Phase Formation in the System Zn(VO₃)₂–HCl–VOCl₂–H₂O

Abstract—The phase and chemical compositions of precipitates formed in the system Zn(VO₃)₂–HCl–VOCl₂–H₂O at pH 1−3, molar ratio V⁴⁺ : V⁵⁺ = 0.1−9, and 80°C were studied. It was shown that, within the range 0.4 ≤ V⁴⁺ : V⁵⁺ ≤ 9, zinc vanadate with vanadium in a mixed oxidation state forms with the general formula Zn_xV$_{y}^{{4 + }}$V$_{{2 - y}}^{{5 + }}$O₅ ⋅ nH₂O (0.005 ≤ x ≤ 0.1, 0.05 ≤ y ≤ 0.3, n = 0.5−1.2). Vanadate Zn_xV₂O₅ ⋅ nH₂O with the maximum tetravalent vanadium content (y = 0.30) was produced within the ratio range V⁴⁺ : V⁵⁺ = 1.5−9.0. Investigation of the kinetics of the formation of Zn_xV₂O₅ ⋅ nH₂O at pH 3 determined that tetravalent vanadium ions VO²⁺ activate the formation of zinc vanadate, and its precipitation is described by a second-order reaction. It was demonstrated that, under hydrothermal conditions at pH 3 and 180°C, zinc decavanadate in the presence of VOCl₂ can be used as a precursor for producing V₃O₇ ⋅ H₂O nanorods 50–100 nm in diameter.