Oxidation of p,p'-DDT and p,p'-DDE in highly and long-term contaminated soil using Fenton reaction in a slurry system

The degradation of DDT [1,1-bis(4-chlorophenyl)-2,2,2-trichloroethane] and DDE [2,2-bis(4-chlorophenyl)-1,1-dichloroethylene] in highly and long-term contaminated soil using Fenton reaction in a slurry system is studied in this work. The influence of the amount of soluble iron added to the slurry versus the mineral iron originally present in the soil, and the influence of H2O2 concentration on the degradation process are evaluated. The main iron mineral species encountered in the soil, hematite (Fe2O3), did not show catalytic activity in the decomposition of H2O2, resulting in low degradation of DDT (24%) and DDE (4%) after 6 h. The addition of soluble iron (3.0 mmol L-1) improves the reaction reaching 53% degradation of DDT and 46% of DDE. The increase in iron concentration from 3.0 to 24 mmol L-1 improves slightly the degradation rate of the contaminants. However, similar degradation percentages were obtained after 24 h of reaction. It was observed that low concentrations of H2O2 were sufficient to degrade around 50% of the DDT and DDE present in the soil, while higher degradation percentages were achieved only with high amounts of this reagent (1.1 mol L-1). (c) 2006 Elsevier B.V. All rights reserved.

Quantitative structural analysis of the transition from LT-LixCoO2 to HT-LixCoO2 using the rietveld method: correlation between structure and electrochemical performance

A quantitative phase analysis was made of LiXCoO2 powders obtained by two distinct chemical methodologies at different temperatures (from 400 to 700degreesC). A phase analysis was made using Rietveld refinements based on X-ray diffraction data, considering the LiXCoO2 powders as a multiphase system that simultaneously contained two main phases with distinct, layered and spinel-type structures. The sults showed the coexistence of both structures in LiXCoO2 obtained at low temperature (400 and 500degreesC), although only the layered structure was detected at higher temperatures (600 and 700degreesC, regardless of the chemical powder process employed. The electrochemical performance, evaluated mainly by the cycling reversibility of LiXCoO2 in the form of cathode insertion electrodes, revealed that there is a close correlation between structural features and the electrochemical response, with one of the redox processes (3.3 v/3.9 v) associated only with the presence of the spinel-type structure. (C) 2003 Elsevier B.V. All rights reserved.

Magnetic susceptibility of an exactly solvable anisotropic spin ladder system

We investigate the thermodynamics of an integrable spin ladder model which possesses a free parameter besides rung and leg couplings. The model is exactly solvable by means of the Bethe ansatz and exhibits a phase transition between a gapped and a gapless spin excitation spectrum. The magnetic susceptibility is obtained numerically and its dependence on the anisotropy parameter is determined. The spin gap obtained from the susceptibility curve and the one obtained from the Bethe ansatz equations are in very good agreement. Our results for the magnetic susceptibility fit well the experimental data for the organometallic compounds (5IAP)(2)CuBr4 . 2H(2)O (Landee C. P. et al., Phys. Rev. B, 63 (2001) 100402(R)) Cu-2(C5H12N2)(2)Cl-4 (Hayward C. A., Poilblanc D. and Levy L. P., Phys. Rev. B, 54 (1996) R12649, Chaboussant G. et al., Phys. Rev. Lett., 19 ( 1997) 925; Phys. Rev. B, 55 ( 1997) 3046.) and (C5H12N)(2)CuBr4 (Watson B. C. et al., Phys. Rev. Lett., 86 ( 2001) 5168) in the strong-coupling regime.

Role of the surface state and structural feature in the thermoreversible sol-gel transition of a zirconyl aqueous precursor modified by sulfuric acid

The sols produced by admixture of ZrOCl2 acidified solutions to hot H2SO4 aqueous solutions were studied to clarify the effects of Cl- and SO42- ions on the kinetic stability of nanoparticles and to obtain some new evidence concerning the mechanism of a thermoreversible sol-gel transition observed in this system. The study of suspensions prepared with different molar ratios R-S = [Zr]/[SO42-] and R-Cl = [Zr]/[Cl-] revealed domains of composition of formation of thermoreversible gels, thermostable sols, and powder precipitation. The effects of R-S and R-Cl on the structural features of nanoparticles and on the particle solution interface were systematically analyzed for samples of thermoreversible and thermostable sol domains. Small-angle X-ray scattering measurements revealed the presence of small fractal aggregates in all samples of thermoreversible domains, while compact packing aggregates of primary particles are present in the thermostable sol. Extended X-ray absorption fine structure and elemental chemical analysis revealed that irrespective of the nominal value of R-S and R-Cl all studied samples of the thermoreversible domain are constituted by a well-defined compound possessing an inner core made of hydroxyl and oxo groups bridging together zirconium atoms surrounded on the surface by complexing sulfate ligands. zeta potentials of powders extracted by freeze-drying from the thermoreversible gel revealed a point of surface charge inversion attributed to the specific adsorption of SO42- ion. Thermoreversible gel formation is rationalized by considering the effect of the specific adsorption on the electrical double-layer repulsion together with the temperature dependency of the physical chemical properties of ions in solution.

Rheological study of the thermoreversible sol-gel transition of sulfate modified zirconyl chloride aqueous sol

The sols prepared by mixing a ZrOCl2 acidified solution to a hot H2SO4 aqueous solutions were studied in order to clarify the mechanism of thermoreversible sol-gel transition observed in this system. The viscoelastic properties of these suspensions were analyzed during the sol-gel transition by dynamic rheological measurements and quasi-elastic light scattering. The rheological properties were correlated to mass fractal and nearly linear growth models, and percolation theory. The results evidence that the thermoreversible sol-gel transition in this system is due to the formation of a network of physically linked aggregates having fractal structure. The decrease of the SO42- contents in the initial solution leads to the decrease of the fractal dimensionality from 2.3 to 1.8, indicating a change of the kinetic mechanism of aggregate growth. Near the gel point these samples have the typical scaling expected from percolation theory. (C) 2004 Elsevier B.V. All rights reserved.

THERMAL-HISTORY-DEPENDENT TRANSITION IN PRESSED PELLETS OF CLO4(-)-DOPED POLY(3-METHYLTHIOPHENE)

Electron-spin-resonance and dc conductivity data show a thermal-history-dependent transition at 240 K in pressed pellets of ClO4--doped poly(3-methylthiophene) (P3MT). We discuss the possibility of this transition to be a Peierls transition from a room-temperature-metallic to a charge-density-wave state driven by anions ordering at this temperature. Below 100 K, dc conductivity shows a change from linear to exponential decay. Nonlinear conductivity has also been observed in this system for very low electric fields.

Testing transposable elements as genetic drive mechanisms using Drosophila P element constructs as a model system

The use of transposable elements (TEs) as genetic drive mechanisms was explored using Drosophila melanogaster as a model system. Alternative strategies, employing autonomous and nonautonomous P element constructs were compared for their efficiency in driving the ry(+) allele into populations homozygous for a ry(-) allele at the genomic rosy locus. Transformed flies were introduced at 1%, 5%, and 10% starting frequencies to establish a series of populations that were monitored over the course of 40 generations, using both phenotypic and molecular assays. The transposon-borne ry(+) marker allele spread rapidly in almost all populations when introduced at 5% and 10% seed frequencies, but 1% introductions frequently failed to become established. A similar initial rapid increase in frequency of the ry(+) transposon occurred in several control populations lacking a source of transposase. Constructs carrying ry(+) markers also increased to moderate frequencies in the absence of selection on the marker. The results of Southern and in situ hybridization studies indicated a strong inverse relationship between the degree of conservation of construct integrity and transposition frequency. These finding have relevance to possible future applications of transposons as genetic drive mechanisms.

Glasses in the SbPO4-WO3 system

Glasses in the binary system (100 - x)SbPO4-xWO3 (20 <= x <= 60, x in mol%) have been prepared and characterized. Differential thermal analysis (DTA) shows that the glass transition temperature, T-g increases from 412 degrees C, for samples containing 20 mol% of WO3 to 481 degrees C observed for glass containing 60 mol%. Sample containing 40 mol% in WO3 were observed to be the most stable against devitrification. The structural organization of the glasses has been studied by using Fourier transform infra-red (FTIR), Raman, P-31 Magic angle spinning (MAS) and spin echo nuclear magnetic resonance (NMR) spectroscopies. Results suggest two distinct networks comprising the glass structure, one with high SbPO4 content and the other characteristic of the highest WO3 content samples. The glasses present photochromic properties. Colour changes are observed for samples after exposure to ultraviolet or visible laser light. XANES, at L-1 absorption edge of tungsten, suggests partial reduction from W6+ to W5+ species during the laser irradiation. The photochromic effects and the colour changes, promoted by laser excitation, are reversible and easily removed by heat for during 1 h at 150 degrees C. Subsequent 'write/erase' cycles can be done without degradation of the glasses. (C) 2007 Elsevier B.V. All rights reserved.

Synthesis, crystal structure, spectroscopic and electrochemical characterization of the dinuclear complex {tetra-mu-[(+/-)-2-(p-methoxyphenoxy)-propionato-O,O']bis(aqua)dicopper(II)}

Structural, electrochemical and spectroscopic data of a new dinuclear copper(II) complex with (+/-)-2-(p- methoxyphenoxy) propionic acid are reported. The complex {tetra-mu-[(+/-)-2-(p-methoxyphenoxy)propionato-O,O']-bis( aqua) dicopper(II)} crystallizes in the monoclinic system, space group P2(1)/n with a = 14.149(1) angstrom, b = 7.495(1) angstrom, c = 19.827(1) angstrom, beta = 90.62(1) and Z = 4. X-ray diffraction data show that the two copper(II) ions are held together through four carboxylate bridges, coordinated as equatorial ligands in square pyramidal geometry. The coordination sphere around each copper ion is completed by two water molecules as axial ligands. Thermogravimetric data are consistent with such results. The ligand has an L' type shape due to the angle formed by the beta-carbon of the propionic chain and the linked p-methoxyphenoxy group. This conformation contributes to the occurrence of a peculiar structure of the complex. The complex retains its dinuclear nature when dissolved in acetonitrile, but it decomposes into the corresponding mononuclear species if dissolved in ethanol, according to the EPR measurements. Further, cyclic voltammograms of the complex in acetonitrile show that the dinuclear species maintains the same structure, in agreement with the EPR data in this solvent. The voltammogram shows two irreversible reduction waves at E-pc = -0.73 and -1.04 V vs. Ag/AgCl assigned to the Cu(II)/ Cu(I) and Cu(I)/Cu degrees redox couples, respectively, and two successive oxidation waves at E-pa = -0.01 and +1.41 V vs. Ag/AgCl, assigned to the Cu degrees/Cu(I) and Cu( I)/Cu( II) redox couples, respectively, in addition to the oxidation waves of the carboxylate ligand.

Transport properties of the transverse charge-density-wave system Fe3O2BO3

We study the transport properties of the charge-density-wave system Fe3O2BO3. ac conductivity measurements for different frequencies are presented for temperatures above and below the structural transition. dc conductivity, as a function of temperature and pressure, yields the variation of the transition temperature with external pressure. Below this transition the conductivity is thermally activated in a wide range of temperature and the gap obtained is strongly pressure dependent. The ac conductivity at sufficiently low temperatures below the transition is ascribed to the excitation of local defects associated with domain walls and which are characteristic of the one-dimensional nature of the Fe3O2BO3 system.

Thermal behaviour of malonic acid, sodium malonate and its compounds with some bivalent transition metal ions

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

Thermal investigation of solid 2-methoxycinnamylidenepyruvate of some bivalent transition metal ions

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

Thermo-reversible sol-gel transition of TiO2 nanoparticles with surface modified by p-toluene sulfonic acid

In this paper an unprecedent thermo-reversible sol-gel transition for titania nanoparticles dispersed in a solution of p-toluene sulfonic acid (PTSH) in isopropanol is reported. The sol formed by the thermo-hydrolysis at 60 degrees C of titanium tetraisopropoxide (Ti((OPr)-Pr-i)(4)) reversibly changes into a turbid gel upon cooling to room temperature. Turbidimetric measurements performed for samples containing different nominal acidity ratios (A = [PTSH]/[Ti]) have evidenced that the gel transformation temperature increases from 20 to 35 degrees C as the [PTSH]/[Ti] ratio increases from 0.2 to 2.0. SAXS results indicate that the thermo-reversible gelation is associated to a reversible aggregation of a monodisperse set of titania nanoparticles with average gyration radius of approximate to 2 nm. From the different PTSH species evidenced by Raman spectroscopy and TG/DTA of dried gels we proposed that the then-no-reversible gelation in this systems is induced by the formation of a supramolecular network, in which the protonated surface of nanoparticles is interconnected through cooperative hydrogen bonds between -SO3 groups of p-toluene sulfonic acid. (C) 2009 Elsevier Ltd. All rights reserved.

Dielectric relaxation and dc conductivity on the PVOH-CF(3)COONH(4) polymer system

In the present paper, the ionic conductivity and the dielectric relaxation properties on the poly(vinyl alcohol)-CF(3)COONH(4) polymer system have been investigated by means of impedance spectroscopy measurements over wide ranges of frequencies and temperatures. The electrolyte samples were prepared by solution casting technique. The temperature dependence of the sample's conductivity was modeled by Arrhenius and Vogel-Tammann-Fulcher (VTF) equations. The highest conductivity of the electrolyte of 3.41x10 (-aEuro parts per thousand 3) (Omega cm) (-aEuro parts per thousand 1) was obtained at 423 K. For these polymer system two relaxation processes are revealed in the frequency range and temperature interval of the measurements. One is the glass transition relaxation (alpha-relaxation) of the amorphous region at about 353 K and the other is the relaxation associated with the crystalline region at about 423 K. Dielectric relaxation has been studied using the complex electric modulus formalism. It has been observed that the conductivity relaxation in this polymer system is highly non-exponential. From the electric modulus formalism, it is concluded that the electrical relaxation mechanism is independent of temperature for the two relaxation processes, but is dependent on composition.

Soil microbial biomass and organic matter fractions during transition from conventional to organic farming systems

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)