
Marta Eloisa MedeirosFederal University of Rio de Janeiro | UFRJ · Departamento de Química Inorgânica
Marta Eloisa Medeiros
Doctor of Philosophy
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Publications (120)
Pyrometallurgical processing of lateritic ore produces huge amounts of ferronickel slags, which may contain valuable metals. This paper describes a novel hydrometallurgical route to recover metals from ferronickel slag samples and reduce liability matters using oxidative acidic leaching. Hydrochloric acid and hydrogen peroxide were employed as leac...
O Programa de Mestrado Profissional em Química em Rede Nacional, PROFQUI, completa 7 anos de atividade em 2024, tendo concedido o título de mestre para mais de 400 professores de química da educação básica em nível nacional. É uma marca significativa e que mostra o potencial do programa em contribuir para a formação continuada de professores e para...
Developing new non-noble metal electrocatalysts for oxygen reduction reaction (ORR) is an essential challenge in electrochemical device research. Among these, we highlight the metal Schiff-base complexes, which can be used as modified carbon paste electrodes (CPE). Herein, we present a facile one-pot method for preparing a new family of cobalt(II)...
Background: Researchers are carried out to assess rocks containing potassium as an alternative source of fertilizers. These studies are important in reducing the external dependence of Brazil on this commodity. Phonolite is a rock of volcanic origin that has in its mineralogical composition the predominance of feldspar and has been potential to use...
Samples of the ternary system MgO-Al2O3-SiO2 with stoichiometric composition in-cordierite (Mg2Al4Si5O18), consisting of 22.2 mol% MgO, 22.2 mol% Al2O3, and 55.6 mol% SiO2, were activated in a low energy mill with a constant speed of 100 rpm, in an aqueous medium. The precursors used were corundum (Al2O3), silica gel HF254 type 60 (SiO2), and peric...
Currently, solution combustion synthesis (SCS) is considered a reproducible, flexible, and lowcost synthesis method for the preparation of nanomaterials. A new trend in the SCS method is the use of less polluting fuels, such as starch. The use of starch as fuel in SCS is very interesting for green chemistry, as it is renewable and has several advan...
The wrong discard of effluents contaminated by organic dyes can cause environmental problems. In this context, ZnO semiconductor and magnetic composite ZnO/ZnFe2O4 were prepared by the combustion method. Both materials synthesized presented adsorption and photocatalysis properties of methylene blue dye in an aqueous medium. After 4h in adsorption,...
The fuel cell is a continuously operating, low environmental impact, highly energy-efficient electrochemical device that has been cited as a clean energy source to replace fossil fuels. However, noble metals, such as platinum, are used as electrocatalysts to improve reaction kinetics, which raises the cost of this renewable energy source. This work...
INFLUENCE OF MAGNESIUM AND ALUMINIUM HYDROXIDES ON THE MECHANOCHEMICAL ACTIVATION OF MgO-Al2O3-SiO2 SYSTEM:
In previous studies on mechanochemical activation of the MgO-Al2O3-
SiO2 system, in a low energy ball mill with a constant speed of 100 rpm, it was observed that the presence of hydroxyls on the surface
of the silica precursor (HF254 type 60...
The presence of cadmium in the environment requires attention, due to its carcinogenic and bioaccumulative power. To remedy water bodies contaminated with trace metal, different materials are reported in the literature. This work describes a method able to remove 10–25% of Cd2+ from aqueous solutions in a single batch using layered and cationic exc...
Highlights Magnetic composites containing ZnO, ZnFe2O4 and Vulcan-X were prepared by combustion synthesis. These materials have adsorption and photocatalytic properties and can be used to remove dyes from solution. Resumo/Abstract 1. Introdução A adsorção é um método de tratamento de efluentes contaminados amplamente utilizado, entretanto, a separa...
Highlights: Magnetic photocatalysts were prepared. The addition of tartaric acid increased the photo Fenton degradation of methylene blue by these photocatalysts. These materials can be easily recovered and reused.
Resumo: O γ-Fe 2 O 3 é um óxido magnético que vem sendo estudado devido as suas propriedades magnéticas e fotocatalíticas. Neste traba...
The present work is focused on the understanding of the CeO2 support interactions with cyclodextrin‐stabilized palladium nanoparticles (PdNPs) and the effect in the Suzuki‐Miyaura reaction outcome. Mostly, it is evidenced the strong influence of the cyclodextrin torus on the reactivity of PdNPs towards the ceria matrix. Structural characterization...
Improper disposal of effluent contaminated with organic dyes may cause environmental problems. In this context, the ZnO semiconductor and the ZnO/ZnFe 2 O 4 magnetic composite were prepared by the combustion method. The synthesized materials showed adsorption and photocatalysis properties for elimination of methylene blue dye from aqueous medium. A...
A crescente demanda por energia aliada ao esgotamento e aos problemas ambientais relacionados às fontes de energia não renováveis, como os combustíveis fósseis, aceleraram a procura e desenvolvimento de novas fontes energéticas limpas e renováveis. Neste escopo, as pilhas a combustível aparecem como alternativa de geração de energia para aplicação...
Embora a Química seja de suma importância no currículo para a formação cidadã, na maioria das vezes é compreendida como algo desnecessário para compreensão do cotidiano e considerada difícil por grande parte do alunado escolar. Esta visão se dá, muitas vezes, devido a metodologia de ensino utilizada para abordar os conteúdos ¹. Os alunos estão cond...
As bauxitas no NE do Pará são rochas que apresentam em sua composição química oxi-hidróxidos de alumínio, sendo o principal deles, a gibbsita (γ-Al(OH)3). Dentre as principais impurezas destacam-se os minerais silicatados, como por exemplo, a caulinita (Al4(Si4O10)(OH)8)¹. Atualmente, no processo industrial de obtenção de alumina (Processo Bayer),...
Ni/NiO composites were obtained by self-propagation synthesis (SHS) in order to investigate their structural
and optical properties, evaluating the effects of ammonium hydroxide in the combustion. All the obtained solids
were analyzed by X-Ray Diffraction (XRD), Ultraviolet–Visible spectroscopy (UV–Vis), Fourier Transform Infrared
Spectroscopy (FT-...
Iron oxide based materials were prepared using the solution combustion method under specific conditions (presence or absence of oxygen); resulting in the synthesis of materials with different phases of iron oxides, as well as the presence of reduced graphene oxide, in the cases of syntheses performed in the absence of oxygen. The presence of Fe3O4,...
Iron oxide has several polymorphic phases, due to its properties the γ-Fe2O3 phase is the most interesting one. There are some studies on metal doping in this material to improve its electrochemical, magnetic and catalytic properties. Iron oxides are also applied in the aerospace industry and are incorporated into the propellant composite to improv...
A new magnetic composite (Fe3O4 @ Carbon Black) was successfully synthesized by a combustion method. The composite was characterized by XRD and IV; their adsorptive and photocatalytic capacities were evaluated against the methylene blue (AM) dye. The synthesis resulted in the formation of magnetite as a major phase, making it possible to couple the...
Fuel cells are a promising alternative to clean energy generation. The main electrocatalyst found in these devices is platinum, an expensive metal with low availability, which increases the importance of investigating new compounds that can play the role of platinum in fuel cells. The objective of this work is to synthesize, characterize and evalua...
Magnetic composites were prepared with composites have activity for methylene blue photo degradation Fotocatálise tem como princípio utilização de luz para ativar um semicondutor, resultando na promoção de um elétron para a banda de condução e gerando uma lacuna na banda de valência. Tal lacuna apresenta energia suficiente para oxidar a água, geran...
Composites of gold mine sludge with Vulcan-X and CeO2 were prepared. These composites have activity for methylene blue degradation by photo Fento process.
Drenagem ácida é um dos principais problemas da mineração de ouro, os minerais de sulfetos extraídos do interior da terra, descartados na superfície, reagem com água e oxigênio produzindo ácidos....
Abstract: Magnetic iron (III) oxide composites were prepared with Vulcan (II) oxalate as a precursor. The composites obtained have considerable dye adsorption capacity and can be removed from the aqueous medium by the application of field.
Resumo: Foram preparados X, utilizando o oxalato de ferro (II) considerável capacidade de adsorção de corante...
Resumo: A industria têxtil gera uma grande quantidade de efluentes contaminados por corantes orgânicos como o azul de metileno. Neste trabalho foram preparados compósitos magnéticos de ferrita de zinco com ZnO, fazendo-se uso do método de combustão. O compósito obtido apresentou considerável eficiência de fotodegradação do azul de metileno em meio...
A Ni(II) coordination polymer [C42H42K2N4Ni4O27] has been synthesized under open-air mild reaction conditions and characterized by physicochemical and spectroscopic methods. The X-ray crystal structure of the complex has been obtained. The crystallographic data revealed that each metal center is in a distorted octahedral geometry where the ligand c...
The Bauxite
from North Brazil is characterized by a geological profile with different layers. The differences among these layers are percentage of bauxite constituents (gibbsite, kaolinite and hematite). Nowadays, only one layer is used for alumina production by Bayer process, the commercial or crystallized bauxite. This work intended to characteri...
Starch, a polysaccharide, has a branched molecular structure, that advantage different chemical procedures used in obtaining nanostructured metal oxides, such as the combustion method. The objective of this work was to analyze the products obtained by the synthesis of the metallic nickel/nickel oxide (Ni/NiO) composite by the starch-assisted combus...
SOLID OXIDE FUEL CELLS: MATERIALS, COMPONENTS AND CONFIGURATIONS.
In this paper the current status of fuel cells is described with particular emphasis on high (T > 800 o
C) and intermediate (T < 800 oC) temperature solid oxide fuel cells. Also the importance of the fuel cell technology is shown. Reviewed are the fundamental features, the basic pri...
No Brasil, o uso de fertilizantes intensificou-se com o proposito de aumentar a sua produtividade agricola. Uma consequencia disso e o aumento nas importacoes de fertilizantes, uma vez que, a producao interna tornou-se insatisfatoria. Baseado neste cenario e importante o desenvolvimento de fontes alternativas de sais de potassio para aplicacao na a...
This work describes the synthesis of composite nickel/nickel oxide to be used in fuel cell anodes using the combustion sol-gel method, assisted by starch. From the results obtained by XRD it can be concluded that samples 1: 6.3 and 1: 5.0 are present in the metallic Ni and NiO phases, differently from samples 1: 8.3 and 1: 2.0 which present pure ph...
This paper describes the application of the combustion sol-gel method, assisted by starch, in the preparation of cobalt doped nickel oxide and the Ni/Co alloy, for application in fuel cell anodes. According to the analysis by XRD was possible to confirm the effectiveness of the method of synthesis. The XRD confirmed the introduction of cobalt ions...
A mineralogia é um dos principais fatores na definição de rochas para aplicação na agricultura. A rocha fonolito, do município de Poços de Caldas – MG, possui um teor de K2O de 8,7% (m/m) e seu principal constituinte é o feldspato potássico. Estudos realizados com essa rocha in natura revelaram que o teor máximo de K liberado foi de cerca de 1% do...
Resumo: Pilha a combustível é um dispositivo eletroquímico, que realiza a conversão de energia gerada numa reação eletroquímica em energia elétrica, sendo altamente eficiente. Na reação de combustão, utilizando o amido como combustível, vários efeitos positivos são esperados: uma propagação sem violência, uma combustão com produção de gases não tóx...
Dye-Sensitized Solar Cells (DSSC) are a prototype of devices with a mesoscopic junction and may present high conversion efficiency. Many studies are related to the development of semiconductor anode component, mainly with sintered titanium dioxide in the anatase phase. However, nickel oxide (NiO) has been largely studied due to its use in the produ...
Alternative sources of inorganic fertilizer are being studied mainly in relation to potassium. The reactivity of rocks and therefore the K+ availability can be changed by modifications in mineral structure. In the present study, K+ availability of phonolite rock was investigated after thermal treatment at different temperatures between 300-1200 °C...
[ABSTRACT] In this work, Ni / NiO composites are synthesized using the starch-assisted sol-gel method. The synthesis was carried out in order to control the formation of metallic nickel by varying the concentration of starch. The combustion method, using starch as fuel, proved to be suitable for the Ni / NiO composite preparation. It was observed t...
Neste trabalho, foi avaliado o efeito da presença de íons Ce (III) na deformação da rede de céria, preparada pelo método hidrotérmico. A combinação da espectroscopia Raman, do refinamento estrutural por Rietveld e da análise de Williamson-Hall, permite a obtenção de importantes informações sobre questões estruturais de cérias não estequiométricas.
As pilhas a combustível permitem a geração de energia elétrica de forma limpa e
eficiente. Dentre seus diferentes tipos destaca-se a pilha a combustível do tipo
óxido sólido (PaCOS). O óxido de cério dopado com samário (SDC) tem sido amplamente
estudado, visando sua aplicação como eletrólito sólido e na elaboração do anodo tipo
cermet. Inicialmente...
Viabilizando uma forma de gerar energia elétrica sem causar danos ao meio ambiente,
ultimamente tem-se pesquisado mais a respeito de pilhas a combustível. Porém,esses
dispositivos necessitam de eletrocatalisadores.O principal eletrocatalisador utilizado
recentemente é a platina,sendo esta de alto custo. Por isso,outros compostos de custo
mais baixo...
Viabilizando uma forma de gerar energia elétrica sem causar danos ao meio ambiente,
ultimamente tem-se pesquisado mais a respeito de pilhas a combustível. Porém,esses
dispositivos necessitam de eletrocatalisadores.O principal eletrocatalisador utilizado
recentemente é a platina,sendo esta de alto custo. Por isso,outros compostos de custo
mais baixo...
Resumo: As baterias secundárias de íon-lítio se destacam dentre as tecnologias alternativas para produção e armazenamento de energia elétrica. Neste trabalho, materiais contendo a fase tipo espinélio do Li 4 Ti 5 O 12 (LTO) foram sintetizados pelo método sol-gel, na pre-sença de amido. No método proposto, diferentes razões molares de lítio, titânio...
The secondary lithium ion batteries stand out among the alternative technologies for the production and storage of electricity. In this work, materials containing the Li 4 Ti 5 O 12 spinel type phase (LTO) were synthesized by sol-gel method in the presence of starch. In the proposed method, diierent molar ratios of lithium, titanium and soluble sta...
Síntese, Caracterização de um complexo de cobalto (II) e investigação de atividade eletrocatalítica frente reações de redução de oxigênio em meio básico. Resumo Pilhas a combustível são dispositivos capazes de converter energia química em energia elétrica e são apresentadas atualm maior eficiência. Estes dispositivos utilizam o oxigênio como princi...
Resumo: A tecnologia das pilhas a combustível vem se mostrando uma alternativa promissora de geração de energia frente às fontes convencionais. Uma pilha a combustível é um dispositivo eletroquímico que produz por um mecanismo de conversão de energia eficiente e não poluente. Nestes dispositivos se faz necessário o uso de eletrocatalisadores, princ...
Characterization and classification of the environmental risk of host rock from a chromite mine in Andorinha / Bahia / Brazil.
The mineral waste Studied was the host rock from chromite mine located in Andorinha / Bahia, extracted and stockpiled in yards without specific application. Host rock was submitted to chemical analysis, XRD, SEM-EDS, IR and...
Resumo: Neste trabalho, preparou-se uma mistura de níquel/α-hidróxido
de níquel e estudou-se a influência do precursor no material
obtido e suas propriedades. A metodologia adotada para a síntese foi
a redução de níquel (II) por boroidreto pela técnica de microemulsão,
e os materiais obtidos foram caracterizados por espectroscopia
de infravermelho,...
Bauxite is composed by an impure mixture of aluminum minerals. The proportions of these
minerals vary greatly through the deposits, so does the type and the quantity of impurity in the ore.
This work proposes a study of technologic characterization of the nodular bauxite (NB) focusing on
the ore dressing processes, in order to make part of this ore...
RESUMO
Como o Brasil é um dos maiores produtores agrícolas mundiais, o uso de fertilizantes intensificou-se com o propósito de aumentar a produtividade agrícola do país. Uma consequência disso é o aumento nas importações de fertilizantes, uma vez que, a produção interna tornou-se insatisfatória. Baseado neste cenário é importante o desenvolvimento...
A bauxita do Pará é constituída pelas seguintes camadas: nodular (BN), nodular cristalizada (BNC), cristalizada (BC), cristalizada - amorfa (BCBA) e amorfa (BA). Deste perfil geológico, somente a camada BC é lavrada, beneficiada, transportada através de mineroduto e purificada no processo Bayer. As camadas BCBA e BA possuem um elevado teor de SiO2...
Bauxite from Para is constituted by the following layers: nodular (BN), nodular crystallized (BNC), crystallized (BC), crystallized - amorphous (BCBA) and amorphous (BA). From this geological profile only the BC layer is mined, dressed, transported through pipelines and purified in the Bayer process. The BCBA and BA layers have a high content of re...
ABSTRACT
The mixed oxides SiO 2 / M x O y obtained by the sol-gel process, called composites
typically combine mechanical and chemical properties of the silica gel with the
chemical properties of the metal oxide (M x O y), with properties such as: high
degree of dispersion and homogeneity of the particles of metal oxide in the silica
matrix, as wel...
The mixed oxides SiO2/MxOy obtained by the sol-gel process, designated as composites, usually combine both mechanical and chemical properties of silica gel with the chemical properties of metal oxide (MxOy), showing properties such as: high degree of dispersion and homogeneity of metal oxide particles in the silica matrix, as well as high mechanica...
Solid propellants are materials with controlled burning and one of the type used as fuel is solid propellant type composite, NH4ClO4 using as oxidizing agent and certain additives. Among them, stands out as CuCr2O4 accelerator burning (Shen, 1983; West, 1984; Meyer, 1987; Campos et al, 2010). Some of sites are activated by adsorption of reagents an...
Nanocrystalline calcium and strontium singly doped ceria and co-doped ceria materials for solid electrolytes were prepared via a hydrothermal route. The effect of the hydrothermal treatment time on the solid solution composition was evaluated. Sr doped ceria was the most difficult to form, due to the Sr2+ large ionic radius. The small crystal size...
PHYSICAL AND CHEMICAL ORE DRESSING STUDIES AND CHARACTERIZATION OF BAUXITES FROM PARÁ
The layers of crystallized bauxite (CB) and crystallized amorphous bauxite (ACB) that compound the bauxite’s geological profile of the northeastern Pará were submitted to the stages of ore dressing in order to become appropriated to the bench tests, being subjecte...
In this work, the characterization of a verdete from Cedro do Abaeté, was carried out to evalute its use as a source of potassium to the development of alternative fertilizers. The chemical and mineralogical characterization of this rock was run by X-ray diffraction, (XRD), X-ray fluorescence (XRF) and infrared spectroscopy (IR). The results show t...
Some bauxites have high chemical contents of reactive silica and other impurities, being considered marginal bauxites. Nowadays, these bauxites are not used for the production of alumina by the Bayer process, such as the marginal bauxites from Northern Brazil. The detailed study of characterization showed that these bauxites contain particles of ka...
Algumas bauxitas tem um elevado conteúdo químico de sílica reativa e outras impurezas, sendo
bauxita considerado marginal. Hoje em dia, estes Bauxitas não são utilizados para a produção de
alumina pelo processo Bayer, como as bauxitas marginais da região Norte do Brasil. o detalhada
estudo de caracterização mostrou que teses bauxita conter partícul...
Evaluation of phonolite rock as a potassium fertilizer alternative.
In recent years, research has been conducted on the possible use of potassium silicates for the production and/or application as potash fertilizers, due to the increased Brazilian external dependence. The stonemeal is an alternative agriculture method that helps to restore and rene...
Resumo: O potássio é o macronutriente com maior consumo no setor agrícola, sendo quase totalmente importado. Atualmente são realizadas pesquisas para verificar o aproveitamento de rochas contendo silicatos potássicos, visando diminuir a dependência externa do país. Este trabalho descreve a avaliação da disponibilidade do K contido na rocha fonolito...
TÍTULO: Síntese e caracterização de um novo complexo de níquel com atividade eletro-catalítica em reações de redução de oxigênio em meio básico
RESUMO: Pilhas a combustível são dispositivos capazes de converter eletroquimicamente a energia gerada em uma reação química em energia elétrica. Nestes dispositivos o principal composto utilizado como oxi...
The mineral waste Studied was the host rock from chromite mine located in Andorinha / Bahia, extracted and stockpiled in yards without specific application. Host rock was submitted to chemical analysis, XRD, SEM-EDS, IR and TGA and classified According to ABNT standards for solid waste classification. Analyses confirmed this que host rock, classifi...
Rocks for crops is a natural practice for soils fertilization which consists on adding rocks to the soil while water decomposes the rock, through chemical weathering, and gradually releases nutrients to the soil solution. This practice can be considered an alternative to the low production of potassium fertilizers in Brazil. In this context, the ph...
Nanocrystalline calcium and strontium singly doped ceria and co-doped ceria materials for solid electrolytes were prepared via a hydrothermal route. The effect of the hydrothermal treatment time on the solid solution composition was evaluated. Sr doped ceria was the most difficult to form, due to the Sr2+ large ionic radius. The small crystal size...
Potassium is one of the major macronutrients present in the soil. However, in Brazil
it becomes scarce due to high acidity of soils. Thus, the demand for alternative
sources of potassium grows considerably. In this context, the chemical and
mineralogical characterization of verdigris Cedars Abaeté, Minas Gerais was
performed, as well as an evaluati...
The potassium is one of the most important macronutrients to the soil. However, in the Brazilian soils this nutrient becomes scarce due to the high acidity of tropical soils. Thus, the demand for alternative sources of potassium grows considerably. In this context, we performed a chemical and mineralogical characterization of a verdete from Cedro d...
The crystallized layer that compounds the bauxite's geological profile from NE Para was ore dressed through the processes of crushing, screening, washing and grinding, in order to reach the same size distribution of that in the alumina production industry. After the preparation process, the sample (90%, < 0.21 mm) containing 5.3% reactive silica an...
The crystallized layer that compounds the bauxite’s geological profile from NE Pará was ore dressed through the processes of crushing, screening, washing and grinding, in order to reach the same size distribution of that in the alumina production industry. After the preparation process, the sample (90%, < 0.21 mm) containing 5.3% reactive silica an...
In recent years, research has been conducted on the possible use of potassium silicates for the production and/or application as potash fertilizers, due to the increased Brazilian external dependence. The stonemeal is an alternative agriculture method that helps to restore and renew the soils poor fertilization of degraded areas through the incorpo...