Microwave-assisted synthesis of silver nanorods
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Pei-Wen Huang and Yu-Cheng Chang Department of Nuclear Science, National Tsing Hua University, 101, Section 2 Kwong Fu Road, 300 Hsinchu, Taiwan
Fu-Hsiang Ko National Nano Device Laboratories, 1001-1 Ta Hsueh Road, 300 Hsinchu, Taiwan
Tieh-Chi Chu Department of Nuclear Science, National Tsing Hua University, 101, Section 2, Kuang Fu Road, 300 Hsinchu, Taiwan (Received 29 August 2003; accepted 7 October 2003)
Described is a method for preparing crystalline silver nanorods in water, in the absence of a surfactant or polymer to direct nanoparticle growth, and without externally added seed crystallites. The procedure used is one in which a silver salt is reduced to silver metal by sodium citrate under the influence of microwave irradiation. Key aspects for the production of these nanorods are the use of a closed-chamber microwave heating system that allows precise temperature control and judicious choice of the citrate concentration. This novel finding demonstrates the utility of microwave-assisted synthesis and provides a promising method for the preparation of silver nanorods. I. INTRODUCTION
Metallic nanoparticles exhibit unusual optical, thermal, chemical, and physical properties that are due to a combination of a large proportion of high-energy surface atoms relative to the bulk solid and the nanometer-scale mean free path of an electron in a metal.1 It is well known that silver is superior to other nanostructured metal particles when considering its electrical conductivity,2 antimicrobial effects,3 optical properties,4 and use in oxidative catalysis.5 The preparation and characterization of silver nanoparticles has been discussed in a great number of publications. Previous strategies to control the growth of anisotropic nanoparticles have involved either hard templates6 or softer directing agents, including surfactants or polymers.7–9 Although good control over nanoparticle dimensions can be realized in these syntheses, removal of the unwanted template or directing agent from the nanoparticle surface can require harsh conditions or multiple washings. For sensing applications, such as surfaceenhanced Raman scattering, which requires adsorption of an analyte to the metallic nanoparticle surface, the presence of residues remaining from the synthesis of the nanoparticle may cause significant interference.10 When linking metallic nanoscale objects together in a rational way, great control is required over which surfaces of the nanoparticle are exposed; 1,11 again, surface-bound a)
Address all correspondence to this author. e-mail address: [email protected] J. Mater. Res., Vol. 19, No. 2, Feb 2004
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residues from the synthesis increase the difficulty of performing such surface chemistry. Recently, thermal factors have been demonstrated to affect the size and uniformity of nanoparticles.12 Controlling particle growth rate is possible through knowledge of a material’s properties and controlling of the reaction by changes to the time and temperature.13 When citrat
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