Titanate nanotubes and their magnetic properties: Effect of ion exchange and calcination temperature

Transition magnetic metals (Fe, Ni, Co) were inserted into sodium titanate nanotubes subjected to calcination. In the calcination process at 400 °C, the nanotubular structure of the samples with magnetic species breaks down, while at 800 °C the formation of TiO 2 nanoparticles occurs mainly in the anatase and rutile phases. Optical studies revealed that the Fe 3+ , Ni 2+ and Co 2+ ions insertion promoted red shift in UV–Vis and the samples, showed smaller energy gap than NaTiNT. In addition, the samples calcined at 400 °C showed higher conductivity due to the greater number of oxygen defects. All samples exhibited ferromagnetic behavior at room temperature in low magnetic fields. The ferromagnetic behavior for these materials may originate from the interaction between the ions intercalated in the titanate lattice from the defects of oxygen incorporated in the nanotubes by the calcination process and from the transition from Ti 4+ to Ti 3+ in some sites of the nanotube structure. Graphical Abstract