Fe-doped nanostructured titanates synthesized in a single step route

In this research nanostructured titanates, containing iron in the structure, were obtained through a single-step alkaline hydrothermal route aiming at reduction of band-gap energy. In the process, a Fe-Ti rich Brazilian mineral sand was mixed with 10 M of NaOH and then submitted to isothermal treatments at temperatures ranging from 110 to 190 °C in an autoclave. The as-obtained products were water-washed and then characterized by transmission electron and scanning transmission electron microscopies, X-ray photoelectron, Mössbauer and diffuse reflectance spectroscopies. Transmission electron microscopy analyses showed a morphological dependence of the product as a function of the temperature, i.e., titanate nanosheets were predominantly formed at lower temperatures (110°C-150°C), while nanoribbons, with some nanosheets and nanoparticles, were the main products at higher temperatures (> 150°C). Using energy dispersive X-ray it was determined that iron was incorporated into nanosheets. On the other hand, the as-obtained nanoribbons were Fe-free, while iron was principally associated with nanoparticles attached to the nanoribbons. By means of X-ray photoelectron and Mössbauer spectroscopies, it was elucidated that iron adopted Fe^{3 +} form in the as-prepared nanosheets, occupying octahedral sites inside the titanate lepidocrocite-like structure. Diffuse reflectance spectroscopy showed a change of absorption pattern from nanosheets to nanoribbon/nanoparticle assembly: nanosheets exhibited high absorption from ultraviolet up to the visible light range, while the nanoribbon/nanoparticle assembly demonstrated a drop in absorption in the visible light range. These results suggest that Fe^{3 +} incorporation inside the titanate structure is responsible for enhancing the visible light absorption, making these nanosheets potentially suitable for applications in photoinduced processes.