Electron-transfer agents semiconductors

Initial evidence for the intermediacy of surface states came from dark current measurements on n-Ti02 and n-SrXi03 in the presence of oxidizing agents such as [Fe(CN)6] ", Fe +, and [IrCle] [177, 178]. Similar evidence that the charge-transfer process was more complex than direct transfer of electrons from the semiconductor CB also came early from AC impedance spectroscopy measurements on n-ZnO, n-CdS and n-CdSe in contact with [Fe(CN)6] species [179, 180],... 

Figure 12. Control of electron transfer reactions at semiconductor solution interfaces (a) electron transfer at a semiconductor solution interface and degradative recombination processes (b) application of charged colloid as a supporting agent of semiconductor particles (c) application of a redox functionalized polymer as a supporting matrix for stabilization of semiconductor colloids and effective trapping of conduction band electrons.

In conclusion, over 130 semiconductors are known to catalyze the photochemical water-splitting reaction according to eq 1 or either water oxidation or reduction in the presence of sacrificial agents. Even though the principle activitycontrolling factors in semiconductor-heterostructures have been identified, many aspects of the function of inorganic photocatalysts are still unclear. Most importantly, the molecular mechanism of water reduction and oxidation on the semiconductor surface has not yet been elucidated in sufficient detail. ° Many questions about charge transfer between semiconductor and cocatalysts, and its dependence on the structural and electronic features of the interface are still open. The effect of variable material preparations and surface impurities on the catalytic activity of semiconductors (e.g. sulfur and oxide on... 

Obviously, the conditions of low-temperature spectroscopy are not relevant for any practical application of the knowledge that has been achieved through the studies described in this chapter. However, one-electron oxidation can also be effected under real conditions, for example, through photoinduced electron transfer to suitable acceptors, such as semiconductor particles that can later be separated from the reaction mixture. Under such circumstances it is likely that the tautomeric radical cations are being reduced and may act as (highly reactive) agents for Diels-Alder-type cycloadditions or other productive chemical reactions. We hope that this chapter will spur novel work in this field. 

---