Electroless recovery of precious metals from acid solutions by n-containing electroactive polymers

Summary form only given. By coupling the metal reduction process in acid solutions with an increase in the intrinsic oxidation state of a N-containing electroactive polymer, such as polypyrrole (PPY), polyaniline (PAN) and their derivatives, and the subsequent reprotonation and reduction of the intrinsically oxidized polymer in acid media, spontaneous and sustained reduction of precious metals, gold in particular, to their elemental form is achieved. The rate of metal reduction is dependent on the intrinsic redox states of the polymer, the effective surface area of the polymer, and the pH of the solution. The X-ray photoelectron spectroscopic (XPS) Nls core-level spectra of protonated and deprotonated PPY and PAN after metal reduction suggest that the intrinsic structure of each polymer at the polymer/Au interface remains intact, even at [Au]/[N] mole ratio much greater than 1. The process, however, is limited by the decreasing effective surface area of the polymer due to metal coverage. Nevertheless, a typical polymer film is capable of accumulating more than 5 times its own weight of Au before the reduction rate is severely retarded.