Mecanismo e aplicações da reação de fenton assistida por compostos fenólicos redutores de ferro

The mechanism and applications of the Fenton reaction assisted by iron-reducing phenolic compounds (IRPC) is reviewed. The presence of IRPC leads to the formation of a larger number of free radicals. The relationship between the redox potential and the IRPC structure is discussed. The effect of humic substances in the degradation of xenobiotics is also included, since these substances are able to reduce metallic ions. The natural occurrence of Fe3+/H2O2/IRPC in wood biodegradation processes, as well as their application is also discussed. The review concludes with the advantages of the Fe3+/H2O2/IRPC systems and some considerations for further process optimization and their applications at industrial levels.

Desenvolvimento de um método empregando quitosana para remoção de íons metálicos de águas residuárias

In this work a method was developed for removing metallic ions from wastewaters by co-precipitation of Cu2+, Pb2+, Cd2+, Cr3+ and Hg2+ with chitosan and sodium hydroxide solution. Solutions of these metallic ions in the range from 0.55 to 2160 mg L-1 were added to chitosan dissolved in 0.05 mol L-1 HCl. For the co-precipitation of metal-chitosan-hydroxide a 0.17 mol L-1 NaOH solution was added until pH 8.5-9.5. A parallel study was carried out applying a 0.17 mol L-1 NaOH solution to precipitate those metallic ions. Also, a chitosan solid phase column was used for removing those metallic ions from wastewaters.

Estudo da influência dos íons K+, Mg2+, SO4(2-) e CO3(2-) na cristalização biomimética de fosfato de cálcio amorfo (ACP) e conversão a fosfato octacálcico (OCP)

The crystallization of hydroxyapatite (HA) in aqueous solution can be described by the mechanism ACP -> OCP -> HA. In this work, it was studied the influence of K+, Mg2+, SO4(2-) and CO3(2-) ions in the formation of ACP and in its conversion to OCP, using biomimetic coatings on metallic substrates of commercially pure titanium (Ti c.p.). The results showed that Mg2+ and CO3(2-) ions favored both the formation of ACP and its conversion to OCP. Differently, K+ and SO4(2-) ions did not influence the formation of ACP and, consequently, interfered in the conversion to OCP.

Utilização de solos locais para tratamento de efluentes do refino de petróleo contendo metais

The employment of local soils for extraction of metallic elements was evaluated through batch tests to treat wastewaters generated in a petroleum refinery plant in southern Brazil. Clay and organic carbon content and clay mineralogy provide these soils, in principle, with moderate metal retention capacity. The following retention order was established: Cr3+ > Pb2+ > Cu2+ > Hg2+ > Cd2+, with total amount of metals retained varying from 36 to 65 meq kg-1. The results show the high efficiency of local soils for extracting metals from liquid effluents through sorption and precipitation processes under acid pH conditions.

De resíduo a insumo: a construção do caminho para uma química mais limpa através de um projeto de ensino

The discussion among teachers, students, and technicians about the destination of residues from chemistry laboratories led to a research project whose results were incorporated into a course in its daily practices. The treatment of the residues from argentimetric practices allowed us to establish cognitive relations of technological basis and of those related to the rising of the level of awareness about environmental aspects and social responsibility of chemistry professionals. The techniques and the results, from the economic point of view, namely that of value aggregation (metallic silver) and the conversion of the residue into input (potassium chromate solution) are shown.

Determinação voltamétrica de metais em águas e fluidos biológicos empregando mineralização de amostras com radiação ultravioleta

This work describes the optimization of pretreatment steps for the destruction of organic matter in samples of waters and biological fluids, by using an UV irradiation system with a high power UV radiation source (400 W). The efficiency of the system constructed for the photo-decomposition of samples of model waters, natural waters and biological fluids was investigated by performing recovery experiments of the metallic species Zn(II), Cd(II), Pb(II), Cu(II), Al(III) and Fe(III). The use of UV irradiation allowed the liberation of metals bound to the organic matrix and the determination of the total content of elements in the samples.

Montagem e caracterização elétrica de pilhas a combustível de óxido sólido (PaCOS)

This paper is focused on a review of the design features and the electrochemistry characterization of anode-supported planar SOFC. Studies and results of metallic alloy interconnectors and recovery for protection against corrosion and for contact layer are showed. Moreover a discussion of examples of measurements of impedance spectrometry, according to the literature and our experimental results are made. For the anode supported fuel cells the power density varies from 0.1 to 0.5 Wcm², according to results in the literature (showed in this paper). For electrolyte supported fuel cell the power density can be 10 Wcm-2 for high temperatures. An English-Portuguese glossary of most used terms in SOFC stack is given for greater clarity and to introduce new terms to the reader.

Aplicação de planejamento fatorial a protocolo de extração e fixação de sulfetos volatilizáveis por acidificação (SVA) em amostras de sedimento

The AVS is defined operationally as acid volatile sulfide, which is a controlling phase on the partition of some metallic species in sediments. A Factorial design was evaluated by means of 16 experiments and using four variables: temperature, extraction time, N2 flow, and volume of the S2- collection solution. The factors that contributed to the efficiency of the process were the extraction time and the N2 flow. Trapping of S2- was efficient in AAB. The S2- was quantified using a potentiometric procedure. Recovery tests for S2- concentrations varying from 1×10-5 to 1×10-4 mol L-1 were in the range from 93 to 116%.

Nanotecnologia: aspectos gerais e potencial de aplicação em catálise

In recent years nanomaterials, such as metallic nanoparticles, nanowires, nanotapes, nanotubes and nanocomposites, have attracted increasing interest for several technological applications. In catalysis, the great potential of nanomaterials is related to the high catalytic activity exhibited by these materials as a function of the high surface/volume ratio when the particles acquire diameter below 5 nm. In this work, a review about concepts and background of nanoscience and nanotechnology is presented with emphasis in catalysis. Special attention is given to gold nanoparticles and carbon nanotubes, focusing the properties and characteristics of these materials in several catalytic reactions.

Corrosão metálica associada ao uso de combustíveis minerais e biocombustíveis

Fuels and biofuels have a major importance in the transportation sector of any country, contributing to their economic development. The utilization of these fuels implies their closer contact to metallic materials, which comprise vehicle, storage, and transportation systems. Thus, metallic corrosion could be related to fuels and biofuels utilization. Specially, the corrosion associated to gasoline, ethanol, diesel, biodiesel, and their mixtures is discussed in this article. Briefly, the ethanol is the most corrosive and gasoline the least. Few investigations about the effect of biodiesel indicate that the corrosion is associated to their unsaturation degree and the corrosion of diesel is related to its acidity.

Determinação simultânea de cátions empregando eletroforese capilar com detecção condutométrica sem contato em equipamento construído em laboratório

This work describes the development of a home-made capillary electrophoresis (CE) system based on the capacitively coupled contactless conductivity detection (C4D) for the separation of the metallic species Zn2+, Cr3+, Pb2+, Cd2+, Co2+, Cu2+, Ni2+ e Tl+. A background electrolyte composed of MES/Histidine 0,02 mol L-1 (pH 5.0) was optimized for the separation of the metallic species by using organic solvents and complexing agents as additives. The system allowed the determination of the metallic species using MES/Histidine 0,02 mol L-1 and methanol 5% (pH 5.0) as a background electrolyte, 15 kV separation voltage and hydrodynamic injection by gravity.

Construção e caracterização de um detector eletroquímico para análises em fluxo

The present work describes a low-cost electrochemical "wall-jet" detector for flow analysis. The electrolytic solution enters into the cell through a tube of stainless steel (200 to 300 µm i.d), reaching to the center of the working electrode perpendicularly and then being mixed to the remaining solution in the cell, which flows under atmospheric pressure into a waste reservoir. The proposed electrochemical detector can be used with any type of working electrode, from commercial to home-made, such as glassy carbon and metallic electrodes (modified or unmodified), which enlarge the applications of the electrochemical detector.

Preparation and characterization oF Ru-Sn/Al2O3 catalysts for the hydrogenation of fatty acid methyl esters

Ru-Sn/Al2O3 catalysts with different Sn loadings were prepared by the coimpregnation method. Several characterization techniques such as TPR, pyridine TPD and catalytic tests for dehydrogenation and hydrogenolysis were used to evaluate and compare such catalysts. TPR results indicate that Sn is deposited both onto the support and as species strongly interacting with Ru. Such non selective deposition modifies the acid and metallic functions of the catalysts. Both total acidity and acid strength distribution are affected: total acidity decreases and new sites of lower acid strength are created. Both dehydrogenating and hydrogenolytic activities are strongly diminished by the addition of Sn. Results of catalytic tests for methyl oleate hydrogenation indicate that methyl stearate is the main product, with only minute amounts of oleyl alcohol produced, and that the addition of Sn diminishes the hydrogenation activity.

Preparação de membranas de acetato de celulose organomodificadas para adsorção dos íons Cu(II), Cd(II), Mn(II) e Ni(II)

Cellulose acetate polymeric membranes had been prepared by a procedure of two steps, combining the method of phase inversion and the technique of hydrolysis-deposition. The first step was the preparation of the membrane, and together was organomodified with tetraethylortosilicate and 3-aminopropyltrietoxysilane. Parameters that exert influence in the complexation of the metallic ion, as pH, time of complexation, metal concentration, had been studied in laboratory using tests of metal removal. The membranes had presented resistance mechanics and reactivity to cations, being able to be an alternative for the removal, daily pay-concentration or in the study of the lability of metals complexed.

Fases estacionárias modernas para cromatografia líquida de alta eficiência em fase reversa

This review first discusses the limitations of many of the supports and stationary phases used in reversed phase high performance liquid chromatography and then describes those, developed more recently, that present better stabilities and more versatile selectivities. Emphases will be given to stationary phases that use higher purity silicas, hybrid silicas, monolithic silicas, metallic oxides and mixed oxides as supports and those that have embedded polar groups or contain phenyl or fluoro groups as the stationary phase as well as the phases used for mixed mode or hydrophilic interaction separations. These modern stationary phases facilitate the analysis of complex mixtures.