Visible-light-derived photocatalyst based on TiO _2-δN _δ with a tubular structure

We succeeded in achieving visible-light responsiveness on a tubular TiO ₂ sample through the treatment of a tubular TiO ₂ that has a large surface area with an aqueous solution of ammonia or triethylamine at room temperature and subsequent calcination at 623 K, which produced a nitrided tubular TiO ₂ sample. It was found that the ease of nitridation is dependent on the surface states; washing the tubular TiO ₂ sample with an aqueous acidic solution is very effective and indispensable. This treatment causes the appearance of acidic sites on the tubular TiO ₂, which was proved by the following experiments: NH ₃ temperature-programmed desorption and two types of organic reactions exploiting the acid properties. The prepared samples, TiO _2-δN _δ, efficiently absorb light in the visible region, and they exhibit a prominent feature for the decomposition of methylene blue in an aqueous solution at 300 K under irradiation with visible light, indicating the achievement of visible-light responsiveness on the tubular TiO ₂ sample. This type of tubular TiO _2-δN _δ sample has merit in the sense that it has a large surface area and a characteristic high transparency for enabling photocatalytic reactions because it has a tubular structure and is composed of thin walls.