Mechano-synthesized orange TiO₂ shows significant photocatalysis under visible light

Nitrogen and carbon co-doped TiO₂ particles with a brilliant yellow-orange color were produced mechanochemically by high-energy ball milling as one-pot synthesis. This facile synthesis required only grinding TiO₂ with melamine at room temperature. Using monochoromatic lights with the same intensity in visible and UV, the photocatalytic activity of the TiO₂ particles was accurately evaluated with respect to the degradation of an aqueous dye (methylene blue) solution. The activities under visible light (450 and 500 nm) were, respectively, 4 and 2 times higher than that of the unmilled TiO₂ under UV light (377 nm), corresponding to 9 and 5 times higher than the UV under the solar light condition. The properties and structure of the co-doped TiO₂ particles before and after milling were analyzed using eight experimental methods. As a result, it was found that the nitrogen replaced as an oxygen site in milled TiO₂ has the highest concertation (2.3%) in the past studies and the structure of milled TiO₂ is composed of a polymorphism of four different solid phases of TiO₂, gives significant higher photocatalytic activity at visible light than that of UV light. A good repeatability of the photocatalyst was investigated by the number of cycles for the decomposition reaction of the aquesous dye solution.