Melanin-like units concentration effects in melanin-like/vanadium pentoxide hybrid compounds

Abstract

An intercalated material has been prepared consisting of a regular alternation of organic/inorganic layers. The films were obtained by reacting 3,4-dihydroxy-phenylalanine (dl-DOPA) with varying concentrations in a solution with freshly prepared HVO₃, which suffered a oxidative polymerization/intercalation ‘in situ’ process, forming a green suspension, in which after de-hydration at room temperature produces a nanocomposite with a dark blue metallic color. Films (C₈H₉NO₂)_xV₂O₅·nH₂O were characterized using FT–IR, ESR, powder X-ray diffraction, conductivity, and cyclic voltammetry. The X-ray diffractograms indicate that the lamellar structure of the V₂O₅ is preserved for low concentrations of melanin-like units (x<0.02), but the inter-planar space increases from 1.2 nm to ca. 1.5 nm. The FT–IR and ESR spectra confirm that the V₂O₅ structure is preserved, however the presence of melanin-like units induces the reduction of V(V) ions to V(IV) ions. The melanin insertion is observed to increase the stability and reproducibility of the electrochemical insertion/de-insertion of Li⁺. The incorporation of melanin-like structures increases the conductivity, followed by a decrease in its temperature activation energy.