3.4. Synthetic processes and conditions
The Zn–Fe(III) LDH phase was apparently generated only when applying the synthetic approach that employed Zn–Fe(II) PPT. This result indicates that Fe(II) atoms were able to incorporate into brucite-like trioctahedral hydroxide layers composed principally of zinc hydroxides, and that these trioctahedral layers were stable even when the Fe(II) BIBF 1202 in the framework were oxidized to obtain Fe(III). In contrast, the Fe(III) species exhibited a tendency not to form trioctahedral layers with Zn species when applying the Zn–Fe(III) PPT synthetic process, and consequently separate simonkolleite and hydrous ferric oxides phases were generated.
As a general rule, both the ionic radius and electronegativity of each element will greatly affect the outcome of isomorphic substitution reactions. The ionic radii of Zn, Fe(II) and Fe(III) are 0.0740, 0.0780 and 0.0645 nm, respectively , while their respective electronegativities are 1.65, 1.83 and 1.96 . Thus, the ionic radius of Zn is closer to that of Fe(II) than that of Fe(III) and the electronegativity of Zn is also closer to that of Fe(II) than that of Fe(III). Therefore, Fe(II) atoms can be predicted to exhibit similar chemical properties and chemoaffinities to those of Zn atoms.