title: Topochemical synthesis of Co-Fe layered double hydroxides at varied Fe/Co ratios: unique intercalation of triiodide and its profound effect.
abstract: Co-Fe layered double hydroxides at different Fe/Co ratios were synthesized from brucite-like Co(2+)(1-x)Fe(2+)(x)(OH)(2) (0 ≤ x ≤ 1/3) via oxidative intercalation reaction using an excess amount of iodine as the oxidizing agent. A new redoxable species: triiodide (I(3)(-)), promoted the formation of single-phase Co-Fe LDHs. The results point to a general principle that LDHs with a characteristic ratio of total trivalent and divalent cations (M(3+)/M(2+)) at 1/2 may be the most stable in the oxidative intercalation procedure. At low Fe content, e.g., starting from Co(2+)(1-x)Fe(2+)(x)(OH)(2) (x < 1/3), partial oxidation of Co(2+) to Co(3+) takes place to reach the M(3+)/M(2+) threshold of 1/2 in as-transformed Co(2+)(2/3)-(Co(3+)(1/3-x)-Fe(3+)(x)) LDHs. Also discovered was the cointercalation of triiodide and iodide into the interlayer gallery of as-transformed LDH phase, which profoundly impacted the relative intensity ratio of basal Bragg peaks as a consequence of the significant X-ray scattering power of triiodide. In combination with XRD simulation, the LDH structure model was constructed by considering both the host layer composition/charge and the arrangement of interlayer triiodide/iodide. The work provides a clear understanding of the thermodynamic and kinetic factors associated with the oxidative intercalation reaction and is helpful in elucidating the formation of LDH structure in general.
authors.affiliation: International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan. MA.Renzhi@nims.go.jp
authors.forename: Renzhi
authors.initials: R
authors.lastname: Ma
authors.forename: Jianbo
authors.initials: J
authors.lastname: Liang
authors.forename: Kazunori
authors.initials: K
authors.lastname: Takada
authors.forename: Takayoshi
authors.initials: T
authors.lastname: Sasaki
mesh_terms: D003035:Cobalt / Q000737:chemistry*; D006878:Hydroxides / Q000737:chemistry*; D007454:Iodides / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D008855:Microscopy, Electron, Scanning; D010084:Oxidation-Reduction; D012542:Scattering, Radiation; D014961:X-Ray Diffraction
chemical_list: D006878:Hydroxides; D007454:Iodides; D003035:Cobalt; D007501:Iron