Thermally induced phase transformations of lepidocrocite-like ferrititanate nanosheets synthesized from a low cost precursor by hydrothermal method

Thermal stability and phase transformation paths of Lepidocrocite-like layered titanates (LTs-NS) are not well established. This is especially true for the ferrititanate nanosheets, recently synthesized from mineral sands. High-temperature phase transformation paths of three types of lepidocrocite-like layered ferrititanate nanosheets were examined by in situ HT-XRPD and TG analyses. We analyzed sodium-rich (NaLTs-NS), protonated (pLTs-NS), and a nanohybrid (pLTs-o-2C18-NS) nanosheets, the last one composed from the individual ferrititanate host layers and dimethyldioctadecylammonium cations (2C18+). We investigated how the presence of Na+, H+ and 2C18+ influences the thermal behavior of LTs nanosheets. The three materials show different thermal evolution paths. Na-LTs-NS exhibit the highest thermal stability, where the layered structure is preserved to at least 600 °C. Na-LTs-NS transform to freudenbergite (Na2(Ti,Fe)8O16) at 700 °C. Rutile and pseudobrookite form at higher temperatures in Na-rich ferrititanate system and coexist with freudenbergite. Thermal stability of protonated nanosheets is much lower since the layered structure is destroyed under 500 °C. High temperature phases pseudobrookite (Fe2TiO5) and rutile (TiO2) crystallize at ∼700 °C which is in accordance with the stability field for the Fe2O3-TiO2 binary phase diagram rich in TiO2. In the case of pLTs-o-2C18-NS rutile and hematite form at 650 °C.