Revisiting Tungsten Trioxide Hydrates (TTHs) Synthesis - Is There Anything New?

• Published in: Inorganic chemistry 2009-07, Vol.48 (14), p.6804-6811
• Main Authors: Kuti, Lisa M, Bhella, Surinderjit Singh, Thangadurai, Venkataraman
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic900738m

We report a very simple precipitation route to prepare a layered perovskite-type structure, tungsten trioxide hydrate (TTH), with the nominal chemical formula of WO3·1.3H2O (≡ 1/2H2W2O7·1.6H2O), using aqueous Na2WO4 and SrCl2. Our investigation shows that the concentration of HCl used to dissolve the SrCl2 plays a crucial role in the stabilization of different structure types of layered TTHs. Highly acidic SrCl2 (dissolved in 9 M HCl) solution yields an orthorhombic layered TTH of WO3·2H2O, while SrCl2 dissolved in 3 M HCl appears to give an A-site-deficient Ruddlesdon−Popper (RP) related double-perovskite-type layered structure (DOLS-TTH). A well-known scheelite-type structure is obtained under weakly basic conditions (pH = 10.3 for Na2WO4(aq), 7.0 for SrCl2(aq)). Previously, RP-type a DOLS of H2W2O7·0.58H2O was prepared, using an acid-leaching method, from the corresponding n = 2 member of the layered Aurivillius phase (AP) Bi2W2O9. Powder X-ray diffraction showed the formation of layered RP DOLS with a large d spacing ∼12.5 Å, which is consistent with acid-leaching (Kuto et al. Inorg. Chem. 2003, 42, 4479−4484; Wang et al. J. Solid State Chem. 2007, 180, 1125−1129) and exfoliation (Schaak et al. Chem. Commun. 2002, 706−707) methods for synthesized TTHs. The proposed DOLS-TTH structure of newly prepared TTHs was further confirmed by an intercalation reaction using n-octylamine (C8A). A transmission electron microscopy study showed the formation of nanosized particles, and scanning electron microscopy coupled with energy dispersive X-ray analysis showed the absence of Na and Sr in the air-dried, as-precipitated products under acidic conditions. The bulk electrical (proton) conductivity of presently prepared TTHs was found to be on the order of 10−4−10−3 S/cm at room temperature in wet N2.