Effect of titanyl sulfate concentration on growth of nanometer-scale rutile rod arrays on the surface of titanium substrate

Nano-scale rod arrays of titania were prepared on commercially available pure titanium (cpTi) substrates by a chemical treatment at 80°C for 3 d and a subsequent aging treatment in ultra-pure water at 80°C for 1 d. Treating solutions (TSs) for chemical treatment contained titanyl sulfate (TiOSO4), hydrogen peroxide (H2O2), and nitric acid (HNO3). Fourier transform infrared spectroscopy analysis indicated that an amorphous titania gel layer containing Ti–O–O bonds formed on the chemically treated cpTi substrate in 0.10 mol·m−3 TS, which was then transformed into anatase rods during aging treatment. Thin-film X-ray diffraction and scanning-electron microscopy analyses showed that the 0.10 mol·m−3 TiOSO4 TS provided randomly packed aggregates of oriented anatase and rutile rods, while 0.14 and 0.18 mol·m−3 TiOSO4 TSs yielded highly ordered rutile rods of ca. 20 nm in diameter. The rutile rods grew perpendicular to the cpTi substrate and the rod array fully covered the surface of the cpTi substrate. It is proposed that the nucleation of rutile occurs on the amorphous titania gel layer, and the rate of nucleation and growth of rutile increase with increasing concentration of TS, accompanied by the consumption of amorphous titania gel. Rutile layers with high rod density and 3.0 µm thickness were successfully prepared on the surface of cpTi substrates.