ABSTRACT
The Greek word photocatalysis is a combination of two words: photo (“phos” means light) and catalysis (“katalyo” means to break apart, decompose). Generally, the term photocatalysis is used to describe a process where light is used to excite a photocatalyst and the rate of chemical reaction is accelerated without involving the photocatalyst. Although the term photocatalysis is quite confusing and there has been a long debate on the denition of this term, the International Union of Pure and Applied Chemistry (IUPAC) has nally decided that the term photocatalysis is reserved for the reactions carried out in the presence of a semiconductor and light. Plotnikow (1936) mentioned photocatalysis in his book entitled Allgemeine Photochemie. Almost four decades later, some researchers actively started conducting surface studies on photocatalysts such as TiO2 and ZnO. In the meantime, some workers also thought on the possibility of using sunlight as the energy source. Fujishima and Honda (1972) conducted the photolysis of water using a semiconductor electrode (TiO2) in a photoelectrochemical cell, which gave momentum to the eld of photocatalysis. This was considered as the real beginning of this eld. In the 1980s and 1990s, many efforts were made to understand the fundamental process and improve the photocatalytic efciency of titania. In the last few years, semiconductor materials have been used as a photocatalyst for air and water remediation, mineralizing hazardous organic pollutants, and industrial and health applications (Rengel et al. 2012).
