Photocatalytic Properties of Coatings Sprayed from TiO_x and Ti_n-2Cr₂O_2n-1 Powders by APS and VPS

Titanium dioxide (TiO₂) has emerged as an excellent photocatalyst material for environmental purification about two decades ago but only recently few works have focused on the photocatalytic properties of sprayed titanium oxide coatings. So far, the role of oxygen deficiency which can appear as a result of the spray process or by use of titanium suboxide powders on the photocatalytic activity has not been investigated. Also the possible influence of the shear plane structure of titanium suboxides (Magnéli phases) on the photocatalytic activity was not taken into consideration. In the present work, the photocatalytic properties of three powders and coatings sprayed from these powders by APS and VPS are investigated: (1) a commercial fused and crushed titanium oxide powder, (2) an agglomerated and sintered titanium suboxide powder consisting predominantly of Magnéli phases Ti₆O₁₁ and Ti₅O₉, (3) an agglomerated and sintered powder consisting of Ti₂Cr₂O₇ and Ti₆Cr₂O₁₅ (Magnéli phases in the TiO₂- Cr₂O₃ phase diagram). The phase compositions of the powders and the coatings were investigated by X-ray diffraction. Neither for the spray powders nor for the coatings any ability to reduce the NOx concentration by the photocatalysis was found. From this it is concluded that both oxygen deficiency as well as Magnéli phase structure are not responsible for photocatalytic properties of materials in the Ti-O phase diagram.