1. Structural Properties of Palladium/Silver Bimetallic Nanoparticles Fabricated by Ultrasound Method Hossein Azizi-Toupkanloo 1 and Elaheh K. Goharshadi 1,2 1 Department of Chemistry, Ferdowsi University of Mashhad, Mashhad 91779, Iran. 2 Center of Nano Research, Ferdowsi University of Mashhad, Iran. *E-Mail: Ho_azizi60@yahoo.com Abstract Experimental part Conclusion Acknowledgements Palladium – Silver (Pd/Ag) bimetallic nanoparticles (NPs) were synthesized by the sonochemical co-reduction of Ag(I) and Pd(II) ions in aqueous solutions of the metal ions using NaBH 4 and PVP as reducing and stabilizer agents, respectively. The X-ray diffraction pattern (XRD), transmission electron microscopy (TEM), and ultraviolet-visible (UV-vis) absorption spectrometry were used to characterize prepared bimetallic NPs. According to TEM image, Pd/Ag bimetallic NPs exhibited the average particle diameter of approximately 9 nm. The authors also express their gratitude to Ferdowsi University of Mashhad for support of this project. References [1] R. Esparza, J.A. Ascencio, G. Rosas, J.F. Sanchez- Ramirez, U. Pal, R. Perez, J. Nanosci. Nanotechnol. 5 (2005) 641. [2] R. Narayanan, M.A. El-Sayed, J. Phys. Chem. B 109, 12 663 (2005). [3] S.K. Singh, Y. Iizuka, Q. Xu, Int. J. Hydrogen Energy 36 (2011) 11794. [4], S.H. Choia, S. Leea, S.J. Kim, S.H. Sohn, H.D. Kang, Y.P. Zhang, K.P. Lee, J.H. Chun, Catal. Lett. 105 (2005) 59. [5] V.K. Tzitzios, V. Georgakilas, Chemosphere 59 (2005) 887. [6] Powder Diffraction File Hanawalt Search Manual, Inorganic Phase, Sets, 1–42 (1992) International Centre for Diffraction Data. Pennsylvania. [7] J. Liu, J.B. Lee, D.H. Kim, Y. Kim, Colloids &Surfaces 302 A, 276–279 (2007). A typical synthesis of the Pd/Ag bimetallic NPs was carried out as follows. First, keeping the total concentration of metal ions at 0.05 mM. In brief, 0.0005 mol AgNO 3, 0.0005 mol Pd(NO 3 ) 2.2H 2 O, and 0.020 g PVP were dissolved in 100 ml DI water under vigorous stirring. Then, 0.0016 mol NaBH 4 was added. The reaction mixture was sonicated for 60 min with a sonicator (S- 4000) operating at 20 kHz. The power transferred to the solution was 33 W cm -2 measured by means of the calorimetric method. The fresh made samples were centrifuged, washed with deionized (DI) water for three times and then dried in the vacuum oven overnight. Results Introduction Results Ferdowsi University of Mashhad Application of nanotechnology in several fields is driven by the use of a variety of nanostructures. The field of nanomaterials is a fast-growing area and has gained great attention by scientists and industry manufacturers because of its multi-functionality along with processing properties that can be tailored. In recent years, many studies have been carried out on NPs of noble metals because metallic NPs display fascinating properties that are quite different from those of bulk. Among the metallic NPs, bimetallic nanoclusters, in particular, have demonstrated to be most attractive for variety applications [1-2] with several important advantages over the monometallic ones. Bimetallic NPs, with palladium based metal have unique catalytic activity for hydrogenation of organic compounds. Singh et al. [3] used the Pd/Ni bimetallic NPs as a catalyst for decomposition of hydrous hydrazine. They found that the Pd/Ni bimetallic NPs, compared with those monometallic of Pd and Ni have a high H 2 selectivity in the reaction. Among the numerous kinds of Pd-based bimetallic NPs, Pd/Ag NPs shows the special properties. These NPs showed catalytic activity for hydrogenation of cis,cis-1,3-cyclo octadieneand [4], catalytic reduction of N 2 O [5], etc. In the present work, the simultaneous reduction method was used for synthesizing the Pd/Ag bimetallic NPs from aqueous solutions of silver and palladium nitrate in the presence of ultrasound (US) waves. Figure 1 shows the XRD patterns of Ag, Pd, the physical mixture of the corresponding NPs, and Pd/Ag bimetallic NPs in the presence of US waves. The XRD data shows Pd and Ag NPs crystallizes in a face-centered cubic (fcc) structure essentially, which are similar to those of the bulk metallic Pd and Ag reported previously [6]. The XRD pattern of Pd/Ag bimetallic NPs also indicate that they are fcc structure with lattice constant 4.013 Å (Table 1). To provide a better illustration, the diffraction angles of (111) Pd/Ag bimetallic NPs (38.839°) locate between the diffraction angles of (111) Ag NPs (38.221°) and the diffraction angles of (111) Pd (39.970°) which is summarized in Table 1. This result indicate that the Pd/Ag bimetallic NPs is formed. Table 1. The diffraction angle and lattice constant of Ag, Pd, and Pd/Ag bimetallic NPs. Figure 1. The XRD pattern in the present of US waves a) Pd NPs b) Pd/Ag bimetallic NPs c) Pd/Ag physical mixture and d) Ag NPs Samples 2θ 111 D 111 (nm) a 111 /Å Bulk Ag38.1164.086 Ag NPs38.22118.44.075 Pd/Ag38.8394.54.013 Bulk Pd40.1193.890 Pd NPs39.9704.83.920 The typical TEM micrograph and the size distribution of Pd/Ag bimetallic NPs in the presence of US waves, presented in Fig. 2. Figure 3. Typical TEM images and Histogram of particle size distributions of Pd/Ag bimetallic NPs in the presence of US waves. The images show that the Pd/Ag bimetallic NPs are monodispersed. According to these figures, Pd/Ag bimetallic NPs exhibited the average particle diameter of approximately 9 nm in the presence of US waves. These results are in reasonable agreement with the results achieved from XRD as shown in Table 1. The colloidal suspensions of Pd/Ag bimetallic NPs prepared by the sonochemichal reduction method are dark brown in color and can stably exist for several days, whereas the colors of Pd and Ag colloids prepared under the same condition are black and dark yellow, respectively. As shown in Figure 3b, the Pd NPs show a broad absorption peak within the UV– vis region because of d–d interband transitions whereas Ag NPs show strong absorbance around 400 nm which is attributed to the surface plasmon excitation of silver nanospheres, indicating the formation of silver NPs (Figure 3c) [7]. Figure 3. The UV–vis spectra a) Pd/Ag physical mixture b) Pd NPs c) Ag NPs, and d) Pd/Ag bimetallic NPs As illustrated in Figure 3a, the physical mixtures of Ag and Pd NPs exhibit simple addition of two individual spectra and also have a specific absorption peak near 400 nm. On the other hand, the prepared Pd/Ag NPs shows no absorption peak, as shows in Figure 3d. Pd/Ag bimetallic NPs were prepared by simultaneous sonochemical reduction method. The XRD data prove that the Pd/Ag NPs is formed. According to the histogram of particle size distribution, the Pd/Ag bimetallic NPs are monodispersed.