Chemical deposition of palladium on leucoemeraldine from solutions: State and distribution of palladium species

Abstract

The reactions of polyaniline in its lowest oxidation state, leucoemeraldine (LM), with palladium ions in PdCl2, Pd(NO3)2, mixed solutions of PdCl2 and Pd(NO3)2 and mixed solutions of PdCl2 and AuCl3 were investigated. The amount of Pd deposited on the leucoemeraldine film was calculated from the decrease in Pd ion concentration in solution as determined by inductively coupled plasma emission spectroscopy. The state and distribution of the Pd species on the film surface was analysed using X-ray photoelectron spectroscopy and atomic force microscopy, respectively. The results showed that a much faster and more complete reduction of Pd ions to Pd0 occurred in the Pd(NO3)2 solution as compared to the PdCl2 solution and the explanation for this difference in reactivity has been offered from an electrochemical and coordination chemistry point of view. The mixing of Pd(NO3)2 with PdCl2 appears to affect the Pd coordination states in solution which in turn affects the Pd uptake rate and the manner in which the Pd is deposited on the LM surface. In mixed solutions of PdCl2 and AuCl3, it was clearly seen that the presence of a small amount of AuCl3 (molar ratio of AuCl3/ PdCl2 of 0.1) can greatly accelerate the uptake of Pd and complete removal of Pd ions from PdCl2 can be accomplished.