Concepts –Why semiconductors are chosen as photo-catalysts?

Water splitting - carry out both the redox reactions simultaneously - reduction of hydrogen ions

oxygen evolution from the hydroxyl ions.

The system that can promote both these reactions simultaneously is essential.

Since in the case of metals the top of the valence band (measure of the oxidizing power) and bottom of the conduction band (measure of the reducing power) are almost identical they cannot be expected to promote a pair redox reactions separated by a potential of nearly 1.23 V.

where the top of the valence band and bottom of the conduction band are separated at least by 1.23V in addition to the condition that the potential corresponding to the bottom of the conduction band has to be more negative with respect to be more negative with respect to while the potential of the top of the valence band has to be more positive to the oxidation potential of the reaction