Reaction of pyrrole and chlorauric acid - A new route to composite colloids

Composite colloids of gold and polypyrrole were prepared using two differen t methods: 1, using pyrrole colloid, created by the oxidation of pyrrole by ferric chloride, to subsequently reduce chlorauric acid and, 2, oxidizing pyrrole monomer with chlorauric acid in a sodium dodecylbenzene sulfonate s olution. In each case, the polypyrrole colloid consisted of irregularly sha ped particles approximately 500 nm in diameter. The gold produced in each c ase was in the form of irregular spheres, approximately 407 nm in diameter in method 1 and 13 nm in method 2. X-ray photoelectron spectroscopy was use d to determine the oxidation state of the species present. Transmission ele ctron microscopy and light scattering data were used to determine the parti cle sizes of both gold and polypyrrole colloids. Energy dispersed spectrum X-ray analysis and electron diffraction were used to confirm the presence o f metallic gold in the composite colloids. The second-order rate constant f or the reaction of chlorauric acid with pyrrole in dilute solution was foun d to be 13 M-1 s(-1). Aqueous solutions of palladium, platinum, rhodium, co balt, tin, silver, zinc, nickel, titanium, cadmium, mercury, arsenic, and s elenium were also examined for their potential to act as oxidants to produc e composite polypyrrole colloids. Palladium, platinum, and rhodium salts we re suitable oxidants, producing polypyrrole in less than 12 h. (C) 2001 The Electrochemical Society.