Parameters Influencing the Photocatalytic Activity of Suspension-Sprayed TiO2 Coatings
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Photocatalytic properties of titania have been studied very intensively for a variety of applications, including air and water purification. In order to clarify the influence of the phase composition and other parameters, thermal spraying with suspensions was applied to produce photocatalytically active titania coatings starting from two commercially available anatase and rutile submicron powders. Aqueous suspensions containing 40% solids by weight were sprayed with an HVOF process using ethylene as the fuel gas. The spray parameters were chosen in order to produce mechanically stable coatings and to preserve a high content of the initial crystalline phases of the powders. The coating microstructures, phase compositions, and surface properties were characterized. The photocatalytic performance was evaluated by degradation of the pink dye Rhodamine B (RB) using two techniques: degradation of an aqueous solution of RB and discoloration of impregnated RB. All the coatings exhibited photocatalytic activity to varying degrees, depending on the phase composition as well as other factors, namely, the coating microstructure, surface morphology, surface hydroxylation, light absorption, and interaction with the pollutant.
KeywordsHVOF nanocomposite structure photocatalysis photocatalytic activity rhodamine B suspension TiO2
The authors would like to thank B. Wolf and S. Schultz (Fraunhofer IWS) for help with the metallographic preparation and the spectroscopy measurements and Dr. M. Yamada (Toyahashi University of Technology, Toyahashi, Japan) for kind delivery of the ceramic substrates. Part of this work was performed under DVS research project 02.064 “Funktionalisierung von Keramikoberflächen durch thermisch gespritzte Schichten” (“Functionalization of ceramic surfaces by thermal spraying”), AiF No. 17.371 BR, funded via AiF by the Federal Ministry of Economics and Technology within the framework of the program for promotion of “Industrial Joint Research (IGF).” The authors gratefully acknowledge this financial support.
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