Novel gold-polypyrrole anisotropic colloids : a TEM investigation

Colloidal Au is prepared by oxidative polymerization of pyrrole (PY) by using HAuCl sub(4). Different amounts of PY were added and stirred in molar relation to Au salt (R identical with [HAuCl sub(4)]/[PY] identical with 0.1, 0.3, 0.5, 1.0). Upon mixing the aqueous solution of HAuCl sub(4) with PY, polymerization occurred within a few minutes. The solution was stirred for 2 days, at room temperature. The black powder was collected after washing with ethanol and water, using centrifugation cycles. The oxidation of PY into polypyrrole (PPY) and the reduction of HAuCl sub(4) to Au occur simultaneously. TEM studies reveal different nanostructure of anisotropic Au-PPY colloids. A mixture of near-spherical and elongated Au particles are observed when R identical with 0.1. At R identical with 0.3, a `ginger'-like growth is seen.