Ação de colorantes na degradação e estabilização de polímeros

Dyes and pigments are additives used in polymers to improve mainly the aesthetic properties of the material. However, the incorporation of these additives can directly affect polymer stability. The colorants can drastically decrease the lifetime and the performance of the material or can act as a stabilizer, improving significantly the stability of the polymer against degradation. Interaction between colorants and polymers is the cause of the stability changes. Some mechanisms are proposed to explain the action of colorants on polymers. However it is difficult to foresee this action without experiments. This work reviews the main mechanisms involved in the degradation and stabilization of polymers containing colorants.

Espectrofotometria derivativa: uma estratégia simples para a determinação simultânea de corantes em alimentos

A very simple spectrophotometric method is described for resolving binary mixture of the food colorants Sunset Yellow (INS 110) and Tartrazine Yellow (INS 102) by using the first derivative spectra with measurements at zero-crossing wavelengths. Before the spectrophotometric measurements, the dyes were sorbed onto polyurethane foam and recovered in N,N-dimethilformamide. Commercial food products (gelatine and juice powder) were analysed by using the proposed method and the HPLC technique. The results are in very good agreement and the differences between the methods is not statistically important. Therefore, the first-order derivative spectrophotometric method is accurate, precise, reliable and could be applied to the routine analysis of food samples.

O emprego de quitosana quimicamente modificada com anidrido succínico na adsorção de azul de metileno

The adsorption capacity of alpha-chitosan and its modified form with succinic anhydride was compared with the traditional adsorbent active carbon by using the dye methylene blue, employed in the textile industry. The isotherms for both biopolymers were classified as SSA systems in the Giles model, more specifically in L class and subgroup 3. The dye concentration in the supernatant in the adsorption assay was determined through electronic spectroscopy. By calorimetric titration thermodynamic data of the interaction between methyene blue and the chemically modified chitosan at the solid/liquid interface were obtained. The enthalpy of the dye/chitosan interaction gave 2.47 ± 0.02 kJ mol-1 with an equilibrium constant of 7350 ± 10 and for the carbon/dye interaction this constant gave 5951 ± 8. The spontaneity of these adsorptions are reflected by the free Gibbs energies of -22.1 ± 0.4 and -21.5 ± 0.2 kJ mol-1, respectively, found for these systems. This new adsorbent derived from a natural polysaccharide is as efficient as activated carbon. However 97% of the bonded dye can be eluted by sodium chloride solution, while this same operation elutes only 42% from carbon. Chitosan is efficient in dye removal with the additional advantage of being cheap, non-toxic, biocompatible and biodegradable.

Elucidando os estados de oxidação do nitrogênio através da espectroscopia de absorção de raios-X na borda K do nitrogênio

The potentialities of X-ray Absorption Near Edge Spectroscopy (XANES) of the N K edge (N K) obtained with the spherical grating monochromator beam line at the Brazilian National Synchrotron Light Laboratory are explored in the investigation of poly(aniline), nanocomposites and dyes. Through the analysis of N K XANES spectra of conducting polymers and many other dye compounds that are dominated by 1s®p* transitions, it was possible to correlate the band energy value with the nitrogen oxidation states. An extensive N K XANES spectral database was obtained, thus permitting the elucidation of the nature of different nitrogens present in the intercalated conducting polymers.

Determinação de nitrito em águas utilizando extrato de flores

Aspects of visible spectrophotometry can be presented to students using simple experiments in which the color of the crude extract of Macroptilium lathyroides (L.) Urb. is bleached in the presence of nitrite ions in acidic medium. The dependence of the absorption intensity with time, the reaction completeness and the Beer law can be demonstrated. Quantitative results for mineral water samples "contaminated" with nitrite ions were obtained from a method based on the Griess reaction and a procedure based on the bleaching reaction between the crude extract and NO2- ions. Both the Griess and the bleaching reactions were found to be time dependent. Recoveries of about 100 - 104% were obtained with these procedures. The use of natural dyes attracted students' interest enhancing the teaching process. Experiments performed by the teaching staff suggested that the proposed methodology can be performed in a 4 h class, with relative errors ranging from 0.19 to 1.86% in relation to the Griess method.

Teores de corantes artificiais em alimentos determinados por cromatografia líquida de alta eficiência

Synthetic dyes are much used in processed foods. HPLC was applied to different types of snacks, such as colored cereals, chocolate confetti, chewing gums and candies for the determination of those additives. In the case of artificially colored breakfast cereals, 71% of the samples exceeded the allowed limits. Regarding the portions recommended for consumption by the makers of two of the samples, the amounts exceeded those allowed by the Brazilian legislation. In the case of chocolate confetti and candies none of the samples showed higher amounts than those allowed. However 37% of the chewing gum samples presented larger contents than the authorized ones, and one sample contained five times more synthetic dyes than allowed.

Seeing smells: development of an optoelectronic nose

The development of an array of chemically-responsive dyes on a porous membrane and in its use as a general sensor for odors and volatile organic compounds (VOCs) is reviewed. These colorimetric sensor arrays (CSA) act as an "optoelectronic nose" by using an array of multiple dyes whose color changes are based on the full range of intermolecular interactions. The CSA is digitally imaged before and after exposure and the resulting difference map provides a digital fingerprint for any VOC or mixture of odorants. The result is an enormous increase in discriminatory power among odorants compared to prior electronic nose technologies. For the detection of biologically important analytes, including amines, carboxylic acids, and thiols, high sensitivities (ppbv) have been demonstrated. The array is essentially non-responsive to changes in humidity due to the hydrophobicity of the dyes and membrane.

Inativação fotodinâmica de microrganismos

Photodynamic Therapy uses photosensitive dyes and visible light that, combined in the presence of oxygen, produce cytotoxic species that cause tumor death. Microorganisms such as bacteria, fungi, yeasts and viruses (including HIV) can also be inactivated by visible light after treatment with an appropriate photosensitizer as an alternative low cost treatment for localized infections, viral lesions such as acnes, and fungical skin lesions for example. Besides, Photodynamic Inactivation can be used for sterilization of blood and its subproducts for clinical use, in the treatment of drinking water as well as in antimicrobial detoxification of foods.

Efecto de la naturaleza del precursor sobre las caracteristicas de las nanoparticulas de SnO2 sintetizadas

Tin oxide (SnO2) is widely used in industry as raw material for electronic devices, plating of different types of materials, for dyes and pigments, for electroplating, heterogeneous catalysis, etc. In this work SnO2 was obtained by a controlled precipitation method with special attention to the effects the tin precursor has on the microstructure of the final product. The most appropriate pH for obtaining SnO2 with the rutile structure as the main phase is 6.25 for SnCl2 and 6.40 for SnSO4. After heat treatment at 600 °C, particles of nanometric order (~10 - 30 nm approx) were obtained. The characterization of the solid phase was made by X-ray diffraction (XRD), thermal analysis (DTA/TG), transmission electron microscopy (TEM) and Fourier transformed infrared spectroscopy (FTIR).

Preparação de carvão ativado em baixas temperaturas de carbonização a partir de rejeitos de café: utilização de FeCl3 como agente ativante

Ferric chloride as a new activating agent was used to obtain activated carbons from agroindustrial waste. This material was prepared at three temperatures of pyrolysis, 200, 280 and 400 ºC. The carbonaceous materials obtained after the activation processes showed high specific surface areas (BET), with values higher than 900 m² g-1. The materials showed different behaviors in the adsorption of methylene blue dye and reactive red textile dye in water solutions. An important fact in the use of FeCl3 as an activating agent is that the activation temperature is at 280 ºC, well below of those commonly employed in chemical or physical activations described in the literature.

Degradação de corantes ácidos por processos oxidativos avançados usando um reator com disco rotatório de baixa velocidade

Three technologies were tested (TiO2/UV, H2O2/UV, and TiO2/H2O2/UV) for the degradation and color removal of a 25 mg L-1 mixture of three acid dyes: Blue 9, Red 18, and Yellow 23. A low speed rotating disc reactor (20 rpm) and a H2O2 concentration of 2.5 mmol L-1 were used. The dyes did not significantly undergo photolysis, although they were all degraded by the studied advanced oxidation processes. With the TiO2/H2O2/UV process, a strong synergism was observed (color removal reached 100%). Pseudo first order kinetic constants were estimated for all processes, as well as the respective apparent photonic efficiencies.

Alographia dos álkalis... de Frei Conceição Veloso: um manual de química industrial para produção da potassa no Brasil colonial

Potassium carbonate, or potash, was the most important industrial chemical of the 18th century. It was essential for producing glass, soap, saltpeter, dyes, several drugs, and also used for bleaching linens, paper, and sugar. We examine here a book in which Brazilian author José Mariano da Conceição Veloso gathered his translations into Portuguese of English and French articles, letters, patents, and pamphlets with instructions on how to prepare potash. We discuss especially his version of Richard Watson's essay entitled 'Of saline substances', and Veloso's own 'Flora Alographica', a description of the Brazilian plants that could be used to prepare potash.

Extração e purificação de clorofila a, da alga Spirulina maxima: um experimento para os cursos de química

This work describes a simple and economical experiment for the extraction and purification of chlorophyll a from Spirulina maxima. Extraction and purification of natural compounds can be considered one of the most illustrative experiments that can be performed in Organic Chemistry courses. Particularly, the chromatography of dyes and pigments allows students to have a better comprehension of the chromatography separations. These compounds represent an important class of organic pigments applied in pharmaceutical, cosmetic, detergent compositions, and various other fields and can be extracted from plants and algae. To extract, separate and purify chlorophyll a from associated pigments such as xanthophylls, carotenes, and pheophytins, very costly processes are reported. The present approach is perfectly adequate for use in Chemistry experiments for undergraduate students.

Caracterização e propriedades do material coloidal nanoestruturado β-FeOOH/bentonita

A new mixed material was obtained through the combination of the suspensions of iron oxy-hydroxide and bentonite clay, denoted BFe. Analysis of its structure (XRD, Mossbauer and TGA) and composition (AAS) suggests the maintenance of the layer structure of the clay and an increase in the thermal stability of the BFe. Electrochemical studies performed in different electrolytes show that only in an alkaline medium it is possible to observe the redox peaks relative to the processes involving Fe+2/Fe+3 pair. Tests that evaluated the potential use of the photo-Fenton process showed an efficient degradation process of the dyes in significantly reduced reaction times.

Nanoestruturas em fotocatálise: uma revisão sobre estratégias de síntese de fotocatalisadores em escala nanométrica

Advanced oxidative processes (AOPs) are based on chemical processes that can generate free radicals, such as hydroxyl radicals (.OH) which are strong, non-selective oxidant species that react with the vast majority of organic compounds. Nanostructured semiconductors, especially titanium dioxide (TiO2) in the anatase phase, are well-established photocatalysts for this process, which have proved to be useful in the degradation of dyes, pesticides and other contaminants. Research in different strategies for the synthesis of nanostructured semiconductors, with particular characteristic is currently a topic of interest in many studies. Thus, this paper presents a review about various synthesis strategies of nanostructured photocatalysts.