A Novel Method for Synthesis of Titania Nanotube Powders using Rapid Breakdown Anodization

The present paper describes a new method utilizing rapid anodization to quickly synthesize high-quality, high aspect ratio, robust titanium dioxide nanotube powders. TiO2 nanotube powders, With a typical nanotube outer diameter of approximately 40 nm, wall thickness of approximately 8-15 nm, and length of about 10-35 mu m, were synthesized by potentiostatic rapid breakdown anodization of titanium foils in aqueous electrolytes of 0.3 M NaCl or 0.1 M HClO4 under an applied potential of 20 V. High reactivity and ultrahigh reaction rate are cornerstones responsible for periodic release of TiO2 nanotubes into solution and formation of a white precipitate of TiO2, nanotubes. The reaction yield is approximately 4-6 g in less than 3 h, and the approximate cost of the material is $3.50/g, based on the laboratory-scale production. Various characterization techniques, including FESEM, HRTEM, EDX, XRD, XPS, FT-IR, UV-visible diffuse-reflectance, and NZ adsorption, have been used to probe morphology, microstructure, crystallographic, composition, bond configuration, optical properties, and surface area of the nanotubes. XPS and EDX investigations show that nanotubes formed in NaCl/phosphate electrolyte solutions contain a significant amount of phosphorus species, which strongly affects crystallization and phase transformation of TiO2. Namely, phosphate-incorporating nanotubes stabilized the anatase phase, and initiation of the rutile phase was observed at annealing temperatures >= 700 degrees C. The resulting nanotube powders have a significant level of OH groups with a band gap ranging from 3.04 to 3.23 eV. Our results indicate that rapid breakdown anodization is highly efficient in the production of good-quality TiO2 nanotube powders, which makes it an alternative to well-documented conventional methods.