Annealing-induced phase transition in TiO₂ nanotube arrays: toward pH-responsive photocatalysis for methylene blue degradation

With the increasing severity of environmental pollution, the treatment of dye-containing wastewater has become a critical issue in the field of water purification. Photocatalytic degradation technology, as an efficient method for water pollution remediation, has attracted widespread attention. Titanium dioxide (TiO₂), due to its excellent photocatalytic properties, has been a focal point of research. In this study, TiO₂ nanotube arrays (TiO₂ NTs) were prepared via the anodization method, and the effects of annealing temperature on their performance in the photocatalytic degradation of methylene blue (MB) were investigated. The crystalline phase and optical absorption characteristics of the TiO₂ NTs were characterized using techniques such as X-ray diffraction (XRD) and UV-vis absorption spectroscopy. The results demonstrated that the photocatalytic performance of TiO₂ NTs is significantly influenced by phase transitions and pH. The TiO₂ NTs annealed at 800 °C achieved a 93.6% degradation efficiency for MB within 70 min, demonstrating the highest photocatalytic activity. Variations in pH affected the surface charge of TiO₂ NTs and their electrostatic interactions with MB molecules, thereby influencing the degradation efficiency. Furthermore, experiments using EDTA-2Na, BQ, and TBA as radical scavengers revealed that photogenerated holes and superoxide radicals played pivotal roles in the degradation process, while hydroxyl radicals contributed minimally. This study provides a theoretical foundation for the optimized design and practical application of TiO₂-based photocatalytic materials.