Bifunctional TiO2/AlZr Thin Films on Steel Substrate Combining Corrosion Resistance and Photocatalytic Properties

Abstract

A novel multi-functional bilayer coating combining an anti-corrosion Al–Zr (4 at.% Zr) underlayer and an anti-biofouling TiO2 top layer was deposited on high-speed steel (HSS) substrates. Al–Zr (4 at.% Zr) film, deposited by DC magnetron sputtering, which is a single phased supersaturated solid solution of Zr in Al, is used to provide sacrificial corrosion resistance of steels and TiO2 is added as a top layer to induce photocatalytic activity and hydrophilic behavior which can generate antifouling properties in order to slow down the biofouling process. The top TiO2 films, deposited at 550 °C by AACVD (aerosol-assisted chemical vapor deposition), consisting of anatase TiO2 microflowers physically attached to the TiO2 thin films present a high decomposition rate of Orange G dye (780 × 10−10 mol L−1·min−1). The enhanced photocatalytic performance is associated with the rough network and the presence of TiO2 microflowers capable of supporting the enhanced loading of organic contaminants onto the film surface. Electrochemical tests in saline solution have revealed that bilayer films provide cathodic protection for the steel substrate. The Al–Zr/TiO2 bilayer presents a lower corrosion current density of 4.01 × 10−7 A/cm2 and a corrosion potential of −0.61 V vs Ag/AgCl, offering good protection through the preferential oxidation of the bilayer and an increased pitting resistance. The proposed functionalized coating combining anticorrosion and photocatalytic properties is a promising candidate for an anti-fouling system in sea water.

Marine Antibiofouling Properties of TiO2 and Ti-Cu-O Films Deposited by Aerosol-Assisted Chemical Vapor Deposition

“…It has been previously proven that these microstructures are reached only when working with a very high precursor flow rate (3 mL•min −1 , meaning 0.027 mol•min −1 of TiO(acac) 2 ) in a narrow deposition temperature window, probably generating supersaturation CVD conditions [24]. The photocatalytic activity of these TiO 2 films was found to be very high, probably due to the high specific surface generated by the nanometric hierarchical flower-like structures [26]. The increase in titanium concentration in the solution (0.06 M) resulted in the increase in the microflowers' density.…”

“…The mixture was stirred until complete mixing at room temperature. The optimization of TiO 2 film deposition was already presented in [26]; we used the same deposition parameter as this study for TiO 2 and Cu-Ti-O films, mainly characterized by a deposition temperature of 550 • C for 40 min. A carrier gas flow of 6 L•min −1 and a solution feeding rate of 3 mL•min −1 were used.…”

“…A carrier gas flow of 6 L•min −1 and a solution feeding rate of 3 mL•min −1 were used. For more details about deposition conditions, see [26].…”

“…The photocatalytic activity of TiO 2 films was evaluated by measuring the decomposition rate of aqueous Orange G solutions (C = 5 × 10 −5 M) using a UV-VIS Perkin Elmer Lambda 35 performing the same protocol explained in our previous study [26].…”

“…This is also a standard way to evaluate the degradation provoked by photoactive materials [50]. Pure TiO 2 films (TiO 2 _3 WF) were previously investigated in our last study [26], and used as internal references for this work. Let us remind the reader that the high photocatalytic activity of these films was explained by the formation of microflowers with nanometric petals, which increase the efficient surface and decrease the crystal size.…”