The term can be generally used to describe a process where light is used to activate a substance.The photocatalyst that modifies the rate of a chemical reaction without itself being involved in the chemical transformation. Thus, the main difference between a conventional thermal catalyst and photocatalyst is that the former is activated by heat whereas the latter is activated by photons of appropriate energy. The principle of photocatalysis is based on the activation of a semiconductor particulate material by the action of radiation with an appropriate wavelength. Photocatalysis is used for the elimination of several pollutants ( alkanes, alkenes, phenols, aromatics, pesticides) and complete mineralization of the organic compounds.
When a photocatalyst is irradiated with a light of suitable wavelength, an electron is excited to the conduction band (CB), leaving behind a positive hole in the valence band (VB). The electron in the CB can be utilized to reduce any substrate, whereas the hole in the VB can be used for oxidizing some compounds.
Reference: Photocatalysis principles and applications by Rakshit ametha
Page number 9-11
TiO2 photocatalysis is widely used in a variety of applications and products in the environmental and energy fields, including self-cleaning surfaces, air and water purification systems, sterilization, hydro- gen evolution, and photoelectrochemical conversion. The development of new materials, however, is strongly required to provide enhanced performances with respect to the photocatalytic properties and to find new uses for TiO2 photocatalysis. In this review, recent developments in the area of TiO2 photo- catalysis research, in terms of new materials from a structural design perspective, have been summarized. The dimensionality associated with the structure of a TiO2 material can affect its properties and func-
tions, including its photocatalytic performance, and also more specifically its surface area, adsorption, reflectance, adhesion, and carrier transportation properties.
https://www.sciencedirect.com/science/article/pii/S1389556712000421
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