title: A novel and easy chemical-clock synthesis of nanocrystalline iron-cobalt bearing layered double hydroxides.
abstract: A novel synthesis of cobalt-iron layered double hydroxide (LDH) with interlayer chlorides was investigated. The method consists in mixing concentrated solutions of hexaamminecobalt(III) trichloride with ferrous chloride at room temperature and in anoxic conditions. Four initial Fe/Co atomic ratios have been tried out (0.12, 0.6, 1.2 and 1.8). Neither heating nor addition of alkali was employed for adjusting the pH and precipitating the metal hydroxides. Still, each mixture led to the spontaneous precipitation of a LDH-rich solid having a crystal-chemistry that depended on the initial solution Fe/Co. These LDHs phases were carefully characterized by mean of X-ray diffraction, (57)Fe Mössbauer spectrometry, transmission electron microscopy and chemical analysis (total dissolution and phenanthroline method). Solution Eh and pH were also monitored during the synthesis. Increasing initial Fe/Co ratio impacted the dynamic of the observed stepwise reaction and the composition of the resulting product. Once the two solutions are mixed, a spontaneous and abrupt color change occurs after an induction time which depends on the starting Fe/Co ratio. This makes the overall process acting as a chemical clock. This spontaneous generation of CoFe-LDH arises from the interplay between redox chemistries of iron and cobalt-ammonium complexes.
authors.affiliation: BRGM, 3 Avenue Claude Guillemin, BP 36009, 45060 Orléans Cedex 2, France. Electronic address: j.hadi@brgm.fr.
authors.forename: Jebril
authors.initials: J
authors.lastname: Hadi
authors.affiliation: BRGM, 3 Avenue Claude Guillemin, BP 36009, 45060 Orléans Cedex 2, France.
authors.forename: Sylvain
authors.initials: S
authors.lastname: Grangeon
authors.affiliation: CRMD CNRS - FRE 3520, Université d'Orléans, 1b rue de la Férollerie, 45071 Orléans Cedex 2, France.
authors.forename: Fabienne
authors.initials: F
authors.lastname: Warmont
authors.affiliation: BRGM, 3 Avenue Claude Guillemin, BP 36009, 45060 Orléans Cedex 2, France.
authors.forename: Alain
authors.initials: A
authors.lastname: Seron
authors.affiliation: IMMM CNRS - UMR 6283, Université du Maine, Le Mans Cedex 9, France.
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Greneche
keywords: Cobalt; Ferrous chloride; Green rust; Hexaamminecobalt trichloride; Iron; LDH