Carbon-doped anatase TiO2 nanotube array/glass and its enhanced photocatalytic activity under solar light

To enhance the photocatalytic activity under solar light, highly ordered TiO₂ nanotube arrays (TNAs) film with anatase phase was fabricated on glass and successfully doped with carbon at various temperatures of 450–550 °C. The characterization results indicate that, after carbon doping, the TNAs still remained nanotubular structure with anatase phase. But their optical response shifted from UV to the visible light region and the recombination of photogenerated carriers was suppressed effectively. It is more important that the carbon-doped TNAs/glass (C-TNAs) samples exhibited high solar light photocatalytic activity, and 68%, 61% and 56% MO was photodegraded in 150 min by the C-TNAs calcined at 550, 500 and 450 °C, respectively. Especially, the apparent reaction rate constant of C-TNAs calcined at 550 (k, 0.065 min⁻¹) with the highest activity is 3.6 times that of pristine anatase TNAs (k, 0.018 min⁻¹). It is clear that carbon doping enhanced the photocatalytic activity under sunlight at optimized annealing temperature. The efficient activity could be attributed to the synergetic effects of strong visible light absorption, good crystallization, large surface, and enhanced separation of photoinduced carriers.