Halide Ion Effect in Shape Transformation from Silver Triangular Nanoprisms to Silver Nanodisks
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Halide Ion Effect in Shape Transformation from Silver Triangular Nanoprisms to Silver Nanodisks Israel A. López1 and Idalia Gómez1 1 Laboratorio de Materiales I, Facultad de Ciencias Químicas, Universidad Autónoma de Nuevo León, 66475, San Nicolás de los Garza, Nuevo León, México ABSTRACT Silver triangular nanoprisms (TNP’s) were transformed into silver nanodisks (NDK’s) by addition of halide ion solution (chloride, bromide and iodide). The shape transformation of the TNP’s is due to the selective etching effect of halide ions at their vertices. TNP’s were synthesized via a photoinduced growth process, and then different concentrations of potassium halide solutions were added into the TNP’s colloids under vigorous stirring. Images of the obtained nanoparticles were recorded by scanning electron microscopy (SEM). The shifts of the in-plane dipole plasmon resonance band allow us to identify the differences among the three halides. These differences might be due to the distinct sizes of halides, and the solubility product constant values of each silver halide. We found that the etching ability of the halides, at a concentration of 1.0 mM, to truncate the vertices of TNP’s is in the order of Br- > Cl- > I-. In contrast, at a concentration of 0.01 mM, the order of the etching ability is Br - > I- > Cl-. INTRODUCTION Silver and gold nanoparticles have been of great interest in the last years because of their unique chemical and physical properties [1-3]. These noble metal nanoparticles have potential applications including surface plasmon resonance [4], surface-enhanced Raman scattering [5], biosensing [6], and optoelectronic devices [7]. The localized surface plasmon resonance highly depends on the particle size and shape, and surface modifications. Silver nanoparticles are easily to use in the design of plasmonic materials and nanodevices [7,8]. Therefore, great efforts have been made to control the size and shape of silver nanoparticles. Nowadays, there are some reports about sculpted nanoparticles obtained by a shape transformation process. It has been reported that the truncation at the vertices of TNP’s in order to obtain NDK’s can be achieved by heating [9], pH changes [10], chemical redox [11], and halide ion solutions addition [12-16]. This last technique has been widely studied. However, the reports are not consistent about the etching ability of the different halides [13,16], therefore, is necessary to study the ability of each halide to truncate the vertices of TNP’s. Besides, concentration of halide ions affects their chemical activity. Herein, we report the study of the halide ion effect in the transformation of TNP’s into NDK’s by addition of solutions with different concentrations of chloride, bromide, and iodide ions. EXPERIMENT All chemical reagents used in this work were of analytical grade and were used without any further purification. A Perkin-Elmer lambda 12 spectrophotometer was employed for the UV-Vis analysis of the silver nanoparticle dispersions without any further preparation. The silver
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