Photocatalytic Activity of Atomic Layer Deposited TiO[sub 2] Coatings on Austenitic Stainless Steels and Copper Alloys

Abstract

Photocatalytic activity of TiO 2 -coated austenitic stainless steel ͑AISI 304͒ and copper alloys ͓deoxidized high phosphorus ͑DHP͒ copper and Nordic Gold͔ 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 TiO 2 coatings were prepared by an atomic layer deposition technique from TiCl 4 and H 2 O. The thicknesses of the prepared coatings were 5, 10, 50, 100, 150, and 200 nm. Morphology and crystal structure of the TiO 2 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 nm͒, with some exceptions.

Photocatalytic Lithography with Atomic Layer–Deposited TiO2 Films to Tailor Biointerface Properties

“…For instance, Pore et al deposited TiO 2 layers from Ti(OCH 3 ) 4 and H 2 O at different temperatures and observed an increase in photocatalytic activity for thicker films up to 100 nm grown at 325 °C. Kawakami et al reported low photocatalytic activity for 5 and 10 nm thin films, while good photocatalytic activity was observed for thicker films of 50 nm or more. They assign these results to the ALD process based on TiCl 4 and H 2 O, where the crystallinity of the films is negligible at the start of the process, but anatase crystal growth occurs when a thickness of 50 nm is reached.…”

Effect of substrate deformation on functional properties of atomic-layer-deposited TiO2 coatings on stainless steel

“…The specimens were coated by TiO 2 using atomic layer deposition in Planar Systems Inc. (Espoo, Finland) with H 2 O as an oxygen source and TiCl 4 as a titanium precursor [32]. Anatase-type coatings with the thickness of 50 and 100 nm (50 nm (A), 100 nm (A)) and rutile-type coatings with the thickness of 100 and 150 nm (100 nm (R), 150 nm (R)) were selected for the investigation based on the previous studies [26,31].…”

“…Following previous studies [2,26,27,33], we assumed the pseudo-first-order kinetics for the MB decomposition by TiO 2 with the time dependence of concentration:…”

“…Contact angle of the studied coatings decreases significantly after the UV illumination is switched on, and after about 30 min of illumination it remains approximately constant [26]. Thus, the average from the contact angles determined after 30 min, 1, 3, and 5 h of UV illumination is presented as the contact angle under UV illumination in this article.…”

“…Kawakami et al investigated the functional properties of atomiclayer-deposited anatase-type TDCs as a function of coating thickness and the type of substrate (stainless steel, copper, and Nordic gold alloy) [26]. Most of the studied TDCs exhibited considerable photocatalytic activity and photohydrophilicity for thickness larger than 50 nm.…”