Composition and formation kinetics of strontium polyvanadates in vanadium(IV,V) solutions

The phase and chemical compositions of the precipitates forming in the Sr(VO3)2-VOCl2-H2O system in the V4+/V5+ = 0.11–9 range at 80–90°C are reported. At pH 1–3 and V4+/V5+ = 0.25−9, the general formula of the precipitated compounds is SrxVy4+ V12−y5+O31−δ·nH2)(0.37 ≤ x ≤ 1.0, 1.7 ≤ y ≤ 3.0, 0.95 ≤ δ ≤ 2.1). Polyvanadates containing the largest amount of vanadium(IV) are obtained at an initial V4+/V5+ ratio of 9 and pH 1.9. Precipitation from solutions at pH 3 takes place only in the presence of the VO2+ ion, and the highest precipitation rate is observed at V4+/V5+ = 0.11. The process is controlled by a second-order reaction on the polyvanadate surface. Under hydrothermal conditions at 180°C, Sr0.25V2O5·1.5H2O nanorods are obtained from solutions with a V4+/V5+ molar ratio of 0.1 at pH 3. The nanorods, 30–100 nm in diameter and up to 2–3 μm in length, have a layered structure with an interlayer spacing of 10.53 ± 0.08 Å.