Controlled growth of gold nanoparticles in AOT/C12E4/isooctane mixed reverse micelles

Stable anisotropic gold nanoparticles were prepared by the reduction of a relatively high concentration of tetrachloroauric acid with hydrazine in mixed reverse micelles formed with anionic surfactant AOT and nonionic surfactant tetraethylene glycol dodecyl ether (C12E4) in isooctane. It was found that the C12E4 serves not only as a structure modifier but also as a stabilizer for Au particles, to prevent their further growth and precipitation. By the analyses of a high-resolution electron microscope, electron diffraction patterns, and energy-dispersive X-ray analysis (EDX), the resultant particles have been found to be pure gold of face-centered cubic structure. In the presence of C12E4, the Au particle size is larger than that in the absence of C12E4, while the particle size decreases with increases in the concentration of C12E4. The molar ratio of hydrazine to HAuCl4 was found to be an important parameter in the control of size and shape for the production of gold nanoparticles. A decrease in the molar ratio of hydrazine to HAuCl4 resulted in larger Au particles with significantly more polydispersity. When the HAuCl4 was injected directly into the mixed reversed micelles containing hydrazine, anisotropic gold nanoparticles, such as cylinders and trigons, were obtained at the molar ratio of hydrazine to HAuCl4 of less than 0.5. (C) 2001 Academic Press.