Enhanced thermal stability and photocatalytic property of highly ordered anodized TiO2 nanotube arrays with interstitial nitrogen as dominant point defect

Highly regular TiO2 nanotube arrays (TNTs) with interstitial nitrogen as the dominant point defect have been successfully prepared by annealing the as-anodized TNTs in N2 in a temperature range of 400–650 °C. Using analysis methods that include field emission scanning electron microscopy, X-ray diffraction patterns, and Raman spectroscopy, the thermal stability of TNTs annealed in N2 was found to be higher than that of TNTs annealed in O2. The interstitial nitrogen is considered as the dominant point defect in TNTs annealed in N2, which results in the notably improved thermal stability of the highly ordered TNTs. However, the content of hydroxyl oxygen on the surface of TNTs is significantly influenced by annealing temperature, which is closely related to photocatalytic activity. Optimized photocatalytic property of photodegradation of MO with a pseudo-first-order reaction constant k value of (5.065 ± 0.139) × 10–2 h−1 is achieved for TNTs annealed in N2 at 600 °C. These findings serve to provide simple and versatile guidelines to fabricate highly ordered TNTs with controllable point defects, enhanced thermal stability, and a high level of photocatalytic activity.