Hidrogenofosfato de titânio lamelar: síntese, troca iônica e intercalação

The development associated with the research field involving crystalline inorganic lamellar titanium hydrogenphosphate, Ti(HPO4).H2O, synthesized as alpha or gamma forms, is directly linked to the huge number of reactions, that occur inside the free interlamellar space. Two distinguishable well-characterized features such as ion-exchange and intercalation reactions are explored here. From the interactive point of view, the acidic OH centres distributed on the lamella can interact with cations or with basic polar molecules to exchange or to intercalate them. These chemical reactions are normally followed by an expansion of the interlamellar space, proportional to the amount intercalated, reflecting in ion radii or organic molecule size lengths used in ion-exchange or insertion processes, respectively. The effectiveness of the exchange increased when the original matrix has the proton of OH group previously ion-exchanged by an alkaline or an alkylammonium cations. Monoalkyl-, dialkyl- and heterocyclic amines are focused in this revision as clear and elucidative examples of acid-base interactive processes, that come out inside of the well-formed infinite sequence of inorganic lamellar structure.

Dissulfeto de molibdênio, um material multifuncional e surpreendente

The aim of this work is to review the chemical and physical properties of layered molybdenum disulfide. The three polymorphic/polytypic modifications of the compound were found, the polytypes 2H (molybdenite) and 3R are semiconductors while the polymorph 1T is an electronic conductor. 2H-MoS2 has several important industrial applications as hydrotreatment catalysts, energy storage devices, solar cells, solid lubricants, among others. When intercalated, the 2H phase changes to a distorted 1T phase, producing unstable intercalation compounds that can be exfoliated in solution, producing single layers and consequently nanocomposites. The direct synthesis of the 1T phase produces stable intercalation compounds. Recently molybdenum disulfide was prepared as nanotubes and fulerene-like structures that bring new insights in the investigation of this important material.

Aspectos relacionados à utilização da equação logística quadrática em processos eletroquímicos

The concepts of dissipation and feedback are contained in the behavior of many natural dynamical systems. They have been used to predict the evolution of populations leading to the formulation of the quadratic logistic equation (QLE). More recently, the QLE has been used to provide a better understanding of physicochemical systems with promising results. Many physical, chemical and biological dynamic phenomena can be understood on the basis of the QLE and this work describes the main aspects of this equation and some recent applications, with emphasis on electrochemical systems. Also, it is illustrated the concept of potential energy as a convenient way of describing the stability of the fixed points of the QLE.

Caracterização textural e estrutural de V2O5/TiO2 obtidos via sol-gel: comparação entre secagem convencional e supercrítica

This work describes a modified sol-gel method for the preparation of V2O5/TiO2 catalysts. The samples have been characterized by N2 adsorption at 77K, x-ray diffractometry (XRD) and Fourier Transform Infrared (FT-IR). The surface area increases with the vanadia loading from 24 m² g-1, for pure TiO2, to 87 m² g-1 for 9wt.% of V2O5. The rutile form is predominant for pure TiO2 but became enriched with anatase phase when vanadia loading is increased. No crystalline V2O5 phase was observed in the catalysts diffractograms. Two species of surface vanadium observed by FT-IR spectroscopy a monomeric vanadyl and polymeric vanadates, the vanadyl/vanadate ratio remains practically constant.

Materiais para cátodos de baterias secundárias de lítio

In this work, cathodes employed in secondary lithium batteries are reviewed. These cathodes have great technologic and scientific importance, specifically, materials for cathodes as electronic conductor polymers (ECP), transition metal oxides (TMO) and nanocomposites of ECP/TMO. The use of a specific cathodic material is based in some intrinsic characteristics that improve the performance of the battery. Thus, some vantages and disvantages of these insertion compounds are discussed, as lithium insertion capacity, energy density, and the ciclability of these materials.

Redução de amidas por boranos

Despite the fact that boranes are frequently used in amide reductions, the reaction mechanisms of the involved are note well known. This work presents the results of a bibliographic search on probable amide reduction mechanisms and an analysis of the existing literature. Steric and electronic effects were considered in light of reactivity since it could be concluded that the formation of intermediates and products depends mainly on the substitution patterns of both the boron and nitrogen atoms. Otherwise, results described in the literature for the reactions of boranes, sodium borohydride, lithium aluminum hydride, alkylboranes or haloboranes with others functional groups such as carboxylic acids, esters, ketones and alkenes were analysed with the aim to obtain something about the N-substituted amide reactions employing boranes.

Preparação de LiNbO3 e LiNbO3:Eu3+ pelo método dos precursores poliméricos

The ferroelectric compound LiNbO3 was prepared by the polymeric precursors method in the polycrystalline form containing different concentrations of Eu3+. The compounds were characterized by X-ray diffraction, vibrational and electronic spectroscopy. Electronic spectroscopy was shown to be sensitive to small concentrations of contaminating phases allowing a good control of the compound purity. The presence of Eu3+ ions leads to the formation of the LiNb3O8 phase in the range of 500 to 800 °C. Above this temperature range LiNbO3 and tetragonal (T') EuNbO4 were obtained.

Comportamento térmico da caulinita hidratada

Well-ordered kaolinite from the Brazilian Amazon Region (State of Pará) was initially reacted at 60 °C with a water dimethylsulfoxide mixture. After washing and characterisation, the resulting material was washed several times with methanol and in the final step with water. The water molecules displace the previously dimethylsulfoxide intercalated molecules and two different hydrated kaolinites were obtained. An unstable phase characterized by an interplanar basal distance of 0,996 nm that after drying collapse to the stable 0,844 nm hydrated kaolinite. The dehydration of the sample to disordered kaolinite was accompanied by Powder X-ray Diffractometry, thermal analysis (simultaneous TG and DSC) and FTIR spectroscopy.

Síntese e caracterização de um composto VOPO4-DMA

A layered matrix, alpha-VOPO4.2H2O was used as host species to produce a VOPO4.dimethylacetamide intercalation compound. The oxovanadium matrix and the synthesized hybrid were characterized by elemental analysis, infrared spectroscopy, thermogravimetry, X-ray diffractometry and SEM microscopy. The X-ray diffraction patterns show that the VOPO4.dimethylacetamide compound is amorphous, but can be turned lamellar after a solubilization-crystallization process. The SEM micrographs obtained for the VOPO4-dimethylacetamide hybrid matrix show that the microstructure of VOPO4.2H2O is changed after reaction, with a delamination of the oxovanadium matrix.

Recuperação de bromo em soluções aquosas residuais

A laboratory procedure was devised to recover bromine from waste alkaline aqueous solutions used in the isotopic determination of N-15. The laboratory apparatus comprises two round bottom flasks (1 and 2 L), a dropping funnel, a gas bubbler, a gas regulator and glass fittings. The waste solution is acidified with sulfuric acid forming molecular bromine that is stripped out by a flow of nitrogen gas bubbled through the solution. This gas is then bubbled through a solution of lithium hydroxide generating lithium bromide and lithium hypobromite. The efficiency of bromine recovery was estimated to be 82±2%. This resulting solution was successfully reused in the isotopic determination of N-15. The procedure can recycle most of the bromine used in the laboratory saving resources and preserving the environment. The procedure can be adapted to recover bromine of other laboratory waste streams.

Transporte de carga em compósitos de polianilina/V2O5

In this work, composites formed from a mixture of V2O5 and polyaniline (PANI) were investigated, for applications as cathode materials for secondary lithium batteries. Electrochemical quartz crystal microbalance (EQCM) data show that charge compensation in the [PANI]0.3V2O5 nanocomposite is achieved predominantly by Li+ migration. However, the charge compensation in the [PANI]V2O5 microcomposite occurs by Li+ and ClO4- transport. Electrochemical Impedance Spectroscopy (EIS) measurements reveal several benefits of nanohybrid formation, including the achievement of shorter ionic diffusion pathways, the higher diffusion rate of the lithium ion and also the higher electronic conductivity, which are responsible for a synergetic effect of the energy storage properties.

Experimentos simples usando fotometria de chama para ensino de princípios de espectrometria atômica em cursos de química analítica

The purpose of this paper is the development of simple strategies to teach basic concepts of atomic spectrometry. Metals present in samples found in the daily lives of students are determined by flame atomic emission spectrometry (FAES). FAES is an accurate, precise, and inexpensive analytical method often used for determining sodium, potassium, lithium, and calcium. Historical aspects and their contextualization for students are also presented and experiments with samples that do not require pre-treatment are described.

Síntese e caracterização de alfa-fosfato de zircônio(IV) contendo agregados de cobre metálico

The alpha-zirconium (IV) hydrogenphosphate (alpha-ZrP) has received great attention in the last years due to its properties like ion exchange, intercalation, ionic conductivity and catalytic activity. This work reports a method to produce metallic copper clusters on alpha-ZrP to be used as catalysts in petrochemical processes. It was found that the solids were non-crystalline regardless of the uptake of copper and the reduction. The specific surface area increased as a consequence of the increase of the interlayer distance to accept the copper ions between the layers. During the reduction, big clusters of copper (0,5-11µ) with different sizes and shapes were produced.

Preparação de compostos lamelares: síntese do hidrogenofosfato de zircônio cristalino e sua intercalação com aminas. Um experimento para estudantes de graduação

The present paper describes the synthesis of crystalline zirconium hydrogen phosphate by direct precipitation and its intercalation with pyridine and n-butylamine. The simple experiment was tested in the undergraduate inorganic chemistry laboratory course for chemistry students at IQ-UNICAMP using inexpensive reagents. The materials were characterized by powder X-ray diffraction and infrared analyses in order to obtain detailed information of the solid structure changes as a result of the intercalation process. Pyridine and n-butylamine are focused in this work as clear and elucidative examples leading to acid-base interactive processes that result in the well-formed infinite sequence of inorganic lamellar structures.

Aspectos estruturais relacionados ao processo de troca iônica no niobato lamelar K4Nb6O17

The niobate with formula K4Nb6O17 has a layered structure formed by stacked negative sheets and exchangeable cations in the interlayer region. In this study we discuss some structural aspects related to the ion exchange in layered hexaniobate based on X-ray diffractometry and vibrational Raman spectroscopy data. Hexaniobate has two distinct interlayer regions and the potassium ions of one interlayer in particular are preferably exchanged by other cations, leading to an interstratified material.