High-Aspect-Ratio Titanium Oxide Nanotubes Anodized in KH2PO4/NH4F/Citric Acid Electrolytes
Titanium of 99.7% purity was anodized in 1M potassium phosphate monobasic (KH2PO4) water solution with 0.15M NH4F. Titanium oxide nanotubes were fabricated at anodization potential of 20 V and 4.64 pH. To control the pH of the solution, we have added weak acid such as citric acid because it has three dissociation constants (pKa) of 3.09, 4.75, and 5.41. Citric acid was very useful to control the pH of the 1M KH2PO4 water electrolyte solution within 3 to 5. The diameter and length of the titanium oxide nanotubes were independent on anodization time. The diameter of 120 nm and length of 2.8 μm at anodization time of 5 hrs were observed by field emission scanning electron microscope (FESEM). Undesired thin oxide layer blocking the top of titanium oxide nanotubes was wiped out by increasing the anodization potential with the multi step voltage by 1 V reached to 25 V. The titanium oxide nanotubes having a very large surface area are very attractive for the battery, gas sensor, photocatalytic application, and biomaterials.
Hyungsun Kim, Junichi Hojo and Soo Wohn Lee
S. J. Cho et al., "High-Aspect-Ratio Titanium Oxide Nanotubes Anodized in KH2PO4/NH4F/Citric Acid Electrolytes", Materials Science Forum, Vols. 544-545, pp. 67-70, 2007