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

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) and polyaniline (PAN), and the subsequent reprotonation and reduction of the intrinsically oxidized polymer in acid media, spontaneuos and sustained reduction of precious metals, such as gold and palladium, to their elemental form is readily achieved. The rate of metal reduction is dependent on the intrinsic redox states of the polymer, the effective surface area, and the pH of the solution. The X-ray photoelectron spectroscopic (XPS) N1s core-level spectra of protonated and deprotonated PPY and PAN after metal reduction suggest that the intrinsic structure of each polymer at the polymer/metal interface remains intact, even at [Metal]/[N] mole ratios much greater than 1. The process is limited, however, by the decreasing effective surface area of the polymer due to metal coverage.