The visible light induced photocatalytic activity of tungsten trioxide powders

The preparation, characterization and photoreactivity of tungsten trioxide powders are presented. Tungsten trioxide powders were prepared by air annealing of various W precursors. The effects of W precursor type and pretreatment conditions on the physical properties, and photocatalytic performance of the obtained WO₃ powders were examined. The photooxidation of water to oxygen and protons in the presence of reducible additives Ce⁴⁺, using the luminous and near IR illumination was used as a test reaction to evaluate the activity of the powders. Increasing annealing temperatures gave materials with a high degree of crystallinity and red-shifted the onset of light absorption. The light absorption of the obtained powders in the long wavelength region versus the type of the W precursor increased in the order: H₂WO₄<(NH₄)₆W₁₂O₃₉<(NH₄)₁₀W₁₂O₄₁. The level of crystallinity of the obtained powders increased in the order: (NH₄)₁₀W₁₂O₄₁≈(NH₄)₆W₁₂O₃₉2WO₄. The activity of the WO₃ powders depended on the type of W precursor used, annealing conditions, and the physico-chemical characteristics of the resulting powders. The activity according to the types of the W precursor increased in the order: (NH₄)₁₀W₁₂O₄₁<(NH₄)₆W₁₂O₃₉2WO₄. The activity as a function of annealing temperature and duration of W precursors goes through a maximum at 700–800°C and 4–8 h, respectively. Increasing the specific surface area of WO₃ powders, did not alter the activity significantly. Addition of 0.1–1% Pt and RuO₂ as co-catalysts improved the initial rates and long-term activity by about 1.3–1.5 times. Small amounts of hydrogen were also produced from photochemical reactions involving the photoexcitation of Ce³⁺.