Recent advances in syntheses, properties and applications of TiO2 nanostructures

Abstract

TiO₂ is a compound of great importance due to its remarkable catalytic and distinctive semiconducting properties. It is also a chemically stable, non-toxic and biocompatible material. Nano TiO₂ is strong oxidizing agent with a large surface area and, hence, high photo-catalytic activities. With low production cost and a high dielectric constant, it is an inexpensive material. It can be prepared by diverse procedures such as solution and gas phase procedures. Nowadays, TiO₂ is being used frequently for photo degradation of organic molecules and water splitting for hydrogen generation. Most important applications include purification, disinfection of waste water, self-cleaning coatings for buildings in urban areas and the production of the green currency of energy (hydrogen) by splitting water. The review describes the advances in the syntheses, properties and applications of TiO₂ nano structures. Besides, efforts are also made to discuss the working mechanism and future challenges and perspectives.

Fig. 1. Crystal structures of the rutile and anatase phases of TiO₂. Small spheres represent Ti atoms, large spheres represent oxygen atoms.

Fig. 2. Lattice structure of brookite TiO₂.

Fig. 3. Reaction boundaries of phase transitions in TiO₂.

Fig. 4. Influence of gas cycle of sequence on electrical conductivity of 0.5% Pt/TiO₂ doped with (A) W⁶⁺ (B) Ta⁵⁺ (C) undoped and (D) Mg²⁺.

Fig. 5. SEM of AAM template, (a) top and (b) side views.

Fig. 6. SEM of TiO₂ nanorods growth in AAM template, (a) low magnification image, (b) high magnification image.

Fig. 7. TEM images of TiO₂ nanoparticles after hydrothermal treatment of TBA peptized gel at (a) 210 °C and (b) 270 °C.

Fig. 8. SEM images of TiO₂ nanowires and a TEM image of a single nanowire prepared by Zhang and colleagues.

Fig. 9. Electron microscopy images of (a) titania powders and (b) titania nanotubes.

Fig. 10. TEM images of titania nanotubes at (a) low magnification and (b) high magnification.

Fig. 11. Depiction of an electrochemical cell in which the Ti samples are anodized. Fabrication variables include temperature, voltage, pH and electrolyte composition.

Fig. 12. Scanning electron micrograph of TA6V anodised in CA electrolyte.

Fig. 13. SEM images of TiO₂ nanotubes prepared with anodic oxidation.

Fig. 14. SEM micrograph of TiO₂ nanowires deposited without NH₃ at 500 °C; (a) with 800 sccm argon flow, and (b) with 500 sccm argon flow.

Fig. 15. SEM images of the TiO₂ nanowire arrays prepared by the PVD method.

Fig. 16. Operation principles and energy levels of nanocrystalline dye-sensitized solar cell.

Fig. 17. Mechanism of TiO₂ photocatalytic water-splitting for hydrogen production.

Fig. 18. Measured current of crystallized porous and nanotubular TiO₂/Ti electrodes under linearly swept potential from 0 to 3500 mV vs. SEC.