Wo _3-x Study On Relationship Between Structure And Properties Of Catalysts For Photocatalytic Decomposition Of Water

WO_3-X is a kind of semiconductor material with excellent performance and has a wide variety of applications in photodecomposition of water, selective catalysis and environmental engineering. However, inconsistent results of photocatalytic activity of different crystal phases of WO_3-X are reported due to its great variation in chemical valence of tungsten, difficulty in determining the atomic ratio between W and O, and complexity in phase transformations and electronic properties.WO_3-X were prepared with APT and H₂WO₄ as raw materials by solid state sintering and hydrothermal methods and were characterized by Raman Spectrum, XRD, SEM, DRS, TG-DTA and XPS. The photodecomposition of water into oxygen with WO_3-X as photocatalyst was investigated using Fe³⁺ as electron donors. The relationship between structure and photocatalytic activity of WO_3-X prepared from different raw materials and by different methods was studied. Conclusions were made as follows:(1) WO_3-X prepared by solid state sintering method with APT as raw material was mainly constituted of monoclinic phase. WO_3-X with oxygen index 2.44 showed the best catalytic activity when APT was heated at 600℃for 4h. Under the ultraviolet radiation at 365nm, the evolution rate of O₂ reached 145.8μmol/L/h. However, WO_3-X prepared by hydrothermal method didn't exhibit a good catalytic performance.(2)The photocatalytic performance of monoclinic phase WO_3-X synthesized by sintering method with H₂WO₄ as raw material remained almost the same under different sintering temperature. But WO_3-X prepared by hydrothermal crystallization exhibited better phtocatalytic activity because orthogonal phase and hexagonal phase appeared. WO_3-X showed the best catalytic activity after 24 hour's hydrothermal process. Under the ultraviolet radiation at 365nm, the evolution rate of O₂ reached 140μmol/L/h.(3) In the hydrothermal process, with the increase of temperature, the phase transformation of WO_3-X was in the sequence of orthogonalâ†' hexagonalâ†'monoclinic until all the orthogonal phase and hexagonal phase were turned into monoclinic phase. The photocatalytic activity of WO_3-X was reduced with the decrease of amount of hexagonal phase. Therefore, the existence of hexagonal phase is significant for the phtocatalytic performance of WO_3-X.(4) With the decrease of oxygen index, the photocatalytic activity of WO_3-X was raised firstly, and then decreased sharply, which indicated that the photocatalytic activity of WO_3-X was determined by the amount of oxygen vacancies. When oxygen index was less than 2.30, the color of WO_3-X was blue. When oxygen index was between 2.44-2.50, WO_3-X exhibited high photocatalytic activity with the evolution rate of O₂ over 108μmol/L/h.