Article pubs.acs.org/IECR
Prunus domestica Fruit Extract-Mediated Synthesis of Gold Nanoparticles and Its Catalytic Activity for 4‑Nitrophenol Reduction Preeti Dauthal and Mausumi Mukhopadhyay* Department of Chemical Engineering, S.V. National Institute of Technology, Surat-395-007, Gujarat, India ABSTRACT: Gold nanoparticles (Au-NPs) were synthesized at room temperature using Prunus domestica (plum) fruit extract as reducing agent. The UV−visible absorption spectrum showed a characteristic optical absorption peak of Au-NPs at 543 nm. The X-ray diffraction pattern suggested the formation and crystallinity of Au-NPs. Spherical Au-NPs synthesized with an average particle size of 20 ± 6 nm were confirmed by transmission electron microscopy. Fourier transform infrared spectroscopy analysis supported the role of water-soluble polyols and amino acids of plum fruit extract for bioreduction and stabilization of Au-NPs. The catalytic activity of Au-NPs was investigated for 4-nitrophenol (4-NP) reduction using UV−visible absorption spectroscopy. Biosynthesized Au-NPs showed a dose-dependent catalytic activity. Catalytic reduction followed pseudo-first-order kinetics with respect to 4-NP. catalytic reduction of 4-nitrophenol (4-NP). 23,24 These polymer-supported Au-NPs possess high catalytic activity. The structure and surface functional groups of supported polymers are influenced by the catalytic behavior of the Au-NPs during the reactions. Despite the high catalytic activity of chemically synthesized nanoparticles, it is difficult to elude contamination caused by unwanted byproduct formation in the reaction medium. Conventional gold nanocatalyst preparation is cumbersome. The use of biologically synthesized Au-NPs for the catalytic conversion of pharmaceutical and medicinally important compounds leads to a final product suitable for various biological applications. Biosynthesized nanoparticles as catalysts are cost-effective and ecofriendly. In the present study, the catalytic activity of colloidal Au-NPs dispersed in Prunus domestica (plum) fruit extract is evaluated for toxic pollutant 4-NP reduction to 4-aminophenol (4-AP). Single-step synthesis of the Au-NPs is presented by reduction of aqueous chloroauric acid (HAuCl4) at room temperature with P. domestica (plum) fruit extracts. The as-synthesized AuNPs are characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), dynamic light scattering (DLS), energy dispersive spectroscopy (EDS), and Fourier transform infrared spectroscopy (FTIR).
1. INTRODUCTION In recent years, the application-based study of noble metal nanoparticles has received great attention around the world. Among the noble metal nanoparticles, gold nanoparticles (AuNPs) are attracting significant consideration among researchers nowadays. The Au-NPs possess special optical and electronic properties, such as unique and tunable surface plasmon resonance (SPR),1 surface-enhanced emission,2 surface-enhanced Raman scattering (SERS),3 and higher Fermi potential.4 For the conventional Au-NPs synthesis, physical and chemical methods are used. High-energy consumption in physical methods and the toxic nonecofriendly nature of the chemical methods are the disadvantages. These methods are unsuitable for the synthesis of ecofriendly and biocompatible Au-NPs. The exploration of natural resources is the most promising ecofriendly alternative for physical and chemical synthesis methods5 of Au-NPs. Thus, biological methods have been explored during recent years for ecofriendly, renewable, and biocompatible Au-NPs synthesis. Research reports are available that are related to the biosynthesis of Au-NPs with biological resources.6 Biological synthesis with living and nonliving organisms (bacteria,7 fungi,8 and viruses9), natural resources (medicinal plants,10 algae,11 and weeds,12), agricultural waste (banana peels13) and spices,14 etc. is reported. The use of agricultural waste like plant extracts for the synthesis of nanoparticles is advantageous over other environmentally benign biological processes because it eliminates the elaborate process of cell cultures maintenance.15 Fruit extracts are the new face in the green synthesis of AuNPs. The biosynthesis of Au-NPs by fruit extracts is currently under exploitation. Fruit extracts such as Emblica off icinalis (amla),16 Tanacetum vulgare (tansy fruit),17 Pyrus communis (pear),18 Citrus sinensis (orange), Prunus persica (peach), Carica papaya (papaya), and Citrus limon (lemon)19 are reported for Au-NPs synthesis. Au-NPs are reported for applications in the area of catalysis.20 Recently supported Au-NPs are extensively explored in the area of catalysis for different oxidation reactions.21,22 Literature is available for polymer-supported Au-NPs for the © 2012 American Chemical Society
2. EXPERIMENTAL SECTION 2.1. Materials. HAuCl4, 4-NP, and sodium borohydride (NaBH4) were procured from HiMedia Pvt. Ltd. (Mumbai, India). Deionized water used for the reaction was prepared by using Elix Millipore water system. Fresh fruits of P. domestica (plum) were purchased from a local market in Almora, Uttarakhand (India). Received: Revised: Accepted: Published: 13014
February 11, 2012 August 31, 2012 September 6, 2012 September 6, 2012 dx.doi.org/10.1021/ie300369g | Ind. Eng. Chem. Res. 2012, 51, 13014−13020
Industrial & Engineering Chemistry Research
Article
2.2. Methods. The fruit extract used for the synthesis was prepared from 50 g of thoroughly washed P. domestica (plum) fruits in a 500 mL Erlenmeyer flask and boiled with 200 mL of double-distilled, deionized water at 60 °C for 10 min. The resultant crude extract was filtered with Whatman filter paper no. 40. The filtered extract was stored at 4 °C for further study. A 400 mL amount of 1 × 10−3 M aqueous solution of HAuCl4 was reduced with 100 mL of P. domestica (plum) fruit extract at room temperature for 0.16 h at pH 6. The effect of interaction time in the SPR of colloidal Au-NPs was evaluated up to 24 h. A long-time interaction study was carried out for the synthesis of Au-NPs up to 48 h. The effect of initial pH (pH 2−10), reaction temperature (15−55 °C), and fruit extract concentration (0.25−2.5 mL) of the reaction mixture in the SPR, size, and stability (ζ-potential, ZP) of colloidal Au-NPs solution was evaluated. The catalytic activity of colloidal Au-NPs dispersed in P. domestica (plum) fruit extract was evaluated at room temperature for 4-NP reduction. To evaluate the catalytic activity of biologically synthesized Au-NPs, 2.0 mL of 4-NP (1 × 10−4 M) was mixed with a freshly prepared aqueous solution of 0.08 mL of NaBH4 (3 × 10−1 M) at room temperature, and 0.05 mL of Au-NPs dispersed in P. domestica (plum) fruit extracts was mixed with the above reaction mixture. Then, a UV−vis absorption spectrum of the total reaction mixture was recorded with time to monitor the change in SPR and absorption intensity of the reaction mixture. The effect of colloidal Au-NPs dosages on the catalytic reduction of 4-NP was also evaluated with 0.05, 0.1, and 0.2 mL of colloidal Au-NPs dispersed in P. domestica (plum) fruit extract. 2.3. Analysis. The biosynthesis and catalytic activity of AuNPs were kinetically monitored in a UV−vis spectrophotometer (DR 5000, HACH, United States). TEM observations were performed on a TEM (CM200, Philips, United Kingdom) operated at an accelerating voltage of 100 kV with resolution 2.4 Å. For TEM analysis, the sample was prepared by placing a drop of the Au-NPs solution over a copper grid and being allowed to stand for 2 min to evaporate the water. The copper grid was allowed to dry prior to measurement. XRD patterns of dried Au-NPs was recorded in an X-ray diffractometer (X'Pert Pro, PANalytical, Holland) operated at a voltage of 45 kV and current of 35 mA with Cu Kα radiation (K = 1.5406 Ǻ ). The scanning range (2θ) was selected from 30 to 80° at a 0.045°/ min continuous speed. The hydrodynamic diameter and ZP of colloidal Au-NPs dispersed in P. domestica (plum) fruit extract were measured using (Malvern, Zetasizer, United Kingdom). The presence of elemental gold was determined by using EDS (INCAX-sight, Oxford, United Kingdom) coupled with scanning electron microscopy (SEM) (JSM-6380LV, JEOL, Japan). The experiment was conducted at an accelerated voltage of 20 kV. FTIR measurements were carried out to identify the possible functional groups of fruit extracts for nanoparticles synthesis and stabilization. FTIR spectra were recorded by using a MAGNA 550 (Nicolet, United States) in a diffuse reflectance mode with a resolution of 2 cm−1.
excitation of SPR. The change in SPR of Au-NPs as a function of the process parameter (reaction time) was as in Figure 1.
Figure 1. (a) UV−vis spectra recorded as a function of time up to 24 h. The inset picture shows the corresponding plot of intensity at λmax vs time showing that maximum reduction takes place within 4 h. (b) Long-term interaction study up to 48 h.
The Au-NPs showed (Figure 1a) a weak SPR band at 543 nm after 0.16 h of reaction. With an increase in the reaction time to 4 h, the absorbance intensity increased steadily, and this indicated continuous reduction of the gold ion as well as an increase in the concentration of Au-NPs. After 4 h, a slight red shift was observed in SPR at 546 nm due to slight modification in the size and shape of nanoparticles. The incubation time beyond 4 h showed a negligible increase in SPR intensity, which means that maximum reduction takes place within 4 h of reaction. This indicated the attainment of saturation in the bioreduction of gold. During this process, bio-organics present in the P. domestica (plum) fruit extract spatially controlled the nucleation and growth of particles and stopped the reduction when the desired size and shape were obtained. The long-term interaction study was carried out by varying the time from 12 to 48 h and to investigate the aging effect and stability of biosynthesized nanoparticles. Figure 1b showed a red shift in SPR from 546 to 552 nm. Broadening in SPR also was observed with a decrease in the absorbance value after 24 h. Au-NPs exhibited SPR vibration in the range of 510−560 nm in an aqueous medium. This red shift in SPR from 546 to 552 nm was due to the slight variation in size and shape of nanoparticles as a shift in SPR depends on the size, shape, and state of aggregation. The broadening in SPR was probably due to the dampening of the SPR caused by the combined effect of an
3. RESULTS AND DISCUSSION 3.1. UV−Visible Spectroscopy and DLS Analysis. The formation of Au-NPs was confirmed by SPR spectra in UV−vis spectroscopy analysis. After the immediate addition of the aqueous P. domestica (plum) fruit extracts to 1 × 10−3 M HAuCl4 solution (pH 6), the initial light yellow color of the reaction mixture changed to a pink−purple color, due to the 13015
dx.doi.org/10.1021/ie300369g | Ind. Eng. Chem. Res. 2012, 51, 13014−13020
Industrial & Engineering Chemistry Research
Article
confirmed less homogeneity in particles size distribution in the colloidal solution. Figure 2b showed that the corresponding average ZP value of −25.7 mV (pH 6) suggested stability of colloidal Au-NPs. The size, SPR, and stability of biosynthesized Au-NPs were evaluated at different pH values (pH 2−10) of the reaction mixtures. It was observed that synthesized Au-NPs were stable at a wide range of pH values (pH 2−10) with ZP values varied from −20.9 to −28.5 mV (Figure 3a) along with a slight blue shift observed in SPR at alkaline pH (Figure 3b). This blue shift along with a higher negative ZP at alkaline pH was associated with a size reduction in the range of 128 (pH 2) to 36 nm (pH 10). This indicated that a higher negative charge dominated on the surface of Au-NPs at alkaline pH. Because of higher negative charges on the Au-NPs surface, particles aggregation was prevented by maximum repulsive electrostatic and electrosteric interactions, which enhanced the stability of particles in colloidal solution and lead to blue shifts in SPR spectra and size reduction. High negative ZP values at different pH values indicated the stability of Au-NPs in a wide range of pH values. The SPR peak sharpness and intensity increased at higher temperature (Figure 3c). This was due to the increase in reaction rate for the conversion of the metal ion to nanoparticles at a higher temperature. The temperature varied from 15 to 55 °C. A slight blue shift in SPR spectra along with a size reduction was observed with a higher reaction temperature. The effect of fruit extract concentration on the SPR and size of Au-NPs was evaluated using 0.25−2.5 mL of extract concentration (Figure 3d). A different color was observed from pink, ruby red to violet with different extract concentrations. These colors were characteristic of the SPR of different sizes of Au-NPs. With an increase in fruit extract from 0.25 to 1.5 mL, a consistent increase was observed in SPR intensity, accompanied with a slight blue shift in λmax. On the
increase in particle size and shape of the Au-NPs in colloidal solution. Figure 2a revealed the Z-average diameter of the synthesized Au-NPs (pH 6) as 71 nm with a polydispersity index (PDI) of
Figure 2. (a) DLS pattern and (b) corresponding ZP distribution of biosynthesized Au-NPs at pH 6.
0.184. The Z-average diameter was higher as compared to the average crystallite size in TEM (Figure 4, 20 ± 6 nm) and XRD (Figure 5, 26 nm) analysis because of DLS measurements based on the hydrodynamic radius of the particles. The observed PDI
Figure 3. (a) Effect of pH on ZP, (b) effect of pH on SPR, (c) effect of reaction temperature on SPR, and (d) effect of fruit extract concentration on SPR of collodial Au-NPs. 13016
dx.doi.org/10.1021/ie300369g | Ind. Eng. Chem. Res. 2012, 51, 13014−13020
Industrial & Engineering Chemistry Research
Article
shape particles. Clear bright circular rings in the selected area electron diffraction (SAED) pattern in the inset correspond to (111), (200), (220), and (311) planes of the fcc lattice of gold. This confirmed the crystalline structure of synthesized nanoparticles. 3.3. Powder XRD. Figure 5 showed the XRD pattern of dried Au-NPs. The intense diffraction peaks were observed at
other hand, upon addition of higher amounts of the extract (2− 2.5 mL), the red shift was observed in λmax. This indicated that a high concentration of reducing moieties initiated more interaction between the surface-capping molecules and ultimately leads to a secondary reduction process on the surfaces of existing nuclei. Thus, the particle size increased at a higher extract concentration. Furthermore, the hydrodynamic size obtained from DLS spectra of Au-NPs also showed a consistent increase in Au-NPs size at higher fruit extract concentrations. 3.2. TEM Study. The size and shape of the synthesized AuNPs (pH 6) was confirmed by TEM analysis. Figure 4a showed
Figure 5. XRD pattern of dried Au-NPs.
2θ values of 38.55°, 44.90°, 65.07°, and 77.86°, which were indexed to the (111), (200), (220), and (311) reflections of crystalline metallic gold, respectively (JCPDS no. 04-0784). The lattice constant calculated from this pattern was 4.06 Å and confirmed the fcc structure of Au-NPs. The ratio between the (200) and the (111) diffraction peaks intensity was calculated to be 0.28 for Au-NPs. This peak intensity ratio was lower compared to the conventional bulk intensity ratio (0.52). Thus, the (111) plane was in the predominant orientation. The absence of any other crystallographic impurities and peak broadening in XRD spectrum was confirmed by the high purity of nanocrystalline Au-NPs. The average crystallite size calculated by the Scherrer equation, using the line width of the (111) diffraction peak, was obtained as 26 nm. This was in line with the particles size obtained from the TEM analysis. 3.4. EDS Study. The appearance of an optical absorption peak approximately at 2.20 keV was due to SPR of gold nanocrystallites (Figure 6). This confirmed the presence of gold
Figure 4. (a) TEM images of biosynthesized Au-NPs at the 100 nm scale (pH 6, room temperature). The inset picture shows the corresponding SAED pattern. (b) Particle size distribution histogram.
Figure 6. EDS spectra of biosynthesized Au-NPs.
that spherical Au-NPs were synthesized along with few triangular and irregular shape particles. Figure 4b showed the size distribution histogram of the nanoparticles. This histogram was prepared by manual analysis of 256 particles. The particle sizes distributed in the range of 4−38 nm, with an average particle size of 20 ± 6 nm synthesized. This large variation in size was due to the presence of a few triangular and irregular
nanoclusters. EDS spectra of Au-NPs also showed strong signals of gold metal at around 9.6 and 11.40 keV and a weak signal at 8.4 and 10.3 keV. The presence of oxygen in EDS spectra indicated the adsorption of extracellular organic moieties on the surface of the metallic nanoparticles. The appearance of Al was due to the use of an aluminum grid in EDS analysis. The Cl signals in EDS spectra indicated the 13017
dx.doi.org/10.1021/ie300369g | Ind. Eng. Chem. Res. 2012, 51, 13014−13020
Industrial & Engineering Chemistry Research
Article
Figure 7. FTIR spectra of (a) aqueous P. domestica (plum) fruit extract before bioreduction, (b) after bioreduction of HAuCl4, (c) dried Au-NPs, and (d) mechanism for the formation of Au-NPs.
decreases in the intensity at 3450 cm−1 and complete absence of 2066 cm−1 stretching. This signified the involvement of the polyols (like flavanols, phenols, and prunasin glycosides) of plum fruits in the bioreduction process. The appearance of a new peak at 1723 cm−1 in Figure 7b and 1704 cm−1 in Figure 7c indicated that the hydroxyl groups in polyols oxidized to carboxylate groups during the reduction of Au3+ to Au0. The peak at 1638 cm−1 in Figure 7a was shifted to 1620 cm−1 in Figure 7b and to 1640 cm−1 in Figure 7c and revealed the binding of a (NH)CO group with Au-NPs. Figure 7b,c also showed a slight shift and increased band intensity for 1018 and 691 cm−1 stretching as compared to Figure 7a and suggested that synthesized Au-NPs were stabilized by negatively charged amino acids molecules. The bioreduction reaction in the present study was in aqueous medium. Terpenoids were poorly water-soluble, so not the prime moieties involved in the bioreduction process. It was inferred that some of the bio-organics of fruit extract such as proteins of different enzymes bind through free amino groups
presence of a small amount of AuCl4− ions in the investigated region. 3.5. FTIR Spectroscopy. FTIR analysis was carried out to identify the functional group of P. domestica (plum) fruit extract used for Au-NPs synthesis. Figures 7a−c represented the FTIR spectra of aqueous P. domestica (plum) fruit extract before bioreduction and after bioreduction of HAuCl4 and dried AuNPs, respectively. The FTIR spectra of fruit extract showed the absorbance bands centered as follows: at 3450 cm−1, O−H stretching vibrations of polyols; 2891 cm−1, C−H stretching vibrations of aldehydes; 2066 cm−1, CN stretching of nitriles groups of glycosides; 1638 cm−1, stretching vibration of (NH)CO group; 1018 cm−1, C−N stretching of amines; and 691 cm−1, N−H wag of amines, respectively. The presence of secondary metabolites like flavanols, terpenoids, phenols, glycosides, and amino acids was reported in P. domestica fruit extract.25,26 Figure 7 showed variations in transmittance and band intensity due to the reduction of Au3+ ions to Au0. Figure 7b,c showed slight shifts along with 13018
dx.doi.org/10.1021/ie300369g | Ind. Eng. Chem. Res. 2012, 51, 13014−13020
Industrial & Engineering Chemistry Research
Article
analysis. These results indicated the catalytic activity of biosynthesized Au-NPs dispersed in P. domestica (plum) fruit extract for 4-NP reduction. A small peak at 543 nm indicated that there was no significant change observed in SPR of Au-NPs during the catalytic reduction of 4-NP. This observation suggested no agglomeration and stability of Au-NPs during the catalytic reaction even in the presence of a higher concentration of reducing agent NaBH4. This observation inferred that the catalytic activity of Au-NPs was a surface reaction phenomenon. A slight decrease in the absorbance intensity of Au-NPs was observed due to dilution of Au-NPs with reaction mixtures. The apparent rate constant (kapp, s−1) in these catalytic reductions (with 0.05, 0.1, and 0.2 mL of colloidal Au-NPs for 4-NP reduction) was calculated using the pseudo-first-order kinetics equation with respect to 4-NP concentration using the following equation:
to the Au atoms and are responsible for the synthesis and stabilization of nanoparticles. These amino groups acted as surface-coating molecules and prevented agglomeration of the nanoparticles. The change in the SPR spectra suggested that the water-soluble polyols were responsible for the reduction of Au3+ ions. Negatively charged carboxylate ions and amino acids molecules stabilized the synthesized Au-NPs. A schematic representation of the proposed mechanism is presented in Figure 7d. 3.6. Catalytic Reduction of 4-NP. The catalytic activity of Au-NPs dispersed in P. domestica (plum) fruit extract was evaluated for the reduction of toxic pollutant 4-NP in presence of excess NaBH4. Figure 8a showed the UV−vis spectra of
⎛A ⎞ ln⎜ t ⎟ = −kappt ⎝ A0 ⎠
(1)
where At = the absorbance of 4-NP at time t and A0 = the absorbance of 4-NP at time 0. The rate of reduction was independent of NaBH4 concentration, as the initial concentration of NaBH4 was high as compared to 4-NP. The pseudo-first-order rate constant (kapp) was calculated from the slop of plot of ln (At/A0) versus time as 1.9 × 10−3, 4.4 × 10−3, and 5.1 × 10−3 s−1 for 0.05, 0.1, and 0.2 mL of colloidal Au-NPs, respectively. It was observed that with an increase in colloidal Au-NPs dosage, the catalytic activity for 4NP increased. This increase in the rate constant value was due to the accessibility of more interaction sites of Au-NPs, which ultimately increased the reduction rate of 4-NP conversion.
4. CONCLUSIONS This study highlights the catalytic activity of biosynthesized AuNPs by using P. domestica (plum) fruit extract. Biosynthesized Au-NPs are nearly spherical in shape and crystalline structure with particle sizes of 4−38 nm (TEM). The observed DLS and Z-average diameters of colloidal Au-NPs are slightly higher, 71 nm (pH 6). This study demonstrates that the initial pH of the reaction mixtures affects the stability, SPR, size, and ZP of colloidal Au-NPs. FTIR analysis suggests that the water-soluble polyols like flavanols, phenols, and glycosides are responsible for the reduction of Au3+ ions. Au-NPs dispersed in P. domestica (plum) fruit extract show dose-dependent catalytic activity for 4-NP reduction.
Figure 8. (a) UV−vis absorption spectra of 4-NP before and after immediate addition of NaBH4. (b) Time-dependent UV−vis absorption spectra for the reduction of 4-NP over 0.05 mL of colloidal Au-NPs dispersed in P. domestica (plum) fruit extract.
aqueous solution of 4-NP with absorption maxima at 317 nm. A red shift was observed with absorption maxima at 400 nm immediately after the addition of NaBH4. This was due to the formation of 4-nitrophenolate ions. It also observed that the absorption peak of 4-nitrophenolate ions remains constant for 2 days, in the absence of catalyst. This observation revealed that no reduction of 4-NP occurred without catalyst. However, after the addition of colloidal Au-NPs dispersed in P. domestica (plum) fruit extract in 4-nitrophenolate ion, successive fading of the characteristic yellow color of the 4-nitrophenolate ions was observed. Figure 8b showed the decrease in absorbance for the 400 nm peak along with a gradual generation of a new peak at 300 nm. This new peak was characteristic of 4-AP. Blank analysis was carried out with P. domestica (plum) fruit extract without nanoparticles under the same experimental condition. There was no sign of 4-AP observed in the UV−vis spectra in blank
■
AUTHOR INFORMATION
Corresponding Author
*Tel: +91 261 2201645. Fax: +91 261 2227334, 2201641. Email:
[email protected] or mausumi_mukhopadhyay@ yahoo.com. Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS
We are thankful to the Sophisticated Analytical Instrument Facility (SAIF), IIT Bombay, and Electrical Research and Development Association (ERDA) Vadodara for providing the research facility for characterizations of samples. 13019
dx.doi.org/10.1021/ie300369g | Ind. Eng. Chem. Res. 2012, 51, 13014−13020
Industrial & Engineering Chemistry Research
■
Article
(19) Tai, Y.; Tran, N. T. T.; Tsai, Y. C.; Fang, J. Y.; Chang, L. W. One-step synthesis of highly biocompatible multi-shaped gold nanostructures with fruit extract. IET Nanobiotechnol. 2011, 5, 52−59. (20) Zanella, R.; Giorgio, S.; Henry, C. R.; Louis, C. Alternative methods for the preparation of gold nanoparticles supported on TiO2. J. Phys. Chem. B 2002, 106, 7634−7642. (21) Hsin-Yu, L.; Yu-Wen, C. Low temperature CO oxidation on Au/FexOy catalysts. Ind. Eng. Chem. Res. 2005, 44, 4569−4576. (22) Tsunoyama, H.; Sakurai, H.; Tsukuda, T. Size effect on the catalysis of gold clusters dispersed in water for aerobic oxidation of alcohol. Chem. Phys. Lett. 2006, 429, 528−532. (23) Panigrahi, S.; Basu, S.; Praharaj, S.; Pande, S.; Jana, S.; Pal, A.; Ghosh, S. K.; Pal, T. Synthesis and size selective catalysis by supported gold nanoparticles: A study on heterogeneous and homogeneous catalytic process. J. Phys. Chem. C 2007, 111, 4596−4605. (24) Kuroda, K.; Ishidaa, T.; Harutaa, M. Reduction of 4-nitrophenol to 4-aminophenol over Au nanoparticles deposited on PMMA. J. Mol. Catal. A: Chem. 2009, 298, 7−11. (25) Pino, J. A.; Quijano, C. E. Study of the volatile compounds from plum (Prunus domestica L. cv. Horvin) and estimation of their contribution to the fruit aroma. Food Sci. Technol. 2012, 32, 76−83. (26) Gorsel, H. V.; Li, C.; Kerbel, E. L.; Smits, M.; Kader, A. A. Compositional characterization of prune juice. J. Agric. Food Chem. 1992, 40, 784−789.
REFERENCES
(1) El-Sayed, M. A. Some interesting properties of metals confined in time and nanometer space of different shapes. Acc. Chem. Res. 2001, 34, 257−264. (2) Frederix, F.; Friedt, J. M.; Choi, K. H.; Laureyn, W.; Campitelli, A.; Mondelaers, D.; Maes, G.; Borghs, G. Biosensing based on light absorption of nanoscaled gold and silver particles. Anal. Chem. 2003, 75, 6894−6900. (3) Huang, X.; Jain, P. K.; El-Sayed, I. H. Special focus: Nanoparticles for cancer diagnosis and therapeuticsReview. Nanomedicine 2007, 2, 681−693. (4) Pradhan, N.; Pal, A.; Pal, T. Catalytic reduction of aromatic nitro compounds by coinage metal nanoparticles. Langmuir 2001, 17, 1800−1802. (5) Shankar, S. S.; Rai, A.; Ahmad, A.; Sastry, M. J. Rapid synthesis of Au, Ag, and bimetallic Au core-ag shell nanoparticles using neem (Azadirachta indica) leaf broth. Colloid Interface Sci. 2004, 275, 496− 502. (6) Durán, N.; Marcato, P. D.; Durán, M.; Yadav, A.; Gade, A.; Rai, M. Mechanistic aspects in the biogenic synthesis of extracellular metal nanoparticles by peptides, bacteria, fungi, and plants. Appl. Microbiol. Biotechnol. 2011, 90, 1609−1624. (7) Mandal, D.; Bolander, M. E.; Mukhopadhyay, D.; Sarkar, G.; Mukherjee, P. The use of microorganisms for the formation of metal nanoparticles and their application. Appl. Microbiol. Biotechnol. 2006, 69, 485−492. (8) Chauhan, A.; Zubair, S.; Tufail, S.; Sherwani, A.; Sajid, M.; Raman, S. C.; Azam, A.; Owais, M. New Fungus-mediated biological synthesis of gold nanoparticles: potential in detection of liver cancer. Int. J. Nanomed. 2011, 6, 2305−2319. (9) Slocik, J. M.; Naik, R. R.; Stone, M. O.; Wright, D. W. Viral templates for gold nanoparticle synthesis. J. Mater. Chem. 2005, 15, 749−753. (10) Raghunandan, D.; Basavaraja, S.; Mahesh, B.; Balaji, S.; Manjunath, S. Y.; Venkataraman, A. Biosynthesis of stable polyshaped gold nanoparticles from microwave-exposed aqueous extracellular antimalignant guava (Psidium guajava) leaf extract. Nanobiotechnology 2009, 5, 34−41. (11) Singaravelu, G.; Arockiamary, J. S.; Kumar, V. G.; Govindaraju, K. A. Novel extracellular synthesis of monodisperse gold nanoparticles using marine alga, Sargassum wightii Greville. Colloids Surf., B 2007, 57, 97−101. (12) Parashar, V.; Parashara, R.; Sharma, B.; Pandey, A. C. Parthenium leaf extract mediated synthesis of silver nanoparticle: A novel approach towards weed utilization. Dig. J. Nanomater. Biostruct. 2009, 4, 45−50. (13) Bankar, A.; Joshi, B.; Kumar, A. R.; Zinjarde, S. Banana peel extract mediated synthesis of gold nanoparticles. Colloid Surf., B 2010, 80, 45−50. (14) Singh, A. K.; Talat, M.; Singh, D. P.; Srivastava, O. N. Biosynthesis of gold and silver nanoparticle by natural precursor clove and their functionalization with amine group. J. Nanopart. Res. 2010, 12, 1667−1675. (15) Shankar, S. S.; Ahmad, A.; Pasricha, R.; Sastry, M. Bioreduction of chloroaurate ions by geranium leaves and its endophytic fungus yields gold nanoparticles of different shapes. J. Mater. Chem. 2003, 13, 1822−1826. (16) Ankamwar, B.; Damle, C.; Ahmad, A.; Sastry, M. Biosynthesis of gold and silver nanoparticles using Emblica of f icinalis fruit extract, their phase transfer and transmetallation in an organic solution. J. Nanosci. Nanotechnol. 2005, 5, 1665−1671. (17) Dubey, S. P.; Lahtinen, M.; Sillanpäa,̈ M. Tansy fruit mediated greener synthesis of silver and gold nanoparticles. Process Biochem. 2010, 45, 1065−1071. (18) Ghodake, G. S.; Deshpande, N. G.; Lee, Y. P.; Jin, E. S. Pear fruit extract assisted room-temperature biosynthesis of gold nanoplates. Colloid Surf., B 2010, 75, 584−589. 13020
dx.doi.org/10.1021/ie300369g | Ind. Eng. Chem. Res. 2012, 51, 13014−13020
