New approach to enhance the photocatalytic activity of plasma sprayed TiO2 coatings using p-n junctions

To investigate the original reasons of the remarkable difference of the photocatalytic activity of plasma sprayed TiO2 and TiO2–Fe3O4 coatings, the photoelectrochemical characteristics of plasma sprayed TiO2 and TiO2–Fe3O4 electrodes were examined. The photo-response of the sprayed TiO2 electrode was comparable to that of single crystal TiO2, but the breakdown voltage was approximately 0.5 V (vs. SCE). The short-circuit current of TiO2 was 1.05 mA/cm2, which was 15 times comparing with that of TiO2–Fe3O4 electrode under 30 mW/cm2 xenon light illumination. N-type TiO2 semiconductor particle reacted with Fe3O4 or Fe2O3 particle and concurrently produced p-type FeTiO3 in plasma spraying process. FeTiO3 compound obviously improved the photocatalytic activity of the TiO2 coating for the formation of p-n junction between p-type FeTiO3 and n-type TiO2, which may spatially separate the photo-generated electrons and holes. From these investigations, a promising approach for manufacturing high performance photocatalytic coating by plasma spraying is suggested.