Fabrication of TiO2 nanotube arrays by electrochemical anodization in an NH4F/H3PO4 electrolyte

Highly ordered TiO2 nanotube arrays were fabricated by electrochemical anodization of titanium in an NH4F/H3PO4 electrolyte. A TiO2 crystal phase was identified by X-ray diffraction, and the morphology, length and pore diameter of the TiO2 nanotube arrays were determined by field-emission scanning electron microscopy (FE-SEM). The anodization parameters including the rate of magnetic stirring, F− concentration, calcination temperature, anodization voltage and anodization time were investigated in detail. The results show that the as-prepared TiO2 nanotube arrays possessed good uniformity, a well-aligned morphology with a length of 750 nm and an average pore diameter of 62 nm at a 150 rpm rate of magnetic stirring for 120 min at 20 V in an electrolyte mixture of 0.2 M H3PO4 and 0.3 M NH4F with a 500 °C calcination to obtain 100% anatase phase. The adsorption of N-719 dye at different tube lengths was determined by UV-vis analysis and found to increase with increasing tube length. We also discuss the formation mechanism of the TiO2 nanotube arrays. The findings indicate that the formation of the TiO2 nanotube arrays proceeds by the combined action of the electrochemical etching and chemical dissolution.