**2. Synthesis of hierarchical nanostructures of TiO2**

Various types of surfactants, organic/inorganic titanium salts, high temperatures and pressures may be used for the preparation of hierarchical nanostructures of Titania. Following are the reported methods for the synthesis of TiO<sup>2</sup> HNSs.


**Figure 2.** Different crystalline forms of TiO<sup>2</sup>

6 Titanium Dioxide - Material for a Sustainable Environment

**Figure 3.** Different forms of TiO<sup>2</sup>

nanoflowers [8], (f) nanoforest [48].

[9].

: (a) nanocubes [24], (b) nanospheres [24], (c) nanorods [24], (d) nanoparticles [52], (e)

	- Chemical vapor deposition
	- Physical vapor deposition
