Accepted: 27 August 2026
A systematic investigation of pure and Fe-doped TiO₂ nanotube array (TNT) photocatalysts is presented, focusing on the influence of annealing temperature on their structural, morphological, optical and compositional characteristics and the resulting photocatalytic performance. Fe doping combined with controlled thermal treatment induces significant phase modulation and electronic-structure modification in the TiO₂ nanotube arrays, including pronounced band-gap narrowing and enhanced visible-light absorption. The optimized Fe-doped and annealed TNT photocatalysts exhibit substantially improved photocatalytic activity towards the degradation of the cationic dyes Rhodamine B (RhB) and malachite green (MG), achieving degradation efficiencies of 98.9% and 99.4%, respectively, within 180 min. Structural and spectroscopic analyses reveal that the enhanced performance is associated with the synergistic effects of Fe incorporation and annealing-induced modification of the TiO₂ nanotube architecture, which facilitate improved light absorption and charge-carrier dynamics. The photocatalytic degradation mechanisms are further elucidated through pH-dependent experiments, zeta-potential measurements and reactive oxygen species scavenger studies, demonstrating the important roles of surface-charge interactions and reactive oxidative species in the degradation of the two dyes. The optimized Fe-doped nanotube photocatalyst also exhibits good stability and recyclability, highlighting its potential for repeated application in wastewater treatment. The facile and low-cost fabrication strategy, together with the efficient visible-light-driven degradation of persistent organic dyes, demonstrates the practical applicability of Fe-doped TiO₂ nanotube arrays for sustainable environmental remediation. Overall, the study establishes a clear correlation between annealing-induced structural and electronic modifications and photocatalytic performance, demonstrating that the combined use of dopant engineering and thermal modulation provides an effective strategy for developing efficient and stable TiO₂-based photocatalysts for dye-contaminated wastewater treatment.