Concerted Two-Electron Transfer and High Selectivity of TiO2 in Photocatalyzed Deoxygenation of Epoxides

摘要

TiO2 photocatalysis has shown promising potential in the degradation of pollutants, fixation of CO2, and splitting of H2O. In recent years, the selective conversions of organic compounds by TiO2 photocatalysis have been explored actively.11' Even though most of the photocatalytic reactions involve the total gain or loss of multiple equivalents of electrons, and the term multielectron reaction is frequently used in documents on TiO2 photocatalysis, these redox processes are conventionally thought to proceed through sequential single-electron-transfer (SET) pathways. For example, the photocatalytic oxidation of an alcohol to an aldehyde (or ketone) is a typical two-electron oxidation process through a SET mechanism.In this process, the alcohol first reacts with a valence band hole (h_(vb)~+) to generate a radical intermediate, which injects another electron into the conduction band to complete the two-electron reaction (the current amplification effect). According to the SET mechanisms radical intermediates are inevitably involved and is extremely unfavorable for the selective transformation of organic substrates.