Photocatalytic Performance of N-Doped TiO₂ Adsorbed with Fe³⁺ Ions under Visible Light by a Redox Treatment

A simple method to prepare the N−TiO 2 adsorbed with Fe 3+ ions only on the surface of catalysts and modify the catalysts by a redox treatment (NaBH 4 reduction and air oxidation treatment) was proposed. The samples were characterized by X-ray diffraction (XRD), UV−vis diffuse reflectance spectroscopy, FTIR, X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron micrograph (HRTEM). The photocatalytic activities of the samples were evaluated for degradation of methylene blue (MB) in aqueous solutions under visible light (λ > 420 nm). The results of XRD, FTIR, XPS, and HRTEM analysis indicated that the structure of Fe compounds changed from Fe 2 O 3 to γ-FeOOH after redox treatment. Compared to N−TiO 2 with Fe 3+ ions, the catalysts after redox treatment showed higher photoactivity under visible light, and the formation of γ-FeOOH was responsible for the improvement of photocatalytic activity. Furthermore, to the catalysts after redox treatment, the mechanism for degradation of MB under visible light is an opening of a central aromatic ring attacked by OH • combined with a process of γ-FeOOH photoreductive dissolution.