Photocatalytic activity of atomic layer deposited TiO₂ coatings on austenitic stainless steels and copper alloys

Photocatalytic activity of TiO₂ -coated austenitic stainless steel (AISI 304) and copper alloys [deoxidized high phosphorus (DHP) copper and Nordic Gold] was studied by means of decomposition of methylene blue model waste water and open-circuit electrochemical potential measurements, and the photoinduced hydrophilicity was studied by means of contact angle measurements of water under ultraviolet irradiation. The TiO₂ coatings were prepared by an atomic layer deposition technique from TiCl₄ and H₂O . The thicknesses of the prepared coatings were 5, 10, 50, 100, 150, and 200 nm . Morphology and crystal structure of the TiO₂ coatings were studied using scanning electron microscope and X-ray diffraction techniques. Photocatalytic activity of the studied coatings was low with a coating thickness of 5 and 10 nm . When the coating thickness was 50 nm or higher for AISI 304 stainless steel, and 100 nm or higher for DHP and Nordic Gold copper alloys, the photoactivity was good, but no saturation or systematic effect of coating thickness or surface finish was observed. The photoinduced hydrophilicity was good with all studied coating thicknesses (50, 100, 150, and 200 nm ), with some exceptions.