Electrochemically Controlling the Size of Gold Nanoparticles

Abstract

This work demonstrates the electrochemical synthesis of nanoscale gold particles using a surfactant solution. Tetradodecylammonium bromide ͑TTAB͒ surfactant was applied to stabilize the gold clusters. Experimental results reveal that the size of the produced gold nanoparticles is controlled by the amount of TTAB surfactant, the current density, and the growth temperature. The size of the gold nanoparticles can be controlled in the range 58.3-8.3 nm. The particle size decreases as the amount of TTAB increases from 1 to 90 mg. The optimal current density in this study was 3 mA/cm 2 . The size of the produced nanoparticles increases linearly with the growth temperature from 25 to 60°C. The gold nanoparticles were observed by transmission electron microscopy, ultraviolet-visible spectrometry, and X-ray photoelectron spectroscopy. A mechanism for electrochemically controlling the size of the gold nanoparticles is presented.Nanoscale materials are of great interest due to their unique optical, electrical, and magnetic properties. Extensive investigations of gold nanoparticles in biology, nonlinear optical switching, the formation of modified surfaces for surface-enhanced Raman scattering, immunoassay labeling, optical contrast agents, and catalysis revealed that the size and shape of the particles strongly determine their physical and chemical properties. 1-6 Hence, controlling the particle size is very important. The electrochemical production of nanoparticles has been widely studied since the early work of Reetz et al. in 1994. 7,8 Their studies indicated that size-selective nanosized transition metal particles could be prepared electrochemically using tetraalkylammonium salts as stabilizers of metal clusters in a nonaqueous medium. The electrochemical method has been demonstrated to be superior to other nanoparticle production approaches because of its lower processing temperature, modest equipment, ease of controlling the yield, low cost, and high quality. 9-14 A recent study synthesized gold nanorods electrochemically by introducing a shapeinducing cosurfactant. 15 Yin et al. 16 developed a novel electrochemical technique for the size-controlled synthesis of spherical nanoparticles in poly͑N-vinylpyrrolidone͒ solution. Bartlett et al. 17 and Wiley et al. 18 reported the deposition of metal using other electrochemical approaches. The authors' research group developed the electrochemical method proposed herein to form crooked gold nanocrystals with a novel structure, using micelle templates formed from two surfactants with isopropanol addition. 19,20 In addition, carefully controlling the amount of acetone solvent added to the solution of surfactants changes the shape of the gold nanoparticles from spherical to cubic. 21 This work experimentally studies the synthesis of gold nanoparticles using a two-electrode electrochemical cell in surfactant solution, with special emphasis on the characteristics of the gold nanoparticles produced. The amount of surfactant, the current density, and the growth temperature are al...

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