Characterization and thermal stability of cobalt-modified 1-D nanostructured trititanates

One-dimensional (1-D) nanostructured sodium trititanates were obtained via alkali hydrothermal method and modified with cobalt via ion exchange at different Co concentrations. The resulting cobalt-modified trititanate nanostructures (Co-TTNS) were characterized by TGA, XRD, TEM/SAED, DRS-UV-Vis and N₂ adsorption techniques. Their general chemical formula was estimated as Na_xCo_y/2H_2−x−yTi₃O₇·nH₂O and they maintained the same nanostructured and multilayered nature of the sodium precursor, with the growth direction of nanowires and nanotubes along 010]. As a consequence of the Co²⁺ incorporation replacing sodium between trititanate layers, two new diffraction lines became prominent and the interlayer distance was reduced with respect to that of the precursor sodium trititanate. Surface area was slightly increased with cobalt intake whereas pore size distribution was hardly affected. Besides, Co²⁺ incorporation in trititanate crystal structure also resulted in enhanced visible light photon absorption as indicated by a strong band-gap narrowing. Morphological and structural thermal transformations of Co-TTNS started nearly 400 °C in air and the final products after calcination at 800 °C were found to be composed of TiO₂-rutile, CoTiO₃ and a bronze-like phase with general formula Na_2xTi_1−xCo_xO₂.