Synthesis of oxygen-deficient blue titanium oxide by discharge plasma generated in aqueous ammonia solution

Abstract When discharge plasma was generated in an aqueous ammonia solution containing titanium dioxide (TiO 2 ) powder, blue TiO 2 was obtained. The blue TiO 2 contained oxygen defects and Ti 3+ formed by the plasma treatment; i.e., reducing species such as hydrogen radicals generated in situ during ammonia decomposition by plasma were considered to reduce TiO 2 . No marked changes in the crystallographic structure and specific surface area of TiO 2 were observed after the plasma treatment, indicating that TiO 2 was not exposed to high temperature. In addition, the plasma-treated TiO 2 remained blue when exposed to air for several months. The photocatalytic activity of anatase TiO 2 under visible light irradiation was enhanced after plasma treatment. In contrast, the plasma-treated rutile TiO 2 showed inferior photocatalytic activity under visible light irradiation compared with that of the untreated rutile TiO 2 .