J. Phys. Chem. B. 108(26) 9121-9125(2004

Characteristics of Water Adsorbed on TiO₂ Photocatalytic Systems on Temperature Increase as Studied by Solid-State ¹H-NMR Spectroscopy

Atsuko Y.Nosaka,^*† Toshimichi Fujiwara, ^‡ Hiromasa Yagi, ^‡ Hideo Akutsu^‡ and Yoshio Nosaka^*,^†
†Department of Chemistry, Nagaoka University of Technology, Nagaoka, 940-2188 Japan, and ^‡Institute for Protein Research, Osaka University, Suita, 565-0871 Japan

(Abstract)
The time profiles of the intensities, line widths and chemical shifts of ¹H-NMR signals of adsorbed water at 358 K were investigated for six different TiO₂ photocatalysts with different properties by solid state ¹H-NMR spectroscopy. The apparent single water peak was found to comprise of the signals with different line widths and chemical shifts, which correspond to those of the water molecules with different structures and mobility. The adsorbed water region observed with NMR is characterized by three layers; (I) the innermost layer with rigid water molecules with highly restricted mobility and/or hydroxyl groups on the solid surface, (II) the intermediate layer with relatively mobile water molecules, (III) the outermost layer with highly mobile water molecules. The thickness of the water layer is almost the same for six photocatalysts. T he ratio of the amount of the water molecules contained in each layer could be roughly estimated to be 3 (I) : 2 (II) : 5 (III). The surface properties of the individual photocatalyst are reflected in the water molecules distinctly in layer I but not those in the layer III

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