Formation of freestanding ZrO2 nanotubes for Cr(VI) removal

Freestanding ZrO2 nanotubes (ZNTs) were produced using a simple anodization method in fluorinated ethylene glycol electrolyte containing 1 ml 1 M K2CO3. The pH of the bath was kept constant at 8. The potassium carbonate (K2CO3) was added into electrolyte to promote the detachment of anodic ZrO2 film from the underlying zirconium (Zr) substrate. The poor adherence of ZNTs layer was due to generation of CO2 gas that was thought to occur between metal|oxide interfaces. The effect of anodization voltages towards the detachment of ZNTs layer was systematically studied at 20 V, 40 V, 50 V and 60 V for 1 hour. The formation of CO2 gas is a function of anodization voltage, in which at 60 V, a good anodic film separation seen due to higher formation of CO2 gas. A preliminary study shown the capability of ZNTs in removing 5 ppm of Cr(VI) aqueous solution under illumination of UV light.