**2.4 Photocatalytical method**

In any chemical conversion reactants are converted into useful products either by photocatalytic or thermal reaction. The photocatalysis reaction method in which light/ photon is used to stimulate a photocatalyst substance (catalyst) which alters the rate of chemical reactions/process favorably without taking actual part in chemical process. Photocatalysis can also explained as a process in which light energy is used to activate the substance, which enhances the rate of a reaction without used in the chemical reaction [16]. Generally, electron-hole pairs are generated after absorption of light when the energy of the incident light/photons exact matches or exceeds the bandgap of that semiconductor photocatalyst material.
