TiO2: A Semiconductor Photocatalyst

*Azrina Abd Aziz, Fatema Khatun, Minhaj Uddin Monir, Sim Lan Ching and Leong Kah Hon*

### **Abstract**

Titanium dioxide (TiO2) is considered as an inert and safe material and has been used in many applications for decades. TiO2 have been widely studied, due to its interesting general properties in a wide range of fields including catalysis, antibacterial agents, in civil as nano-paint (self-cleaning) and especially photocatalysis, and that affect the quality of life. Thus, the development of nanotechnologies TiO2 nanoparticles, with numerous novel and useful properties, are increasingly manufactured and used. TiO2 doped with noble metal are good candidates in the performance these applications. The fascinating physical and chemical features of TiO2 depend on the crystal phase, size and shape of particles. For example, varying phases of crystalline TiO2 have different band gaps that rutile TiO2 of 3.0 eV and anatase TiO2 of 3.2 eV, determine the photocatalytic performance of TiO2. This chapter explains basic information on TiO2 and theoretical concepts of nanostructure of TiO2 nanoparticles as a semiconductor photocatalyst.

**Keywords:** TiO2, nanoparticles, semiconductor, photocatalyst

### **1. Introduction**

An ideal photocatalyst should posseses following nature: biologically and chemically inert, inexpensive, nontoxic, stable towards photocorrosion and certainly highly active and suitable towards the visible/UV light photoreaction. An additional criterion for such ideal photocatalyst is better redox potential of the H2O/• OH couple (EOP = 2.80 V) [1]. Among the available semiconductors, TiO2, ZnO, ZnS and WO3 have gap energies sufficient for catalyzing a wide range of chemical reactions [2].

Binary metal sulphide semiconductors such as CdS, CdSe or PbS are regarded as unstable photocatalyst due to easy photoanodic corrosion property and their toxic nature [2, 3]. Furthermore, the iron oxide semiconductors are not suitable as they readily perform the photocathodic reaction and finally produced corrosive materials [1]. ZnO on the other hand is known to have the similar quality of band gap energy like TiO2 (3.0 eV) but it is highly unstable towards pH condition, where precipitate of Zn (OH)2 is formed on the particle surface and resulted in photocatalyst deactivation [2].

Of these, titanium dioxide (TiO2) is the most ideal semiconductor for photocatalytic destruction of organic compounds [2, 4]. It also provides an excellent conciliation between catalytic performance and stabilization in aqueous media [5].
