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Synthesis of Near-Monodispersed AuAg Nanoalloys by High Intensity Laser Irradiation of Metal Ions in Hexane Yuliati Herbani,* Takahiro Nakamura, and Shunichi Sato Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai, Miyagi, 980-8577, Japan ABSTRACT: A wet photochemical reduction approach was performed using highly intense femtosecond laser pulses to synthesize goldsilver (AuAg) alloy nanoparticles in hexane in the presence of dodecylamine in various composition ratios. Not only monometallic gold (Au) and silver (Ag) but also its bimetallic particles were successfully fabricated with the average size of 25 nm, well separated to each other and thus, essentially near-monodispersed. The formation of AuAg alloy nanoparticles was confirmed by UVvisible spectroscopy of the synthesized organosols showing only a single absorption peak and its position linearly varies with Au molar fraction in the prepared solution. The trend in plasmon modifications such as the decrease of absorbance and plasmon bandwidth with an increase of Au molar fraction as suggested by Mie theory were not observed, indicating the fabricated particles were different in size for the different molar ratios in the solution.
’ INTRODUCTION A growing research interest has been directed toward the synthesis of metal nanoparticles due to their remarkable properties in catalysis, optics, and electronics. Particularly, the use of organic solvent to prepare bimetallic nanoparticles has been growing rapidly in recent years because it is important in the catalytic applications,1 where most of reactions are carried out in nonaqueous media. The organosols are of importance because the efficiency of catalytic process is reported to be inversely proportional to the particle size,2 and the use of water to disperse nanoparticles is avoided since high surface energy of nanoparticle may lead to severe aggregation.3 Another drawback is the existence of free capping agents in aqueous solution which obstruct the activity of the post-added molecules to modify surface chemistry of nanoparticles. To extend the applicability of a colloid-chemical approach toward the development of advanced materials, the synthesis of nanoparticles in organic solvent has become an essential issue. The primary route to prepare metal nanoparticles in organic solvent is BrustSchiffrin method in which metal ions from aqueous solution were first transferred to a hydrocarbon phase by means of a phase transfer agent. The reduction was then carried out by employing strong reducing agent, such as sodium borohydride (NaBH4), in the presence of a stabilizer.4 Despite of its superior controllability over size and shape of nanoparticle to form 2D self-assembly pattern, the excess use of NaBH4 may causes the adsorption of unused BH4 ions onto the nanoparticle surface resulting in the borides contamination on the nanoparticle surface. Indeed, even the used BH4 ions may contribute on the contamination after releasing hydrogen atoms in the reduction process leaving borides in the solution. In addition, as the phase transfer agent and the stabilizer were sometimes chemically different, and the reducing agent was used excessively, r 2011 American Chemical Society
a long route of post-synthesis cleaning is still an issue in this technique. At this point, irradiation based synthesis becomes an alternative way due to the advantage of being free from preadded reducing agents. Reduction of metal ions is facilitated by an abundant of high energetic electrons and radicals produced in situ through the ionization and excitation of solvent molecules by irradiation energy. Nanoparticle synthesis using an intense γ-ray5 has been explored as a major method in irradiation based techniques for the past two decades, while synchrotron X-ray6,7 and femtosecond laser816 recently attracted much attentions as well as the former due to the identical process underlying in the reduction process of metal precursors to zero valence nanoparticles. Particularly, water molecules have been reported to be decomposed by femtosecond laser via two-photon absorption generating solvated electrons, hydrogen and hydroxyl radicals along with the dissociation products such as hydronium ion, H3O+, at decimolar concentration.17 Moreover, different additives such as dispersant and ion scavenger into the system will generate a series of reducing radicals with various reduction potential, which can reduce metal precursors selectively. Even though γ-ray and synchrotron X-ray irradiation sources are highly efficient, these methods have some drawbacks such as radioactivity and poor accessibility. From this point of view, femtosecond laser irradiation method seems to be more promising to date due to its simple, safe and “green” properties. In the relation to femtosecond laser-induced formation of noble metal nanoparticles through the reduction of metal salts, several works810 has been devoted to synthesize monometallic cluster of Au, Ag and palladium (Pd) respectively. In these Received: June 14, 2011 Revised: September 12, 2011 Published: September 27, 2011 21592
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The Journal of Physical Chemistry C papers, they have performed the synthesis in aqueous media or in alcohol but not in organic solvent. When titanium dioxide (TiO2) nanoparticles as a catalyst were used, fabrication of Ag nanoparticles using a 0.5 mJ femtosecond laser was also reported in a mixture of water and ethanol, resulted in the AgTiO2 composite nanoparticles with the particle size less than 20 nm and Ag nanoparticles could not be fabricated using TiO2-free solution.11 Using a 6 mJ laser power, our group has also reported the formation of Au, Ag and platinum (Pt) nanoparticles in the presence of polyvynilpyrrolidone (PVP) in aqueous solution and the particles with the mean particle size as small as 3 nm with a reasonable particle size distribution have been fabricated.1214 In addition to monometallic nanoparticles, only few reports are available for bimetallic system of noble metal nanoparticles synthesized in intense laser field. In this case, our group synthesized Au-rich nanoalloys from mixed solution of Au and Ag salts at low concentration to hinder the formation of silver halide precipitates which is not preferable.15 Despite the low yield, the work is the first literature available so far for bimetallic system fabricated by femtosecond laser in aqueous system. Other group16 has also followed for AuPt system where they found that the fabricated particles were alloys but possessed a wide size distribution with an average about 15 nm. They urged that it might be due to middle level of laser pulse energy used in this work or because of the miscibility gap of Au and Pt system for making solid solution. While several papers have been published on femtosecond laser-induced synthesis of noble metal nanoparticles in aqueous phase as described above, there is no report on the femtosecond laser induced synthesis of nanoparticles in organic solvent, even for the common case like AuAg bimetallic system. In the viewpoint of co-reduction synthesis, preparing Au and Ag ions in organic solvent is the best way to prevent the formation of silver chloride (AgCl) precipitate which always exists in aqueous phase. It is well-known that AgCl may introduce problems in compositional control and possible contamination of the alloy nanoparticles, and thus it is not convenient in most cases. Consequently, high concentration of AuAg alloy nanoparticles can be prepared. Moreover, by considering high stability and monodispersity of nanoparticles that are chemically synthesized in organic solvent compared to the ones prepared in aqueous solution, it is worth to try to perform the synthesis of AgCl-free AuAg alloy nanoparticles utilizing femtosecond laser-induced formation. In this paper, we report the synthesis of bimetallic AuAg nanoparticle prepared in hexane in the presence of dodecylamine as a dispersant. Instead of transferring the fabricated nanoparticles prepared in aqueous to the organic phase, the synthesis is performed by irradiating the hexane solution of metal ions directly by femtosecond laser. The hexane solutions of metal ion are prepared using phase transfer protocol introduced by Yang et al.18 Hexane is chosen over the other organic solvent as it is less decomposed by high intensity femtosecond laser to generate carbon-derivative molecules (such as polyynes, and so on), besides that the refractive index of hexane is very similar to that of water.
’ EXPERIMENTAL METHODS Chemicals. Metallic salts such as chloroauric acid trihydrate (HAuCl4 3 3H2O, 99.9%), Ag nitrate (AgNO3, 99.9%), dodecylamine (C12H27N, >99%), and hexane (C6H14, infinity pure) were obtained from Sigma-Aldrich Co., and ethanol (C2H6O,
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99.5%) was purchased from Wako Pure Chemical Industries, Ltd. The aqueous solutions of Au and Ag ions were prepared separately using deionized water at the concentration of 1.0 103 M and used as stock solutions. All chemicals were of the highest purity available and were used as-received without further purification. Preparation of Metallic Ion Precursors in Hexane by Phase Transfer Protocol. Phase transfer of metallic ions from aqueous to hexane phase was performing using the method introduced by Yang et al.18 Typically, 15 mL of 1 mM aqueous gold salt solution was mixed with 15 mL of ethanol containing 0.3 mL of dodecylamine (8.7 mM). The dodecylamine was used as phase transfer agent and stabilizer for metal ions and metal nanoparticles, respectively. After 3 min vigorous stirring, 15 mL of hexane was added and the stirring was continued for 1 min. The hexane phase containing metal ions separated quickly from the aqueous phase, resulting in the color bleaching of the aqueous phase. The bleaching indicates that Au ions have been transferred completely into the hexane medium. The hexane phase was then subsequently collected. Hexane solution of Ag ion is also prepared by the same procedure. The color of the hexane solution containing Au and Ag ions were light yellow and transparent, respectively. The final concentration of Au and Ag ions in hexane solution were determined by measuring the concentration of metal ions left in ethanol/water solution using ICP-AES (Optima 3300SYS XL, Perkin-Elmer), and the transfer efficiencies were 96 and 92% for Au and Ag ions, respectively. The hexane solutions of the two metal ions were then mixed each other in different molar ratios prior to the femtosecond laser irradiation. Samples were labeled by the molar fractions of Au ions contained in the solution. For example, Au50 denotes the sample consisting of 50% Au solution and 50% Ag solution. Under the same irradiation condition, pure Au and Ag organosols were also synthesized separately to compare the formation kinetics of these two nanoparticles. Femtosecond Laser-Induced Synthesis and Nanoparticle Characterization. In laser irradiation experiment, 3 mL of the mixed solution was introduced into a 10 10 45 mm quartz glass cuvette and irradiated for several minutes by highly intense femtosecond laser pulses. The glass cuvette was equipped with a cover lid to prevent the evaporation of hexane during irradiation. The laser source was a Ti:sapphire laser working at the wavelength of 800 nm generated by a chirped pulse amplification system (Spitfire Pro, Spectra-physics Inc.). The typical pulse width, repetition rate, and maximum pulse energy per pulse used in this study were 100 fs, 30 Hz, and 5.7 mJ, respectively. The laser beam was focused using an aspheric lens with a focusing length of 8 mm (NA = 0.5) and directed perpendicularly to the side-wall of the glass cuvette. The intensity of laser beam at the focal point inside the solution was estimated to be about 1014 W/cm2. The sketch of the experimental setup is in Figure 1. Besides solutions containing metallic ions, the neat hexane was also irradiated by femtosecond laser to check whether additional solutes such as carbon particles are fabricated. The prepared organosols were characterized by UVvisible spectrometer (V630iRM, JASCO Co.) to observe an absorption spectrum between 200 and 700 nm. The surface morphology and particle size of the nanoparticles were analyzed by transmission electron microscopy (JEOL2000-EXII, JEOL Ltd.). The irradiated solutions were washed three times with ethanol to eliminate the excess of dodecylamine in the solution prior to TEM observation. The TEM samples were prepared by dropping a few drops of the 21593
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Figure 1. Sketch of the experimental setup.
solution on a carbon-coated copper grid (Okenshoji Co., Ltd., microgrid B) immediately after the irradiation and drying in air at room temperature.
’ RESULTS AND DISCUSSION Synthesis of Monometallic Au and Ag Nanoparticles in Hexane. UVvisible spectroscopy could be used to examine the
formation of the metal nanoparticles by reduction of metal ions in the solution being exposed to highly intense femtosecond laser. In aqueous solutions, the formation of monometallic Au and Ag nanoparticles can be monitored by observing the decrease in the characteristic peaks of AuCl4 (5d f 6s,p) and Ag+ (4d f 5s,p) ions at 29019 and 302 nm,20 respectively, and the appearance of the surface plasmon resonance (SPR) peaks at 520 and 400 nm for Au and Ag nanoparticle respectively. In contrast, hexane solution of Au and Ag ions after phase transfer in the presence of dodecylamine showed no characteristic peak in the same spectral range. Therefore, the formation of Au and Ag nanoparticles was examined by observing the variation of peak absorbance (i.e., absorbance at the corresponding peak position of SPR) as a function of irradiation time, as shown in Figure 2. After 60 min irradiation, the solution of Ag ion exhibited a yellowish-brown color with the peak position at 434 nm, while the solution of Au ion was a reddish-brown with the peak position at 515 nm in hexane. The peak at 434 nm is characteristic SPR of ligand capped-Ag nanoparticles in organic solvent,21 while the extinction band of uncapped-Ag nanoparticles has a maximum at 400 nm. The shift of the SPR peak position between capped- and uncapped-Ag nanoparticles could be explained as the decrease of free electron density on the surface of Ag nanoparticle due to the formation of covalent bond with the lone pair electrons of amine group. In the case of Au nanoparticles, such a covalent bond does not take place owing to the different nature of interband transitions from the filled d-bands to the sp- conduction bands of Au. Additionally, irradiation of pure hexane and its solution with dodecylamine were also performed. There was no significant change in the absorption spectra and no solute (e.g., carbon particles) was found in the sample of the irradiated solution of pure hexane as well as in dodecylamine contained hexane solution by TEM observation. The liquids remained transparent after leaving the irradiated liquids, even after long stand in room temperature. Figure 2a and b show the variation of absorption spectra of hexane solution of Ag and Au ions solution during irradiation with femtosecond laser up to 60 min, respectively. The measurement of spectra is performed ex-situ for every 10 min. The black
Figure 2. UVvisible absorption spectra of solutions containing 1.0 103 M of (a) Au and (b) Ag ions recorded every 10 min in a continuous irradiation with femtosecond laser.
Figure 3. Comparison of peak absorbances of Au and Ag nanoparticles as a function of irradiation time.
solid curve represents the spectrum before irradiation. Comparison of the peak absorbance at λ = 434 nm for Ag and 515 nm for Au nanoparticles as a function of irradiation time is presented in Figure 3. In general, the increase of the absorption peak with time clearly indicates that the formation of metal nanoparticles takes place through the reduction of Ag and Au ions induced by femtosecond laser, even though both metal nanoparticles are not formed immediately after the irradiation of femtosecond laser to the solutions. There are induction times about 10 min for Ag nanoparticle and 30 min for Au nanoparticles before their SPR peaks appear in the spectra at 423 and 508 nm, respectively. This induction time is a consequence of the high ionization potential of hexane, which is 1.3 times higher than that of water,22 so hexane needs more photons to reach the ionization state and eject solvated electrons. As shown in Figure 3, the variation of 21594
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Figure 4. (a) UVvisible absorption spectra of AuAg alloy nanoparticles as-synthesized after irradiation for 60 min and the corresponding photographs of organosol. (b) Plasmon band position vs Au molar fraction.
peak absorbance of both monometallic colloids starts with a slow induction phase, then increases steeply and reaches saturation at longer irradiation times (sigmoid response), which corresponds to a complete reduction. Induction phase can be regarded as a nucleation stage, while the part in the curve with a sharp increase is a growth state in the nanoparticle formation. Basically, the slower the nucleation rate, the more disperse the particles would be formed.23,24 Based on the fact that the nucleation rate of Ag nanoparticles is considerably greater than that of Au nanoparticles, the final size distribution of Ag nanoparticles would be expected to be broader than that of Au nanoparticles in hexane. This prediction will be confirmed further by TEM analysis in the next section. When the irradiation is stopped after 60 min, final positions of SPR were at 434 and 515 nm for monometallic Ag and Au nanoparticles, respectively. Synthesis of Bimetallic AuAg Nanoparticle in Hexane. The mixed solution of Au and Ag ions in hexane were prepared for the synthesis of the bimetallic AuAg alloy nanoparticles. The UVvisible spectra of the mixed solution with various compositions of ions showed no absorption in the long wavelength (λ > 500 nm), indicating that there was no precipitates due to the formation of silver chloride. No turbidity was observed in the mixed solutions. As mentioned previously, monometallic Ag and Au nanoparticles in hexane after 60 min irradiation have plasmon absorption peak at 434 and 515 nm, respectively. So, two plasmon bands would be expected to observe for the physical mixture of these monometallic Au and Ag nanoparticles, while one plasmon peak would be appeared if AuAg nanoparticles are alloy. Figure 4a shows the UVvisible absorption spectra for bimetallic AuAg system after 60 min irradiation. The absorption spectra of monometallic Au and Ag are also incorporated for comparison. Only one plasmon band was observed for every bimetallic system
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and its position was red-shifted almost linearly from 434 to 515 nm with the increase of Au molar fraction as shown in Figure 4b, confirming the formation of bimetallic AuAg alloy nanoparticle. The quasi linear relationship between plasmon band position of bimetallic nanoparticles and Au molar fraction also indicated that the elemental composition in the fabricated alloy nanoparticles was similar to the concentration ratio of the ions in the mixed solution. It might not be the case, if the irradiation was preformed shorter than 60 min when the growth kinetics of Au atoms and Ag atoms were not similar (see Figure 3). Additionally, the photographs of the irradiated solutions are presented in the inset of Figure 4a, where the colors clearly indicate a gradual variation of SPR peak between those of two metals. However, the trends in plasmon modification such as the linear decrease of peak absorbance and plasmon bandwidth with an increase of Au contents as suggested by Mie theory were not observed. For example, the peak absorbance of Au25 is much lower than that of Au75, which is in contrast to the case observed in water.25 This indicates that the particles with different average sizes have been prepared in each composition and it will be confirmed further by the TEM analysis. The TEM images and the particle size distribution of AuAg alloy nanoparticles are presented in Figure 5, together with those of the monometallic Au and Ag nanoparticles for comparison. TEM samples were prepared by using hexane suspensions of nanoparticles directly without size selection. Most particles are nearly spherical with high uniformity in size and well separated to form 2D self-assemble on the microscopy grid (highly monodispersed). The mean diameter of AuAg alloy nanoparticles, Au25, Au50 and Au75, were 2.09 ( 0.49, 2.27 ( 0.39, and 4.38 ( 1.11 nm, respectively, and the coefficient of variation (CV) were all less than 25%. It is clear that the average size of alloy nanoparticles increased with the increase in the Au molar fraction in the solution. This confirmed the tendency shown in the UV visible absorption spectra previously mentioned, where some spectra (Au25 and Au50) show a faint absorption peak, indicating the most particles are below 3 nm in size.26 While maintaining the four main ring pattern of fcc structures with crystal plane of the (111), (200), (220), and (311), the selected area diffraction pattern (SAED) of Au25 and Au50 alloy nanoparticles in the inset also show the hollow ring (diffuse features without bright spots), confirming the presence of particle with very small particle size. On the other hand, the mean diameter of monometallic Au nanoparticles is 4.56 ( 1.20 nm, while for Ag nanoparticles is 5.52 ( 1.75 nm with a broad size distribution as shown in Figure 5(a). The broad distribution of Ag nanoparticles has been predicted earlier by evaluating its formation kinetics. In addition, high magnification of TEM images of Au75 nanoparticles (Figure 6) shows the visible lattice fringes of 0.237 nm with (111) plane, confirming the cystrallinity of fabricated alloy. Although multiple twinned particle and with stacking faults were observed for most of particles, no coreshell or phase segregation are observed, revelead the formation of alloy. Furthermore, XRD method could not be used effectively to distinguish the AuAg alloy from the pure metals of Au and Ag nanoparticles due to the similarity in the lattice structures (space group: Fm3m (No. 227)) and the lattice constants of the two metals (0.408 nm for Au and 0.409 nm for Ag) with the consequence that their diffraction pattern would be the same. That is why the formation of AuAg alloys can be solely confirmed from the UVvisible absorption spectra. Nevertheless, 21595
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Figure 6. High resolution TEM image of bimetallic Au75 nanoparticles. Crystallinity of fabricated alloy is confirmed by the presence of lattice fringes that are visible in the (111) plane indicated by white arrow. No coreshell or phase segregation is observed.
electrons (e) and hydrogen radicals (H•) from multiphoton ionization of hexane (RCH3, where R = CH3(CH2)4) by a highly intense femtosecond laser may be described by the following reaction scheme:
Figure 5. Transmission electron micrographs and the particle size distribution of the monometallic and bimetallic nanoparticles: (a) Ag, (b) Au25, (c) Au50, (d) Au75, and (e) Au. The selected area diffraction (SAED) pattern is also included in the inset. d = mean particle size, σ = standard deviation, CV = coefficient of variation.
the mechanism that rules the size reduction of AuAg alloy nanoparticles with high Ag content is still unclear so far. The formation of bimetallic AuAg nanoparticles by the intense laser irradiation of the mixed hexane solution of Au and Ag ions can be attributed to the generation of high energetic electrons and hydrogen radicals produced during the laser irradiation. These energetic electrons and hydrogen radicals are more likely generated from the ionization of hexane through multiphoton absorption, because hexane is the most abundance in the system. Adopting the result of multiphoton ionization of water molecules17 and two-photon ionization of hexane with an intense subpicosecond laser excitation,27 the generation of
In this case, the ionization of hexane is induced by excitation with photon with a wavelength of 800 nm, corresponding to a photon energy of 1.55 eV. Since the ionization threshold of hexane is between 8.3 8.9 eV,27 an excitation by absorption of 5 to 6 photons is needed for ionization to occur. Multiphoton excitation of hexane is assumed to initially lead to the production of highly excited state (RCH3**) and to direct ionization which produce the radical cation (RCH3•+) and the electron (e). According to Sander et al.,27 the RCH3** states can decay to the lowest excited state (RCH3*) (reaction (1)), and produce the RCH2• and H• radicals (reaction (2)). The electrons and the cations produced will move due to diffusion and drift in each other’s Coulomb field and can recombine or escape from each other. While the recombination may lead to the production of excited molecular states (RCH3** and RCH3*), the electrons may also be collided with metal ions present in the solution for further reduction process if they can be able to escape from the cations. Furthermore, the unbound-dodecylamines may also become a source of electrons and hydrogen radicals, by considering the fact that free dodecylamines are easier to be oxidized than hexane. The same ionization channel as hexane may also be applied for dodecylamine by simply changing RCH3 in reactions (1) and (3) with RNH2, where R is CH3(CH2)11. However, the number of dodecylamine molecules is much smaller than the number of hexane molecules, and hence, the electrons generated from the ionization of dodecylamine can be neglected. Once the electrons or hydrogen radicals meet metal ions protected by dodecylamine, metal ions will be reduced to zero valences:
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Agþ þ e ðH• Þ f Ag0 þ ð1=2H2 Þ
ð3Þ
Au3þ þ 3e ð3H• Þ f Au0 þ ð3=2H2 Þ
ð4Þ
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and the alloying process will follow afterward due to the coalescence and collision between the two atoms in the energetic surrounding in the solution during laser irradiation: Ag0 þ Au0 f ðAuAgÞ0 f ... f ðAuAgÞn 0
ð5Þ
When the particles become several nanometers in size, most of the atoms generated by the laser irradiation are expended so that particle growth terminates. Dodecylamine acts as stabilizer and suppresses crystal growth by adsorption onto the nanoparticle surface preserving the particle size when electrons and hydrogen radicals are exhausted. Fourier transform infrared (FT-IR) spectroscopy of dodecylaminecapped Au100 and Au50 nanoparticles indicates that the dodecylamine are indeed adsorbed onto the nanoparticle surface evidenced by the absence of NH stretching band at 33003500 cm1. This result is consistent with other reports.28,29 While the dodecylamine has been known to bind weakly on the nanoparticle surface compared with dodecanethiol, further study on the surface chemistry of dodecylamine-capped nanoparticles is definitely necessary to apply these particles as catalyst. This work is an ongoing project in our laboratory and the result will be reported elsewhere.
’ CONCLUSION We prepared Au, Ag, and their bimetallic nanoparticles using femtosecond laser irradiation of hexane solution of metallic ions. Metal nanoparticles with narrow size distribution can be achieved. Not only Au and Ag but also the AuAg bimetallic particles are very fine with the particle size of 25 nm, well separated to each other and essentially near-monodispersed. The AuAg bimetallic system was confirmed to be solid solution alloy from the appearance of single plasmon bands that were in intermediate between those for monometallic nanoparticles. The mechanism of nanoparticle formation was also proposed. ’ AUTHOR INFORMATION Corresponding Author
*E-mail:
[email protected].
’ ACKNOWLEDGMENT The authors would like to acknowledge Associate Prof. Kiyoshi Kanie and Mr. Masaki Matsubara of IMRAM, Tohoku University, for their kind guidance and assistance in FT-IR measurement and analysis of the dodecylamine-capped nanoparticles. ’ REFERENCES (1) Haruta, M.; Date, M. Advances in the catalysis of Au nanoparticles. Appl. Catal. A: General 2001, 222, 427–437. (2) Emeline, A.; Ryabchuk, V.; Serpone, N. Factors affecting the efficiency of a photocatalyzed process in aqueous metal oxide dispersions: Prospect of distinguishing between two kinetic models. J. Photochem. Photobiol. A: Chem. 2000, 133, 89–97. (3) Nath, S.; Jana, S.; Pradhan, M.; Pal, T. Ligandstabilized metal nanoparticles in organic solvent. J. Colloid Interface Sci. 2010, 341, 333–352. (4) Goulet, P. J. G.; Lennox, R. B. New insights into BrustSchiffrin metal nanoparticle synthesis. J. Am. Chem. Soc. 2010, 132, 9582–9584. (5) Belloni, J. Nucleation, growth and properties of nanoclusters studied by radiation chemistry: Application to catalysis. Catal. Today 2006, 113, 141–156.
(6) Wang, C-. L.; Hsao, B-. J.; Lai, S-. F.; Chen, W-. C.; Chen, H-. H.; Chen, Y-. Y.; Chien, C-. C.; Cai, X.; Kempson, I. M.; Hwu, Y.; Margaritondo, G. One pot synthesis of AuPt alloyed nanoparticles by intense x-ray irradiation. Nanotechnology 2011, 22, 065605(1) (6). (7) Cai, X.; Wang, C-. L.; Chen, H-. H.; Chien, C-. C.; Lai, S-. F.; Chen, Y-. Y.; Hua, T-. E.; Kempson, I. M.; Hwu, Y.; Yang, C. S; Margaritondo, G. Tailored Au nanorods: optimizing functionality, controlling the aspect ratio and increasing biocompatibility. Nanotechnology 2010, 21, 335604(1) (8). (8) Zhao, C.; Qu, S.; Qui, J; Zhu, C. Photoinduced formation of colloidal Au by a nearinfrared femtosecond laser. J. Mater. Res. 2003, 18, 1710–1714. (9) Abid, J. P.; Wark, A. W.; Brevet, P. F; Girault, H. H. Preparation of silver nanoparticles in solution from a silver salt by laser irradiation. Chem. Commun. 2002, 792–793. (10) Fan, G.; Qu, S.; Wang, Q.; Zhao, C.; Zhang, L.; Li, Z. Pd nanoparticles formation by femtosecond laser irradiation and the nonlinear optical properties at 532 nm using nanosecond laser pulses. J. Appl. Phys. 2011, 109, 023102 (1) (8). (11) Zeng, H.; Zhao, C.; Qiu, J.; Yang, Y; Chen, G. Preparation and optical properties of silver nanoparticles induced by a femtosecond laser irradiation. J. Cryst. Growth 2007, 300, 519–522. (12) Nakamura, T.; Mochidzuki, Y.; Sato, S. Fabrication of gold nanoparticles in intense optical field by femtosecond laser irradiation of aqueous solution. J. Mater. Res. 2008, 23, 968–974. (13) Nakamura, T.; Takasaki, K.; Sato, S. Fabrication of platinum particles by intense, femtosecond laser pulse irradiation of aqueous solution. Appl. Surf. Sci. 2009, 255, 9630–9633. (14) Nakamura, T.; Magara, H.; Herbani, Y.; Sato, S. Fabrication of silver nanoparticles by highly intense laser irradiation of aqueous solution. Appl. Phys. A: Mater. Sci. Process. 2011, 104, 1021–1024. (15) Herbani, Y.; Nakamura, T.; Sato, S. Femtosecond laser-induced formation of Au-rich nanoalloys from the aqueous mixture of AuAg ions. J. Nanomater. 2010, 2010, 154210 (1) (9). (16) Chau, J. L. H.; Chen, C-. Y.; Yang, M-. C.; Lin, K-. L.; Sato, S.; Nakamura, T.; Yang, C-. C.; Cheng, C-. W. Femtosecond laser synthesis of bimetallic PtAu nanoparticles. Mater. Lett. 2011, 65, 804–807. (17) Pommeret, S.; Gobert, F.; Mostafavi, M.; Lampre, I.; Mialocq, J.-C. Femtochemistry of the hydrated electron at decimolar concentration. J. Phys. Chem. A 2001, 105, 11400–11406. (18) Yang, J.; Sargent, E.; Kelley, S.; Ying, J. Y. A general phasetransfer protocol for metal ions and its application in nanocrystal synthesis. Nature Mater. 2009, 8, 683–689. (19) Kan, C.; Cai, W.; Li, C.; Zhang, L. Optical studies of polyvinylpyrrolidone reduction effect on free and complex metal ions. J. Mater. Res. 2005, 20, 320–324. (20) Szyma nska-Chargot, M.; Gruszecka, A.; Smolira, A.; Bederski, K.; Gzuch, K.; Cytawa, J.; Michalak, L. Formation of nanoparticles and nanorods via UV irradiation of AgNO3 solutions. J. Alloys Comp. 2009, 486, 66–69. (21) Yamamoto, M.; Kashiwagi, Y.; Nakamoto, M. Size-controlled synthesis of monodispersed silver nanoparticles capped by long-chain alkyl carboxylates from silver carboxylate and tertiary amine. Langmuir 2006, 22, 8581–8586. (22) Casanovas, J.; Grob, R.; Delacroix, D.; Guelfucci, J. P.; Blanc, D. Photoconductivity studies in nonpolar liquids. J. Chem. Phys. 1981, 75, 4661–4668. (23) Patakfalvi, R.; Papp, S.; Dekany, I. The kinetics of homogeneous nucleation of silver nanoparticles stabilized by polymers. J. Nanopart. Res. 2007, 9, 353–364. (24) Esumi, K.; Hosoyo, T.; Suzuki, A.; Torigoe, K. Formation of gold and silver nanoparticles in aquoues solution of sugar-persubstituted poly(amidoamine) dendrimers. J. Colloid Interface Sci. 2000, 226, 346–352. (25) Besner, S.; Meunier, M. Femtosecond laser synthesis of AuAg nanoalloys: Photoinduced oxidation and ions release. J. Phys. Chem. C 2010, 114, 10403–10409. (26) Hussain, I.; Graham, S.; Wang, Z.; Tan, B.; Sherrington, D. C.; Rannard, S. P.; Cooper, A. I.; Brust, M. Size-controlled synthesis of 21597
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near-monodiperse gold nanoparticles 14 nm range using polymer stabilizer. J. Am. Chem. Soc. 2005, 127, 16398–16399. (27) Sander, M. U.; Brummund, U.; Luther, K.; Troe, J. Subpicosecond transient absorption study of the UV two-photon excitation of liquid alkanes. J. Phys. Chem. 1993, 97, 8378–8383. (28) Mo, L; Liu, D.; Li, W.; Li, L.; Wang, L.; Zhou, X. Effect of dodecylamine and dodecanethiol on the conductive properties of nanoAg films. Appl. Surf. Sci. 2011, 257, 5746–5753. (29) Leff, D. V.; Brandt, L.; Heath, J. R. Synthesis and characterization of hydrophobic, organically-soluble gold nanocrystals functionalized with primary amines. Langmuir 1996, 12, 4723–4730.
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