Preparation of a Reduced Layered Tungstic Acid H_xW_2O_7 via Acid Treatment of Bi_2W_2O_9 in the Presence of Sn~(2+) Ions

摘要

A reduced layered tungstic acid with a double-octahedral structure was prepared by acid treatment of Aurivillius-type Bi_2W_2O_9 in the presence of Sn~(2+) ions. While the color of the product formed by acid treatment with no Sn~(2+) ions present, H_2W_2O_7, was yellow, a blue powder was obtained after the acid treatment in the presence of Sn~(2+) ions. No notable change in the morphology was observed after acid treatment. The X-ray diffraction pattern of the product acid-treated in the presence of Sn~(2+) ions was very similar to that of H_2W_2O_7. Essentially all the Bi~(3+) ions were lost upon acid treatment, indicating the occurrence of selective leaching of bismuth oxide sheets in Bi_2W_2O_9. A UV-visible absorption spectrum and XPS analysis demonstrated that the W~(6+) ions were partially reduced to W~(5+) ions, and the number of protons in the product was correspondingly 2.4 per [W_2O_7]. These results suggest the successful formation of a reduced layered tungstic acid, H_(2.4)W_2O_7.