Formation of anodic zirconia nanotubes in fluorinated ethylene glycol electrolyte with K2CO3 addition

The influence of K2CO3 on the morphology of anodic zirconia (ZrO2) nanotubes array were investigated by anodizing zirconium (Zr) foil at 60 V in fluorinated ethylene glycol (EG) electrolyte added to it varying amount of K2CO3: 0.5 vol.%, 1 vol.%, 2 vol.% and 3 vol.%. The adhesion of ZrO2 on Zr is affected by the volume of K2CO3 added whereby at lower volume, i.e. 0.5 vol.% and 1 vol.%, poor adhesion of anodic film was observed leading to the formation of loose ZrO2 flakes. At higher 2 vol.% and 3 vol.% addition the adhesion was improved. All anodic films are comprised of nanotubes with length increases when more K2CO3 was added in EG. Nanotubes grown in 3 vol.% K2CO3 are 9.4 μm long with 48.8 nm outer diameter and 9.1 nm wall thickness. Reducing the applied potential to 20 V resulted in compact oxide and at 40 V, nanotubes with smaller diameter of < 50 nm were produced. Crystallization of the ZrO2 nanotubes was achieved by annealing at 400 °C. The crystalline ZrO2 nanotubes (mostly in monoclinic and tetragonal phases) grown in 3 vol.% K2CO3 exhibits the highest photocurrent density (0.12 mA/cm− 2) and rapid methyl orange (MO) degradation under ultra-violet (UV) radiation. This is attributed to the good adhesion of ZrO2 on Zr, longer length of the tubes and perhaps from the effect of adsorbed carbonate ions on the surface of the oxide.