Fabrication of TiO2 Nanotube Arrays by Rectified Alternating Current Anodization

Anodization is a popular method of preparing TiO2 nanotube array films (TiNTs) by using direct current (DC) power as the driving voltage. In this study, three driving voltage modes, namely, the sine alternating current (sine) mode, the full-wave rectification of sine waves via four diodes (sine-4D, where D means diode) mode, and the DC mode, were used to prepare TiNTs by anodization. At 20 V, TiNTs were formed under sine-4D mode but only irregular porous TiO2 films were formed under DC mode. At 50 V, TiNTs formed under both the sine-4D and DC modes. No TiNTs formed in the sine mode anodization at either 20 or 50 V. Compared with the DC mode, the sine-4D mode required a lower oxidation voltage for TiNT formation, which suggests that sine-4D is an economical, convenient, and efficient driving voltage for TiNT preparation by anodization. The morphologies and structures of TiNT samples anodized at 50 V in the sine-4D and DC modes at different oxidation time (1, 5, 10, 30, 60, and 120 min) were analyzed. TiNT growth processes were similar between the studied modes. However, the growth rate of the films was faster under the sine-4D mode than the DC mode during the first 30 min of anodization.