Conversion of potassium titanate nanowires into titanium oxynitride nanotubes

Abstract

Tunnel-structured potassium titanate with a K3Ti 8O17 phase was synthesized by direct oxidation of titanium powder mixed with KF(aq) in water vapor at 923 K. The reaction conditions were adjusted so that uniform single crystalline potassium titanate nanowires with [010] growth direction (length: 5-30 μm, diameter: 80-100 nm) were obtained. Nitridation of the nanowires by NH3(g) at 973-1073 K converted the titanate nanowires into rock-salt structured cubic phase single crystalline titanium oxynitride TiNxOy nanotubes (x = 0.88, y = 0.12, length = 1-10 μm, diameter = 150-250 nm, wall thickness = 30 × 50 nm) and nanorods (x = 0.5, y = 0.5, length = 1-5 μm, diameter = 100-200 nm) with rough surfaces and [200] growth direction. The overall conversion of the titanate nanowires into the nanotubes and the nanorods can be rationalized by Ostwald ripening mechanism. We fabricated an electrode by adhering TiN xOy nanotubes (0.2 mg) on a screen-printed carbon electrode (geometric area: 0.2 cm2). Electrochemical impedance spectroscopy demonstrated its charge transfer resistance to be 20ω. The electrochemical surface area of the nanotubes on the electrode was characterized by cyclic voltammetry to be 0.32 cm2. This property suggests that the TiNxOy nanostructures can be employed as potential electrode materials for electrochemical applications. © 2011 American Chemical Society.