Redox Transition and Property Modulation in Vanadium Oxide Nanourchins: From V2O5 to long hydrocarbon alkylammonium V7O162-.

Abstract

Urchin-like vanadium oxide nanostructures (VOₓ–NUs) were synthesized using V⁵⁺ alkoxide precursors [VO(OCH(CH₃)₂)₃] and long-chain primary alkylamines (1 hexadecylamine and 1 octadecylamine) as structure-directing agents. The process involves intercalation-driven sol–gel assembly followed by hydrothermal treatment at 180 °C for seven days in aqueous–ethanolic media. The resulting spherical clusters are composed of densely packed, radially aligned vanadium oxide nanotubes stabilized by mixed-valence V⁴⁺/V⁵⁺ within a V₇O₁₆²⁻ lattice. Despite surface similarities to conventional VOₓ nanotubes, these urchin architectures exhibit distinct structural and electronic behavior due to their curved three-dimensional configuration and dense interfacial organization. Oxidation-state transitions were quantified via X-ray photoelectron spectroscopy (XPS) and volumetric titration, revealing progressive reduction of V⁵⁺ to V⁴⁺ templated by the amines. Magnetic characterization by SQUID magnetometry uncovered unusual room-temperature magnetic behavior, linked to the stabilization of mixed-valence states within the layered lattice. These results demonstrate how controlled intercalation and redox tuning enable the formation of VOₓ–NUs with emergent magnetic properties, expanding their potential in magnetoelectronic, catalytic, and sensing applications. The findings offer a novel framework for engineering multifunctional transition metal oxide nanostructures through oxidation-state modulation and self-assembly.