The relation between structural features and electrochemical activity of MnO2 nanoparticles synthesized from a polyol-made Mn 3O4 precursor

A simple hybrid synthesis processing method was developed to synthesize γ-MnO2 nanocrystalline particles. The polyol method was modified by the addition of nitric acid in order to allow the synthesizing of single-phase Mn3O4 in a large scale. In the sequence, the acid digestion technique was used to transform Mn3O4 into γ-MnO2. Structural and morphological characterization was carried out by X-ray diffractometry, Infrared and Raman spectroscopy, thermogravimetric analysis, nitrogen adsorption isotherm, scanning electron microscopy, and transmission electron microscopy. The electrochemical properties were investigated by cyclic voltammetry and galvanostatic charge-discharge measurements. The synthesized material exhibits a specific capacitance of 125.1 F g-1 at a mass loading of 0.98 mg cm-2. The relation between structural features and electrochemical activity is discussed by comparing the synthesized material with commercial electrolytic manganese dioxide. © 2013 Springer-Verlag Berlin Heidelberg.

Intrinsic magnetic properties of BixCo2-xMnO 4 spinels obtained by short-time etching

We report the structural and magnetic properties of Co2MnO 4, partially substituted by Bi at the octahedral site. Bismuth enhances ferromagnetism due to a decrease of the Co2+-Co2+ antiferromagnetic interactions and an increase of the Mn3+-Mn 4+ exchanges. Spurious phases (magnetic and/or nonmagnetic oxides) can easily form because of the large differences between the ionic radii of Bi3+ and Co3+, hiding or altering the intrinsic physical properties of the main BixCo2-xMnO4 phase. An easy way to eliminate the secondary phases is using acid reagents. Short-time etching of Bi0.1Co1.9MnO4 using nitric acid was successfully used, keeping most of the properties of the initial compound, with no alteration of the crystallographic structure. Final stoichiometry was respected (∼Bi0.08Co1.82MnO4), meaning that the material after etching definitely contains bismuth elements in its structure and the observed properties are intrinsic to the oxide spinel. Additional experiments were performed as a function of the synthesis conditions, showing that an optimal pH value of 7 allowed the best magnetic response of the non-doped material. © 2013 Elsevier B.V. All rights reserved.

Evaluation of sample preparation procedures and krypton as an interference standard probe for arsenic speciation by HPLC-ICP-QMS

Different conditions of extraction using water, a methanol-water mixture and nitric acid solutions were evaluated for speciation of As(iii), As(v), DMA and MMA in plant samples that previously received As(v) after being sown and emergence was investigated. Microwave-assisted extraction (MAE) using diluted nitric acid solutions was also performed for arsenic extraction from chicken feed samples. The separation and determination of arsenic species were performed using HPLC-ICP-MS. The interference standard method (IFS) using 83Kr+ as the IFS probe was employed to minimize spectral interferences caused by polyatomic species, such as 40Ar 35Cl+. The extraction procedures tested presented adequate extraction efficiencies (90%), and the four arsenic species evaluated were found in plant samples. Extractions with diluted nitric acid solution at 90 °C were the most efficient strategy, with quantitative recoveries for all four As species in plant tissues. On the other hand, the methanol-water mixture was the solvent with the lowest extraction efficiency (50-60%). For chicken feed samples, MAE at 100 °C for 30 min resulted in an extraction efficiency of 97% and only As(v) was found, without any species interconversion. The IFS method contributed to improving precision and limits of detection and quantification for all tested extraction procedures. Significant improvements on accuracy were obtained by applying the IFS method and recoveries between 77 and 94%, and 82 and 93% were obtained for plant extracts and chicken feed samples, respectively. This journal is © 2013 The Royal Society of Chemistry.

Anthropogenic impacts on mineral weathering: A statistical perspective

Correspondence Analysis was adopted as tool for investigating the statistical structure of hydrochemical and weathering datasets of groundwater samples, with the main purpose of identifying impacts on mineral weathering caused by anthropogenic activities, namely fertilizing of farmlands. The hydrochemical dataset comprised measured concentrations of major inorganic compounds dissolved in groundwater, namely bicarbonate, silica (usually by-products of chemical weathering), chloride, sulphate and nitrate (typically atmospheric plus anthropogenic inputs). The weathering dataset consisted of calculated mass transfers of minerals being dissolved in loess sediments of a region located in SW Hungary (Szigetvár area), namely Na-plagioclase, calcite and dolomite, and of pollution-related concentrations of sodium, magnesium and calcium. A first run of Correspondence Analysis described groundwater composition in the study area as a system of triple influence, where spots of domestic effluents-dominated chemistries are surrounded by areas with agriculture-dominated chemistries, both imprinted over large regions of weathering dominated chemistries. A second run revealed that nitrification of N-fertilizers is promoting mineral weathering by the nitric acid reaction (anthropogenic pathway), in concurrence with the retreating of weathering by carbonic acid (natural pathway). It also indicated that dolomite and calcite are being players in a dedolomitization process driven by dissolution of gypsum fertilizers and nitrification of N-fertilizers. © 2013 Elsevier Ltd.

Potencial do eucalipto na fitorremediação de um solo contaminado por chumbo

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Avaliação do uso de radiação micro-ondas e ultrassom combinados com agentes químicos como pré-tratamentos de bagaço de cana-de-açúcar para posterior sacarificação enzimática

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Caracterização do efeito corona em isoladores poliméricos do tipo bastão submetidos à poluição salínica

Pós-graduação em Ciência e Tecnologia de Materiais - FC

Aplicação de sílica organicamente modificada em sistema de extração em fase sólida de íons Cu(II), Cd(II) e Pb(II) em meio aquoso

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Pontas e velocidade de deslocamento na deposição de gotas da pulverização na cultura do algodão

Pós-graduação em Agronomia (Proteção de Plantas) - FCA

Avaliação de interface de reação e colisão para eliminar interferências poliatômicas na análise de etanol combustível por ICP-MS

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Determinação direta e simultânea de 'AL', 'AS', 'CU', 'FE', 'MN' e 'NI' em álcool etílico hidratado combustível por espectrometria de absorção atômica em forno de grafite

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Estudos da preparação de superfície da liga AA6063T5 e do desenvolvimento de revestimentos híbridos orgânico-inorgânicos a base de siloxano-PMMA para aplicação anticorrosiva

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Caracterização mecânica e microestrutural de um aço de baixo carbono

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Síntese, caracterização e estudo do comportamento térmico dos 2-metoxicinamalpiruvatos de lantanídeos (III), exceto promécio, e ítrio (III) no estado sólido

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Aplicação de fluido de corte em quantidades reduzidas para usinagem do aço SAE 52100 no processo de retificação centerless de passagem

Pós-graduação em Ciência e Tecnologia de Materiais - FC