Herenilton P. Oliveira

Electrochromic and conductivity properties: a comparative study between melanin-like/V2O5 nH2O and polyaniline/ V2O5 nH2O hybrid materials

In this work, we report the synthesis and some properties of melanin-like/V2O5·nH2O and polyaniline/V2O5·nH2O hybrid materials that have potential applications in optics and electronics. The hybrid materials were obtained by an oxidative polymerization/intercalation process reacting the gel with the monomers of the polymers. The optical properties of the compounds in film forms were measured using ultraviolet–visible (UV–Vis) spectroscopy. Thermogravimetric analysis, differential gravimetric analysis and dc conductivity techniques were also used to study the compounds. The X-ray diffractograms indicate that the lamellar structure of the V2O5 is preserved with the increase of the inter-planar space from 1.18±0.05 to 1.40±0.05 nm. The presence of the organic phase induced the reduction of V(V) ions to V(IV) and increased the dc conductivity and affected the spectroelectrochemical properties of the samples.

Synthesis and structural characterization of tetrakis(n-methyl-4-pyridyl) porphyrin copper into v2o5 xerogel

This paper reports on the intercalation of the cationic water-soluble tetrakis(N-methyl-4-pyridyl) porphyrin copper into V2O5 xerogel and the structural and spectroscopic characterization of the obtained products. The preparation procedure is carried out to preserve the anisotropic lamellar structure nature of the xerogel. The X-ray diffraction, FTIR, EPR, and SEM data show the maintenance of the matrix framework during the intercalation, which is consistent with a topotatic reaction, and the formation of nucleation centers promoting the organization of polimeric chains. The results also indicate weak interaction between the host and guest species leading to the formation of an ordered organic–inorganic composite.

Spectroscopic characterization and electrocatalytical activity of tetrapyridylporphyrins intercalated into hydrated vanadium(V) oxide

The intercalation ofmeso-tetrapyridylporphyrins into hydrated vanadium(V) pentoxide has been studied using X-ray diffraction; FTIR, electronic and Mössbauer spectroscopy; cyclic voltammetry and spectroelectrochemistry. The intercalation compound containing iron tetrapyridylporphyrin exhibits pronounced electrocatalytical activity in the reduction of molecular dioxygen, reflecting an enhanced reactivity of the catalyst in a confined medium.

Thermal annealing effects on vanadium pentoxide xerogel films

The effect of water molecules on the conductivity and electrochemical properties of vanadium pentoxide xerogel was studied in connection with changes of morphology upon thermal annealing at different temperatures. It was demonstrated that the conductivity was increased for the samples heated at 150 o C and 270 o C compared to the vanadium pentoxide xerogel. It was also verified a stabilization of electrochemical processes of the insertion and de-insertion of lithium ions the structure of thermally annealed vanadium pentoxide.

Electrochemical study of vanadia–silica xerogel film

Abstract In this report, the sol–gel synthesis and electrochemical properties of a homogeneous multicomponent material composed of vanadium pentoxide xerogel dispersed in a silica matrix are described. The cyclic voltammetric and electrochemical impedance spectroscopy studies demonstrated that the silica matrix provides an improvement of the electrochemical properties mainly in relation to the kinetics of the lithium electroinsertion into the oxide matrix with little decrease of total charge during successive redox cycles. This attractive behavior can be explained by the structural stability produced by the silica matrix that favors the kinetic of V IV /V V solid state redox transitions.

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

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.

The effects of Sb incorporation into vanadium pentoxide xerogel

Abstract In this work we report the effects on structural and conductivity properties of incorporating different amounts of antimony ions into vanadium pentoxide xerogel. Powder X-ray diffraction, Fourier-transform infrared spectroscopy, electronic paramagnetic resonance and thermogravimetric analysis were used in order to characterise the obtained products. Powder X-ray diffraction data indicate that the presence of Sb ions induces a decrease in crystallinity with the maintenance of the lamellar organisation, evidenced by 001 reflection with a higher basal distance (d=1.26 nm). FT-IR spectra show the characteristic vibrational modes of the matrix, indicating that the presence of Sb ions did not affect the short range structure. EPR spectra, in addition, show that Sb ions induce a reduction of V5+ ions to V4+. The conductivity is enhanced by small amounts of Sb ions with a decrease in activation energy.

Synthesis, Characterization and Properties of New Vanadia-Alumina and Vanadia-Silica Composites Prepared by Interpenetrating Polymer Network Approach

In this study, we incorporated vanadium pentoxide xerogel into an alumina matrix and into a silica matrix in order to improve the structural stability by incorporating the electroactive material into an inert matrix which provides structural stability to the electrode. The novel materials were characterized by powder X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, energy dispersive X-ray spectrometry, cyclic voltammetry and impedance spectroscopy. V 2 O 5 /SiO 2 and V 2 O 5 /Al 2 O 3 xerogel composites prepared by soft chemistry present conductivity almost five orders of magnitude higher than other related systems. The electrochemical behavior is quite similar to that found for V 2 O 5 xerogel. In addition, the cyclic voltammetric and electrochemical impedance spectroscopy studies demonstrated that the alumina and silica matrices provide an improvement of the electrochemical properties mainly in relation to the kinetics of the lithium electroinsertion into the oxide matrix with little decrease of total charge during successive redox cycles. Overall, the synthetic approach applied in this study is extremely attractive due to its simplicity and can provide new strategies for tailoring new materials and future family members for electrochromic devices, batteries and chemical sensing.