The infuence of the mixed phase (Ti–TiO2(A): TiO2(R)) on the optical band gap of TiO2 nanotubes heat treated at diferent temperatures

Abstract

Highly ordered TiO2 nanotubes (NTs) were synthesized by electrochemical anodization than annealed at diferent temperatures between 300 and 900 °C for 3 h. The elaborated NTs adhere well to the Ti substrate over the annealing temperature range of 300–600 °C. The TiO2 NTs morphology begins to gradually evolve for temperatures up to 700 °C and approaches that of nanoparticles until the latter become predominant at T above 800 °C. Refection measurements show that the NTs present refection of 7% at 600 °C, corresponding to the lowest band gap 2.59 eV. This can be related to the presence of the mixed phase (Ti–TiO2(A)–TiO2(R)).The charge carrier density decreases from 2.34× 10+21 to 3.61× 10+13 cm−3when the annealing temperature increases, that accompanied by a reduction in the resistivity from 142.23 to 29.56Ω.cm which is adequate to photo anode application.