Studies on Fe-modified nanostructured trititanates

Abstract

1D nanostructured sodium trititanate was synthesized by alkali hydrothermal treatment of TiO2 anatase, coexisting with incompletely converted precursors like nanosheets and poorly crystalline aggregates. This product easily exchanged with Fe3+ at room temperature to saturation at approximately 8 wt% Fe,following the Langmuir adsorption model. Iron exchange caused changes on the structural (interlayer shrinkage) and optical properties of the nanomaterial without affecting significantly its original morphology and mesoporous structure. According to consistent XRD and TEM/EDS data, iron was saturated within the interlayers of the 1D nanostructured particles at a lower content as compared to the coexisting poorly crystalline aggregates. Based on XPS results iron was found to be also in a lower oxidation state Fe2+, likely on the layered surface of the 1D nanostructured particles, through a mechanism tentatively explained by formation of structural iron defects promoted by the acidic medium. The iron modified trititanate nanostructure (Fe/TTNS) is stable up to 400 ◦C and at high temperatures it is eventually transformed into rutile(TiO2) and pseudobrookite (Fe2TiO5), whereas some freudenbergite phase (Na2Fe2Ti6O16) is generated due to residual sodium.