Synthesis and Properties of Monometallic and Bimetallic Silver and Gold Nanoparticles
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1207-N10-62
Synthesis and Properties of Monometallic and Bimetallic Silver and Gold Nanoparticles †
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Xavier E. Guerrero-Dib , Ubaldo Ortiz-Méndez , Selene Sepúlveda-Guzmán , Oxana V. Kharissova , Domingo ‡ ‡ Ferrer-Luppi , , Miguel Jose-Yacaman †
Programa Doctoral en Ingeniería de Materiales (PDIM), Facultad de Ingeniería Mecánica y Eléctrica, Universidad Autónoma de Nuevo León, Av. Universidad s/n. Ciudad Universitaria, San Nicolás de los Garza, Nuevo León, C.P. ‡ 66451; The Texas Materials Institute, The University of Texas at Austin, 1 University Station C0400, Building CPE 5.404, Austin, Texas 78712-0231
ABSTRACT Synthesis of Au, Ag monometallic, and Au-Ag bimetallic nanoparticles have been synthesized by successive reduction of metal salts with ascorbic acid on prefabricated seeds in the presence of cetyltrimethylammonium bromide (C16H33)N(CH3)3Br (CTAB), as a cationic surfactant, is presented in this paper. This coverage method for the prefabricated seeds is uniform, although in some cases deviations from a spherical shape are observed with the formation of nanorods or nanoprisms. Results using high-resolution STEM-XEDS elemental mapping suggest that the actual distribution of the two metals within the multilayer spheres may involve partial alloying of the metals. KEY WORDS Nanoparticles, Cetyltrimethylammonium Bromide (CTAB), Transmission Electron Microscopy (TEM), multishell nanostructured particles. Introduction Bimetallic nanoparticles are of great interest because of the modification of properties observed not only due to size effects, but also as a result of the combination of different metals,1,2 either as an alloy or as a core-shell structure, modifying the catalytic, electronic, and optical properties of the monometallic nanoparticles.1-5 One of this characteristics are the optical properties due to the resonance of surface plasmons with visible light at well defined frequencies.6 The specific resonance frequency depends on a number of parameter such as nanoparticle composition,7,8 morphology,9,10 concentration,11 solvent refractive index,12 surface charge,13 and temperature.14 These effects are only observed in the visible range for a few metals, among which gold and silver have been most often studied, mainly because of their chemical stability. When more than one metal atom type is present in the composition of the nanoparticles, the actual distribution of the metal atoms within the particle is of prime importance for correct interpretation of the optical properties. The case of gold and silver is particularly difficult to control, since they can form perfectly miscible alloys over the whole composition range, and their crystalline lattice constants are extremely similar (4.078 A° for Au; 4.086 A° for Ag), so that there is still a debate as to whether or not pure core–shell geometries can be obtained. For this purpose, many colloidal methods of synthesis have been approached to obtain bimetallic nanoparticles,15-26 such as homogeneous reduction in aqueous solutions,18 or phase transfer
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