ELECTRODEPOSITION OF POLYCRYSTALLINE CD-RICH HG1-XCDXTE AND PHOTOELECTRO-CHEMICAL BEHAVIOR OF HG0.09CD0.91TE THIN-FILM

Electrodeposition process of polycrystalline Cd-rich Hg_(1-z)Cd_xTe (x>0.5) in acidic bath of CdSO_4+HTeO_2~+HgCl_2 was investigated. The simultaneous electrodeposition technique of three kinds of ions at the same potential has been achieved. The XRD, SEM and EDAX analysis of the thin film electrodeposited on titanium substrate showed a typical cubic zinc blende polycrystalline structure and homogeneous dispersion. The photoelectrochemical behavior of (1-x)=0.09 polycrystalline thin film in a polysulfide re...

Three-dimensional macroporous silicon photonic crystal with large photonic band gap

Three-dimensional photonic crystals based on macroporous silicon are fabricated by photoelectrochemical etching and subsequent focused-ion-beam drilling. Reflection measurements show a high reflection in the range of the stopgap and indicate the spectral position of the complete photonic band gap. The onset of diffraction which might influence the measurement is discussed.

Metal Oxide Nanoparticle Mediated Enhanced Raman Scattering and Its Use in Direct Monitoring of Interfacial Chemical Reactions

Metal oxide nanoparticles (MONPs) have widespread usage across many disciplines, but monitoring molecular processes at their surfaces in situ has not been possible. Here we demonstrate that MONPs give highly enhanced (X10(4)) Raman scattering signals from molecules at the interface permitting direct monitoring of their reactions, when placed on top of flat metallic surfaces. Experiments with different metal oxide materials and molecules indicate that the enhancement is generic and operates at the single nanoparticle level. Simulations confirm that the amplification is principally electromagnetic and is a result of optical modulation of the underlying plasmonic metallic surface by MONPs, which act as scattering antennae and couple light into the confined region sandwiched by the underlying surface. Because of additional functionalities of metal oxides as magnetic, photoelectrochemical and catalytic materials, enhanced Raman scattering mediated by MONPs opens up significant opportunities in fundamental science, allowing direct tracking and understanding of application-specific transformations at such interfaces. We show a first example by monitoring the MONP-assisted photocatalytic decomposition reaction of an organic dye by individual nanoparticles.

Changed reactivity of the 1-bromo-4-nitrobenzene radical anion in a room temperature ionic liquid

Radical anions of 1-bromo-4-nitrobenzene (p-BrC6H4NO2) are shown to be reactive in the room temperature ionic liquid N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, ([C(4)mPyrr][NTf2]), by means of voltammetric measurements. In particular, they are shown to react via a DISP type mechanism such that the electrolysis of p-BrC6H4NO2 occurs consuming between one and two electrons per reactant molecule, leading to the formation of the nitrobenzene radical anion and bromide ions. This behaviour is a stark contrast to that in conventional non-aqueous solvents such as acetonitrile, dimethyl sulfoxide or N,N-dimethylformamide, which suggests that the ionic solvent promotes the reactivity of the radical anion, probably via stabilisation of the charged products.

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.

Efficient and low cost devices for solar energy conversion: Efficiency and stability of some natural-dye-sensitized solar cells

Dye-sensitized solar cells, named by us Dye-Cells, are one of the most promising devices for solar energy conversion due to their reduced production cost and low environmental impact, especially those sensitized by natural dyes. The efficiency and stability of devices based on natural sensitizers such as mulberry (Morus alba Lam), blueberry (Vaccinium myrtillus Lam), and jaboticaba`s skin (Mirtus cauliflora Mart) were investigated. Dye-Cells prepared with aqueous mulberry extract presented the highest P(max) value (1.6 mW cm(-2)) with J(sc) = 6.14 mA cm(-2) and V(oc) = 0.49 V, Photoelectrochemical parameters of 16 cm(2) active area devices sensitized by mulberry dye were constant for 14 weeks of continuous evaluation. Moreover, the cell remained stable even after 36 weeks with a fairly good efficiency. Therefore, mulberry dye opens up a perspective of commercial feasibility for inexpensive and environmentally friendly Dye-Cells. (C) 2009 Elsevier B.V. All rights reserved.

Deposition and characterization of BiVO4 thin films and evaluation as photoanodes for methylene blue degradation

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Photoelectrocatalytic treatment of p-nitrophenol using Ti/TiO2 thin-film electrode

The photoelectrochemical degradation of p-nitrophenol (PNP) was investigated using titanium dioxide thin-film photoelectrode. The effects of different supporting electrolytes, pH, applied potential and PNP concentration were examined and discussed. Complete photodegradation was obtained in perchlorate medium at pH 2 when the photoanode was biased at +1.0 V (versus SCE) during a 3-h experiment. Under these conditions, carbon removal of approximately 60% was achieved. (C) 2005 Elsevier B.V. All rights reserved.

Photo-electrochemical investigation of anodic oxide films on cast Ti-Mo alloys I. Anodic behaviour and effect of alloy composition

The anodic behaviour of cast Ti-Mo alloys, having different Mo contents (6-20 wt.%), was investigated in acidic and neutral aerated aqueous solutions. All sample showed a valve-metal behaviour, owing to formation and thickening of barrier-type anodic oxides displaying interference colours Growth kinetics. of passive films is influenced by both anodizing electrolyte and composition of the starting alloy. This last parameter was found to change also the solid-state properties of the films, explored by photoelectrochemical and impedance spectroscopy experiments. Thicker films (U(f) = 8 V/MSE) grown on alloys richer in Mo showed more resistive character and a photocurrent sign inversion under negative bias, that revealed an insulating character, whereas corresponding films grown on alloys with lower Mo content, as well as thinner films, behaved as n-type semiconductors. Results are discussed in terms of formation of a mixed Ti-Mo oxide phase. (C) 2008 Elsevier Ltd. All rights reserved

Comparison of oxidation efficiency of disperse dyes by chemical and photoelectrocatalytic chlorination and removal of mutagenic activity

Degradation of Disperse Orange 1, Disperse Red 1 and Disperse Red 13 dyes has been performed using electrochemical oxidation on Pt electrode, chemical chlorination and photoelectrochemical oxidation on Ti/TiO(2) thin film electrodes in NaCl or Na(2)SO(4) medium. 100% discoloration was obtained for all tested methods after 1 h of treatment. Faster color removal was obtained by photoelectrocatalytic oxidation in 0.1 mol L(-1) NaCl pH 4.0 under UV light and an applied potential of +1.0V (vs SCE reference electrode), which indicates also values around 60% of TOC removal. The conventional chlorination method and electrochemical oxidation on Pt electrode resulted in negligible reduction of TOC removal. All dyes showed positive mutagenic activity in the Salmonella/microsome assay with the strain TA98 in the absence and presence of S9 (exogenous metabolic activation). Nevertheless, there is complete reduction of the mutagenic activity after 1 h of photoelectrocatalytic oxidation, suggesting that this process would be good option to remove disperse azo dyes from aqueous media. (C) 2008 Elsevier Ltd. All rights reserved.

Evaluation of color removal and degradation of a reactive textile azo dye on nanoporous TiO2 thin-film electrodes

The feasibility of the photobleaching of a textile azo dye, reactive orange 16 (C.I. 17757), in aqueous solution using titanium dioxide thin-film electrodes prepared by the sol-gel method was investigated. The best conditions for maximum photoelectrocatalytic degradation were found to be pH > 10 for Na2SO4 medium and pH < 6 for NaCl. In both situations, an applied potential of +1.0 V and low dye concentration are recommended, when 100% of color removal is obtained after 20 min of photoelectrocatalysis. The effects of side reaction pathway on the degradation rate of dye in sulfate and chloride medium were presented and the best performance are optimized to situations closed to that verified in the textile effluent. The influence of variables as applied potential, pH, supporting electrolyte and dye concentration on the kinetics of photoelectrochemical degradation also were investigated. Oxalic acid is identified by HPLC and UV-Vis spectrophotometric methods as the main degradation product generated after 180 min of photoelectrocatalysis of 4 x 10(-5) mol l(-1) dye in sodium sulphate pH 12 and NaCl pH 4.0 and a maximum reduction of 56 and 62% TOC was obtained, respectively. (C) 2004 Elsevier Ltd. All rights reserved.

Impedance spectroscopy study of solid-state dye-sensitized solar cells with varying Spiro-OMeTAD concentration

This work reports on the changes of performance of solid-state cells dye-sensitized solar cells with the variation of concentration of spiro-OMeTAD between 5% and 25% in the fabrication of the cell. Variations of charge recombination and capacitance correlate with the improvement of current-potential characteristics at increasing spiro-OMeTAD content, which is explained by reduction of transport resistance for hole transport, the increase of charge separation in the dye molecules, and importantly, with the increase of the β-factor in the recombination resistance, that causes a reduction of the diode ideality factor. © 2010 Materials Research Society.

Nitrate Removal on a Cu/Cu2O Photocathode under UV Irradiation and Bias Potential

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Estudo da degradação do corante azo disperso azul 291 por cloração química e fotoeletroquímica

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)