XRD patterns of Au and Ag NPs (Fig. 6a and b) show five intense peaks of (1 1 1), (2 0 0), (2 2 0), (3 1 1) and (2 2 2) facets of face centered cubic crystal structure with lattice parameter, a = 4.04 A˚ and 4.06 A˚ respectively. The broadening of Bragg’s peaks indicates the formation of nanoparticles. For both Au and Ag NPs the peak corresponding to the (1 1 1) plane was more intense than the other planes suggesting (1 1 1) is the predominant orientation [11,67,68]. The mean size of NPs were calculated using Scherrer formula, D=
K ˇs cos
where D is the size of the particles, K is the shape dependent Scherrer’s constant, is the wavelength of radiation and ˇs is the full peak width and is the diffraction angle [35,69]. Using the FWHM
D.S. Sheny et al. / Spectrochimica Acta Part A 79 (2011) 254–262
261
Fig. 7. FTIR spectra of dried (a) Au NPs and (b) Ag NPs.
Fig. 6. (a) XRD pattern of dried Au NPs. (b) XRD pattern of dried Ag NPs.
of (1 1 1) peak, the size of Au NP is found to be 8.5 nm and that of Ag NP is 19 nm which are in good agreement with the particle size obtained from TEM analysis. 4.4. FTIR studies In order to identify the possible molecules present in cashew leaf which are responsible for the reduction of Au3+ and Ag+ and their stabilization, FTIR measurement were carried out. A variety of secondary metabolites such as tannins, terpenoids, alkaloids, flavanols, phenols, glycosides are present in cashew leaf [65]. It has been also reported that Cashew contains gallic acid, anacardic acid, anacardol, hydroxyl benzoic acid, capryllic acid, gadoleic acid, lauric acid, leucine, leucocyanides, ocimene, limonene, caryophyllene and alpha cadinene [24,70]. The FTIR spectrum of Au NPs (Fig. 7a) shows bands due to the C–O–C and C–OH vibrations at 1024 cm−1 , C–N stretching mode of aromatic amine group at 1363 cm−1 , C–O–H bending vibrations at 1425 cm−1 , amide I band of proteins at 1624 cm−1 , C–H stretching vibration modes in hydrocarbon chains at 2904 cm−1 and hydroxyl functional groups in polyphenols and alcohols around 3381 and 1109 cm−1 [3,4,15,60,71–73]. All these reveal the presence of proteins, aromatic amines and polyphenols along with the Au NPs. In the case of Ag NPs, FTIR spectrum shows medium absorptions at 1026, 1099, 1448, 1622 cm−1 which are similar to the spectra of Au NPs. Additionally intense peaks were observed at 1205 cm−1 due to stretching vibrations of C–O in polyols, 1516 cm−1 due to stretching vibrations of –C–C– in aromatic rings, 1703 cm−1 due to C O stretching modes of carboxylic acid group and 3134, 3603 cm−1 due to –OH stretching vibrations [74]. The intense band at 1721 cm−1 in the IR spectra of Ag NPs shows the presence of –COOH group in the molecule bounded to Ag NPs. This band showed a shift from 1730 cm−1 confirming the above state-
ment. The bands at 1205 cm−1 and 1622 cm−1 reveal the presence of polyols and proteins along with Ag NPs. Therefore the capping agents are different for gold and silver nanoparticles. In Fig. 8, curves a–c represent the FTIR spectra of dried leaf powder before reduction, dried leaf powder after reduction of Au3+ and Ag+ respectively. In the first curve, the most intense peak occurred at 1641 cm−1 (amide I band) and in curve b the band at 1026 cm−1 (C–N stretching vibrations of aliphatic amines) appears as most intense one. The band at 1641 cm−1 due to amide I band in curve 1 (Fig. 8) has shown a shift to 1624 cm−1 in the IR spectrum of Au NPs (Fig. 7a) suggesting proteins as binding molecule [2,31]. Similarly band at 1033 cm−1 due to C–N stretching vibration of aliphatic amines shifted to 1024 cm−1 and the band at1328 cm−1 due to C–N stretching vibrations of aromatic amines shifted to 1363 cm−1 for gold nanoparticles. The bands at 1730 cm−1 (C O stretching vibrations of carboxylic acid), 1641 cm−1 (amide I), 1521 cm−1 (amide II) in curve 1 became comparatively weaker in curve b suggesting proteins as reducing agents for gold (Fig. 8). On comparing curve a and c, it is observed that the bands at 1219 cm−1 (polyols) and 1109 (phenols) became weaker in curve c indicating polyols as reducing agent for silver [23,75,76]. It is suggested that water soluble tannin, gallic acid present in Cashew leaf was responsible for the reduction of silver nitrate and leucine and glutamic acid from protein chains, again gallic acid are bounded to Ag NPs as capping agents. Simillarly for HAuCl4 , proteins acts as reducing agent and gallic acid, aliphatic amines, again proteins are present as capping agents with Au NPs.
Fig. 8. FTIR spectra of dried leaf powder (a) before reduction, (b) after reduction of Au. ions and (c) after reduction of Ag ions.
262
D.S. Sheny et al. / Spectrochimica Acta Part A 79 (2011) 254–262
5. Conclusion Biosynthesis of gold and silver nanoparticles using cashew leaf powder and extract were investigated. The amount of plant material was found to play a critical role in the size dispersity of NPs. It is found that lower amounts of plant material were sufficient to bring about reduction. Use of leaf powder is advantageous over leaf extract as it eliminates the seasonal effects and its concentration can be optimized. Similarly leaf powder is found to be useable at any time at any place. Au NPs were more stable at pH 6 while Ag NPs shows maximum stability at pH 8. Au–Ag alloy NPs were formed with 66% of Au. The biomolecules responsible for the reduction and stabilization of Au and Ag NPs are found to be different. Mainly proteins and polyols present in cashew leaves are responsible for the reduction. The plant material responsible for reduction and stabilization need further study including extraction and identification of compounds present in the leaf. Acknowledgements Sheny D S thanks the UGC for the Junior Research Fellowship. The authors are pleased to acknowledge Prof. T. Pradeep, DST unit of Nanoscience, IIT Madras and SAIF, IIT Bombay for TEM measurements. References [1] A.D. Dwivedi, K. Gopal, Colloids Surf. A 369 (2010) 27–33. [2] N. Ahmad, S. Sharma, V.N. Singh, S.F. Shamsi, A. Fatma, B.R. Mehta, Biotechnol. Res. Int. (2011). [3] R. Sarkar, P. Kumbhakar, A.K. Mitra, J. Digest, Nanomater. Biostruct. 5 (2010) 491–496. [4] S. Soisuwan, W. Warisnoicharoen, K. Lirdprapamongkol, J. Svasti, Am. J. Appl. Sci. 7 (2010) 1038–1042. [5] S.K. Nune, N. Chandra, R. Shukla, K. Katti, R.R. Kulkarni, S. Thilakavathy, S. Mekapothula, R. Kannan, K.V. Katti, J. Mater. Chem. 19 (2009) 2912–2920. [6] A.R. Binupriya, M. Sathishkumar, K. Vijayaraghavan, S. Yun, J. Hazard. Mater. 177 (2010) 539–545. [7] A.S. Reddy, C.Y. Chen, C.C. Chen, J.S. Jean, H.R. Chen, M.J. Tseng, C.W. Fan, J.C. Wang, J. Nanosci. Nanotechnol. 10 (2010) 6567–6574. [8] S. Sinha, I. Pan, P. Chanda, S.K. Sen, J. Appl. Biosci. 19 (2009) 1113–1130. [9] P.K. Sahoo, S.S.K. Kamal, T.J. Kumar, B. Sreedhar, A.K. Singh, S.K. Srivastava, Def. Sci. J. 59 (2009) 447–455. [10] J.Y. Song, H.K. Jang, B.S. Kim, Process Biochem. 44 (2009) 1133–1138. [11] B. Ankamwar, M. Chaudhary, M. Sastry, Synth. React. Inorg. Met. -Org. Chem. 35 (2005) 19–26. [12] N. Roy, A. Barik, Int. J. Nanotechnol. Appl. 4 (2010) 95–101. [13] K.B. Narayanan, N. Sakthivel, Mater. Charact. 61 (2010) 1232–1238. [14] R. Hu, SPIE Newsroom (2010), doi:10.1117/2.1201009.003119. [15] P.K. Jain, X. Huang, I.H. EI-Sayed, M.A. EI-Sayed, Acc. Chem. Res. 41 (2008) 1578–1586. [16] H. Xiao, Y. Xia, Society of Plastics Engineers (SPE) (2010), doi:10.1002/spepro.002978. [17] F.K. Alanazi, A.A. Radwan, I.A. Alsarra, Saudi Pharm. J. 18 (2010) 179–193. [18] P. Mohanpuria, N.K. Rana, S.K. Yadav, J. Nanopart. Res. 10 (2008) 507–517. [19] T. Pradeep, Anshup, Thin Solid Films 517 (2009) 6441–6478. [20] W. Cai, T. Gao, H. Hong, J. Sun, Nanotechnol. Sci. Appl. 1 (2008) 17–32. [21] D. Philip, K.G. Gopchandran, C. Unni, K.M. Nissamudeen, Spectrochim. Acta A 70 (2008) 780–784. [22] B. Zheng, L. Qian, H. Yuan, D. Xiao, X. Yang, M.C. Paau, Talanta 82 (2010) 177–183. [23] J. Hu, Z. Wang, J. Li, Sensors 7 (2007) 3299–3311. [24] M. Sathishkumar, K. Sneha, S.W. Won, C.W. Cho, S. Kim, Y.S. Yun, Colloids Surf. B 73 (2009) 332–338. [25] E.K. Elumalai, T.N.V.K.V. Prasad, J. Hemachandran, S.V. Therasa, T. Thirumalai, E. David, J. Pharm. Sci. Res. 2 (2010) 549–554. [26] M. Safaepour, A.R. Shahverdi, H.R. Shahverdi, M.R. Khorramizadeh, A.R. Gohari, Avicenna J. Med. Biotechnol. 1 (2009) 111–115. [27] K. Kalishwaralal, V. Deepak, S.R.K. Pandian, M. Kottaisamy, S.B. Manikanth, B. Kartikeyan, S. Gurunathan, Colloids Surf. B 77 (2010) 257–262.
[28] J. Huang, Q. Li, D. Sun, Y. Lu, Y. Su, X. Yang, H. Wang, Y. Wang, W. Shao, N. He, J. Hong, C. Chen, Nanotechnology 18 (2007) 105104. [29] S.P Dubey, M. Lahtinen, H. Sarkka, M. Sillanpaa, Colloids Surf. B 80 (2010) 26–33. [30] D. Philip, Phys. E 42 (2010) 1417–1424. [31] D. Philip, C. Unni, doi:10.1016/j.physe.2010.10.1006. [32] S.S. Shankar, A. Rai, A. Ahmad, M. Sastry, J. Colloid Interface Sci. 275 (2004) 496–502. [33] A.R. Vilchis-Nestor, V. Sanchez-Mendieta, M.A. Camacho-Lopez, R.M. GomezEspinosa, M.A. Camacho-Lopez, J.A. Arenas-Alatorre, Mater. Lett. 62 (2008) 3103–3305. [34] D. Jain, H.K. Daima, S. Kachhwaha, S.L. Kothari, Digest J. Nanomater. Biostruct. (2009) 723–727. [35] S.P. Dubey, M. Lahtinen, M. Sillanpaa, Process Biochem. 45 (2010) 1065–1071. [36] G.S. Ghodake, N.G. Deshpande, Y.P. Lee, E.S. Jin, Colloids Surf. B 75 (2010) 584–589. [37] T.C. Prathna, N. Chandrasekaran, A.M. Raichur, A. Mukherjee, Colloids Surf. B 82 (2011) 152–159. [38] B. Ankamwar, C. Damle, A. Ahmad, M. Sastry, J. Nanosci. Nanotechnol. 5 (2005) 1665–1671. [39] S.S. Shankar, A. Ahmad, M. Sastry, Biotechnol. Prog. 19 (2003) 1627–1631. [40] B. Ankamwar, E-J. Chem. 7 (2010) 1334–1339. [41] Gardea-Torresday, J.G. Parsons, E. Gomez, H.E. Peralta-Videa, P. Tronani, M.J. Santiago, Yacaman, Nano Lett. 2 (2002) 397–401. [42] Y. Wang, X. He, K. Wang, X. Zhang, W. Tan, Colloids Surf. B 73 (2009) 75–79. [43] S.P. Chandran, M. Chaudhary, R. Pasricha, A. Ahmad, M. Sastry, Biotechnol. Prog. 22 (2006) 577–583. [44] D. Philip, Spectrochim. Acta A 75 (2010) 1078–1081. [45] D. Philip, Spectrochim. Acta A 78 (2011) 327–331. [46] D. Philip, Spectrochim. Acta A 77 (2010) 807–810. [47] D. Philip, C. Unni, S.A. Aromal, V.K. Vidhu, Spectrochim. Acta A 78 (2011) 899–904. [48] D. Philip, Spectrochim. Acta A 73 (2009) 374–381. [49] V.R. Kannan, C.S. Sumathi, V. Balasubramanian, N. Ramesh, Bot. Res. Int. 2 (2009) 253–257. [50] J.G.S. Maia, E.H.A. Andrade, M.G.B. Zoghbi, J. Food Compos. Anal. 13 (2000) 227–232. [51] S. Yusuf, M. Aliyu, R. Ndanusa, J. Med. Plant Res. 3 (2009) 493–497. [52] L. Tedong, T. Dimo, P.D.D. Dzeufiet, A.E. Asongalem, D.S. Sokeng, P. Callard, J.F. Flejou, P. Kamtchouing, Afr. J. Trad. CAM 3 (2006) 23–35. [53] L. Tedong, P.D.D. Dzeufiet, T. Dimo, E.A. Asongalem, S.N. Sokeng, J.F. Flejou, P. Callard, P. Kamtchouing, Afr. J. Trad. CAM 4 (2007) 140–147. [54] D. Inbakandan, R. Venkatesan, S.A. Khan, Colloids Surf. B 81 (2010) 634–639. [55] R. Deshpande, M.D. Bedre, S. Basavaraja, B. Sawle, S.Y. Manjunath, A. Venkataraman, Colloids Surf. B 79 (2010) 235–240. [56] A.N. Mishra, S. Bhadauria, M.S. Gaur, R. Pasricha, B.S. Kushwah, Int. J. Green Nanotechnol. 1 (2010) 118–124. [57] A. Sugunan, J. Dutta, Mater. Res. Soc. Symp. Proc. 901E (2006). [58] D. Philip, Spectrochim. Acta A 71 (2008) 80–85. [59] S.L. Smitha, K.M. Nissamudeen, D. Philip, K.G. Gopchandran, Spectrochim. Acta A 71 (2008) 186–190. [60] K.B. Narayanan, N. Sakthivel, Mater. Lett. 62 (2008) 4588–4590. [61] C.E. Rayford II., G. Schatz, K. Shuford, Nanoscape 2 (2005). [62] E. Filippo, A. Serra, A. Buccolieri, D. Manno, J. Non-Cryst. Solids 356 (2010) 344–350. [63] P. Raveendran, J. Fu, S.L. Wallen, Green Chem. 8 (2006) 34–38. [64] S.L. Smitha, D. Philip, K.G. Gopchandran, Spectrochim. Acta A 74 (2009) 735–739. [65] H. Bar, D.K. Bhui, G.P. Sahoo, P. Sarkar, S.P. De, A. Misra, Colloids Surf. A339 (2009) 134–139. [66] D. Zheng, C. Hu, G. Tian, X. Dang, S. Hu, Sens. Actuators B148 (2010) 247–252. [67] N. Ahmad, S. Sharma, K. Alam, V.N. Singh, S.F. Shamsi, B.R. Mehta, A. Fatma, Colloids Surf. B81 (2010) 81–86. [68] A. Ingle, M. Rai, A. Gade, M. Bawaskar, J. Nanopart. Res. 11 (2009) 2079–2085. [69] M. Dubey, S. Bhadauria, B.S. Kushwah, Digest J. Nanomater. Biostruct. 4 (2009) 537–543. [70] D.A. Ofusori, B.U. Enaibe, A.E. Adelakun, O.A. Adesanya, R.A. Ude, K.A. Oluyemi, C.U. Okwuonu, O.A. Apantaku, Int. J. Altern. Med. 5 (2008) 1540–1584. [71] H. Schulz, M. Baranska, Vib. Spectrosc. 43 (2007) 13–25. [72] L. Castro, M.L. Blazquez, F. Gonzalez, J.A. Munyz, A. Ballester, Chem. Eng. J. 164 (2010) 92–97. [73] A. Bankar, B. Joshi, A.R. Kumar, S. Zinjarde, Colloids Surf. B 80 (2010) 45–50. [74] A.K. Singh, M. Talat, D.P. Singh, O.N. Srivastava, J. Nanopart. Res. 12 (2010) 1667–1675. [75] R.K. Das, B.B. Borthakur, U. Bora, Mater. Lett. 64 (2010) 1445–1447. [76] J. Kasthuri, K. Kathiravan, N. Rajendiran, J. Nanopart. Res. 11 (2009) 1075–1085.