Hydrothermal synthesis of polyaniline intercalated vanadium oxide xerogel hybrid nanocomposites: effective control of morphology and structural characterization

Abstract

Polyaniline (PANI) intercalated layered vanadium oxide xerogel hybrid nanocomposites have been successfully synthesized via a simple hydrothermal route. FESEM images reveal the surface morphology of fiber and rod shaped PANI/vanadium oxide xerogel (PV) nanocomposites. The fiber and rod like morphologies of the PV nanocomposite have been tailored by controlling the relative concentration in between PANI and peroxovanadic acid solution and it leads to the formation of a V₂O₅·nH₂O xerogel. The growth mechanism of the specific morphology has been proposed on the basis of the detailed structure and microstructure characterization of nanocomposites by analyzing their XRD patterns employing Rietveld refinement and FESEM/HRTEM images. Both FTIR and XPS spectra confirm the formation of PANI/vanadium oxide xerogel nanocomposites, the presence of polyaniline and water molecules in the nanocomposites and partial reduction of V⁵⁺ to V⁴⁺. This corroborates well with the results of XRD pattern analysis. XPS spectra analysis also reveals the relative contents of V⁵⁺ and V⁴⁺ in both composites. UV-Vis spectra further confirm the formation of these nanocomposites. The growth direction of the synthesized nanorods along 〈00l〉 is confirmed by Rietveld refinement and HRTEM image analyses. The core shell structure of the composite, in which, an amorphous PANI sheath layer acts as the shell covering the crystalline V₂O₅·nH₂O core, is confirmed from the HRTEM images. STEM-HAADF images and EDX spectra confirm the chemical composition and uniform distribution of PANI and V₂O₅·nH₂O over the entire area of the nanocomposites. Intercalation of water and PANI layers into the V₂O₅·nH₂O layer resulted in an orthorhombic to monoclinic structural phase transition due to a substantial increase in the interplanar spacing of the (00l) plane of orthorhombic V₂O₅. Atomic modeling reveals the lamellar like structure of the nanocomposite wherein PANI chains are sandwiched between double layers of VO₆ octahedra. Rietveld refinement estimates the quantitative measure of intercalated V₂O₅·nH₂O, VO₂ and PANI in the composites. It is reported for the first time that the relative contents of these phases regulate the morphology of these nanocomposites.