Synthesis and characterization of carbon-doped TiO2 nanostructures with enhanced visible light response

Carbon-doped TiO2 micro-/nanospheres and nanotubes have been synthesized via a single source chemical vapor deposition in an inert atmosphere. Organic compound Ti(OC4H9)(4) was used as the titanium, oxygen, and carbon source, while argon served as the carrier gas. The effect of the temperature, substrate, and the flow rate of the carrier gas is investigated. The diameter of the formed carbon-doped TiO2 spheres can be adjusted from 100 nm to several micrometers by varying the flow rate of the carrier gas. The as-prepared TiO2 nanotubes are highly ordered with a diameter of about 100 nm and a wall thickness of around 15 nm. The estimated optical band gap is 2.78 eV for the formed carbon-doped TiO2 microspheres and 2.72 eV for the synthesized carbon-doped TiO2 nanotubes, both of which are much smaller than that of bulk anatase TiO2 (3.20 eV). The photocurrent of the carbon-doped TiO2 spheres is much higher than that of commercial P-25, which is currently considered as one of the best TiO2 photocatalysts, especially under visible light irradiation. The possible mechanism of the formation of TiO2 spheres and nanotubes is also discussed.