Redox transition and property modulation in vanadium oxide nanourchins: from V2O5 to long hydrocarbon alkylammonium V7O162−

Abstract

Urchin-like vanadium oxide nanostructures (VO_x-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 VO_x 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 VO_x-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.