Selected-Control Synthesis of NaV₆O₁₅ and Na₂V₆O₁₆·3H₂O Single-Crystalline Nanowires

NaV 6 O 15 and Na 2 V 6 O 16 ·3H 2 O nanowires were selectively prepared from the reaction between V 2 O 5 and NaHSO 4 ·H 2 O/Na 2 SO 4 under hydrothermal conditions. The synthesized products were characterized by XRD, SEM, TEM, SAED, EDX, HRTEM, and XPS analytical techniques. SAED and HRTEM analyses confirm the single-crystalline nature of both NaV 6 O 15 and Na 2 V 6 O 16 ·3H 2 O nanowires. The nanowires of NaV 6 O 15 are uniform and straight, with around 80 nm in diameter and several tens of micrometers in length. Na 2 V 6 O 16 ·3H 2 O nanowires have an average diameter of 60 nm and length up to 10 μm. The key factors to control the phase composition and morphology, such as the amount of sulfates and the selective absorption of SO 4 2- in different crystal facets, are discussed. The optimum hydrothermal temperatures for the nanowire growth are 180 °C for NaV 6 O 15 and 180 to 140 °C for Na 2 V 6 O 16 ·3H 2 O. A tentative formation mechanism is proposed.