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. TiO 2 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 μm, were synthesized by potentiostatic rapid breakdown anodization of titanium foils in aqueous electrolytes of 0.3 M NaCl or 0.1 M HClO 4 under an applied potential of 20 V. High reactivity and ultrahigh reaction rate are cornerstones responsible for periodic release of TiO 2 nanotubes into solution and formation of a white precipitate of TiO 2 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 N 2 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 TiO 2 . Namely, phosphate-incorporating nanotubes stabilized the anatase phase, and initiation of the rutile phase was observed at annealing temperatures ≥700 °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 TiO 2 nanotube powders, which makes it an alternative to well-documented conventional methods.