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.