Fe3+ intercalation/deposition on vermiculites and interaction with pyrrole: a Mössbauer spectroscopic investigation

Abstract

AbstractThe Fe3+ uptake from aqueous and methanol solutions of FeCl3·6H2O in two vermiculites from Santa Olalla and Ojén (Spain) and in a montmorillonite from Wyoming has been investigated by Mössbauer spectroscopy at room temperature and 4.2 K. The samples were further characterized by X-ray diffraction. The low temperature Mössbauer spectra reveal the deposition of akaganeite and perhaps some ferrihydrite on the external surface of the clay minerals. The room temperature spectra exhibit two Fe3+ quadrupole doublets in addition to the Fe2+ components of the structural iron in the sheet silicates. On treatment in ⩾0.04 M Fe3+ solutions the Fe3+ quadrupole splittings of 0.90 mm/s and 0.55 mm/s can be assigned to the mineral akaganeite; at smaller Fe3+ concentrations one of these doublets has a quadrupole splitting similar to that of the Fe3+ in the original vermiculites, the other one a quadrupole splitting of 0.6–0.7 mm/s, which can be considered as a hint for an uptake of Fe dimers in the interlayer space irrespective of the solvent used for iron deposition. Preliminary results show that the adsorption of pyrrole in all of our Fe3+-containing samples, regardless of the preparation in aqueous or methanol solution, results in the formation of polypyrrole and a concomitant reduction of some of the Fe3+. An uptake of pyrrole into the interlayer space has been observed only in the Fe3+-containing Wyoming montmorillonite and in the Ojén vermiculite treated with the methanol solution of iron chloride.