Vanadium oxide-porphyrin nanocomposites as gas sensor interfaces for probing low water content in ethanol

Vanadium pentoxide xerogels (VXG) incorporating meso(3- and 4-pyridyl)porphyrin cobalt(III) species coordinated to four [Ru(bipy)(2)Cl](+) complexes were employed as gas sensing materials capable of detecting small amounts of water in commercial ethanol and fuel supplies. According to their X-ray diffraction data, the original VXG lamellar framework was maintained in the nanocomposite material, but the interlamellar distance increased from 11.7 to 15.2 angstrom, reflecting the intercalation of the porphyrin species into the vanadium pentoxide matrix. The films generated by direct deposition of the nanocomposite aqueous suspensions exhibited good electrical and electrochemical performance for application in resistive sensors. The analysis of water in ethanol and fuels was carried out successfully using an especially designed electric setup incorporating a laminar gas flow chamber and interdigitated gold electrodes coated with the nanocomposites. (C) 2010 Elsevier B.V. All rights reserved.

V(2)O(5) nanoparticles obtained from a synthetic bariandite-like vanadium oxide: Synthesis, characterization and electrochemical behavior in an ionic liquid

Highly stable and crystalline V(2)O(5) nanoparticles with an average diameter of 15 nm have been easily prepared by thermal treatment of a bariandite-like vanadium oxide, V(10)O(24)center dot 9H(2)O. Their characterization was carried out by powder X-ray diffractometry (XRD). Fourier transform infrared (FT-IR) and Raman spectroscopies, and transmission electron microscopy (TEM). The fibrous and nanostructured film obtained by electrophoretic deposition of the V(2)O(5) nanoparticles showed good electroactivity when submitted to cyclic voltammetry in an ionic liquid-based electrolyte. The use of this film for the preparation of a nanostructured electrode led to an improvement of about 50% in discharge capacity values when compared with similar electrodes obtained by casting of a V(2)O(5) xerogel. (C) 2009 Elsevier Inc. All rights reserved.

Flow injection amperometric determination of hydrogen peroxide in household commercial products with a ruthenium oxide hexacyanoferrate modified electrode

Hydrogen peroxide was determined in oral antiseptic and bleach samples using a flow-injection system with amperometric detection. A glassy carbon electrode modified by electrochemical deposition of ruthenium oxide hexacyanoferrate was used as working electrode and a homemade Ag/AgCl (saturated KCl) electrode and a platinum wire were used as reference and counter electrodes, respectively. The electrocatalytic reduction process allowed the determination of hydrogen peroxide at 0.0 V. A linear relationship between the cathodic peak current and concentration of hydrogen peroxide was obtained in the range 10-5000 mu mol L(-1) with detection and quantification limits of 1.7 (S/N = 3) and 5.9 (S/N = 10) mu mol L(-1), respectively. The repeatability of the method was evaluated using a 500 mu mol L(-1) hydrogen peroxide solution, the value obtained being 1.6% (n = 14). A sampling rate of 112 samples h(-1) was achieved at optimised conditions. The method was employed for the quantification of hydrogen peroxide in two commercial samples and the results were in agreement with those obtained by using a recommended procedure.

Lithium Ion Electro-Insertion and Spectroelectrochemical Properties of Films from Hexaniobate

Layer-by-layer (LbL) films from K(2)Nb(6)O(17)(2-) and polyallylamine (PAH) and dip-coating films of H(2)K(2)Nb(6)O(17) were prepared on a fluorine-doped tin-oxide (FTO)-coated glass. The atomic force microscopy (AFM) images were carried out for morphological characterization of both materials. The real surface area and the roughness factor were determined on the basis of pseudocapacitive processes involved in the electroreduction/electrooxidation of gold layers deposited on these films. Next, lithium ion insertion into these materials was examined by means of electrochemical and spectroelectrochemical measurements. More specifically, cyclic voltammetry and current pulses under visible light beams were used to investigate mass transport and chromogenic properties. The lithium ion diffusion coefficient (D(Li)) within the LbL matrix is significantly higher than that within the dip-coating film, ensuring high storage capacity of lithium ions in the self-assembled electrode. Contrary to the LbL film, the potentiodynamic profile of absorbance change (Delta A) as a function of time is not similar to that obtained in the case of current density for the dip-coating film. Aiming at analyzing the rate of the coloration front associated with lithium ion diffusion, a spectroelectrochemical method based on the galvanostatic intermittent titration technique (GITT) was employed so as to determine the ""optical"" diffusion coefficient (D(op)). In the dip-coating film, the method employed here revealed that the lithium ion rate is higher in diffusion pathways formed from K(2)Nb(6)O(17)(2-) sites that contribute more significantly to Delta A. Meanwhile, the presence of PAH contributed to the increased ionic mobility in diffusion pathways in the LbL film, with low contribution to the electrochromic efficiency. These results aided a better understanding of the potentiodynamic profile of the temporal change of absorbance and current density during the insertion/deinsertion of lithium ions into the electrochromic materials.

Layer-by-layer TiO(2) films as efficient blocking layers in dye-sensitized solar cells

Charge recombination at the conductor substrate/electrolyte interface has been prevented by using efficient blocking layers of TiO(2) compact films in dye-sensitized solar cell photoanodes. Compact blocking layers have been deposited before the mesoporous TiO(2) film by the layer-by-layer technique using titania nanoparticles as cations and sodium sulfonated polystyrene, PSS, as a polyanion. The TiO(2)/PSS blocking layer in a DSC prevents the physical contact of FTO and the electrolyte and leads to a 28% increase in the cell`s overall conversion efficiency, from 5.7% to 7.3%. (C) 2009 Elsevier B.V. All rights reserved.

Electrostatic layer-by-layer deposition and electrochemical characterization of thin films composed of MnO(2) nanoparticles in a room-temperature ionic liquid

Thin films of MnO(2) nanoparticles were grown using the layer-by-layer method with poly (diallyldimetylammonium) as the intercalated layer. The film growth was followed by UV-vis, electrochemical quartz crystal microbalance (EQCM), and atomic force microscopy. Linear growth due to electrostatic immobilization of layers was observed up to 30 bilayers, but electrical connectivity was maintained only for 12 MnO(2)/PPDA bilayers. The electrochemical characterization of this film in 1-butyl-2,3-dimethyl-imidazolium (BMMI) bis(trifluoromethanesulfonyl)imide (TFSI) (BMMITFSI) with and without addition of a lithium salt indicated a higher electrochemical response of the nanostructured electrode in the lithium-containing electrolyte. On the basis of EQCM experiments, it was possible to confirm that the charge compensation process is achieved mainly by the TFSI anion at short times (<2 s) and by BMMI and lithium cations at longer times. The fact that large ions like TFSI and BMMI participate in the electroneutrality is attributed to the redox reaction that occurs at the superficial sites and to the high concentration of these species compared to that of lithium cations.

XPS characterization of sensitized n-TiO2 thin films for dye-sensitized solar cell applications

TiO2 thin films, employed in dye-sensitized solar cells, were prepared by the sol-gel method or directly by Degussa P25 oxide and their surfaces were characterized by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The effect of adsorption of the cis-[Ru(dcbH(2))(2)(NCS)(2)] dye, N3, on the surface of films was investigated. From XPS spectra taken before and after argon-ion sputtering procedure, the surface composition of inner and outer layers of sensitized films was obtained and a preferential etching of Ru peak in relation to the Ti and N ones was identified. The photoelectrochemical parameters were also evaluated and rationalized in terms of the morphological characteristics of the films. (c) 2007 Elsevier B.V. All rights reserved.

Electrodeposition and characterization of undoped and nitrogen-doped ZnSe films

Semiconducting films of (n-type) ZnSe and (p-type) nitrogen-doped ZnSe were electrodeposited by a linear-sweep voltammetric technique on to a substrate of fluorine-tin oxide (FM) glass ceramics. The films were characterized by scanning electron microscopy, energy-dispersive X-ray analysis and grazing-incidence X-ray diffraction. The results indicated that the material was deposited uniformly over the substrate, forming clusters when the Zn content of the bath was 0.1 mol L(-1) and a film when it was 0.2 or 0.3 mol L(-1). The effectiveness of doping the films with nitrogen by adding ammonium sulfate to the deposition solution was assessed by measuring the film-electrolyte interface capacitance (C) at various applied potentials (E(ap)) and plotting Mott-Schottky curves (C(-2) vs E(ap)), whose slope sign was used to identify p-type ZnSe. (C) 2009 Elsevier B.V. All rights reserved.

Electrochemical Behaviour of the AA2024 Aluminium Alloy Modified with Self-Assembled Monolayers/Polyaniline Double Films

The electrochemical characteristics of the AA2024 aluminium alloy modified with octadecyltrimethoxysilane (ODTMS) + polyaniline (PANi) and propiltrimethoxysilane (PTMS) + (PANi) were studied in the present work. The results show that the different protective coatings shift the values of corrosion and pit potentials to more positive values making the system nobler and indicate that the double film ODTMS + PANi present the best protection against corrosion characteristics, that is probably due to the two contributions: anodic protection associated with the barrier effect.

Study of a gold electrode modified by trans-[Ru(NH(3))(4)(Ist)SO(4)](+) to produce an electrochemical sensor for nitric oxide

The modification of a gold electrode surface by electropolymerization of trans-[Ru(NH(3))(4)(Ist)SO(4)](+) to produce an electrochemical sensor for nitric oxide was investigated. The influence of dopamine, serotonin and nitrite as interferents for NO detection was also examined using square-wave voltammetry (SWV). The characterization of the modified electrode was carried out by cyclic voltammetry, electrochemical quartz crystal microbalance (EQCM) and SERS techniques. The gold electrode was successfully modified by the trans-[Ru(NH(3))(4)(Ist)SO(4)](+) complex ion using cyclic voltammetry. The experiments show that a monolayer of the film is achieved after ten voltammetric cycles, that NO in solution can coordinate to the metal present in the layer, that dopamine, serotonin and nitrite are interferents for the detection of NO, and that the response for the nitrite is much less significant than the responses for dopamine and serotonin. The proposed modified electrode has the potential to be applied as a sensor for NO. (C) 2011 Elsevier Ltd. All rights reserved.