Comment
Author: Admin | 2025-04-27
Than that of the valence band of the semiconductor for oxidation of the species to occur.[22]Near the surface of a semi-conducting metal oxide the valence and conduction bands are of higher energy, causing the upward bending of the band energy as shown in the band energy diagram, such that promotion of an electron from the valence band to the conduction band by light of energy greater than the band gap results in migration of the electron towards the bulk of the solid or to a counter electrode, while the hole left in the valence band moves towards the surface. The increased concentration of holes near the surface facilitates electron transfer to the solid, such as the example shown in the figure of the oxidation of redox couple D-/D.[2] In the absence of any mechanism to remove electrons from the bulk of the solid irradiation continues to excite electrons to the conduction band producing holes in the valence band. This leads to the reduction of the upward bending of the band energies near the surface, and the subsequent increase in excited electron availability for reduction reactions.[2]This band diagram shows the excitation of an electron to the conduction band, and the reaction of a hole in the valence band with a redox couple at the surface of the solid.The following equations are useful in describing the populations of valence and conduction bands in terms of holes and electrons for the bulk metal. is the density of electrons in the bulk metal conduction band, and is the density of holes in the bulk metal valence band. Ec is the lowest energy of the conduction band, Ef is the Fermi energy (electrochemical energy of the electrons), Ev is the highest energy of the valence band, Nc is the effective mass and mobility of an
Add Comment