X-ray absorption spectroscopy of iron-doped conducting polymers

X-ray absorption spectroscopy (XAS) measurements were performed at the Fe K edge to determine the iron local structure in chemically prepared polyanil ine (PANI) and polypyrrole (PPy) samples prepared with FeCl3 as an oxidant. The samples were conditioned at different pHs by an acid-base treatment. I n both as synthesized-doped polymers, the observed dispersed Fe atoms were predominantly coordinated to chlorine as Fe(III)Cl-x species, where x = 6 f or PANI and x = 4 for PPy samples suggesting that the polymer-counteranion bonding is weaker than the iron-chelate one. For the PANI samples submitted to basic treatment, three different sets of Fe distances were found: five Fe-O at 2.00 Angstrom, three Fe-Fe at approximately 2.80 Angstrom and five Fe-Fe at 3.00 Angstrom and the near-edge spectra showed the presence of oct ahedrally coordinated Fe+3. These results strongly suggest the presence of small oxide/hydroxide aggregates. Similar data were obtained for PPy treate d with NH4OH. (C) 1999 Elsevier Science S.A. All rights reserved.