Synthesis and characterization of P-doped TiO2 nanotubes

Titanium dioxide (TiO2) doped with phosphorus (P) was synthesized by anodization of Ti in the mixed acid electrolyte of H3PO4 and HF and characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and UV-vis spectrum. The morphology greatly depends on the applied voltage. The as-formed nanotubes under the optimized condition, at 20 V for 2 h, are highly ordered with ∼ 200 nm in length and the average tube diameter is about 100 nm. By annealing the initial samples at different temperatures, the importance of the crystalline nature is confirmed. Significantly, the peak positions of anatase in XRD patterns shifts to lower diffraction angles with an increase in the amount of H3PO4 ion. A remarkable red shift of the absorption edge has been observed for the sample formed in the electrolyte of HF and H3PO4, which is related to the introduction of P5+ into TiO2 crystallization and the possible impurity energy level formed in the TiO2 band gap. The presence of P 2p state in XPS spectrum can further confirm the P5+ which can replace a part of Ti4+ has been introduced into TiO2 crystallization. The present convenient synthesis technique can be considered to the composition of other doped oxide materials.