Détermination de la spéciation du samarium dans l'environnement

Les éléments de terres rares (REEs) sont de plus en plus utilisés dans une multitude d’applications, notamment la fabrication d’aimants, de batteries rechargeables et les écrans de téléviseurs. Ils sont pour la plupart des métaux trivalents peu solubles dans les eaux naturelles. Comme pour les métaux divalents, le risque écologique des REEs est très probablement étroitement lié à leurs spéciations chimiques. Cependant, le comportement du samarium (Sm) dans les matrices environnementales est très peu connu et il n'existe actuellement aucune technique pour évaluer sa spéciation chimique. Dans cette optique, la technique d'échange d'ions (IET) sur la résine Dowex a été optimisée pour mesurer le samarium libre en solution. Les temps d'équilibre ont d'abord été déterminés pour des solutions tamponnées de samarium (Sm 6,7x10-8 M ; MES 1,0 mM M ; pH 6,0) en présence du nitrate de sodium (de 0,01M à 0,5 M). Pour ces diverses forces ioniques, l’équilibre thermodynamique n’est atteint que pour NaNO3 0,5M. Un autre mode d’utilisation de la résine (mode dynamique) a donc été développé pour tenir compte des conditions environnementales et évaluer efficacement le samarium libre. Les impacts des ligands organiques tels le NTA, l’EDTA, le citrate, l’acide malique et l’acide fulvique Suwannee River Standard I (SRFA) ont été étudiés par l’IET en mode dynamique. Une grande corrélation a été trouvée plus entre les taux d’accumulation de samarium sur la résine d’échange pour différents rapports NTA : Sm, EDTA : Sm, SRFA : Sm et le samarium libre. Par contre, aucune corrélation significative n’a été observée pour les ligands citrate et acide malique compte tenu des complexes qu’ils forment avec le samarium et qui s’adsorbent aussi sur la résine Dowex. Les concentrations Sm3+ mesurées par la technique IET ont été fortement corrélées avec celles prédites par le modèle WHAM 7.0 en utilisant la constante de stabilité obtenue par titration de SRFA par extinction de la fluorescence. Par ailleurs, la formation de colloïdes de samarium en fonction du pH influe grandement sur la détermination du samarium libre et doit être prise en compte dans la spéciation du samarium. L'IET assisté par des techniques auxiliaires comme le dosage par extinction de la fluorescence et le SP-ICPMS pourrait être une technique utile pour évaluer les concentrations de Sm biodisponible dans les eaux naturelles.

Preparation and characterization of grafted nonwoven membranes for bioseparations

Protein purification plays a crucial role in biotechnology and biomanufacturing, where downstream unit operations account for 40%-80% of the overall costs. To overcome this issue, companies strive to simplify the separation process by reducing the number of steps and replacing expensive separation devices. In this context, commercially available polybutylene terephthalate (PBT) melt-blown nonwoven membranes have been developed as a novel disposable membrane chromatography support. The PBT nonwoven membrane is able to capture products and reduce contaminants by ion exchange chromatography. The PBT nonwoven membrane was modified by grafting a poly(glycidyl methacrylate) (GMA) layer by either photo-induced graft polymerization or heat induced graft polymerization. The epoxy groups of GMA monomer were subsequently converted into cation and anion exchangers by reaction with either sulfonic acid groups or diethylamine (DEA), respectively. Several parameters of the procedure were studied, especially the effect of (i) % weight gain and (ii) ligand density on the static protein binding capacity. Bovine Serum Albumin (BSA) and human Immunoglobulin G (hIgG) were utilized as model proteins in the anion and cation exchange studies. The performance of ion exchange PBT nonwovens by HIG was evaluated under flow conditions. The anion- and cation- exchange HIG PBT nonwovens were evaluated for their ability to selectively adsorb and elute BSA or hIgG from a mixture of proteins. Cation exchange nonwovens were not able to reach a good protein separation, whereas anion exchange HIG nonwovens were able to absorb and elute BSA with very high value of purity and yield, in only one step of purification.

Détermination de la spéciation du samarium dans l'environnement

Les éléments de terres rares (REEs) sont de plus en plus utilisés dans une multitude d’applications, notamment la fabrication d’aimants, de batteries rechargeables et les écrans de téléviseurs. Ils sont pour la plupart des métaux trivalents peu solubles dans les eaux naturelles. Comme pour les métaux divalents, le risque écologique des REEs est très probablement étroitement lié à leurs spéciations chimiques. Cependant, le comportement du samarium (Sm) dans les matrices environnementales est très peu connu et il n'existe actuellement aucune technique pour évaluer sa spéciation chimique. Dans cette optique, la technique d'échange d'ions (IET) sur la résine Dowex a été optimisée pour mesurer le samarium libre en solution. Les temps d'équilibre ont d'abord été déterminés pour des solutions tamponnées de samarium (Sm 6,7x10-8 M ; MES 1,0 mM M ; pH 6,0) en présence du nitrate de sodium (de 0,01M à 0,5 M). Pour ces diverses forces ioniques, l’équilibre thermodynamique n’est atteint que pour NaNO3 0,5M. Un autre mode d’utilisation de la résine (mode dynamique) a donc été développé pour tenir compte des conditions environnementales et évaluer efficacement le samarium libre. Les impacts des ligands organiques tels le NTA, l’EDTA, le citrate, l’acide malique et l’acide fulvique Suwannee River Standard I (SRFA) ont été étudiés par l’IET en mode dynamique. Une grande corrélation a été trouvée plus entre les taux d’accumulation de samarium sur la résine d’échange pour différents rapports NTA : Sm, EDTA : Sm, SRFA : Sm et le samarium libre. Par contre, aucune corrélation significative n’a été observée pour les ligands citrate et acide malique compte tenu des complexes qu’ils forment avec le samarium et qui s’adsorbent aussi sur la résine Dowex. Les concentrations Sm3+ mesurées par la technique IET ont été fortement corrélées avec celles prédites par le modèle WHAM 7.0 en utilisant la constante de stabilité obtenue par titration de SRFA par extinction de la fluorescence. Par ailleurs, la formation de colloïdes de samarium en fonction du pH influe grandement sur la détermination du samarium libre et doit être prise en compte dans la spéciation du samarium. L'IET assisté par des techniques auxiliaires comme le dosage par extinction de la fluorescence et le SP-ICPMS pourrait être une technique utile pour évaluer les concentrations de Sm biodisponible dans les eaux naturelles.

Nitrogen use efficiency and optimization of nitrogen fertilizer application for stable yields and high quality of cereals grown in conservation agriculture

In most agroecosystems, nitrogen (N) is the most important nutrient limiting plant growth. One management strategy that affects N cycling and N use efficiency (NUE) is conservation agriculture (CA), an agricultural system based on a combination of minimum tillage, crop residue retention and crop rotation. Available results on the optimization of NUE in CA are inconsistent and studies that cover all three components of CA are scarce. Presently, CA is promoted in the Yaqui Valley in Northern Mexico, the country´s major wheat-producing area in which from 1968 to 1995, fertilizer application rates for the cultivation of irrigated durum wheat (Triticum durum L.) at 6 t ha-1 increased from 80 to 250 kg ha-1, demonstrating the high intensification potential in this region. Given major knowledge gaps on N availability in CA this thesis summarizes the current knowledge of N management in CA and provides insights in the effects of tillage practice, residue management and crop rotation on wheat grain quality and N cycling. Major aims of the study were to identify N fertilizer application strategies that improve N use efficiency and reduce N immobilization in CA with the ultimate goal to stabilize cereal yields, maintain grain quality, minimize N losses into the environment and reduce farmers’ input costs. Soil physical and chemical properties in CA were measured and compared with those in conventional systems and permanent beds with residue burning focusing on their relationship to plant N uptake and N cycling in the soil and how they are affected by tillage and N fertilizer timing, method and doses. For N fertilizer management, we analyzed how placement, time and amount of N fertilizer influenced yield and quality parameters of durum and bread wheat in CA systems. Overall, grain quality parameters, in particular grain protein concentration decreased with zero-tillage and increasing amount of residues left on the field compared with conventional systems. The second part of the dissertation provides an overview of applied methodologies to measure NUE and its components. We evaluated the methodology of ion exchange resin cartridges under irrigated, intensive agricultural cropping systems on Vertisols to measure nitrate leaching losses which through drainage channels ultimately end up in the Sea of Cortez where they lead to algae blooming. A throughout analysis of N inputs and outputs was conducted to calculate N balances in three different tillage-straw systems. As fertilizer inputs are high, N balances were positive in all treatments indicating the risk of N leaching or volatilization during or in subsequent cropping seasons and during heavy rain fall in summer. Contrary to common belief, we did not find negative effects of residue burning on soil nutrient status, yield or N uptake. A labeled fertilizer experiment with urea 15N was implemented in micro-plots to measure N fertilizer recovery and the effects of residual fertilizer N in the soil from summer maize on the following winter crop wheat. Obtained N fertilizer recovery rates for maize grain were with an average of 11% very low for all treatments.

Stability of clay-based catalysts in contact with water vapour

The search for cleaner processes is one of the major challenges in modern chemical industries. In this context clay derived materials are environmentally friendly catalysts that can be easily tailored to optimize their catalytic activity for a precise reaction of interest. Furthermore, clay-based catalysts can be easily separated, recovered and reused and their versatility, low cost, high catalytic activity and/or selectivity render them very attractive materials. Considering that the stability towards water vapour is a crucial aspect for catalytic performance and reuse of the catalysts, we present a study of the pore structure stability, in the presence of water vapour, of clay catalysts prepared by acid activation with HCl solutions and ion-exchange with sodium, aluminium and iron, from a natural clay collected at Serra de Dentro (Porto Santo Island, Portugal) [1]. For elucidating the influence of water vapour on the pore structure stability, water vapour adsorption- -desorption isotherm, at 298 K, was determined on each sample by gravimetric method as well as n-pentane adsorption−desorption isotherms, at 298 K, which were determined before and after the corresponding water adsorption-desorption isotherms. Prior to the measurements, the samples were outgassed during 5 h at 473 K and the adsorptives were outgassed by repeated freeze–thaw cycles. The results to be reported in the communication allow us to state that, upon contact with water vapour, the less acid activated catalysts suffered some reduction in pore volume reflecting changes in the pore structure, while the more acid activated catalysts and those prepared by ion-exchange presented excellent stability upon one cycle of water vapour adsorption-desorption. The results are corroborated by nitrogen adsorption-desorption isotherms determined, at 77 K, before and after the water and n-pentane adsorption-desorption measurements.

Recent Developments in Wine Tartaric Stabilization

Tartrate precipitation is still a relevant subject in Enology, being one of the most common problems of wine physical-chemical instability. Potassium bitartrate and calcium tartrate precipitations are undesirable phenomena which can occur in bottled wines, especially when these are stored at low temperatures. The occurrence of tartrate salt crystals (potassium hydrogen tartrate – KHT and calcium tartrate – CaT) in bottles has severe consequences in the final aspect of the wine and therefore on the consumer’s acceptance, making tartrate wine stabilization virtually mandatory before bottling. Currently, several solutions to prevent this haze are available: subtractive methods including the conventional cold treatments that promote the cristalization of KHT, removal of potassium and calcium ions either by electrodialysis or ion exchange resins; and additive methods such as the addition of carboxymethylcellulose, mannoproteins or metatartaric acid. For monitoring the KHT stability, several analytical methods have been developed based on conductivity evaluation, namely the mini-contact test and the saturation temperature measurements (TS). These methods will also be revisited, aiming to raise awareness of their utility as tools in quality control of wines. This review addresses tartrate precipitation subject and the most recent preventive solutions available, pointing out the advantages and drawbacks of each one, and its impact on the final characteristics of the wine.

Tailoring of ion species composition in complex plasmas with charge exchange collisions

A generic approach towards tailoring of ion species composition in reactive plasmas used for nanofabrication of various functional nanofilms and nanoassemblies, based on a simplified model of a parallel-plate rf discharge, is proposed. The model includes an idealized reactive plasma containing two neutral and two ionic species interacting via charge exchange collisions in the presence of a microdispersed solid component. It is shown that the number densities of the desired ionic species can be efficiently managed by adjusting the dilution of the working gas in a buffer gas, rates of electron impact ionization, losses of plasma species on the discharge walls, and surfaces of fine particles, charge exchange rates, and efficiency of three-body recombination processes in the plasma bulk. The results are relevant to the plasma-aided nanomanufacturing of ordered patterns of carbon nanotip and nanopyramid microemitters.

Relation between Stabilization Energy, Crystal Field Coefficient and the Magnetic Exchange Interaction for Tb3+ Ion

Based on a single ion model, Hamiltonian of the simplest form about magnetocrystalline anisotropy for Tb3+ ion was solved by using the numerical method. The relation between the stabilization energy, crystal field coefficient B-2(0) and the magnetic exchange interaction was studied as temperature approaches to 0 K. The results show that the stabilization energy contributed by Tb3+ is linear with crystal field coefficient B-2(0) approximately, but it is insensitive to the change of magnetic exchange interaction for the strong magnetic substances such as TbCo5, Tb2Co17 and Tb2Fe14B compounds.

H/D exchange reaction of cyclopropane derivatives in the ion system of CD3OD

The fragmentation properties of the product ions [M + 1](+), [M + 2](+) and [M + 3](+) formed by ion-molecule reaction of four cyclopropane derivatives with the ion system of CD3OD were investigated by using collision-induced dissocation technique. The experiment results indicated that the product ions were produced via the H/D exchange reaction between reactants and reactive reagent ions of CD3OD. There are two exchangable hydrogen atoms on the ring of compounds 1 and 2, and only one for compound 3 and 4.

The transfer of chloride ion across an anion exchange membrane

The transfer of chloride ions into a low resistance anion exchange membrane (AEM) was investigated by cyclic voltammetry (CV) and electrochemical impedance spectra. In all cases, concentration polarization of Cl- ions is exterior to the membrane. It controls the flux and produces the limiting currents: either steady state or transient (peak type) current. In CV experiments, when the size of the holes in the membrane was much smaller than the distance between membrane holes, the Cl- anion transfer showed steady state voltammetric behavior. Each hole in the membrane can be regarded as a microelectrode and the membrane was equivalent to a microelectrode array in this condition. When the hole in the membrane was large or the distance between membrane holes was small, the CV curve of the Cl- anion transfer across the membrane showed a peak shape, which was attributed to linear diffusion. In AC impedance measurement, the impedance spectrum of the membrane system was composed of two semicircles at low DC bias, corresponding to the bulk characteristics of the membrane and the kinetic process of ion transfer, respectively. The bulk membrane resistance increases with increasing DC bias and only one semicircle was observed at higher DC bias. The parameters related to kinetic and membrane properties were discussed.

Dissociative charge exchange and ionization of O-2 by fast H+ and O+ ions: Energetic ion interactions in Europa's oxygen atmosphere and neutral torus

Measurements of electron capture and ionization of O-2 molecules in collisions with H+ and O+ ions have been made over an energy range 10 - 100 keV. Cross sections for dissociative and nondissociative interactions have been separately determined using coincidence techniques. Nondissociative channels leading to O-2(+) product formation are shown to be dominant for both the H+ and the O+ projectiles in the capture collisions and only for the H+ projectiles in the ionization collisions. Dissociative channels are dominant for ionizing collisions involving O+ projectiles. The energy distributions of the O+ fragment products from collisions involving H+ and O+ have also been measured for the first time using time-of-flight methods, and the results are compared with those from other related studies. These measurements have been used to describe the interaction of the energetic ions trapped in Jupiter's magnetosphere with the very thin oxygen atmosphere of the icy satellite Europa. It is shown that the ionization of oxygen molecules is dominated by charge exchange plus ion impact ionization processes rather than photoionization. In addition, dissociation is predominately induced through excitation of electrons into high-lying repulsive energy states ( electronically) rather than arising from momentum transfer from knock-on collisions between colliding nuclei, which are the only processes included in current models. Future modeling will need to include both these processes.

Monitoring charged particles in indoor air using a neutral cluster and air ion spectrometer

While there are sources of ions both outdoors and indoors, ventilation systems can introduce as well as remove ions from the air. As a result, indoor ion concentrations are not directly related to air exchange rates in buildings. In this study, we attempt to relate these quantities with the view of understanding how charged particles may be introduced into indoor spaces.