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 Sr _x V _y ⁴⁺ V_12−y ⁵⁺O_31−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, Sr_0.25V₂O₅·1.5H₂O 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 ?.