Iodine-Doped TiO₂ Photocatalysts: Correlation between Band Structure and Mechanism

Iodine-doped TiO 2 powders (I-TiO 2 ) prepared via hydrothermal treatment have absorption in the region of ultraviolet (UV) and visible light, and were used as a photocatalyst with irradiation of UV or visible light. The I-TiO 2 powders were characterized by XRD, TEM, EDS, XPS, FTIR, and steady-state UV−vis diffuse reflectance spectra (DRS), and their photocatalytic activities were investigated based on the photodegradation of 4-chlorophenol (4-CP) in water. A higher photodegradation efficiency of 4-CP was observed for I-TiO 2 under UV- and visible-light irradiation, when compared to the undoped TiO 2 . The transient behavior of the photogenerated charge carriers, such as trapped electrons (e − ) and holes (h + ), and the one-electron oxidation dynamics of substrates during UV or visible laser flash photolysis of undoped TiO 2 and I-TiO 2 powders were investigated using time-resolved diffuse reflectance (TDR) spectroscopy. The time evolution of transient signals indicated that the long-lived photogenerated h + were formed upon the laser excitation of I-TiO 2 powders, while no trapped e − were observed. From the experimental results, it is suggested that the recombination of e − −h + pairs is inhibited because the doping I sites act as trapping site to capture the e − during the I-TiO 2 photocaltalytic reaction. Furthermore, the trapped h + generated in I-TiO 2 have no significant oxidation reactivity toward substrates, such as aliphatic and aromatic compounds, adsorbed on the surface under both UV- and visible-light irradiation.