Facile synthesis of a narrow-gap titanium dioxide anatase/rutile nanofiber film on titanium foil with high photocatalytic activity under sunlight

• Interstitial N–TiO2 nanofiber film with narrowed bandgap was synthesized.
• The bandgap was narrowed to 0.87 eV by N, Vo, and mixed crystal structure.
• The film extends the optical absorption from ultraviolet to near-infrared light.
• Solar-to-hydrogen efficiency was improved to 0.62%.

A narrow-gap TiO2 nanofiber film was synthesized on Ti foil by chemical polishing and anodization. The morphology, crystal structure, chemical states, and optical properties were characterized by scanning electron microscopy, X-ray diffraction, X-ray photon electron spectroscopy, and ultraviolet-visible-infrared absorption spectroscopy, respectively. Transient photocurrent response, linear sweep voltammetry, and photoconversion efficiency were also measured. The photocatalytic activity was evaluated from both hydrogen generation and methyl orange degradation experiments. Our results suggested that the film was composed of small uniform TiO2 nanofibers, having interstitial nitrogen-doping, oxygen vacancies and a mixture of anatase and rutile crystal phases. The films exhibited strong and broad optical absorption from 200 to 2500 nm. Owing to this strong absorption and rapid transport of photogenerated electrons, the nanofiber films exhibited a high photoconversion efficiency of 0.62%, and a hydrogen generation rate of 0.62 mL h−1 cm−2 under visible light irradiation. Under solar irradiation the films also showed remarkable efficiency and stability for the degradation of methyl orange.