Effect of ethylene glycol and current density on the morphology and anatase/rutile ratio of anodized commercial grade titanium

Titanium oxide (TiO2) in both its allotropic forms, anatase (A) and rutile (R), has shown enhanced catalytic effects as well as antimicrobial properties. Even if the specific A/R phase ratio needed for the best results is still not fully understood, it is evident that the possibility to tune that ratio as well as the control of surface morphology, are mandatory requirements to optimize the properties of such complex active material. In this research we studied the formation of nanostructured titania layers from a commercial grade 2 titanium foil by means of a simple one-step anodization procedure. Thin layers of as electrochemically growth titania were characterized for anatase/rutile (A/R) phase ratio and pore distribution as a function of both used bath composition and current density by means of X-ray diffraction and scanning electron microscope investigation. Results indicate the targeted phase ratios were achieved by tuning the current density as well as the amount of ethylene glycol. Oxide layers with pores ranging from 10 to 500 nm diameter and specific anatase/rutile phases ratios were obtained by adding ethylene glycol up to 80% by volume in 0,5 M H2SO4 solution and varying the anodization current. Lower current density (20 mA.cm^-2) promotes the formation of larger pores mainly constituted by anatase phase, whereas higher values (80 - 100 mA.cm^-2) serve to the formation of a more compact structure constituted by a mix of anatase and rutile.