Structural changes of anodic layer on titanium in sulfate solution as a function of anodization duration in constant current mode

摘要

The present study investigated the effect of anodization time, in constant current mode, on the anodic oxide layer formed on titanium (Ti). Anodization of the Ti substrate was carried out in a 0.1 M (NH_4)_2SO_4 aqueous solution with reaction times of various durations, after which the characteristics and photo-catalytic activity were investigated in detail. The TiO_2 layer fabricated in a short duration exhibited comparatively flat surface morphology and an anatase-type crystal structure. This layer acted as a pho-tocatalyst only under ultraviolet light (UV) illumination. Upon prolonging the anodization, the layer structure changed drastically. The surface morphology became rough, and the crystal structure changed to rutile-type TiO_2. Furthermore, the layer showed photocatalytic activity both under UV and visible light illumination. Further anodization increased the amount of methylene blue (MB) adsorbed on the surface, but did not cause additional change to the structure of the anodic layer. The surface morphology and crystal structure of the anodic layer were predominantly controlled by the anodization time; thus, the anodization time is an important parameter for controlling the characteristics of the anodic layer.