Synthesis and transformation of iron-based layered double hydroxides

Iron-based layered double hydroxides (LDHs) obey to the general chemical formula [MII(1-x)MIIIx(OH)2]x+. [(x/n) An-, m H2O]xand contain a minimum of 50 % of iron, i.e. FeII or FeIII, in the cationic sheets. As LDHs contain FeII species, these are interesting minerals for several applications such as the reduction of anionic pollutants or the degradation of organic pollutants. They are mostly prepared either by coprecipitation of dissolved species or by oxidation of hydroxilated FeII species. The synthesis routes are visualised in binary and ternary massbalance diagrams. The LDH[FeII-FeIII] crystals are well crystallised hexagonal plates, the size of which diminishes rapidly when divalent or trivalent cations substitute iron. The LDH[FeII-FeIII-CO3] transforms into a mixture of magnetite Fe3O4 and siderite FeCO3 in alkaline conditions, but the adsorption of silicate or phosphate anions on the lateral faces of the crystal prevents this decomposition. In oxic conditions, two mechanism of transformation are identified depending upon the kinetics: (i) fast in situ oxidation within the solid, (ii) dissolution-precipitation of the LDH that leads to the formation of ferric oxyhydroxides such as goethite (FeOOH). Submitted to Applied Clay Science Special Issue: Synthesis of Clay Minerals and Clay-based Materials. Synthesis and transformation of iron-based layered double hydroxides C. Ruby*, M. Usman, S. Naille, K. Hanna, C. Carteret, M. Mullet, M. François, M. Abdelmoula a Laboratoire de Chimie Physique et Microbiologie pour l’Environnement (LCPME), UMR7564 CNRS-Nancy Université, 405, Rue de Vandœuvre 54600 Villers-Lès-Nancy (France) b Institut Jean Lamour, Département P2M, Matériaux-Métallurgie-Nanosciences-Plasmas-Surfaces UMR 7198 CNRS Nancy-Université UPV-Metz ABSTRACT Iron-based layered double hydroxides (LDHs) obey to the general chemical formula [M(1-x)M III x(OH)2] . [(x/n) A, m H2O] xand contain a minimum of 50 % of iron, i.e. Fe or Fe, in the cationic sheets. As LDHs contain Fe species, these are interesting minerals for several applications such as the reduction of anionic pollutants or the degradation of organic pollutants. They are mostly prepared either by coprecipitation of dissolved species or by oxidation of hydroxilated Fe species. The synthesis routes are visualised in binary and ternary mass-balance diagrams. The LDH[Fe-Fe] crystals are well crystallised hexagonal plates, the size of which diminishes rapidly when divalent or trivalent cations substitute iron. The LDH[Fe-Fe-CO3] transforms into a mixture of magnetite Fe3O4 and siderite FeCO3 in alkaline conditions, but the adsorption of silicate or phosphate anions on the lateral faces of the crystal prevents this decomposition. In oxic conditions, two mechanism of transformation are identified depending upon the kinetics: (i) fast in situ oxidation within the solid, (ii) dissolution-precipitation of the LDH that leads to the formation of ferric oxyhydroxides suchIron-based layered double hydroxides (LDHs) obey to the general chemical formula [M(1-x)M III x(OH)2] . [(x/n) A, m H2O] xand contain a minimum of 50 % of iron, i.e. Fe or Fe, in the cationic sheets. As LDHs contain Fe species, these are interesting minerals for several applications such as the reduction of anionic pollutants or the degradation of organic pollutants. They are mostly prepared either by coprecipitation of dissolved species or by oxidation of hydroxilated Fe species. The synthesis routes are visualised in binary and ternary mass-balance diagrams. The LDH[Fe-Fe] crystals are well crystallised hexagonal plates, the size of which diminishes rapidly when divalent or trivalent cations substitute iron. The LDH[Fe-Fe-CO3] transforms into a mixture of magnetite Fe3O4 and siderite FeCO3 in alkaline conditions, but the adsorption of silicate or phosphate anions on the lateral faces of the crystal prevents this decomposition. In oxic conditions, two mechanism of transformation are identified depending upon the kinetics: (i) fast in situ oxidation within the solid, (ii) dissolution-precipitation of the LDH that leads to the formation of ferric oxyhydroxides such as goethite (FeOOH).