This study attempted the synthesis of Zn–Fe(III) LDHs through two different pathways, using either Fe(II) or Fe(III) with Zn as the initial reagents. The two precipitates obtained were subsequently oxidized to fully convert Fe(II) into Fe(III) within the solid framework. The products exhibited different colors, although in both cases the valency of Fe species incorporated in the precipitates was considered to be Fe(III) based on 57Fe Mössbauer spectroscopic data. The Zn–Fe(II) PPT derived from the synthesis using the Fe(II) reagent was composed of a Zn–Fe(III) LDH phase, as determined from the results of XRD and ATR-FTIR studies. In contrast, the Zn–Fe(III) PPT obtained from the Fe(III) reagent did not contain an LDH phase, but rather consisted of simonkolleite and hydrous ferric oxide.
During this study of the synthesis of Zn–Fe(III) LDHs, it was found that the Fe valency in the initial reagent affected the formation of LDH phases. Fe(II) species, which are similar to Zn in terms of ionic radii and electronegativities, are more likely to form trioctahedral hydroxide layers with Zn species, and these are maintained in a stable manner within the framework of the material even after oxidation to form Fe(III) species.