Hydrothermal Synthesis of NH4V3O8 in Solutions of Tetra- and Pentavalent Vanadium

Abstract

The formation conditions and morphology of ammonium trivanadate NH₄V₃O₈ formed in mixed solutions of tetra- and pentavalent vanadium in the presence of various ammonium-containing additives (NH₄Cl, (NH₄)₂SO₄, NH₄NO₃, and CH₃COONH₄) were studied. NH₄V₃O₈ formation under hydrothermal conditions was observed at 180°С, acidities of 2.5 ≤ рН ≤ 8.0, and the ratio V₂O₅ : VOSO₄ ⋅ 3H₂O = 2 : 1 mol/mol. The presence of vanadyl sulfate VOSO₄ ⋅ 3H₂O favors ammonium trivanadate formation, expanding its formation range to weak alkalinities. Variations in synthetic parameters, in particular, рН, provide the production of various NH₄V₃O₈ morphologies. Additives of ammonium-containing salts favor the formation of NH₄V₃O₈ single crystals mostly in the form of plates of various sizes. Ammonium trivanadate nanoparticles have been for the first time prepared in the form of nanowires with the extreme ratio l/d ∼ 100.