Abstract

The efficient electroless deposition of gold from aqueous solutions has been achieved via redox interaction between Au(III) ions and conducting polymers such polypyrrole, polyaniline and poly(3,4-ethylenedioxythiophene). When using the doped, conductive bulk powder forms of these polymers, the average size of the gold deposits decreased from ca. 10 to ca. 1 µm as the initial pH of the reaction solution was increased from pH 0 to 7. In experiments conducted at neutral pH, pH drift down to pH 3 occurred during the redox reaction. However, if the base-treated, non-conductive forms of the polymers were added to AuCl₃ solutions at pH 7, the solution pH remained close to neutral, and finely dispersed gold deposits of 100–400 nm were obtained, strongly suggesting that the gold nucleation is pH-dependent. These findings were then used in attempts to prepare gold-clad latex particles by using micrometer-sized, conducting polymer-coated polystyrene latexes as redox templates for the reduction of gold from solution. Although it was not possible to obtain homogeneous gold coatings, a series of latex particles randomly decorated with 40–60 nm gold nanoparticles was obtained, with gold loadings of up to 12.5 wt% as measured by TGA. XPS studies confirmed the presence of metallic gold at the latex surface, in addition to an increase in the oxidation state of the conducting polymer overlayer, thus confirming that a redox interaction had indeed occurred. Disk centrifuge studies clearly indicated a marked decrease in the colloidal stability of the latexes after gold decoration. Finally, pressed pellet solid-state conductivity measurements showed the composite particles to be non-conductive, which is no doubt due to the discrete, well-sepa0rated nature of the gold nanoparticles on the latex, which prevents efficient charge transport.