Métodos de preparação de nanopartículas metálicas suportadas em carbono de alta área superficial, como eletrocatalisadores em células a combustível com membrana trocadora de prótons

Fuel cells are attracting much interest as efficient and clean energy conversion devices. The main components of low temperature fuel cells are the electrocatalysts used to promote the anodic and cathodic reactions, which are based on platinum and platinum alloys. These electrocatalysts are normally prepared in the form of metal nanoparticles supported on a conductive material, usually high surface area carbon, to improve catalyst utilization and reduce cost. This work presents and comments some methods used presently to produce these electrocatalysts. The performances of the produced electrocatalysts are compared to that of state-of-the-art commercial E-TEK electrocatalysts.

Programa de gerenciamento de resíduos dos laboratórios de graduação da Universidade Regional Integrada do Alto Uruguai e das Missões - Campus Erechim

This work presents a proposal for the management of residues from teaching laboratories. The main goals of the proposal are: scale reduction of experiments, reuse of residues as raw materials for new experiments and appropriate treatment and storage of residues. The methodology includes standardized labels for residue classification and registration of experimental classes and their residues in files. The management seemed to be efficient, resulting in a reduction of the amount of reagents utilized and residues generated, and an increase of reutilization of residues. A considerable decrease of needed storage space and suitable methods for correct residue disposal were achieved. We expect that all laboratories, including those exclusively for research activities, become involved, in a near future, in the Residue Management Project of URI - Campus Erechim.

Otimização da preparação de eletrodo de pasta de carbono contendo riboflavina imobilizada em suporte inorgânico

The aim of this work was to optimize the preparation of electrodes with riboflavin (RF) immobilized on a silica surface modified with niobium oxide and carbon paste. Electrode preparation was optimized employing a factorial design consisting of two levels and three factors. The electrochemical properties of immobilized RF were investigated by cyclic voltammetry. The factorial analysis was carried out analysing the current intensity (Ipa). It was possible to optimize the electrode to get the best reversibility in the redox process, i. e. the lowest separation between anodic and cathodic peak potentials and a current ratio close to unity. The concentration of supporting electrolyte has a small effect. The proportion has the highest effect and the interaction factor between proportion and mixture has also a significant effect on the current intensity.

Eletrodos de pasta de carbono modificados com ácidos húmicos: estudo e determinação de metais em meio aquoso

Since 1992, the carbon paste electrodes modified with humic acids have been used for studying the behavior of metals in aqueous solutions. Many parameters influence the performance of the electrodes, such as the humic acid ratio, the nature of the humic acid, the accumulation time, the pH, the scan rate, and the preparation of the electrodes itself. There are various methos of preparing the electrodes. The goal of this paper is to review some of them. The advantages of using electrodes modified with humic acids as electrochemical sensors for evaluating metals in aqueous solution are stressed.

Tecnologia dos nanotubos de carbono: tendências e perspectivas de uma área multidisciplinar

An overview of the properties of carbon nanotubes is presented as a function of the structural characteristics and of the method of synthesis of these novel advanced materials. Emphasis is given to the catalytic decomposition of hydrocarbons over metal-supported catalysts and also the role of the support in obtaining homogeneous carbon nanotubes in high yelds is discussed. Some potential and real applications of carbon nanotubes are presented in a perspective view.

Decomposição catalítica da hidrazina sobre irídio suportado em compósitos à base de nanofibras de carbono para propulsão espacial: testes em condições reais

The aim of this work is to present the catalytic performance of iridium supported on carbon nanofibers with macroscopic shaping in a 2 N hydrazine microthruster placed inside a vacuum chamber in order to reproduce real-life conditions. The performances obtained are compared to those of the commercial catalyst Shell 405. The carbon-nanofiber based catalyst showed better performance than the commercial catalyst from the standpoint of activity due to its texture and its thermal conductivity.

Carbono do solo e a mitigação da mudança climática global

The soils of the world contain more carbon than the combined total amounts occurring in vegetation and the atmosphere. Hence soils are a major reservoir of carbon in terrestrial ecosystems and an important sink. Recently, emphasis has been placed on the need to sequester carbon from atmospheric carbon dioxide into soil organic matter because of international concerns about greenhouse gas emissions and global climate change. The best strategies to built-up carbon stocks in the soil are basically those that increase the input of organic matter to the soil, and/or decrease the rate of soil organic matter decomposition. Grain crop systems based on soil ploughing and harrowing lead to CO2 emissions combined with tremendous soil losses. In Brazil, no-tillage system was introduced to combat soil erosion by water and this soil management led to the build-up of soil carbon stocks with simultaneous high crop yields. However, the present procedure used to quantify carbon stocks in soils is laborious and of high cost. The use of infrared spectroscopy is very promising as an alternative low-cost method of soil carbon determination.

Implantação de um programa de gerenciamento de resíduos químicos e águas servidas nos laboratórios de ensino e pesquisa no CENA/USP

The aim of this work is to establish a program for the treatment of chemical residues and waste waters at the Centro de Energia Nuclear na Agricultura (CENA/USP), for environmental preservation and training of staff. Five tons of stored residues and the ones currently generated in the laboratories have to be treated. Rational use of water is also part of the program. The traditional purification by distillation has been replaced by purification with ion exchange resins. Lower energy consumption and better water quality were achieved.

Los electrodos de pasta de carbono en el estudio electroquímico de minerales metálicos

This paper shows the applicability of the carbon paste electrode-mineral (CPE-mineral) to study the dissolution mechanisms of minerals in powder form and in flotation concentrates. A potentiodynamic strategy to find the dissolution mechanism of galena (PbS) is presented. In this way, minerals less studied such as orpiment (As2S3) and realgar (As2S2) are investigated. The electrochemical activity of a more complicated mineral such as sphalerite (ZnS), containing 12.3 and 0.43% of iron in solid solution, is discussed. The mechanism of a complex zinc concentrate (containing 63.4% ZnS, 20.1% FeS2, 5% CuFeS2, 0.33% PbS, 0.45% Cu12Sb4S13 and 0.4% FeAsS) is described. Finally, an electrochemical method for the detection of the different leachable and refractory silver phases (contained in two mineral concentrates) is presented. This paper reviews the power of the use of CPE-mineral coupled to electrochemical techniques in hydrometallurgy.

Gerenciamento dos resíduos da disciplina química inorgânica II do curso de química da Universidade Federal do Rio Grande do Sul

Beginning students in chemistry usually do not realize that wastes generated in their experimental classes constitute an environmental problem and that residues must be treated or disposed of in a suitable way. In this manuscript we describe the work that we have been doing in the inorganic chemistry course of the Federal University of Rio Grande do Sul with the objective of creating a critical consciousness in the students about the chemical wastes they generate. With this policy, students are required to take into account the nature of the residues they generate, how they can treat or segregate them, and how they can keep them in a suitable way for final destination, instead of simply throwing them away.

Obtenção de filmes espessos de seleneto de cobre sobre carbono vítreo, ouro, titânio e cobre

Copper selenide (berzelianite) films were prepared on the title substrates using the chemical bath deposition technique (CBD). Film composition was determined by energy dispersion of x-rays. The kinetics of film growth is parabolic and film adherence limits the film thickness. On titanium, copper selenide forms islands that do not completely cover the surface, unless the substrate is prepared with a tin oxide layer; film composition also depends on the titanium oxide layer. On vitreous carbon, CBD and mechanical immobilization techniques lead to films with similar resistances for the electron transfer across the film/substrate interface. On gold, composition studies revealed that film composition is always the same if the pH is in the range from 8 to 12, in contrast to films prepared by an ion-ion combination route. On copper, a new procedure for obtaining copper selenide films as thick as 5 µm has been developed.

Estudo comparativo da eficiência da difenilcarbazida e do óleo de coco saponificado microemulsionados na inibição da corrosão de aço carbono

The effectiveness of microemulsions (ME) of saponified coconut oil (OCS-ME) and diphenylcarbazide (DC-ME) on a carbon steel corrosion inhibition process was evaluated using an electrochemical method of polarization resistance. The ME was prepared with OCS, butanol, kerosene and saline solutions. OCS-ME and DC-ME showed highest inhibitions effects (77% and 92%, respectively) at lower concentrations (0.5% and 0.48 - 0.50%, respectively). The surfactant OCS (in H2O) showed lower efficiency (63% at 0.20 - 0.25% concentration). The greatest inhibitory effect of DC-ME could be correlated with the chemical structure and the rich O/W ME system, which are very important for adsorption phenomena in interfacial ME systems.

Determinação voltamétrica por redissolução anódica de Cu(II) em águas residuárias empregando um eletrodo de pasta de carbono modificado com quitosana

The electrochemical applications of a CPE modified with chitosan for the determination of Cu(II) in wastewater samples using anodic stripping voltammetry are described. The best voltammetric response was observed for a paste containing 25% m/m of chitosan. A 0.10 mol L-1 NaNO3 solution (pH 6.5) as supporting electrolyte, a pre-concentration potential of -0.20 V, pre-concentration time of 270 s and a scan rate of 25 mV s-1 were selected. The calibration graph was linear in the Cu(II) concentration range from 2.0 x 10-7 to 7.4 x 10-6 mol L-1, with a detection limit of 8.3 x 10-8 mol L-1.

Funcionalização de nanotubos de Carbono

Carbon nanotubes are very stable systems having considerable chemical inertness due to the strong covalent bonds of the carbon atoms on the nanotube surface. Many applications of carbon nanotubes require their chemical modification in order to tune/control their physico-chemical properties. One way of achieving this control is carrying out functionalization processes where atoms and molecules interact (covalent or non-covalent) with the nanotubes. We review some of the progress that has been made in chemical functionalization of carbon nanotubes. Emphasis is given to chemical strategies, the most used techniques, and applications.

Estudo comparativo de métodos para a determinação da concentração de carbono em solos com altos teores de Fe (Latossolos)

Soil organic matter (SOM) plays an important role in physical, chemical and biological properties of soil. Therefore, the amount of SOM is important for soil management for sustainable agriculture. The objective of this work was to evaluate the amount of SOM in oxisols by different methods and compare them, using principal component analysis, regarding their limitations. The methods used in this work were Walkley-Black, elemental analysis, total organic carbon (TOC) and thermogravimetry. According to our results, TOC and elemental analysis were the most satisfactory methods for carbon quantification, due to their better accuracy and reproducibility.