Kinetics analysis of interfacial electron-transfer processes in goethite suspensions systems.

The photochemical behavior of goethite has been one of the most important topics in the field of environmental science due to it plays a significant role in the removal and transformation process of numerous pollutants. However, the interfacial electron transfer process of goethite is not clear. Using a nanosecond laser flash photolysis spectrometer, we report the transient spectroscopic observations of interfacial electron-transfer reactions in goethite dispersion under UV irradiation. Excitation of goethite generated conduction-band electron (ecb - ) and hole (h+ ). The conduction band electron (ecb - ) reacted with an electron acceptor, methylviologen dichloride hydrate (MV2+ ), forming reduced methylviologen (MV+ ) with a second-order rate constant of (2.6 ± 0.3) × 109  L mol-1 s-1 . The concentration of MV+ was strongly influenced by MV2+ initial concentration and pH values. The flat band potential of goethite was calculated to be Efb (goethite, pH = 7) = 0.24 V (vs NHE). Oxygen did not react with conduction band electron of goethite. The present study provides a reliable method to investigate the photo-induced interfacial charge transfer of goethite.