Photoinduced oxygen formation and silver-metal deposition in aqueous solutions of various silver salts by suspended titanium dioxide powder

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Abstract
The photochemical reaction of Ar-purged aqueous solutions containing various silver salts and TiO2 powder in suspension has been studied at room temperature. Photoirradiation (λex < 300 nm) resulted in O2 formation and deposition of Ag metal on the TiO2 particles. The apparent reaction rate depended on the anions of the silver salt and increased in the order ClO– 4 < NO– 3≈ SO2– 4 < F–(≈ PO3– 4). The sensitizing activity of the rutile [TiO2(R)] was comparable to that of the anatase [TiO2(A)]. The molar ratio of deposited Ag metal to liberated O2, which was independent of the reaction rate, was equal to ca. 5 except for the case of TiO2(A)/AgClO4. The pH of the reaction mixture decreased with irradiation time, resulting in deactivation of the TiO2. Although O2 formation and Ag-metal deposition did not occur at pH < 2, the photosensitizing activity of the TiO2 powder was recovered by the addition of NaOH. The addition of propan-2-ol to the deactivated acidic suspension of TiO2 was also effective for Ag-metal deposition but not for O2 formation.

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