title: Effects of thermal treatments on the recovery of adsorbed water and photocatalytic activities of TiO2 photocatalytic systems.
abstract: The effects of thermal treatments on the rehydration process and photocatalytic activity were investigated by 1H NMR spectroscopy for six anatase abundant TiO2 photocatalysts with different properties. Acetic acid and benzoic acid were employed for photodecomposition in aqueous suspension. After the calcinations at 973 K, physisorbed water layers recovered relatively fast for P25, F4, and AMT-600 (shorter than 24 h) with no significant enhancement of the photocatalytic decomposition. On the other hand, for ST-01, UV-100, and AMT-100, the recovery was very slow (longer than 1 week) and only partially reversible, and the photocatalytic decomposition was considerably enhanced but retarded with rehydration. In the presence of adsorbed water, the binding of a carboxyl group of the molecules with adsorbed water is considered to compete with the direct adsorption on the surface, which reduces the amount of the direct adsorption and results in the reduction in the photocatalytic efficiency. In addition, the photocatalytic decomposition of benzoic acid with an aromatic ring was much faster in all of the TiO2 aqueous suspensions and more enhanced for the fully dehydroxylated TiO2 than that of acetic acid. These results suggest that the most efficient photocatalytic sites should be the hydrophobic sites on the TiO2 surface. The difference among the rehydration rates of different TiO2 is discussed in terms of thermally induced changes of surface morphology.
authors.affiliation: Department of Chemistry, Nagaoka University of Technology, Nagaoka 940-2188, Japan. nosaka@nagaokaut.ac.jp
authors.forename: Atsuko Y
authors.initials: AY
authors.lastname: Nosaka
authors.forename: Junichi
authors.initials: J
authors.lastname: Nishino
authors.forename: Toshimichi
authors.initials: T
authors.lastname: Fujiwara
authors.forename: Takahisa
authors.initials: T
authors.lastname: Ikegami
authors.forename: Hiromasa
authors.initials: H
authors.lastname: Yagi
authors.forename: Hideo
authors.initials: H
authors.lastname: Akutsu
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Nosaka
mesh_terms: D000042:Absorption; D019342:Acetic Acid / Q000737:chemistry; D019817:Benzoic Acid / Q000737:chemistry; D002384:Catalysis; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D006358:Hot Temperature; D009682:Magnetic Resonance Spectroscopy; D010316:Particle Size; D010777:Photochemistry; D014025:Titanium / Q000737:chemistry*; D014466:Ultraviolet Rays; D014867:Water / Q000737:chemistry*
chemical_list: D014867:Water; C009495:titanium dioxide; D019817:Benzoic Acid; D014025:Titanium; D019342:Acetic Acid