Página 11 dos resultados de 741 itens digitais encontrados em 0.018 segundos

Hazelnut (Corylus avellana L.) kernels as a source of antioxidants and their potential in relation to other nuts

Delgado, Teresa; Malheiro, R.; Pereira, J.A.; Ramalhosa, Elsa
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
274.83902%
The present work evaluates the potential of hazelnut kernels as a source of antioxidants to be incorporated into new products. First, the effects of extraction conditions on the isolation of hazelnut kernels’ total phenols and antioxidants were evaluated. Six conditions, involving different solvents (water, methanol and aqueous acetone) and contact times, were studied. The highest total phenol contents were obtained with boiling water for 30 min, 44.3±7.7mgGAE/gextract, and 80% (v/v) aqueous acetone solution for 24 h, 36.2±8.8mgGAE/gextract. Increasing the contact time for the acetonic extractions did not improve the total phenols content. Regarding antioxidant activity, the highest DPPH-scavenging effect value was obtained with 80% (v/v) aqueous acetone for 24 h with an effective concentration (EC50) equal to 1.12±0.07 mg/mL. When other nuts – walnuts, almonds, pine nuts and peanuts – were extracted under this condition, only walnut extract exhibited higher phenol content (268±32mgGAE/gextract), antioxidant activity as measured by reducing power (EC50 = 0.091±0.015 mg/mL) and free radical scavenging capacity (DPPH assay) (EC50 = 0.060±0.010 mg/mL) than hazelnut extract. The present work demonstrates that some nuts might be a natural source of bioactive compounds that can be incorporated into new health-related products or be substitutes of synthetic compounds of questionable safety...

Determinação de dioxido de carbono por titulação potenciométrica (Gran) após absorção em hidróxido de sódio; Determination of carbon dioxide by potenciometric titration (GRAN) after absorption in sodium hydroxide

Cardoso, Luiza Maria Nunes
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 21/03/1989 PT
Relevância na Pesquisa
274.8159%
O presente trabalho consistiu no desenvolvimento de metodologia simples e de baixo custo para determinação de gás carbônico da atmosféra. O CO2 é absorvido em solução aquosa de NaOH, 10-4M e, a solução resultante é adicionado NaCl para concentração final de 1,0M. A seguir, titula-se com ácido clorídrico 10-3M, potenciometricamente. A fim de se evitar interferência de íons carbonato possivelmente existentes na solução original de NaOH. Uma alíquota desta é titulada préviamente antes da absorção de CO2, constituindo o "branco". A solução de hidróxido de sódio e carbonato é titulada a seguir e, considera-se a diferença do volume no ponto final da solução do branco e da amostra; a avaliação é efetuada segundo Gran II, estudado por Pressinotti (9). Foram efetuados estudos experimentais de introdução do gás carbônico em solução de hidróxido de sódio. Estudaram-se os métodos com o uso de: a - com o uso de bomba misturadora; b - com o uso de frascos lavadores; c - com o uso de injeção com seringa em frasco plástico. Esta última mostrou ser simples e rápida para o processo.; This work deals with the development of a simple and low cost methodology the determination of carbonic gas in the atmosphere. The CO2 is absorved in aqueous solution of NaOH 10-4; M and...

Desenvolvimento de métodos de extração e determinação de bifenilas policloradas por cromatografia gasosa e detector de captura de elétrons em óleo Ascarel, reator anaeróbio e solo; Development and validation of a method for determination of Polychlorinated Biphenyls (PCBs) of a standard solution PCB Congener MIX 1 by gas chromatography and electron capture detector in three different matrices: Askarel oil, samples from batch anaerobic reactors and soil

Adorno, Maria Angela Tallarico
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 23/08/2013 PT
Relevância na Pesquisa
274.54945%
Bifenilas policloradas (PCBs) são componentes de óleo ascarel, usado extensamente (no Brasil até os anos 80) como isolante em transformadores de energia devido às suas propriedades físico-químicas como estabilidade térmica e alta constante dielétrica. Apesar de ter sido proibido em todo o mundo devido à alta toxicidade dos PCBs presentes em sua composição, ainda resta grande quantidade de ascarel em circulação como resíduo "passivo" e resultante de contaminação em trocas dos fluidos dos transformadores, além de vazamentos. A principal forma de eliminação é por incineração, que, além de ser um processo caro, pode provocar a formação de compostos mais tóxicos, as dioxinas. Por isso é importante o monitoramento da concentração dessas substâncias, a fim de evitar maiores impactos ambientais na sua disposição, bem como em estudos de biodegradação. Esta matriz é extremamente complexa, o que torna a extração e determinação desses analitos um processo trabalhoso e difícil. Neste trabalho avaliaram-se métodos de extração e determinação de PCBs presentes na solução padrão comercial PCB Congener MIX 1, SUPELCO (PCBs 10, 28, 52, 138, 153 e 180). O desenvolvimento de métodos de extração (cromatografia em coluna...

Estudo da preparação de catalisadores de Ni e Ru suportados em carvão ativado para a hidrogenólise da sacarose; Study of preparation of Ni and Ru catalysts supported on activated carbon for hydrogenolysis of sucrose

Cristiane Zanutelo
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
PT
Relevância na Pesquisa
274.83902%
A hidrogenólise da sacarose é uma reação química de interesse industrial, uma vez que os produtos obtidos, sob a forma de glicóis e polióis, podem ser empregados em diversos setores produtivos, tais como indústrias farmacêuticas e de alimentos. Nesse contexto, o presente trabalho tem como objetivo estudar a preparação de catalisadores de Ni e Ru suportados em carvão ativado, destinados à hidrogenólise da sacarose em meio aquoso. Para tanto, catalisadores com uma fração mássica total de 5 % de metal foram preparados através dos métodos de impregnação incipiente e úmida, a partir de soluções aquosas de precursores clorados. Antes das impregnações, o suporte de carvão ativado comercial foi submetido a um tratamento químico com solução aquosa de KOH. Os sólidos preparados por meio da impregnação incipiente foram reduzidos a 473 K (200 ºC), sob fluxo de H2. Por sua vez, a impregnação úmida foi conduzida a 353 K (80 ºC), para diversos valores de pH, sendo a redução dos catalisadores realizada com formaldeído ou NaBH4. Os sólidos foram caracterizados através das técnicas de adsorção de N2 (método de B.E.T.), titulação de Boehm, titulação potenciométrica, espectroscopia de fotoelétrons excitados por raios X...

Oxidação electrocatalítica de hidratos de carbono utilizando complexos de metais de transição

Cunha, Paula Cristina Bastos Ferreira Leal
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Dissertação de Mestrado
Publicado em 03/03/2006 POR
Relevância na Pesquisa
274.91947%
Os hidratos de carbono podem ser convertidos em produtos químicos, energia, têxteis, materiais de construção, papel e muitos outros produtos industriais. Estes constituem uma matéria prima barata, renovável e facilmente disponível. No início dos anos noventa, 95% da biomassa produzida eram hidratos de carbono e correspondiam a duzentos biliões de toneladas. Nos dias de hoje, apenas 3 a 5% desta biomassa são utilizados em termos industriais. Os restantes sofrem degradação e são reciclados segundo processos naturais. As principais razões para o uso limitado dos hidratos de carbono como matéria prima estão directamente ligadas à sua funcionalização excessiva devido à existência de grupos hidroxilo com reactividade similar, e ainda devido à baixa solubilidade nos vulgares solventes orgânicos. Assim conseguir uma oxidação directa e selectiva dos sacáridos pressupõe uma estratégia preliminar de protecção, sendo esta difícil nos métodos clássicos. Os métodos electroquímicos surgem como uma alternativa, em que as transformações são realizadas em solução aquosa, associando os conceitos e os métodos da electroquímica interfacial com os da catálise heterogénea. O presente trabalho tem como objectivo a oxidação regiosselectiva da D-galactose em meio aquoso...

Kinetics and dynamic evaluation of specific immunotherapy

Pereira, C; Botelho, F; Tavares, B; Lourenço, C; Baeta, C; Palma-Carlos, AG; Pedroso de Lima, J; Chieira, C
Fonte: Centro Hospitalar e Universitário de Coimbra Publicador: Centro Hospitalar e Universitário de Coimbra
Tipo: Artigo de Revista Científica
Publicado em //2004 ENG
Relevância na Pesquisa
274.83902%
Specific immunotherapy (SIT) is frequently used in the treatment of allergic diseases. However, the mechanisms by which SIT achieves clinical improvement remained unclear. We decided to study the in vivo kinetics of this therapy, using a nuclear medicine approach (leukocytes labelled with 99mTc-HMPAO) in patients on maintenance doses of specific immunotherapy with confirmed clinical efficacy. MATERIAL AND METHODS: We studied 13 allergic patients grouped according to different treatment schedules: subcutaneous aqueous allergenic extract (3 latex and 2 hymenoptera venom), subcutaneous depot extract (2 house dust mite and 2 pollens), subcutaneous modified allergens (2 pollens), sublingual extract (2 house dust mites). The control group included two allergic patients submitted to subcutaneous injections of bacterial extract (1 patient--positive control), and aqueous solution (1 patient). At the same time that the therapeutic allergen was administered subcutaneously, the autologous labelled white cells were injected intravenously in a peripheral vein in the contralateral arm. A thoracic dynamic acquisition of 60 mins, 64x64 matrix, 2 frame/min, in anterior view was performed. Static acquisition for 256x256 matrix, during 5 mins each at 60...

Analysis of Cancer Metabolism by Imaging Hyperpolarized Nuclei: Prospects for Translation to Clinical Research

Kurhanewicz, John; Vigneron, Daniel B; Brindle, Kevin; Chekmenev, Eduard Y; Comment, Arnaud; Cunningham, Charles H; DeBerardinis, Ralph J; Green, Gary G; Leach, Martin O; Rajan, Sunder S; Rizi, Rahim R; Ross, Brian D; Warren, Warren S; Malloy, Craig R
Fonte: Neoplasia Press Inc. Publicador: Neoplasia Press Inc.
Tipo: Artigo de Revista Científica
Publicado em /02/2011 EN
Relevância na Pesquisa
276.2751%
A major challenge in cancer biology is to monitor and understand cancer metabolism in vivo with the goal of improved diagnosis and perhaps therapy. Because of the complexity of biochemical pathways, tracer methods are required for detecting specific enzyme-catalyzed reactions. Stable isotopes such as 13C or 15N with detection by nuclear magnetic resonance provide the necessary information about tissue biochemistry, but the crucial metabolites are present in low concentration and therefore are beyond the detection threshold of traditional magnetic resonance methods. A solution is to improve sensitivity by a factor of 10,000 or more by temporarily redistributing the populations of nuclear spins in a magnetic field, a process termed hyperpolarization. Although this effect is short-lived, hyperpolarized molecules can be generated in an aqueous solution and infused in vivo where metabolism generates products that can be imaged. This discovery lifts the primary constraint on magnetic resonance imaging for monitoring metabolism—poor sensitivity—while preserving the advantage of biochemical information. The purpose of this report was to briefly summarize the known abnormalities in cancer metabolism, the value and limitations of current imaging methods for metabolism...

Phase Difference Optimization of Dual-Wavelength Excitation for the CW-Photoacoustic-Based Noninvasive and Selective Investigation of Aqueous Solutions of Glucose

Camou, Serge
Fonte: MDPI Publicador: MDPI
Tipo: Artigo de Revista Científica
Publicado em 07/07/2015 EN
Relevância na Pesquisa
274.83902%
Towards the noninvasive and continuous monitoring of blood glucose levels, we chose the continuous-wave photoacoustic (CW-PA) technique and developed the optical power balance shift (OPBS) method. However, operating with optical wavelengths in the near-infrared (NIR) region ensures deep penetration inside human soft-tissue, but also leads to two serious issues: strong background level noise from water molecules in this wavelength range and small differences between the absorbance spectra of diluted compounds. To resolve them, the OPBS method relies on simultaneous optical excitation at two wavelengths for differential measurements. However, the first validation in vitro with calibrated aqueous solutions of glucose and albumin revealed strong dependence on the phase difference between the two lights sources. In this paper, we report a systematic investigation of this parameter, from PA-based measurements over a wide range of phase differences and an extensive characterization in the frequency domain. The process of maintaining the phase quadrature of the two optical signals is demonstrated in real time through an analysis of the PA signal and therefore does not require any additional equipment. Finally, a comparison of aqueous glucose solution characterizations at high concentration levels with the two methods was performed and consistent results were obtained.

Chemical recognition with broadband THz spectroscopy

Fischer, B.; Helm, H.; Jepsen, P.
Fonte: IEEE-Inst Electrical Electronics Engineers Inc Publicador: IEEE-Inst Electrical Electronics Engineers Inc
Tipo: Artigo de Revista Científica
Publicado em //2007 EN
Relevância na Pesquisa
274.91947%
THz science is developing rapidly in Europe as well as the rest of the world. There is a strong interest in the exploitation of optical technologies in the THz frequency range in virtually all fields of basic and applied sciences of physics, chemistry, biology as well as medicine. Commercial interest in this field has also been growing, spurred by the potential of THz tools in quality control and the biotechnology sector. We will review some contrast mechanisms, which form the basis for real-world applications of THz technology, in particular in the fields of applied chemistry and biotechnology. Whereas narrow bandwidth THz technology may become important for, e.g., real-time imaging at larger standoff distances, we will concentrate on broad bandwidth THz technologies for spectroscopic identification of various substances. It has recently been established that the 0.1-5 THz spectral range contains unique fingerprints of a very large number of crystalline materials, including explosives, illicit drugs as well as most other chemicals in powder form. Since many packaging materials are transparent to THz radiation this fundamental property of crystalline compounds allows remote (contact- free) sensing combined with chemical recognition. On the other hand...

Dynamics of Globular Proteins in Crowded Electrolyte Solutions. Studied by Neutron Scattering; Die Dynamik Globulärer Proteine in hochkonzentrierten elektrolytischen Lösungen.Untersucht mittels Neutronenstreuung

Hennig, Marcus
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Dissertação
EN
Relevância na Pesquisa
275.63775%
Proteins are molecular machines crucial for the function of living cells. Some proteins occur in the cell membrane, whilst others, in particular globular proteins, occur freely in the extra- and intracellular environment. These globular proteins carry out their biological function in an environment filled with both other molecules of a multitude of shapes and sizes and ions. Such a highly concentrated solution is termed “crowded”. Macromolecular crowding plays an important role for processes involving volume-change such as thermal unfolding and those including particularly protein diffusion as a limiting or driving factor. In the present thesis we investigate the dynamics and structural properties of a crowded aqueous solution of a model globular protein, namely bovine serum albumin, depending on several environmental parameters such as the protein volume fraction, the ionic strength of the solution, and the temperature including in particular the denaturing transition. The motivation is to understand proteins under biologically relevant conditions by, inter alia utilizing knowledge and methods established in soft matter macromolecular research. To this end, we employ cold neutron high-resolution backscattering spectroscopy to record quasi-elastic and elastic signals. Using this technique we retrieve the short- time self-diffusion coefficient and the total mean-squared displacement of the protein in solution. Moreover...

Certification of Equivalent Spherical Diameters of Silica Nanoparticles in Water - Certified Reference Material ERM®-FD100

BRAUN ADELINA; FRANKS KATRIN; KESTENS Vikram; ROEBBEN Gert; LAMBERTY MARIE ANDREE; LINSINGER Thomas
Fonte: Publications Office of the European Union Publicador: Publications Office of the European Union
Tipo: EUR - Scientific and Technical Research Reports Formato: Online
ENG
Relevância na Pesquisa
274.91947%
This report describes the certification of the equivalent spherical diameters of silica nanoparticles suspended in aqueous solution, Certified Reference Material (CRM) ERM-FD100®. The CRM has been certified by the European Commission, Joint Research Centre, Institute for Reference Materials and Measurements (IRMM), Geel, BE. The intended use of this ERM-FD100 is to check the performance of instruments and methods that determine the particle diameter of nanoparticles (particle size ranging from approximately 1 nm to approximately 100 nm) suspended in a liquid medium. It is available in 10 mL pre-scored amber glass ampoules containing approximately 9 mL of suspension. The CRM was prepared from commercially available colloidal silica (Koestrosol 1530, Chemiewerk Bad Koestritz GmbH, DE). Certification of the CRM included testing of the homogeneity and stability of the ampouled diluted raw material, as well as the characterisation using an intercomparison approach. The material has been certified for the equivalent diameter of the silica nanoparticles in aqueous suspension using different methods. Certified values are the cumulants dynamic light scattering (DLS) intensity-weighted harmonic mean particle diameter, the line-start centrifugal liquid sedimentation (CLS) intensity-based modal (Stokes) particle diameter...

Chromatographic methods for the separation and analysis of gold nanocrystals

Al-Somali, Ali M.
Fonte: Universidade Rice Publicador: Universidade Rice
ENG
Relevância na Pesquisa
276.2751%
With the ever growing applications of nanomaterials, fast, accurate and cost effective characterization methodologies are needed to ensure high quality materials and practical manufacturing. This problem is a challenging one as nanoparticle shape, size and size distribution are all important features which govern properties as diverse as sample melting point and chemical reactivity. New methods that provide key analytical information, along with a means of improving size and shape distributions would have substantial impact on this growing area. Chromatography is a technique which traditionally has been used to both provide analysis as well as separation of high valued added chemicals. Its applications in nanoscience are to date quite limited, and the objective of this thesis is to demonstrate that chromatographic techniques can be used to measure the dimensions of gold nanocrystals in solution as well as provide methods for physically separating complex distributions of particles. Recycling size exclusion chromatography (RSEC) has been employed to effect physical, base-line separation of subpopulations of spherical gold nanocrystals. This method can be easily applied on other nanocrystalline systems and is scalable to large production. Anisotropic gold nanocrystals...

Effect of calcium (II) and iron (II) on the precipitation of calcium carbonate and iron carbonate solid solutions and on scale inhibitors retention

Alsaiari, Hamad Amer
Fonte: Universidade Rice Publicador: Universidade Rice
ENG
Relevância na Pesquisa
275.35559%
Mineral scale formation is important to many areas of science and engineering, from drinking water treatment to oceanography to oil and gas production. In some cases mineral deposition is beneficial, as in water treatment for heavy metal or arsenic removal, and sometimes it is deleterious, as occurs in oil and gas production due to co-produced water. In either case, understanding the mechanisms of precipitation and inhibition is critical. Work in this thesis has focused on the impact of metal ions on mineral scale formation, and control. The results reveal that the addition of metal ions in the pill solution significantly improved the retention of scale inhibitors. Both BHPMP and DTPMP returns were significantly extended by the addition of Ca 2+ and Fe 2+ Also trace levels of Zn 2+ significantly enhanced the performance and retention of both BHPMP and DTPMP. The enhanced scale inhibition may be caused by a complex of metal ions with amine group of polyamino- polyphosphonates. It is known that the effectiveness of inhibitors varies upon the type of scale formed where it has been mentioned in the literature that common calcium carbonate inhibitors are not effective for preventing iron carbonate. Therefore, this work was also intended to investigate the impact of calcium and iron ions in the co-precipitation of iron-calcium carbonate solid solutions (Fe x Ca 1-x CO 3 ). Three different experimental methods were applied to investigate and predict the precipitation of Fe x Ca 1-x CO 3 : Free drift...

Hydrophobic and hydrophilic interactions in aqueous mixtures of alcohols at a hydrophobic surface

Ballal, Deepti; Chapman, Walter G.
Fonte: Universidade Rice Publicador: Universidade Rice
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
274.83902%
Aqueous solutions of alcohols are interesting because of their anomalous behavior that is believed to be due to the molecular structuring of water and alcohol around each other in solution. The interfacial structuring and properties are significant for application in alcohol purification processes and biomolecular structure. Here we study aqueous mixtures of short alcohols (methanol, ethanol, 1-propanol, and 2-propanol) at a hydrophobic surface using interfacial statistical associating fluid theory which is a perturbation density functional theory. The addition of a small amount of alcohol decreases the interfacial tension of water drastically. This trend in interfacial tension can be explained by the structure of water and alcohol next to the surface. The hydrophobic group of an added alcohol preferentially goes to the surface preserving the structure of water in the bulk. For a given bulk alcohol concentration, water mixed with the different alcohols has different interfacial tensions with propanol having a lower interfacial tension than methanol and ethanol. 2-propanol is not as effective in decreasing the interfacial tension as 1-propanol because it partitions poorly to the surface due to its larger excluded volume. But for a given surface alcohol mole fraction...

Evaluation of the antifungal activity by plant extracts against Colletotrichum gloeosporioides Penz

Silva,Polyanna Alves; Oliveira,Denilson Ferreira; Prado,Ney Robson Taironi do; Carvalho,Douglas Antônio de; Carvalho,Gilvane Aparecida de
Fonte: Editora da Universidade Federal de Lavras Publicador: Editora da Universidade Federal de Lavras
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/04/2008 EN
Relevância na Pesquisa
276.45844%
Aiming to develop more efficient and environmental friendly methods than those available to control Colletotrichum gloeosporioides Penz, which causes blister spot in coffee trees, a search for plants able to produce substances active against such pathogen was carried out. Thus, extracts of 48 plant species, collected at Alto Rio Grande region, in Minas Gerais, were prepared and submitted to in vitro assays with that fungus. The best results were obtained with the extracts prepared from Digitalis lanata Ehrh, Origanum manjorona L., Plantago lanceolata Hook. and Stevia rebaudiana (Bertoni) Bertoni, which inhibited C. gloeosporioides spores germination. After dilution of some active extracts with aqueous 1 % Tween 80 solution in a 1:2 or 1:3 ratio (extract:aqueous solution), their antifungal activity vanished. Some of the active extracts were also submitted to freeze drying and none of them presented any alteration in their antifungal activity. Concluding, several plants presented potential to be used in the search for new bioactive substances to control C. gloeosporioides, especially O. manjorona L., which inhibited 96 % of the fungus spores germination.

Molecular dynamics simulation of electrokinetic flow of an aqueous electrolyte solution in nanochannels

Yoshida, Hiroaki; Mizuno, Hideyuki; Kinjo, Tomoyuki; Washizu, Hitoshi; Barrat, Jean-Louis
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
276.45844%
Electrokinetic flows of an aqueous NaCl solution in nanochannels with negatively charged surfaces are studied using molecular dynamics (MD) simulations. The four transport coefficients that characterise the response to weak electric and pressure fields, namely the coefficients for the electrical current in response to the electric field ($M^{jj}$) and the pressure field ($M^{jm}$), and those for the mass flow in response to the same fields ($M^{mj}$ and $M^{mm}$), are obtained in the linear regime using a Green--Kubo approach. Nonequilibrium simulations with explicit external fields are also carried out, and the current and mass flows are directly obtained. The two methods exhibit good agreement even for large external field strengths, and Onsager's reciprocal relation ($M^{jm} = M^{mj}$) is numerically confirmed in both approaches. The influence of the surface charge density on the flow is also considered. The values of the transport coefficients are found to be smaller for larger surface charge density, because the counter-ions strongly bound near the channel surface interfere with the charge and mass flows. A reversal of the streaming current and of the reciprocal electro-osmotic flow, with a change of sign of $M^{mj}$ due to the excess co-ions...

Preparation of a clay-modified carbon paste electrode based on 2-thiazoline-2-thiol-hexadecylammonium sorption for the sensitive determination of mercury

Dias Filho, Newton L.; Carmo, Devaney R. do; Gessner, Fergus; Rosa, André H.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 1309-1316
ENG
Relevância na Pesquisa
276.45844%
A montmorillonite from Wyoming-USA was used to prepare an organo-clay complex, named 2-thiazoline-2-thiol-hexadecyltrimethylammonium-clay (TZT-HDTA-clay), for the purpose of the selective adsorption of the heavy metals ions and possible use as a chemically modified carbon paste electrode (CMCPE). Adsorption isotherms of Hg 2+, Pb 2+, Cd 2+, Cu 2+, and Zn 2+ from aqueous solutions as a function of the pH were studied at 298 K. Conditions for quantitative retention and elution were established for each metal by batch and column methods. The organo-clay complex was very selective to Hg(II) in aqueous solution in which other metals and ions were also present. The accumulation voltammetry of Hg(II) was studied at a carbon paste electrode chemically modified with this material. The mercury response was evaluated with respect to the pH, electrode composition, preconcentration time, mercury concentration, cleaning solution, possible interferences and other variables. A carbon paste electrode modified by TZT-HDTA-clay showed two peaks: one cathodic peak at about 0.0 V and an anodic peak at 0.25 V, scanning the potential from -0.2 to 0.8 V (0.05 M KNO 3 vs. Ag/AgCl). The anodic peak at 0.25 V presents excellent selectivity for Hg(II) ions in the presence of foreign ions. The detection limit was estimated as 0.1 μg L -1. The precision of determination was satisfactory for the respective concentration level. 2005 © The Japan Society for Analytical Chemistry.

Spectroscopic Determination of Optimal Hydration Time of Zircon Surface

Ordóñez-Regil,Eduardo; García-Rosales,Genoveva; García-González,Nidia
Fonte: Sociedad Química de México A.C. Publicador: Sociedad Química de México A.C.
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/09/2010 EN
Relevância na Pesquisa
276.45844%
When a mineral surface is immersed in an aqueous solution, it develops an electric charge produced by the amphoteric dissociation of hydroxyl groups created by the hydration of the solid surface. This is one influential surface property. The complete hydration process takes a time which is specific for each mineral species. The knowledge of the aqueous solution contact time for complete surface hydration is mandatory for further surface phenomena studies. This study deals with the optimal hydration time of the raw zircon (ZrSiO4) surface comparing the classical potentiometric titrations with a fluorescence spectroscopy technique. The latter is easy and reliable as it demands only one sample batch to determine the optimal time to ensure a total hydration of the zircon surface. The analytical results of neutron activation analysis (NAA) showed the presence of trace quantities of Dy3+, Eu3+ and Er³ in the bulk of zircon. The Dy3+ is structured in the zircon crystalline lattice and undergoes the same chemical reactions as zircon. Furthermore, the Dy3+ has a good fluorescent response whose intensity is enhanced by hydration molecules. The results show that, according to the potentiometric analysis, the hydration process for each batch (at least 8 sample batches) takes around 2 h...

Preparation and characterisation of tamarind 4-hydroxybenzoic acid (THBA) resin and its use in extraction of heavy metal ions from industrial wastewater

Singh,AV; Kumawat,Indraj Kumar
Fonte: Water SA Publicador: Water SA
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2012 EN
Relevância na Pesquisa
276.45844%
The adsorption of heavy metal cations, Pb(II), Cd(II), Cu(II), Zn(II) and Fe(II) from aqueous solution by newly-synthesized tamarind 4-hydroxybenzoic acid (THBA) resin was investigated. The resin was characterised on the basis of FTIR, elemental analysis, ion-exchange capacity and physico-chemical properties. The distribution coefficients (Kd) and percentage adsorption of metal ions on resin were determined by batch methods using atomic absorption spectrophotometry (AAS). The effect of experimental parameters, such as pH, treatment time, temperature, adsorbent dose, initial metal ion concentration and flow rate, on the removal of metal ions was also studied. THBA resin proved to be an effective adsorbent for the removal of different heavy metal ions from aqueous solution; removal efficiency followed the order: Fe(II) > Cu(II) > Zn(II) > Cd(II) > Pb(II). These results suggest that the cation exchange resin THBA holds great potential to remove cationic heavy metal species from industrial wastewater.

Using PXRD to investigate the crystallization of highly concentrated emulsions of NH4NO3

Ferg,E.E.; Masalova,I.
Fonte: South African Journal of Chemistry Publicador: South African Journal of Chemistry
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2011 EN
Relevância na Pesquisa
276.45844%
The process of crystallization of highly concentrated emulsions of ammonium nitrate can be studied using powder X-ray diffraction. The dispersed particles comprise a supercooled aqueous solution of the ammonium nitrate salt and are dispersed in a paraffin-based oil. This results in a thermodynamically unstable system that 'ages' with time resulting in changes in rheological properties and its phase composition where the collapse of the supercooled aqueous solution forms the crystallized salt. The crystallization processes of these emulsions are kinetically slow and can take up to a few months to crystallize completely. The general approach to this type of analysis is to determine the change in crystalline diffraction peak intensities relative to the halo due to the amorphous content. However, there are a number of problems associated with this method which are addressed by using Rietveld refinement methods which can take into account factors such as preferred orientation, crystallite size variations and mixtures of solid phases. The study showed that the ammonium nitrate emulsions kept at room temperature slowly crystallize predominantly to the room temperature solid ammonium nitrate phase IV. However, depending on the formulations used some samples showed crystallization to the high temperature ammonium nitrate phase II before changing to phase IV. The crystallization change could be modelled by the well-known JMAK kinetic relationship.