Exploration of Mid-Temperature Alkali-Metal-Ion Extraction Route Using PTFE (AEP): Transformation of α-NaFeO₂-Type Layered Oxides into Rutile-Type Binary Oxides

Abstract

Alkali-metal-ion extraction reactions using poly­(tetrafluoroethylene) (PTFE; AEP reactions) were performed on two kinds of α-NaFeO₂-type layered compounds: Na_0.68(Li_0.68/3Ti_1–0.68/3)­O₂ and K_0.70(Li_0.70/3Sn_1–0.70/3)­O₂. At 400 °C in flowing argon, these layered compounds were reacted with PTFE. By these reactions, alkali-metal ions in the layered compounds were successfully extracted, and TiO₂ and SnO₂ with rutile-type structure were formed. The structural similarity between the alkali-metal-ion-extracted layered compounds and the binary metal oxide products in these unique alkali-metal-ion extraction reactions was interpreted in terms of their interatomic distance distribution by atomic pair distribution function analysis. The results of this study indicate that PTFE is an effective agent to extract alkali-metal ions from layered compounds, and AEP reaction is not limited to the previously reported γ-FeOOH-type layered titania K_0.8(Li_0.27Ti_1.73)­O₄, but is also applicable to other layered titania and other non-titanium-based layered metal oxides. Therefore, it was clarified that AEP reactions are widely applicable routes to prepare various compounds, including those that are difficult to synthesize by other reactions