1. Crystal Structure
Base Unit
Coordination polyhedron: A layered structure formed by VO₅ tetrahedra and VO₄ tetrahedra connected by common faces or angles.
Interlayer forces: The layers are held together by weak van der Waals forces and can easily stratify (similar to graphite).
Space Group
Crystal system: Orthorhombic system (space group Pmmn).
Cell Options:
a = 11,51 Å, b = 4,37 Å, c = 3,56 Å.
Each unit cell contains 2 vanadium atoms and 5 oxygen atoms.
Structural Characteristics
Vanadium-oxygen bond lengths:
Short bonds (~1.58 Å): V=O double bonds (tetrahedral apex oxygen).
Long bonds (~1.78-2.02 Å): V-O single bonds (intralayer bridge oxygen).
Layered anisotropy: easily eroded along the b-axis, resulting in V₂O₅ often taking on a scaly or needle-like shape.
2. Chemical Properties
Redox Properties
Strong oxidizer:
At high temperatures, HCl, HBr, etc. can be oxidized, for example:
V2O5+6HCl Δ2VOCl2+Cl2+3H2O
Reacts with reducing agents (e.g., H2, C) to form low-valence oxides (VO2, V2O3, or vanadium metal).
Self-healing:
decomposes when heated to 690°C and above:
2V2O5 Δ4VO2+O2↑
Acid-Base Reaction (Amphoteric)
Reacts with acids to form vanadate ions (VO₂⁺), e.g. when dissolved in sulfuric acid:
V2O5+2H2SO4→2VO2SO4+H2O
Reacts with alkalis to form vanadates (e.g., sodium metavanadate NaVO₃):
V2O5+2NaOH→2NaVO3+H2O
Further dissolution in strong alkalis produces colorless [VO₄]³- (orthovandate).
Catalytic Activity
Sulfuric acid industry: catalyzes the oxidation of SO₂ to SO₃ (mechanism includes the V⁵⁺↔V⁴⁺ cycle):
2SO2+O2V2O52SO3
Selective oxidation: e.g., oxidation of benzene to maleic anhydride and propane to acrylic acid.
Reaction With Organic Substances
Oxidation of alcohols and aldehydes: e.g., ethanol is oxidized to acetaldehyde and further to acetic acid.
Polymerization reactions: acts as a catalyst for the synthesis of certain polymers (e.g., polyethylene).
3. Electronic Properties And Strip Structure
Semiconductor properties: bandgap of about 2.3 eV (absorption in the visible range of light).
Charge Transfer: The d⁰ electron configuration of V⁵⁵⁺ allows it to easily accept electrons and participate in redox cycles.
4. Special Phenomena And Reactions
Intercalation chemistry: Li and Na ions can be intercalated between layers, which is used in lithium-sodium ion batteries:
V2O5+xLi++xe-→LixV2O5
Photosensitivity: Can catalyze the degradation of organic matter (e.g., dye decomposition) under the influence of ultraviolet light.
