Synthesis, characterization, and thermal stability study of sodium and sodium–aluminum titanate nanotubes

This study aimed to investigate the synthesis, characterization, and thermal stability of pure and Al ion-exchange titanate nanotubes (Na2Ti3O7 and NaxAlyTi3O7, respectively), observing their vibrational and structural properties. The samples were synthesized by the conventional hydrothermal method and characterized by X-ray diffraction, electron paramagnetic resonance (EPR), Raman, and Fourier Transform Infrared (FTIR) spectroscopies, revealing the obtainment of sodium titanate and aluminum titanate nanotubes, with average lengths and diameters of 130 nm and 10 nm for sodium titanate and 150 and 6.2 nm for sodium-aluminum titanate nanostructures, obtained in a basic medium. When the nanotubes are subjected to an acid medium, the nanostructures have average sizes of 9 and 10 nm. EPR analyses show that Al's presence in the crystal lattice results in a greater exchange of energy between the unpaired species with the lattice. Experimental temperature-dependent Raman scattering studies were performed on samples in a temperature range of 298–813 K. The results showed that sodium ions played a significant role in the structural stability of sodium titanate nanotubes, differently from the aluminum titanate nanotubes, which indicated lower thermal stability of these nanostructures after the incorporation of Al3+ ions into the nanotube lamellae.