The photoelectrochemical characteristics of plasma sprayed porous TiO 2 , TiO 2 -5%ZnO and TiO 2 -10%ZnO electrodes in 0.1N NaOH solution were studied through a three-electrode cell system. The microstructure, morphology and composition of the electrodes were analyzed using electron probe surface roughness analyzer (ERA-8800FE), scanning electron microscope (SEM) and X-ray diffraction. The results showed that the sprayed electrodes had a porous microstructure, which was affected by the plasma spraying parameters and composition of the powders. TiO 2 -ZnO electrodes consisted of anatase TiO 2 , rutile TiO 2 and Zn 2 Ti 3 O 8 phase. The photoresponse characteristics of the plasma sprayed electrodes were comparable to that of single crystal TiO 2 , but the breakdown voltage was approximate to 0.5V (vs. SCE). The short-circuit photocurrent density increased with a decrease of donor concentration, which was calculated according to Garner-Bulter model. For the lowest donor concentration of a TiO 2 -5%ZnO electrode prepared under the arc current of 600A, the short-circuit photocurrent density was approximately 0.4mA/cm 2 higher than that of the TiO 2 electrodes under 30mW/cm 2 xenon light irradiation. The photocurrent density increased linearly with light intensity.

Titanium dioxide (TiO 2 ) is one of the most important photocatalyst that allows the environmental purification of water and air by the decomposition of toxic organic compounds and removal of harmful gases. In the photocatalytic applications, TiO 2 can be used in form of powder or coating. In this paper, two techniques of deposition were used to elaborate thin deposits starting from an agglomerated TiO 2 anatase nanopowder: conventional plasma spraying in atmospheric conditions and suspension plasma spraying. The photocatalytic efficiency of the coatings was performed with respect to nitrogen oxides (NOx) and compared with the photocatalytic activity of the TiO 2 Degussa P25 powder. Differences in the photocatalytic efficiencies of the nanocoatings obtained by the two techniques of plasma spraying were obtained. The coatings elaborated by suspension plasma spraying have poor mechanical properties but better photocatalytic efficiencies. This method is a promising technique to elaborate photocatalytic coatings for the removal of different air pollutants.

Extensive research activities were conducted over the last few years on coatings made of titanium oxide, an established material for thermally sprayed coating solutions. Multiple existing and potential applications are closely connected with the existence of different titanium dioxide modifications and the formation of suboxides. This provides a basis for discussions on the Ti-O phase diagram as well as the properties and conditions of formation of relevant phases. Coating microstructures, phase compositions and mechanical properties are discussed as a result of interactions of different spray powders in different spray conditions of atmospheric and vacuum plasma spraying (APS and VPS), as well as of high-velocity oxyfuel (HVOF) spraying. The discussion on applications is focused on electrically conductive coatings, coatings with photocatalytic properties and coatings for wear applications.

Titanium dioxide (TiO 2 ) 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 Ti 6 O 11 and Ti 5 O 9 , (3) an agglomerated and sintered powder consisting of Ti 2 Cr 2 O 7 and Ti 6 Cr 2 O 15 (Magnéli phases in the TiO 2 - Cr 2 O 3 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.