Biomediated Silver Nanoparticles for the Highly Selective Copper(II

In situ green synthesis of Ag nanoparticles on herbal tea extract ( Stachys lavandulifolia )-modified magnetic iron oxide nanoparticles as ... Journal...
9 downloads 0 Views 2MB Size
Download PDF
Article pubs.acs.org/IECR

Biomediated Silver Nanoparticles for the Highly Selective Copper(II) Ion Sensor Applications C. Joseph Kirubaharan,† D. Kalpana,‡ Yang Soo Lee,‡ A. R. Kim,§ Don Jin Yoo,§ Kee Suk Nahm,*,§ and G. Gnana Kumar*,† †

Department of Physical Chemistry, Madurai Kamaraj University, Madurai-625 021, Tamilnadu, India Department of Forest Science and Technology, Institute of Agricultural Science and Technology, Chonbuk National University, Jeonju 561-756, South Korea § Department of Hydrogen and Fuel Cells Engineering, Specialized Graduate School, Chonbuk National University, Jeonju 561-756, South Korea ‡

S Supporting Information *

ABSTRACT: Nanoparticles synthesis is an evergreen research field of 21st century in which the connotation of the biomediated experimental process is highly imperative. Biomediated silver nanoparticles were synthesized with the aid of an eco-friendly biomaterial, namely, aqueous Azadirachta indica extract. The effect of pH and temperature on the formation of silver nanoparticles was analyzed. Formation of the silver nanoparticles was verified by surface plasmon spectra using a UV−vis spectrophotometer. Morphology and crystalline structure of the prepared silver nanoparticles were characterized by TEM and XRD techniques, respectively. Furthermore, the biomediated silver nanoparticles without any surface modification were used for the heavy metal ion sensors in aqueous media. The prepared silver nanoparticles were successful in detecting even the minimal amount of heavy metal copper(II) ion and exhibited excellent specific metal ion selectivity. corrosion of copper pipes.9 An increase in the Cu2+ level in the biological cells leads to kidney related and neurodegenerative diseases,10 and the free Cu2+ elicits toxicity to cells as they generate hydroxyl radicals, causing apoptosis.10 Cu2+ binds with the histidine-rich regions of the Prion Protein, which results in misfolding and protein fibrilization.11 Therefore, on-site and real-time detection of Cu2+ ions is important to avoid its toxic effects. For the successive detection of heavy metal copper ions, copper(II) sensitive optical sensors have been reported using immobilized Lucifer Yellow fluorophore,12 copper chelators such as Zincon,13 fast sulphon black F (FSBF),14 urease enzyme,15 and PAN and PAR indicators.16 However, the mentioned reports exhibited major limitations such as complex preparation, expensive, high time consumption, and sample pretreatment and analyte preconcentration steps which limit the sensor applications at a large scale. It urges the identification and development of a copper sensor to satisfy the simple, rapid, inexpensive, selective, and sensitive characteristics. Nanoparticles find extensive application in bio- and ecosensors, especially for the detection of heavy metal ions. Though few nanoparticles have been reported for heavy metal ion sensors, all of the nanoparticles have been synthesized via chemical routes and are to be stabilized with the aid of external chemical stabilizers in which most of them were toxic.17 An objective of the sensors is to detect pollutants in the effluents,

1. INTRODUCTION Nanoscience is one of the most vibrant growing fields ever known and continues to rigorously reach its branches into various modern technologies such as hydrogen storage, photocatalysis, green energy devices, sensors, biomedical implants, and photovoltaics.1−4 Though chemical synthesis has been widely adopted for the preparation of a variety of nanostructures, their cost effectiveness, need of sophisticated equipments, environments, stabilizing and capping agents, and environmental hitches fade not only the applications of nanoparticles but also the dream of a green world.5 For the emphasis of biological protocol applications of nanoparticles, there is also an immense need for synthesizing nanoparticles with a greater biocompatibility.6 Hence, there is an alarming demand for finding cheaper and environmentally friendly nanoparticles synthesis. In recent years, biomediated synthesis has been considered as an enthralling method for the synthesis of nanoparticles by bridging the two major criteria, satisfying the green chemistry principles and stabilizing the formed nanoparticles with not much more than the bioextract itself.5 The state of the art biomediated nanoparticles synthesis satisfies all of the necessary requirements, especially the mentionable dual nature of the biomass as a reducing as well as a stabilizing agent.7 The detection and quantification of heavy metal ions is a rapid subject of enrollment in recent days which influences their significant applications in environmental monitoring, waste management, and clinical toxicology fields.8 Specifically, the detection of heavy metal copper is vital due to the existence of copper(II) ions in wastewater originated from the electroplating plants and other metal manufacturing industries and © 2012 American Chemical Society

Received: Revised: Accepted: Published: 7441

February 6, 2012 May 7, 2012 May 8, 2012 May 17, 2012 dx.doi.org/10.1021/ie3003232 | Ind. Eng. Chem. Res. 2012, 51, 7441−7446

Industrial & Engineering Chemistry Research

Article

adsorbed silver nanoparticles was calculated by the equation F/ F0, where F0 is the fluorescence intensity of Rh6G adsorbed silver nanoparticles and F is the fluorescence intensity of different metal-ion-incorporated Rh6G adsorbed silver nanoparticles. 2.4. Characterizations. Primary confirmations for the formation of silver nanoparticles and their heavy metal ion sensing properties were performed by using an Agilent 8453 diode array UV visible spectrophotometer in the range from 300 to 550 nm. The reduction of Ag+ ions was monitored from the spectra of the solutions, obtained by diluting it with deionized water, using the same as a blank. The shape and size of the formed nanoparticles were analyzed from the conventional TEM micrographs recorded on JEOL JEM-2010 transmission electron microscope. The crystallinity and crystal phases of the prepared nanoparticles was determined by a Rigaku X-ray powder diffractometer (XRD) with Cu Kα radiation (l = 1.54178 Å) with Bragg angle ranging from 30 to 80°. The sensing ability was monitored exclusively by Fluoromax -4 Spectrofluorometer (HORIBA JOBIN YVON) with the excitation slit set at 2.0 nm bandpass and emission at 4.0 nm bandpass in a 1 cm × 1 cm quartz cell.

but what if the sensors themselves are toxic in nature? Due to the inevitable needs in the current perspectives for sensing the metal ions in the biological systems, the need of bio- and ecocompatible systems led to the aspiring initiative for emphasizing these biomass mediated and stabilized silver nanoparticles. Surface plasmon resonance involved colorimetric sensors require highly uniform size- and shape-controlled nanoparticles. To prevent the agglomeration and control of the size of silver nanoparticles without the addition of stabilizing and capping agents, an eco-friendly biomediated route utilizing the Azadirachta indica extract has been proposed. This functional and aesthetic work is the first of its kind ever known in incorporating the biomediated nanoparticles for the heavy metal sensor applications.

2. EXPERIMENTAL SECTION 2.1. Materials. Azadirachta indica leaves were obtained from local premises. Silver nitrate (AgNO3) (99.99%), Rhodamine 6G (Rh6G), copper(II) chloride (99.99%), potassium chloride (99%), magnesium(II) chloride (98%), manganese(II) chloride (99.99%), sodium chloride (99.5%), ferric(III) chloride (97%), zinc acetate (99.99%), nickel(II) chloride (99.99%), cobalt(II) chloride (98%), and barium(II) chloride (99.99%) were acquired from Aldrich and used without any further purification. 2.2. Preparation of Silver Nanoparticles. Azadirachta indica leaves were washed and finely cut into small pieces. A total of 20 wt % of leaf extract was prepared by boiling the weighed Azadirachta indica leaves in deionized water at 80 °C for 10 min. The extract was filtered by using a Whatman filter paper no. 1, and the filtrate was refrigerated at 4 °C for 24 h. A total of 1.25 mL of 20 wt % Azadirachta indica leaf extract was gradually added to the 50 mL of 1 mM aqueous AgNO3 solution, and the mixture was magnetically stirred for 90 min at room temperature. The effect of temperature on the synthesis of silver nanopaticles was studied by carrying out the reaction at 75 °C. The silver nanoparticles prepared at room temperature exhibited pH in the range of 6. To study the effect of pH on formation of silver nanoparticles, the pH of the silver nanoparticles prepared at room temperature was varied from 6 to 8 by the addition of sodium hydroxide. 2.3. Sensor Studies. The colloidal silver nanoparticles solution was centrifuged at 10000 rpm for 1 h, and the obtained sediment was resuspended in deionized water. The centrifugation process was repeated two times to remove any adsorbed substances, and the obtained sediment was dried overnight. A total of 1 mL of Rh6G dye (1 × 10−6 mol·L−1) was gradually added to 1 mL of biomediated silver nanoparticles (1 × 10−6 mol·L−1) and magnetically stirred for 30 min. Sensor studies were performed only with silver nanoparticles prepared at room temperature. And to this, 1 mL of the test solution containing the metallic ions such as copper(II) chloride/potassium chloride/magnesium(II) chloride/manganese(II) chloride/sodium chloride/ferric (III) chloride/zinc acetate/nickel(II) chloride/cobalt(II) chloride/barium(II) chloride of 1.0 × 10−6 mol·L−1 was added and stirred for 30 min. To investigate the sensitivity effect of the biomediated silver nanoparticles toward Cu2+ metal ion, cupric ions with the concentrations of 10−6/10−7/10−8/10−9/10−10/10−11/10−12/10−13 mol·L−1 was added to the silver nanoparticles−Rh6G solution. The sensing ability and selectivity of the prepared silver nanoparticles were studied by using UV/visual and fluorescence spectroscopies. The effect of different metal ions on the fluorescence of Rh6G

3. RESULTS AND DISCUSSIONS 3.1. Absorption Studies. The formation of silver nanoparticles was confirmed by the change in color, that is, light yellow to brown, of the reaction mixture as a straightforward approach, once the extract has been added to it. This needs further a heavy confrontation for the complete reduction of metallic solutions where UV/visual absorption spectroscopy plays a vital role and UV absorption measurements were performed in the visible regions. The color exhibited by the samples is due to the excitation of d electrons of the transition metals which affects the absorbance in the ultraviolet region. The formed nanoparticles exhibited brown coloration whose absorption measurements revealed that a sharper surface plasmon resonance (SPR) band was observed at 400 nm (Figure 1a), the characteristic wavelength representing the formation of silver nanoparticles.18 The SPR band arises due to the absorbance change of the nanoparticles, which were reduced from their corresponding metallic solutions. A sharper

Figure 1. UV−vis spectra of Azadirachta indica extract mediated silver nanoparticles prepared at (a) room temperature, (b) 75 °C, and (c) pH = 8. 7442

dx.doi.org/10.1021/ie3003232 | Ind. Eng. Chem. Res. 2012, 51, 7441−7446

Industrial & Engineering Chemistry Research

Article

Figure 2. TEM images of Azadirachta indica extract mediated silver nanoparticles prepared at (a) room temperature, (b) pH = 8, and (c) 75 °C.

SPR band observed for the Azadirachta indica extract mediated silver nanoparticles prepared at room temperature indicates the formation of monodispersed spherical particles. However, a broad band was observed for the biomediated silver nanoparticles prepared at pH 8 (Figure 1c), and the band was little sharpened for the nanoparticles prepared at 75 °C (Figure 1b). A broad band observed for the prepared nanoparticles indicates the formation of polydispersed silver nanoparticles. The prepared silver nanoparticles are stable for at least four months under room temperature and are confirmed from the morphological image of four months aged silver nanoparticles (Supporting Information). 3.2. Morphological Characterizations. The unique morphology and size distribution of the prepared nanoparticles were elucidated from the transmission electron micrographs. Figure 2 exhibits morphological images of the prepared silver nanoparticles. The uniform size with an average diameter of 15−20 nm along with the monodispersion were obtained for the Azadirachta indica extract mediated silver nanoparticles prepared at room temperature as shown in Figure 2a. However, the incorporation of sodium hydroxide distorted the size uniformity and resulted in the polydispersed nanoparticles (Figure 2b). Though a decrement in the particle size has been observed for the nanoparticles prepared at 75 °C (Figure 2c) due to the reduction in aggregation of the growing nanoparticles at high temperatures, their uniformity in size is inferior to the nanoparticles prepared at room temperature. The HR-TEM image of a region of the biomediated spherical nanoparticle pointed out in Figure 3 exhibited internal high-

diffraction pattern (SAED) of the formed silver nanoparticles which elucidates that the growth of silver nanoparticles occurs preferentially on the (111) plane. Thus, the diffraction pattern elucidates the crystalline nature of the prepared particles and could be indexed for the fcc structure. Though certain literature has reported the similar route for the biomediated silver nanoparticles preparation,19,20 the obtained morphological images in the current report with the perspective of size, shape, and lattice fringes arrangements are far superior to that of the reported research works. Minimal reducing agents, that is, extract volume and minimal time availed for the reaction, yielded homogeneously shaped, sized, and monodispersed nanoparticles (Figure 2) by avoiding the agglomeration of nanoparticles. The effective stirring given via magnetic stirrer adds value to the aforementioned issues along with the high crystallinity of the prepared nanoparticles. 3.3. Diffraction Studies. The crystalline character of the prepared silver nanoparticles was further supported from X-ray diffraction (XRD) analysis. Figure 4 exhibits the XRD pattern

Figure 4. XRD spectrum of Azadirachta indica extract mediated silver nanoparticles prepared at room temperature. Figure 3. (a) Highly magnified TEM image of biomediated silver nanoparticles prepared at room temperature and corresponding (b) FFT (inset of b) typical SAED patterns.

of the dried silver nanoparticles obtained from the prepared colloidal solution. Four index peaks were observed at 37.4, 43.5, 63.9, and 76.8° and can be assigned to (111), (200), (220), and (311) reflections, respectively. It confirms the pure crystalline nature and fcc structure of the synthesized nanometric silver particles.22 The obtained peaks are well matched with the metallic silver.23 The crystallite size of the prepared nanoparticles calculated from the full width at half-maximum of the (111) peak of silver by using Scherrer’s equation is 18 nm and is well matched with the obtained morphological images of the

ordered lattice fringes (Figure 3a,b) with the lattice spacing of 0.23 nm, corresponding to the d-spacing of the crystal plane of the face centered crystalline (fcc) silver nanoparticles. The interplanar distance of the nanosilver (111) plane is in good agreement with the (111) d-spacing of bulk Ag (0.2359 nm).21 The inset of Figure 3b exhibits the selected area electron 7443

dx.doi.org/10.1021/ie3003232 | Ind. Eng. Chem. Res. 2012, 51, 7441−7446

Industrial & Engineering Chemistry Research

Article

prepared nanoparticles. In addition to the characteristic peaks of nanosilver, certain additional peaks were identified which correspond to the crystalline materials present in the Azadirachta indica extract. Thus, the XRD spectrum firmly elucidates the formation of crystalline silver nanoparticles and supports the obtained UV−vis spectrum and morphological images. 3.4. Detection of Heavy Metal Ions. Based on the unique morphological properties such as uniformity in size and homogeneous distribution, the biomediated nanoparticles prepared at room temperature have been chosen for the sensor studies. The sensing mechanism of silver nanoparticles toward Cu2+ ions is proposed in Figure 5. In this study, silver

Figure 6. UV−vis absorbance spectra of (a) Ag nanoparticles, (b) Rh6G adsorbed Ag nanoparticles, and (c) Rh6G adsorbed Ag nanoparticles upon the addition of Cu2+ ions.

strong fluorescent emission peak as shown in Figure 7. Rh6G exhibited maximum fluorescence intensity in its free state Figure 5. Sensing mechanism of silver nanoparticles toward Cu2+ ions.

nanoparticles−Rh6G act as probe for the detection of Cu2+ ions. The involved heavy metal sensation mechanism occurs via two steps, the first step involving the fixation of Rh6G dye molecules over the surface of biomediated silver nanoparticles. The second step is the replacement of dye moiety by the metallic ions, and the released dye moiety acts as a visual colorimetric sensor for the easier detection of Cu2+ ions. Rh6G dye exhibits purple color in its free state. When it is noncovalently attached with the biomediated silver nanoparticles, it loses its purple color, and the original color of the silver nanoparticles in solution was retained. The addition of copper(II) chloride provides Cu2+ ions, and the Cu2+ ions started to adhere on the surface of silver nanoparticles by replacing Rh6G dye and are confirmed from the purple color of the solution. Figure 6 exhibits absorption studies of bare silver nanoparticles, Rh6G dye adsorbed silver nanoparticles, and copper ions adsorbed silver nanoparticles. Bare silver nanoparticles exhibited single absorption SPR band at 400 (Figure 6a), whereas, Rh6G dye adsorbed silver nanoparticles and copper ions adsorbed (including free Cu2+ ions) silver nanoparticles exhibited double absorption values and are attributed to the silver nanoparticles and Rh6G. The intensity of the SPR band decreases for the Rh6G dye adsorbed silver nanoparticles and further decreases for the copper ion adsorbed silver nanoparticles compared to that of the bare silver nanoparticles. The exposed silver nanoparticles surface effectively combined with Rh6G or copper ions and resulted in the high amalgamation for the complex formation. It further proves the decrement in the concentration of bare silver nanoparticles. The sensor studies were further evaluated by using a fluorescence spectrometer, and Rh6G fluorophore exhibited a

Figure 7. Fluorescence spectra of (a) Rh6G, (b) Rh6G adsorbed Ag nanoparticles, and (c) Rh6G adsorbed Ag nanoparticles upon the addition of Cu2+ ions.

(Figure 7a). The noncovalent attachment of Rh6G over the surface of silver nanoparticles quenched the fluorescent emission (Figure 7b) through the fluorescence resonance energy transfer. It confirms the attachment or collision of Rh6G over the surface of silver nanoparticles. After the addition of 1.0 × 10−6 mol·L−1 of Cu2+ metal ions, a fluorescent emission was restored (Figure 7c) with the concordant color change. The restoration of fluorescent emission ensures the detachment of the Rh6G fluorophore by Cu2+ metal ions and thereby proves the sensing ability of silver nanoparticles toward Cu2+ metal ions. 3.5. Sensitivity Studies. Sensing ability of the biomediated silver nanoparticles toward heavy metal ions was studied by using fluorescence spectrometry. The fluorescence sensors are 7444

dx.doi.org/10.1021/ie3003232 | Ind. Eng. Chem. Res. 2012, 51, 7441−7446

Industrial & Engineering Chemistry Research

Article

3.6. Selectivity Studies. A visual colorimetry is a highly desirable characteristic of sensors and can be effectively achieved by the biomediated silver nanoparticles. The selectivity of biomediated nanoparticles was examined with various metallic ions like Cu2+, K+, Mg2+, Mn2+, Na+, Fe3+, Zn2+, Ni2+, Co2+, and Ba2+ at a concentration of 1.0 × 10−6 mol·L−1. The biomediated nanometric silver particles effectively sensed Cu2+ ions over the other metal ions. As can be seen from a pictorial representation (Figure 10a), it is clear that the

designed with the perspective of selectivity and sensitivity properties,24 and the characterizations of biomediated silver nanoparticles were performed with respect to the above. The sensitivity of biomediated nanoparticles toward Cu2+ metal ions has been estimated for the different concentrations like 10−6, 10−7, 10−8, 10−9, 10−10, 10−11, 10−12, and 10−13 mol·L−1 of cupric ions (Figure 8). The fluorescence intensity increases

Figure 8. Fluorescence response of (a) Rh6G, Rh6G adsorbed Ag nanoparticles upon the addition of (b) 1.0 × 10−6, (c) 1.0 × 10−7, (d) 1.0 × 10−8, (e) 1.0 × 10−9, (f) 1.0 × 10−10, (g) 1.0 × 10−11, (h) 1.0 × 10−12, and (i) 1.0 × 10−13 mol·L−1 concentrations of Cu2+ ions, and (j) Rh6G adsorbed Ag nanoparticles.

with an increase in the amount of Rh6G released and is purely dependent upon the concentration of cupric ions. The quantitative characteristics such as calibration curve equation, correlation coefficients, and limit of detection (LOD) were studied. The obtained results and the construed calibration curve are shown in Figure 9. As an astonishing fact, the constructed Cu2+ ion sensors using biomediated silver nanoparticles exhibited a high correlation coefficient (R2 = 0.997) and were also successful in detecting the very minimal concentration (10−13 mol·L−1) of cupric ions.

Figure 10. (a) Colorimetric response and (b) fluorescence spectra of the Rh6G adsorbed Ag nanoparticles toward various representative metal ions and (c) effect of metal ions on the fluorescence of Rh6G adsorbed Ag nanoparticles.

synthesized silver nanoparticles specifically interacted with the copper ions. The addition of copper(II) chloride (1.0 × 10−6 mol·L−1) involves in the attachment of Cu2+ ions over the surface of silver nanoparticles and liberates Rh6G dye moieties, which has been observed from a color change of yellow to purple (Figure 10a). However, no color change was observed for the remaining ions, and the original color of the silver nanoparticles was retained (Figure 10a). Fluorescence spectra

Figure 9. Plot of fluorescence intensity of silver nanoparticles versus Cu2+ concentration at λex = 400 nm. 7445

dx.doi.org/10.1021/ie3003232 | Ind. Eng. Chem. Res. 2012, 51, 7441−7446

Industrial & Engineering Chemistry Research

Article

(7) Yang, X.; Li, Q.; Wang, H.; Huang, J.; Lin, L.; Wang, W.; Sun, D.; Su, Y.; Opiyo, J. B.; Hong, L.; Wang, Y.; He, N.; Jia, L. Green synthesis of palladium nanoparticles using broth of Cinnamomum camphora leaf. J. Nanopart. Res. 2010, 12, 1589. (8) Lu, Y.; Liu, J.; Li, J.; Peter, J.; Caroline, M.; Pavot, B.; Brown, K. A. New highly sensitive and selective catalytic DNA biosensors for metal ions. Biosens. Bioelectron. 2003, 18, 529. (9) Forzani, E.; Zhang, H. Q.; Chen, W.; Tao, N. J. Detection of heavy metal ions in drinking water using a high-resolution differential surface plasmon resonance sensor. Environ. Sci. Technol. 2005, 39, 1257. (10) Durgadas, C. V.; Sharmaa, C. P.; Sreenivasan, K. Fluorescent gold clusters as nanosensors for copper ions in live cells. Analyst 2011, 136, 933. (11) Kozlowski, H.; Brown, D. R.; Valensin, G. Metallochemistry of neurodegeneration; RSC Publishing: Cambridge, U.K., 2006. (12) Werner, T.; Mayr, T. Dual lifetime referenced optical sensor membrane for the determination of copper(II) ions. Analyst 2002, 127, 248. (13) Oehme, I.; Prokes, B.; Murkovic, I.; Werner, T.; Klimant, I.; Wolfbeis, O. S. LED-compatible copper(II)-selective optrode membrane based on lipophilized zincon. J. Anal. Chem. 1994, 350, 563. (14) Mahendra, N.; Gangaiya, P.; Sotheeswaran, S.; Narayanaswamy, R. A Simple inexpensive detection method of Nickel in water using optical sensor. Sens. Actuators, B 2002, 81, 196. (15) Preininger, C.; Wolfbeis, O. S. Disposable cuvette test with integrated sensor layer for enzymatic determination of heavy metals. Biosens. Bioelectron. 1996, 11, 981. (16) Malcik, N.; Caglar, P.; Narayanaswamy, R. Investigations into optical sensing of cupric ions using several immobilized reagents. Quim. Anal. 2000, 19, 94. (17) Hajizadeh, S.; Farhadi, K.; Forough, M.; Sabzi, R. E. Silver nanoparticles as a cyanide colorimetric sensor in aqueous media. Anal. Methods 2011, 3, 2599. (18) Silva, A. M. B.; Araújo, C. B. D.; Silva, S. S.; Galembeck, A. Silver nanoparticle insitu growth within crosslinked poly(ester-costyrene) induced by UV irradiation: aggregation control with exposure time. J. Phys. Chem. Solids 2007, 68, 729. (19) Tripathy, A.; Ashok, M.; Raichur, N.; Chandrasekaran, T.; Prathna, C.; Mukherjee, A. Process variables in biomimetic synthesis of silver nanoparticles by aqueous extract of Azadirachta indica (Neem) leaves. J. Nanopart. Res. 2010, 12, 237. (20) Shankar, S. S.; Rai, A.; Ahmad, A.; Sastry, M. Rapid synthesis of Au, Ag, and bimetallic Au core−Ag shell nanoparticles using Neem (Azadirachta indica) leaf broth. J. Colloid Interface Sci. 2004, 275, 496. (21) Yogev, D.; Shtutina, S.; Efrima, S. Electron diffraction studies of the composition and structure of silver metal liquidlike films. J. Phys. Chem. 1990, 94, 753. (22) Wen, X.; Xie, Y. T.; Mak, M. W. C.; Cheung, K. Y.; Li, X. Y.; Renneberg, R.; Yang, S. Dendritic nanostructures of silver: facile synthesis, structural characterizations, and sensing applications. Langmuir 2006, 22, 4836. (23) Xu, H.; Li, H.; Xia, J.; Yin, S.; Luo, Z.; Liu, L.; Xu, L. One-pot synthesis of visible-light-driven plasmonic photocatalyst Ag/AgCl in ionic liquid. ACS Appl. Mater. Interfaces 2011, 3 (1), 22. (24) He, H.; Mortellaro, A. M.; Leiner, J. P. M.; Fraatz, J. R.; Tusa, K. J. A fluorescent sensor with high selectivity and sensitivity for potassium in water. J. Am. Chem. Soc. 2003, 125 (6), 1468.

of the different metal ions incorporated Rh6G adsorbed silver nanoparticles and their effect are given in Figure 10b,c, respectively. Rh6G exhibited maximum fluorescence intensity in its free state (Figure 10b). Cu2+ ions including Rh6G adsorbed silver nanoparticles exhibited higher intensity than the remaining metal ions and are almost closer to the Rh6G free state. From the observed fluorescence spectra (Figure 10b) and their effect toward different metal ions (Figure 10c), it is clear that Cu2+ ions detached Rh6G dye moieties in a greater extent than the other metal ions and specifies the high selective and quantitative measurement of the prepared silver nanoparticles toward Cu2+ ions.

4. CONCLUSION Highly crystalline and monodispersed spherical silver nanoparticles were prepared by using a single step and green biosynthetic method employing Azadirachta indica extract. The biomediated silver nanoparticles exhibited fcc structure and were revealed from the TEM and XRD analyses. Fourier transform infrared spectroscopy exhibited the possible groups involved in the reduction and stabilization processes. The excellent selectivity and sensitivity of the prepared nanoparticles toward copper(II) heavy metal ions has proven their potential caliber in the heavy metal ion sensor fields.

■

ASSOCIATED CONTENT

S Supporting Information *

TEM image of four months aged Azadirachta indica. This material is available free of charge via the Internet at http:// pubs.acs.org.

■

AUTHOR INFORMATION

Corresponding Author

*G.G.K.: e-mail, [email protected]; tel., 919585752997. K.S.N.: e-mail, [email protected]; fax, +82 63 270 2306. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS C.J.K. and G.G.K. were supported by Department of Science and Technology−SERC, New Delhi, Fast Track Project for Young Scientist Grant No. SR/FT/CS-113/2010(G). K.S.N. was supported by the Human Resources Development of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korea Government Ministry of Knowledge Economy (No. 20114030200060).

■

REFERENCES

(1) Nozik, J. A. Nanoscience and nanostructures for photovoltaics and solar fuels. Nano Lett. 2010, 10 (8), 2735. (2) Shirai, Y.; Morin, J. F.; Sasaki, T.; Guerrero, J. M.; Tour, J. M. Recent Progress on Nanovehicles. Chem. Soc. Rev. 2006, 35, 1043. (3) Kohler, J. M.; Csaki, A.; Reichert, J.; Moller, R.; Straube, W. Selective labeling of oligonucleotide monolayers by metallic nanobeads for fast optical readout of DNA-chips. Sens. Actuators, B 2001, 76 (1− 3), 166. (4) Gnana Kumar, G. Irradiated PVdF-HFP-montmorillonite composite membranes for the application of direct ethanol fuel cells. J. Mater. Chem. 2011, 21, 17382. (5) Dahl, A. J.; Bettye, L.; Maddux, S.; Hutchison, E. J. Toward Greener Synthesis. Chem. Rev. 2007, 107, 2228. (6) Qi, L.; Xu, Z. In vivo antitumor activity of chitosan nanoparticles. Bioorgan. Med. Chem. Lett. 2006, 16, 4243. 7446

dx.doi.org/10.1021/ie3003232 | Ind. Eng. Chem. Res. 2012, 51, 7441−7446