Figure 2 Schematic demonstration of the photochemical steps in semiconducting TiO2. A: Light irradiation to TiO2 surface, B: generation of electrons and holes as charge carriers, C: recombination of the electrons and holes, D and E: reductive and oxidative pathways of substances absorbed on TiO2 sites, and F: redox reaction to decompose organic contaminants in water.
summarized in a book by Ollis and Al-Ekabi , discussed by Hoffmann and his coworkers [5,6], and overviewed in several review articles [7—11]. The primary photochemical events in TiO2 semiconductors are simplified in Fig. 2. In its electronic structure, TiO2, like other semiconductors, exhibits a void energy region between the top of the filled valance band and the bottom of the vacant conduction band, which is called the band gap (BG).
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