Photocatalytic Activity of the Oxide Layer Formed on NiTi Surface through Thermal Oxidation Process

Abstract

In the present study, we attempted to prepare a photocatalytic titanium dioxide (TiO₂) layer on nickel-titanium (NiTi) alloy surface through a simple thermal oxidation process in air. At 723 K, an amorphous TiO₂ layer including a slight amount of Ni was formed on the surface. Above 873 K, the TiO₂ layer crystallized into a rutile phase. At 1023 K, a complex oxide of NiTiO₃ was also formed. The methylene blue degradation test for evaluating photocatalytic activity showed that the formed TiO₂ layers act as photocatalyst under ultraviolet (UV) light illumination, and its activity is superior to that of the surface layer formed by oxidizing a pure Ti substrate. The adhesion strength of the surface layers formed at 723 K on NiTi alloy was higher than that of a commercially available TiO₂-coating. We conclude that thermal oxidation as a surface modification technique is expected to make NiTi alloys give photocatalytic activity.