The performance of urea-intercalated and delaminated kaolinites-adsorption kinetics involving copper and lead

Brazilian kaolinite clay was used to study urea intercalation (K UR) and delamination (Kur/DL) processes. The intercalated sample was delaminated by ultrasonic treatment in acidic solution. The basal distance changed from 0.72 to 1.08 nm with increasing surface area from 20.3 to 90.5 m² g-1 for K UR and K UR/DL. Suspended pristine, intercalated and delaminated clays at pH 5.0 adsorbed copper and lead cations at the solid/liquid interface. The Langmuir, Redlich-Peterson and Toth adsorption isotherm models were employed in linear and nonlinear regression processes, to give b and K L values for all kaolinites. The highest adsorption capacity of 12.8 mmol g-1 was obtained with delaminated kaolinite. The kinetic parameters analyzed by the Lagergren and Elovich models gave a good fit for a pseudo-second order reaction with k2 in the 5.0 to 11.0 and the 4.9 to 13.0 mmol-1 min-1 ranges for copper and lead cations, respectively.Amostras brasileiras de caulinita foram usadas no estudo dos processos de intercalação com uréia (K UR) e de deslaminação (K UR/DL). A amostra intercalada foi deslaminada por tratamento com ultra-som em solução ácida. A distância basal inicial de 0,72 nm passa a 1,08 nm com aumento na área superficial de 20,3 para 90,5 m²g-1 para K NAT e K UR/DL. Amostras de argila intercalada e deslaminada adsorveram cátions cobre e chumbo na interface sólido/líquido. Os modelos de isotermas de adsorção de Langmuir, Redlich-Peterson e Toth foram utilizados em processo de regressão linear e não linear para a obtenção de valores de b e K L para todas as amostras de caulinita. A capacidade de adsorção mais alta, de 12,8 mmol g-1, foi obtida com a caulinita deslaminada. Os parâmetros cinéticos analisados pelos modelos de Lagergren e Elovich forneceram um bom ajuste para uma reação de pseudo-segunda ordem com valores de k2 variando de 5,0 a 11,0 e de 4,9 a 13,0 mmol-1 min-1 para cátions cobre e chumbo, respectivamente.1930Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Lamellar titanium hydrogenphosphate: synthesys, ion-exchange and intercalation

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.799807Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES

The performance of urea-intercalated and delaminated kaolinites-adsorption kinetics involving copper and lead

Brazilian kaolinite clay was used to study urea intercalation (K UR) and delamination (Kur/DL) processes. The intercalated sample was delaminated by ultrasonic treatment in acidic solution. The basal distance changed from 0.72 to 1.08 nm with increasing surface area from 20.3 to 90.5 m² g-1 for K UR and K UR/DL. Suspended pristine, intercalated and delaminated clays at pH 5.0 adsorbed copper and lead cations at the solid/liquid interface. The Langmuir, Redlich-Peterson and Toth adsorption isotherm models were employed in linear and nonlinear regression processes, to give b and K L values for all kaolinites. The highest adsorption capacity of 12.8 mmol g-1 was obtained with delaminated kaolinite. The kinetic parameters analyzed by the Lagergren and Elovich models gave a good fit for a pseudo-second order reaction with k2 in the 5.0 to 11.0 and the 4.9 to 13.0 mmol-1 min-1 ranges for copper and lead cations, respectively

Alkoxide as precursors in the synthesis of new materials through the sol-gel process

An overview about the role of alkoxides in the most recent uses of the sol-gel process in the synthesis of new materials is presented. Special attention is focused on the uses of silicon, aluminum, zirconium and titanium alkoxides. This review shows that the alkoxides enable the synthesis of new matrices with controlled surface area, acidity and porosity, as well as some unusual properties. The property associated with the solubility of metal alkoxides opens enormous possibilities of combining them for the synthesis films of powders with a very large range of metal compositions.848

Processo De Preparação De Novos Trialcoxissilanos Com Grupos Reativos Derivados Da Uréia

Compreendendo a síntese de novos agentes sililantes a partir da reação do precursor do tipo trialcoxissilano com várias aminas alifáticas de cadeia carbônica de diferentes tamanhos, pela rota sintética em meio homogêneo e em condições anidras, onde acontece, a formação de uma nova função química, formando um derivado da ureia do tipo -NH-C=O-NH-.BR9903110 (B1); BR9903110 (A)C07F7/18C07F7/18BR19999903110C07F7/18C07F7/1

The use of organofuntionalized silica gel as sequestrating agent for metals

An overview about the homogeneous and heterogeneous methods of synthesizing silylating agents and applications of the organofunctionalized silica-gel samples was explored. The pendant molecules attached covalently to the inorganic surface displayed important properties to act as sequestrating agents for metals in aqueous and non-aqueous solutions. The large variety of basic centres anchored on organic molecules improve the capacity in adsorbing cations. The increase in adsorption is dependent on the number of basic atoms disposed on the pendant molecules on the surface. The combination of acidic and basicity properties favours the selectivity, such is exemplified by the thiol modified silicas towards mercury (II) cations.496503Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES

Hexamethylenetetramine reaction with graphite oxide (GO) as a strategy to increase the thermal stability of GO: synthesis and characterization of a compound

In this paper, the synthesis and characterization of a GO–hmta compound (GO – graphite oxide; hmta – hexamethylenetetramine) are presented. It is shown that the presence of hmta molecules inside the GO matrix, with very strong interactions, stabilize the GO matrix from a thermal point of view. Such a fact could be used to explore possible applications of GO matrix, especially in catalysis

Mercury adsorption on natural and organofunctionalized smectites - thermodynamics of cation removal

A natural smectite clay sample from Piauí State, Brazil, was organofunctionalized with 3-mercaptopropyltrimethoxysilane and 3-aminopropyltriethoxysilane silyating agents. The basal spacing of 0.99 nm and surface area of 48 m² g-1 for natural clay increased to 1.84 and 2.01 nm, and 781 and 795 m² g-1 for modified clays, respectively. The natural and chemically immobilized clay samples adsorb mercury cations from aqueous solutions at pH 3.0 at 298 ± 1 K. The Langmuir, Redlich-Peterson and Toth adsorption isotherm models were applied to fit the experimental data with a nonlinear approach. From the cation/basic center interactions for each smectite at the solid-liquid interface, by using calorimetry methodology, the equilibrium constant and exothermic thermal effects were obtained. By considering the net interactive number of moles for each cation and the equilibrium constant, the enthalpy, intHº (-11.98 to -13.93 kJ mol-1) and negative free Gibbs energy, intGº (-22.4 ± 0.1 to -23.9 ± 0.1 kJ mol-1) were calculated. These values enabled the determination of positive entropy, intSº (51 ± 01 to 55 ± 2 J K-1 mol-1). The cation-basic center interactions are spontaneous in nature as demonstrated from favorable enthalpic and entropic results. Natural and anchored smectites have the ability to complex mercury, acting as useful materials for removal of this hazardous metal from an ecosystem.Uma amostra natural de esmectita oriunda do estado do Piauí, Brasil, foi organofuncionalizada com 3-mercaptopropiltrimethoxissilano e 3-aminopropiltriethoxissilano. O espaçamento basal da argila natural é de 0,99 nm e área superficial 48 m² g-1. Houve um aumento no espaçamento basal para 1,84 e 2,01 nm e o aumento da área específica para 781 e 795 m² g-1 para as argilas quimicamente modificadas, respectivamente. A argila natural e a argila quimicamente modificada adsorveram cátions mercúrio em solução aquosa em pH 3,0 e 298 ± 1 K. Os modelos de isotermas de adsorção de Langmuir, Redlich-Peterson e Toth foram aplicados para ajuste dos dados experimentais com aproximação não linear. Para as interações cátion/centros básicos para cada esmectita na interface sólido/líquido foi utilizada metodologia calorimétrica e foram obtidas as constantes de equilíbrio e os efeitos térmicos exotérmicos. Considerando o número interativo de moles para cada cátion e as constantes de equilíbrio, a entalpia, intHº (-11,98 a -13,93 kJ mol-1) e a energia livre de Gibbs negativa, intGº (-22,4 ± 0,1 a -23,9 ± 0,1 kJ mol-1) foram calculadas, o que permitiram a determinação da entropia positiva intSº (51 ± 01 a 55 ± 2 J K-1 mol-1). As interações cátion/centros básicos são de natureza espontânea como demonstram os valores de energia livre de Gibbs, dando o conjunto de dados favoráveis como expressam a entalpia exotérmica e a entropia positiva, mostrando que a esmectita natural e as quimicamente modificadas têm habilidade em complexar mercúrio. Logo, esses materiais são úteis na remoção de mercúrio em um ecossistema.594603Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq