Sunlight active antibacterial nanostructured N-doped TiO2 thin films synthesized by an ultrasonic spray pyrolysis technique

Sunlight active antibacterial N-doped anatase TiO2 nanocrystalline thin films were synthesized on Si(100), quartz and glass substrates at 300-550 degrees C, in a single step by ultrasonic spray pyrolysis, using hexamine as the nitrogen source and characterized using field emission scanning electron microscopy, X-ray diffraction, Raman spectrometry, secondary ion mass spectrometry, X-ray photoelectron and UV-visible spectroscopy. The antibacterial activity under UV, sunlight and normal room lighting was studied and compared. The TiO2-x-3yN2y films showed enhanced antibacterial activity under room light and sunlight compared to the pristine TiO2 films. The enhanced activity with nitrogen doping is due to the photo-generated holes on the localized N 2p states above the O 2p valence band, which are mobile enough to participate in the surface redox reaction. The microstructure of the films varied from nanodot chains to triangular platelets to cuboids with increase in synthesis temperature, confirming control of morphology and size with synthesis temperature. The secondary ion mass spectrometric studies of the films revealed a uniform distribution of titanium, oxygen and nitrogen across the thickness of the film. The N-doping concentration was similar to 3.4%, as confirmed by XPS. The films had a band gap of about 3.30 eV obtained from UV-Vis studies.