Template assisted fabrication of TiO₂ and WO₃ nanotubes

Anodic aluminum oxide (AAO) templates with diameters of 200-500 nm were generated by anodizing a commercial aluminum (Al) substrate (99.7%) in 1 vol% phosphoric acid (H₃PO₄), with an applied voltage of 195 V. Titania and tungsten oxide nanotubes (NTs) were successfully grown on AAO template by the sol-gel process. Thermal gravimetric analyzer (TGA) curves showed that gel can be transfered to nanocrystalline particles after 19% weight loss of water molecule by evaporation. The results showed that the nanocrystalline TiO₂ NTs presented at 200 °C, and grains grew as temperature increased. At a temperature of 550 °C, the (101), (103), (004), (112), (200), (105), and (211) planes of anatase TiO₂ were detected clearly, whereas tungsten oxide NTs are amorphous after heat treatment at 200 °C or 300 °C. But the (110), (111), (002), (022), (222), and (004) planes of γ-WO₃ phase can be observed obviously after the heat treatment at 400 °C.