Tio2 Photocatalysis

TITANIUM DIOXIDE(TiO2) photocatalysis

Among the various catalysts used for photocatalysis TiO2 is the material which is most suitable for industrial use in the present and has a great scope for in the future.

Properties of TiO2

TiO2 is a chemically stable compound and has the highest thermodynamic stability among photocatalysts. It has the most efficient photoactivity and is a benign compound as it has been used in skin care products from ancient times. It does not absorb light in the visible region, its region of absorbance being from 350nm to 420nm and is a stable compound.

Crystal Structures of TiO2

There are three types of crystal structures namely Anatase, Rutile and Brookite.

Out of these three Anatase and Rutile both Tetragonal in crystal structure are used mainly(WHY?) with Anatase showing a significantly higher photocatalytic activity than Rutile (Karran Woan, 2009). Various reasons for this could be -

* Higher charge carrier mobility in Anatase.

* Larger band gap in Anatase as compared to Rutile, 3.2 eV and 3.0 eV respectively.

* The bottom of the conduction band of Anatase is located 0.1V more negative than Rutile.

Photochemical Reactions

Two types of chemical reactions take place when TiO2 is irradiated with ultraviolet light-

* Photo induced redox reactions of adsorbed substances.

* Photo induced hydrophilic conversion of TiO2 itself.

Water Photolysis with TiO2 Electrode

When the surface of the rutile TiO2 electrode was irradiated with light about 415nm(3.0eV), photocurrent flew from the Platinum electrode to the TiO2 electrode, which showed that water can be decomposed, using UV light, into Oxygen and Hydrogen, without the application of external voltage (A. Fujishima et al., 1969).

The following mechanism was proposed-

Figure 2.1 Schematic representation of photoelectrochemical water electrolysis using illuminated oxide semiconductor electrode (Kazuhito Hashimoto et al., 2007) .

A disadvantage observed here was...