Role of carbon in titania as visible-light photocatalyst prepared by flat-flame chemical vapor condensation method

In this article, the authors report that titania nanopowders synthesized by low-pressure flat-flame metal-organic chemical vapor condensation show visible-light photocatalytic ability. Using acetylene and oxygen as fuel and oxidizer for the flame, the titanium isopropoxide was decomposed and oxidized, and the nanoparticles of titania were formed. From the methylene blue decomposition study they found that the powder synthesized under low precursor feed rate possesses high photocatalytic efficiency under illumination of visible light. The visible-light absorption is resort to the presence of carbon since no other chemical elements were found associated with titania. The presence of carbon species is coincident with the presence of visible-light absorption and carbon is in the form of C-C bond. It also suggests that carbon species are associated with catalytic site on anatase surface so that carriers generated by photon absorption by the carbon species can transfer quickly onto catalytic sites and perform the subsequent catalytic reactions. A possibly unreported mechanism of visible-light TiO2 photocatalysis induced by carbon doping is identified.