• investigation of phase transitions for the hydrothermal formation of tio2 in the presence of f− ions

    جزئیات بیشتر مقاله
    • تاریخ ارائه: 1392/01/01
    • تاریخ انتشار در تی پی بین: 1392/01/01
    • تعداد بازدید: 614
    • تعداد پرسش و پاسخ ها: 0
    • شماره تماس دبیرخانه رویداد: -
     the hydrothermal phase transition of ammonium titanate into tio2 in aqueous ammonia media was investigated in the presence of f− ions by adding various kinds of electrolytes such as nacl, nh4cl, naf, and nh4f. the phase composition and the morphologies of the products were examined by x-ray diffraction (xrd) and scanning electron microscopy (sem). with the assistance of f ions, pure brookite tio2 can be hydrothermally prepared with a wide range of na+ ion concentrations from 0.25 m to 1.5 m in just 24 h, which has obvious advantages over the previous nacl scheme  and . moreover, photocatalytic degradation of mo shows that both anatase and brookite prepared in the presence of f ions show superior photocatalytic activities than those prepared in the absence of f ions. the phase transition mechanism from ammonium titanate into tio2 was also proposed. besides the introduction of na+ ions that benefits the phase transition from titanate to brookite, f ions are suggested to play two key roles during the hydrothermal process: catalyzing the condensation reaction of ti--oh to produce ti—o--ti linkages by forming ti--f and regulating the intercalation and the de-intercalation of na+ ions by counteracting the electrostatic interaction between the na+ ions and the titanate layers.

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