Luciana Almeida Silva

Photocatalytic production of hydrogen: an innovative use for biomass derivatives

Hidrogenio e considerado o vetor energetico do futuro por ser nao poluente e muito flexivel quanto a conversao a diferentes formas de energia, como calor por combustao ou energia eletrica via celulas a combustivel. Tradicionalmente, o hidrogenio e produzido a partir da reforma a vapor de gas natural de origem fossil, o que torna a implantacao efetiva da economia de hidrogenio insustentavel do ponto de vista ambiental. Para contornar esse problema, diversas rotas de producao de hidrogenio a partir de fontes renovaveis estao sendo propostas. Pesquisas recentes apontam a reforma foto-induzida de biomassa como uma possibilidade promissora, uma vez que utiliza radiacao solar, fonte inesgotavel de energia e materias primas renovaveis como derivados de biomassa e agua. Os trabalhos nesse campo sao ainda muito incipientes, porem bastante animadores. O processo consiste na combinacao da decomposicao fotocatalitica da agua com a reacao de fotodecomposicao de substâncias orgânicas mediadas por um semicondutor irradiado. Neste processo, a reacao de oxidacao da agua e suprimida pela presenca de um doador de eletrons de sacrificio (biomassa), assim como a formacao de radical superoxido quando a reacao e realizada em condicoes anaerobicas. Os resultados de reforma foto-induzida apontam para rendimentos semelhantes ou superiores a outros processos de producao de hidrogenio a partir de biomassa como hidrolise enzimatica e reforma catalitica em fase aquosa. No entanto, os trabalhos desenvolvidos ate o momento estao focados no TiO2, o que limita a porcao absorvida da radiacao solar a luz UV. Deste modo, o grande desafio atual nesta area e o desenvolvimento de semicondutores de banda estreita capazes de conduzir a reacao de reforma foto-induzida de biomassa com luz visivel, que consiste de cerca de 40% da radiacao solar.

Determination of moisture content and water activity in algae and fish by thermoanalytical techniques

The water content in seafoods is very important since it affects their sensorial quality, microbiological stability, physical characteristics and shelf life. In this study, thermoanalytical techniques were employed to develop a simple and accurate method to determine water content (moisture) by thermogravimetry (TG) and water activity from moisture content values and freezing point depression using differential scanning calorimetry (DSC). The precision of the results suggests that TG is a suitable technique to determine moisture content in biological samples. The average water content values for fish samples of Lutjanus synagris and Ocyurus chrysurus species were 76.4 ± 5.7% and 63.3 ± 3.9%, respectively, while that of Ulva lactuca marine algae species was 76.0 ± 4.4%. The method presented here was also successfully applied to determine water activity in two species of fish and six species of marine algae collected in the Atlantic coastal waters of Bahia, in Brazil. Water activity determined in fish samples ranged from 0.946 - 0.960 and was consistent with values reported in the literature, i.e., 0.9 - 1.0. The water activity values determined in marine algae samples lay within the interval of 0.974 - 0.979.

Synthesis, identification and thermal decomposition of double sulfites like Cu2SO3·MSO3·2H2O (M=Cu, Fe, Mn or Cd)

Double sulfites with empirical formula Cu2SO3·MSO3·2H2O (where M is Cu, Fe, Mn, or Cd) were obtained by saturation with sulfur dioxide gas of an aqueous mixture of MII sulfate and copper sulfate at room temperature. The salts obtained were identified by infrared spectra, X-ray powder diffraction and elemental analysis. The compounds studied are isostructural with the CuII replacement by MnII, FeII, and CdII in Chevreul’s salt (Cu2SO3·CuSO3·2H2O). The thermal behavior of the double sulfites was evaluated by thermogravimetry analysis (nitrogen and air atmospheres) and differential scanning calorimetry. These salts are thermally stable up to 200°C. The structures of sulfite ion coordination influence strongly the course of the thermal decomposition. The sulfite species coordinated to the metal through the oxygen are easier oxidized to sulfate than sulfur-coordinated species, leading to preferential formation of MIISO4 and Cu2O in the first step. The weight gain relative to the second step can be due to oxidation of Cu2O to CuO and/or oxidation of MIISO3 to MIISO4 probably by self-generated atmosphere formed by dense volatile products liberated in the latter step.

Efeito da presença e concentração de compostos carbonílicos na qualidade de vinhos

Studies on identification of compounds that make up the aroma and flavor in wines involve research evaluating mainly the influence of terpenes, esters, lactones and alcohols upon these sensory characteristics. However, carbonylic compounds (CC) play an important role concerning the substances that impact aroma to these drinks. Their origin is reported to be linked to the grapes chemical composition, must fermentation or micro-oxidation occurring during storage in barrels. Some CCs, like E-ionone, E-damascenone, siryngaldehyde, can contribute a pleasant aroma and improve the wine quality whereas others are responsible for unpleasant characteristics (acetaldehyde, furfural, 5-hydroxy-methyl furfural, diacetil, E-non-2-enal, etc). A fraction of CCs present is associated with bisulfite ions in the form of hydroxyalkylsulfonic acids. Some of them are stable and play an important role in determining wine quality. The reaction involving the formation of this aduct commonly occurs with CCs of low molar mass, such as formaldehyde and acetaldehyde. The reaction involving CCs with more than three carbon atoms demands further studies.

Isomorphic series of double sulfites of the Cu2SO3.MSO3.2H2O (M = Cu, Fe, Mn, and Cd) Type: a review

Although the first mixed valence double sulfite, Cu2SO3.CuSO3.2H2O, was prepared in the early 19th century by M. Chevreul, interest in this type of compound was only rekindled in the mid-1960s, when the crystalline structure of Chevreuls salt was determined and its infrared spectrum characterized. Studies of this type of compound have been intensified in recent years, especially after the discovery that the isomorphic Cu(II) in Chrevreuls salt could be replaced by a divalent metal ion, forming an isomorphic series whose properties are strongly dependent on the nature of the M(II) cation. Because of their interesting properties, these mixed valence systems can be used as models to identify intermediates in atmospheric corrosion processes, and to evaluate the role of transition metals as catalysts of S(IV) autoxidation in the conversion of SO2 in the atmosphere.

A liquid chromatographic method optimization for the assessment of low and high molar mass carbonyl compounds in wines

Carbonyl compounds (CC) play an important role in beverage aroma since they may affect flavor of wines, brandies, and beers, among others. For this reason, it is necessary to identify and quantify CC through adequate analytical techniques. This study is a proposal of both developing and optimization of a new analytical methodology that allows investigate C(1)-C(8 )CC in wines simultaneously by quantifying even those ones that are predominantly present in the adduct form hydroxylalkylsulfonic acids (HASA). The HASA dissociation is undertaken by specific alkaline media (pH 11). The developed methodology employed the LC with UV/VIS detection (lambda = 365 nm) technique under gradient elution in the way to reach both free-CC and bound-CC quantification. Results showed that binary gradient system using eluent A (MeOH/ACN/H(2)O 74.5:0.5:25% v/v/v) and eluent B (MeOH) reached the best separation condition of both lower and higher molecular mass CC. This proposed method allowed simultaneous quantification of formaldehyde, acetaldehyde, propanone, furfuraldehyde, butyraldehyde, benzaldehyde, hexanaldehyde, 2-ethyl-hexanaldehyde, E-pent-2-en-1-al, and cyclohexanone--all of them were found in white wine (Moscato Canelli) and red wine (Shiraz) produced in the São Francisco Valley, in the Northeastern Region of Brazil--although this optimized method may probably be suitable for quantification of propionaldehyde, isobutyraldehyde, heptanaldehyde, octanaldehyde, benzaldehyde, and E-hex-2-en-1-al as well. We could not prove if this method is also able to determine the latter CC group since we have not found these substances present in detectable levels in our real samples considered in this study.

Use of Cu2+ as a metal ion probe for the EPR study of metal complexation sites in the double sulfite CuI 2SO3.CdII SO3 .2H2O

An evaluation was made of the presence of paramagnetic ions in the host lattice of CuI2SO3.CdII SO3.2H2O by the electron paramagnetic resonance (EPR) technique, using copper(II) ions as paramagnetic probes. The existing MI and MII complexation sites in the double sufite structure were successfully differentiated. The results indicate that the CuI2SO3.CdII SO3.2H2O structure was doped with CuII ions in the two metal ion substitutional positions. The low g||/A|| ratio for the CuII probe in the distorted octahedral site resulted from the interaction of copper ions with oxygen donor atoms in a distorted tetragonal environment, with elongation of the molecule in the z direction. The very low value of the A33 hyperfine coupling constant was explained considering the admixture of the dx2 -y2 and dz2 orbitals and the almost trigonal pyramidal structure of the other site.

Electronic Spectra of Chevreul's Salts

The isomorphic series of double sulfites with empirical formula Cu2SO3.MSO3.2H 2O (where M is Cu, Fe, Mn, or Cd) have been prepared from the Cu(II) replacement by transition metal ions such as Mn(II), Fe(II) and Cd(II) ions in Chevreuls salt, Cu2SO3.CuSO3.2H 2O. As a consequence, the isomorphic species present distinct colors. Molecular modeling calculations were carried out for the dimeric [CuI2(SO3) 2(SO3)2]6- center. The electronic spectra of the Chevreuls salt consist of a charge-transfer band around 425 nm associated with the [CuI2(SO3) 2(SO3)2]6- chromophore and two ligand field transitions at 785 and 1000 nm involving the Jahn-Teller splitting of the Cu(II) levels. An additional intervalence-transfer band, responsible for its characteristic red color, can be found at 500 nm. The replacement of the Cu(II) ions for Fe(II), Mn(II) and Cd(II) does not eliminate the absorption band at 425 nm, supporting its assignment as a charge-transfer transition centered on the Cu(I) sites; while the original band at 500 nm disappears, in agreement with its intervalence transfer nature.

A fast sonochemical method to prepare 1D and 3D nanostructures of bismuth sulfide

In this work, a sonochemical method to synthesize nanostructures of bismuth sulfide in 1D and 3D framework was developed and compared with a synthetic route with heating under reflux. The sonochemical method showed to be faster and more efficient than refluxing method to obtain nanostructures with high morphological homogeneity. Form and quality of the nanocrystals were dependent on the type of solvent employed in the synthesis procedure. 3D flower-like superstructures were obtained when ethylene glycol was used as solvent, while 1D nanorods were obtained when a mixture of dimethyl sulfoxide and ethylene glycol was used as solvent.

Por que todos os nitratos são solúveis

The solubility rules presented in the majority of introductory texts of chemistry usually do not comprise a systematic analysis of the dissolution processes, neither from a microscopic nor from a macroscopic point of view. The solubility of nitrates in aqueous solution is discussed in this article, focusing on the thermodynamic data and the properties of the nitrate ion.