Microstructure and photocatalytic activity of suspension plasma sprayed TiO2 coatings on steel and glass substrates

In this study, TiO2 coatings were deposited by suspension plasma spraying (SPS) from a commercial TiO2 nanoparticle suspension on two different substrates: a standard stainless steel and a Pyrex glass. Coatings were sprayed on both substrates with an F4-MB monocathode torch; a Triplex Pro tricathode torch was also used to spray coatings just on the stainless steel substrates. Spraying distance and cooling were varied. The anatase content in the coatings, determined by XRD, ranged from 32 to 72 wt.%. A significant amount of anatase to rutile transformation was found to occur during cooling. Examination of the microstructure revealed that the coating microstructure was bimodal, involving a non-molten region consisting mainly of anatase nanoparticle agglomerates and a molten region. The glass substrate coatings displayed a segregated phase distribution, particularly when the surface to be coated was cooled. Photocatalytic activity was determined by a methylene blue test. The experimental data fitted well to a first-order kinetic. All the coatings exhibited high photocatalytic activity in comparison with that of a commercial sol-gel coating. However, unlike much of the previous research, photocatalytic activity did not correlate with the anatase content determined by XRD. (C) 2011 Elsevier B.V. All rights reserved.