Quantum dots show great potential for use as spectral converters in solar cells, lighting applications, and biological imaging. These applications require precise control of quantum dot size to maximize performance. The quality, size, and fluorescence of quantum dots depend on parameters that are difficult to control using traditional batch synthesis processes. An alternative, high precision process was developed for the synthesis of cadmium-selenide quantum dots using a microfluidic reactor and fluorescence flow cell. The process required creating separate cadmium and selenium precursors that were then mixed in a nitrogen environment at 17°C. Using an NE-300® syringe pump, the solution was pumped through a microfluidic reactor submerged in a 240°C oil bath. The reactor then fed through a water quench bath at 25°C to terminate the nucleation and growth reaction. The fluorescence profiles of the quantum dot solutions were then characterized with an in-line fluorescence flow cell used in conjunction with an Ocean Optics® USB4000® spectrometer and a ThorLabs® LED UV light source. Flow rates through the reactor were varied from 0.05ml/min to 2ml/min. A central peak wavelength was registered in the fluorescence profiles for each flow rate. Monodisperse Cd-Se quantum dot solutions were synthesized across a broad spectrum of wavelengths ranging from 490nm to 620nm. An empirical relationship between flow rate and center wavelength was determined.

Für die Reinigungseffizienz ist die Kenntnis des Wirkzusammenhangs zwischen Schmutzbeschaffenheit und Reinigungsverhalten bedeutsam, da der Reinigungsbedarf von den Schmutzeigenschaften bestimmt wird. Bisher ist jedoch unzureichend dokumentiert, worauf der Reinigungsbedarf von kohäsiven Lebensmittelrückständen im immergierten System zurückgeführt werden kann. Anhand von Reinigungsuntersuchungen in einer Fließzelle werden die Auswirkungen physikochemischer Schmutzparameter (z.B. elektrisches Potential, energetischer Zustand, Molekülgröße) von Proteinen und Stärken getestet, um Empfehlungen für eine ressourceneffiziente Reinigungspraxis abzuleiten. Die Vielfalt der physikochemischen Eigenschaften von Lebensmittelinhaltsstoffen wird durch gezielte Modifizierung (physikalisch, chemisch, enzymatisch) simuliert und unter Anwendung verschiedener Analysetechniken charakterisiert. Die vorgestellte Durchflusszelle ermöglicht vergleichende Untersuchungen zum Abtragsverhalten an einer Vielzahl von Verschmutzungen in verschiedenen Messkonfigurationen. Es konnten Prozessbedingungen (Fließrate, Temperatur) identifiziert werden und die Genauigkeit der Fließmethode durch Vergleich von spektroskopisch und gravimetrisch ermittelten Abtragswerten gezeigt werden. Die Reinigungsuntersuchungen an Polymerverschmutzungen zeigten eine deutliche Differenzierung hinsichtlich Polymerart und pH der Modifizierung und können auf Lifschitz van der Waals- oder elektrostatische Wechselwirkungen zurückgeführt werden. Die Auswirkungen hitzeinduzierter Strukturveränderungen und der Proteinvernetzung waren nicht signifikant. Der Grad der enzymatischen Stärkehydrolyse wurde über rheologische Messungen und den DE-Wert charakterisiert, wobei mit zunehmender Inkubationsdauer die Reinigungseffizienz in ähnlicher Weise zur Löslichkeit steigt. Die Anwendung eines Enzymreinigers aus Diastase verbesserte signifikant die Reinigungseffizienz von Stärke- sowie Dextrinverschmutzungen und es wurde eine Modellvorstellung abgeleitet, nach der geringer kationisch geladene, niederenergetische und niedermolekulare Rückstände einen kleineren Reinigungsbedarf erfordern.

Modéliser les phénomènes de transport de solutés organiques en milieux poreux colonisés par des populations bactériennes se développant sous forme de biofilms est un domaine de recherche important pour un certain nombre d’applications environnementales, comme par exemple pour les méthodes de bioremédiation des sols et des eaux contaminés par des polluants organiques (biosparging, bio-barrières …). Les biofilms, qui sont composés principalement de bactéries et de substances polymériques extracellulaires, peuvent se développer sur les parois de grains d’un milieu poreux. Le métabolisme bactérien dégrade les solutés organiques et contribue ainsi à la diminution de la contamination. Le transport bio-réactif de composés organiques dans un milieu poreux incluant un biofilm est un problème fortement multi-échelle (depuis l’échelle de la bactérie jusqu’à l’échelle de l’aquifère) et fortement couplé (avec des phénomènes hydrodynamiques, physico-chimiques et biochimiques). Le soluté organique est transporté par convection et diffusion dans la phase fluide et diffuse dans la phase biofilm, où il est dégradé par le métabolisme bactérien. Le but de ce travail est de développer des modèles de transport bio-réactif définis à l’échelle de Darcy à partir des données disponibles à l’échelle du pore, en adoptant la méthode de changement d’échelle dite de prise de moyenne volumique. Dans le cas général, une telle approche conduit à un modèle macroscopique de transport à deux équations couplées (une équation par phase de transport). En considérant les relations entre les concentrations moyennées dans chaque phase, plusieurs régimes de transport permettant de dégénérer ce modèle en modèle à une seule équation peuvent être identifiés. L’hypothèse d’équilibre de masse local conduit à un tel modèle simplifié. En condition de non-équilibre, deux cas limites permettent également de développer des modèles de transport à une équation : le cas où le taux de biodégradation est contrôlé par le transfert de masse externe et le cas ou il est contrôlé par la cinétique de réaction. L’utilisation de ces quatre modèles implique la résolution numérique de problèmes de fermeture, afin d’évaluer les paramètres macroscopiques de transports (tenseur de dispersion, taux de dégradation …). Des calculs de coefficients effectifs ont été effectués dans différentes conditions de transport afin d’étudier leur comportement. Les résultats de ces modèles ont été comparés avec ceux obtenus par simulations directe à l’échelle microscopique pour une géométrie de pore bidimensionnelle stratifiée. À partir de ces comparaisons, les domaines de validité de chaque modèle ont été identifiés en termes de conditions hydrodynamique et biochimique de transport. (i.e. le nombre de Péclet et le nombre de Damköhler). Le développement d’un modèle expérimental de transport en milieux poreux incluant un biofilm a également été entamé, afin d’une part d’effectuer une validation expérimentale des modèles numériques préalablement développés et d’autre part de fournir un outil supplémentaire pour l’étude des phénomènes considérés / Modeling transport in porous media of organic chemical solute in presence of a bacterial population growing as biofilms is an important area of research for environmental applications, for example for remediation of groundwater contaminated by organic pollutants (biosparging, bio-barriers …). Biofilms, which are composed of bacteria and extracellular organic substances, grow on the pore walls of the porous medium. Bacteria degrade the organic solute by their metabolism and thus may contribute to pollution decrease. Bio-reactive transport of an organic solute in a porous medium including a biofilm phase is a strongly multi-scale (from the bacteria scale to the heterogeneity scale of the aquifer) and coupled (involving hydrodynamic, physicochemical and biochemical phenomena) process. The organic solute is transported by convection and diffusion in the fluid phase and diffuses into the biofilm phase, where it is degraded by bacterial metabolism. The goal of this work is to develop macroscopic models of bio-reactive transport at the Darcy-scale through volume averaging based on the data available at pore-scale. In the general case, the macroscopic system obtained by averaging pore-scale equations is a two coupled equations system (one equation for each phase), called two-equation model. By considering the relation between averaged concentration in the fluid phase and averaged concentration in the biofilm phase, several regimes of transport can be found which allow simplifying this system into a one equation system. The local mass equilibrium assumption leads to such a simplified model. When an equilibrium relationship between phases cannot be considered, a one equation model may though be developed if the biodegration rate is limited by external mass transfer or by the kinetics of bacterial metabolism. The use of these models implies the numerical solving of closure problems, in order to set up the values of the macroscopic transport parameters (dispersion tensor, interfacial flux …). Computations of these effective coefficients have been performed in different situations of mass transport in porous medium in order to study their behaviour. The results of these models have then been compared with direct simulations performed on a simplified geometry representative of a two-dimensional porous medium including a biofilm phase. Based on these comparisons, the validity domain of this model has been identified in terms of hydrodynamic and biochemical conditions of transport (i.e. the Péclet number and the Damköhler number). The set up of an experimental model of transport in a porous media including a biofilm phase has also been started, in order to make experimental validations of the previously developed numerical models and to build up an additional tool to study the considered phenomena

No description available.

The main aim of the work reported is the design of proof-of-concept of at point-of-use hydrogen peroxide electrogeneration from air. The experimental work discussed within this thesis explores five major areas: the kinetics of electrocatalysis, ion-pairing, change of solvent media, the electrode surface modication by a redox mediator, and the electrochemical reduction of oxygen within enhanced mass transport systems. The electrocatalytic rates and mass transport of two oxygen reduction redox meditors, viz. anthraquinone and methyl viologen, are studied in aqueous solutions. The investigation is facilitated through the use of a boron-doped diamond electrode, allowing the catalytic response to be clearly delineated from that of the direct oxygen reduction process. The use of simulation software is highlighted in combination with experimental voltammograms to extract kinetic data. Specifically, the voltammetric features, such as the `reverse' peak and the `split waves', are given particular attention. Consequently, it is possible to deconvolute the electrocatalytic reaction mechanisms. The reactivity of the viologen radical cation is comparable to the semiquinone radical anion in aqueous solution ((4.8~6)x10^9 M^-1 s^-1), but over a far wider pH range (pH 2.5 - pH 8.5). The change of local proton concentration, and sequential electron transfers play key roles here. Moreover, the reduced reactivity of semiquinone is observed upon formation of ion-pairs with tetrabutylammonium cations in alkaline solutions. The electro-reduction of oxygen and its mediated pathways are also investigated in non-aqueous media; in particular the thermodynamics, the kinetics, and mass transport involved in these processes. Through a variable temperature study in electrolytic acetonitrile solution, the oxygen dissolution is quantitatively shown to be an endothermic process. Moreover, the diffusion coeficients and concentration of oxygen upon change of acetonitrile mole fraction is also explored in water-acetonitrile mixtures. The rates of bimolecular reactions are extracted from simulation programs, involving semiquinone in anhydrous acetonitrile and viologen radical cation in ethanol, and show a 3 - 4 orders of magnitude reduction compared to that in aqueous solution. Although the solubility of oxygen is ca. 6 - 8 times larger in non-aqueous solvents, the much reduced homogeneous rates limit the electrogeneration of hydrogen peroxide in pure organic media. Novel surface modification methodologies for graphitic surfaces with covalently attached anthraquinonyl groups are studied and characterised. The anthraquinonyl-modified carbon surfaces show much reduced overpotentials required for oxygen reduction. In the final chapter, utilising the new surface modification methodology and novel designs, two gravity-feed flow cells for electrochemical reduction of oxygen in aqueous solutions are proposed and characterised, one based upon the tubular electrode geometry. The other exhibits much enhanced current conversion by using a porous reticulated vitreous carbon electrode. The latter may provide a prototype hydrodynamic system to produce dilute hydrogen peroxide solution at point-of-use.

Esta tese tem como foco o desenvolvimento de procedimentos analíticos automáticos, visando as determinações fotométricas de vanádio e de estanho em águas e em alimentos empregando o processo de multicomutação em fluxo. Um microcontrolador da família PIC e um programa escrito em linguagem Visual Basic 6.0 foram empregados para controle dos dispositivos e aquisição de dados. A unidade de detecção foi construída empregando LED de alto brilho e celas de fluxo com longo caminho óptico (50-200 mm) para ganho em sensibilidade. O módulo de análises, empregando bombas solenoide como propulsores de fluido e o fotômetro foram integrados, formando uma unidade compacta. A determinação de vanádio em águas, mineral e de rio, foi baseada na redução do V(V) à V(IV) com ácido ascórbico e posterior complexação com Eriocromo Cianina R (ECR). Empregando uma cela de 150 mm, o sistema apresentou resposta linear de 0,02 a 1,00 mg L-1, limite de detecção estimado em 13 ?g L-1, coeficiente de variação de 0,87% (n=10) e frequência analítica de 47 determinações por hora. Recuperações entre 89 e 109% foram obtidas para adição de V(V) nas amostras de águas. O procedimento para a determinação de estanho em alimentos foi desenvolvido empregando bomba de multi-seringa como unidade de propulsão de fluidos, cela de fluxo com caminho óptico de 200 mm e parada de fluxo de 50 s. Baseado na reação do Sn(IV) com o violeta de pirocatecol (PCV) na presença de surfactantes, o sistema apresentou resposta linear de 0,10 a 1,25 mg L-1, limite de detecção estimado em 0,04 mg L-1, coeficiente de variação de 1,30% (n=10) e frequência analítica de 49 determinações por hora. Recuperações entre 95 e 115% foram obtidas com a adição de Sn(IV) às amostras de alimentos. / Automatic analytical procedures for photometric determinations of vanadium in water and tin in foods were developed using the multicommutation flow analysis process. A microcontroller of the PIC family and a software written in Visual Basic 6.0 language were used for devices control and data acquisition. Detection unit was designed to use high brightness LED and long optical pathlength flow cells (50-200 mm) to improve sensitivity. The flow analysis module using solenoid mini-pumps as fluid propelling devices and the photometer were integrated in order to form a compact unit. The determination of vanadium in mineral and river waters was based on the reduction of V(V) to V(IV) with ascorbic acid and subsequent complexation with Eriochrome Cyanine R (ECR). Employing flow cell of 150 mm, the system presented linear response between 0.02 and 1.00 mg L-1, detection limit of 13 ?g L-1, variation coefficient of 0.87% (n=10) and sampling throughput of 47 determinations per hour. Recoveries between 89 and 109% were attained for vanadium spiked to mineral and river water. The procedure for determination of tin in foods was development employing a multi-syringe pump as fluid propelling device, a flow cell with optical pathlength of 200 mm and stop flow of 50 s. The procedure was based on the reaction of Sn(IV) with pyrocatechol violet (PCV) in the presence of surfactants, presented linear response between 0.10 and 1.25 mg L-1, detection limit of 0.04 mg L-1, variation coefficient of 1.30% (n=10) and sampling throughput of 49 determination per hour. Recoveries between 95 and 115% were attained for tin spiked samples

Esta tese tem como foco o desenvolvimento de procedimentos analíticos automáticos, visando as determinações fotométricas de vanádio e de estanho em águas e em alimentos empregando o processo de multicomutação em fluxo. Um microcontrolador da família PIC e um programa escrito em linguagem Visual Basic 6.0 foram empregados para controle dos dispositivos e aquisição de dados. A unidade de detecção foi construída empregando LED de alto brilho e celas de fluxo com longo caminho óptico (50-200 mm) para ganho em sensibilidade. O módulo de análises, empregando bombas solenoide como propulsores de fluido e o fotômetro foram integrados, formando uma unidade compacta. A determinação de vanádio em águas, mineral e de rio, foi baseada na redução do V(V) à V(IV) com ácido ascórbico e posterior complexação com Eriocromo Cianina R (ECR). Empregando uma cela de 150 mm, o sistema apresentou resposta linear de 0,02 a 1,00 mg L-1, limite de detecção estimado em 13 ?g L-1, coeficiente de variação de 0,87% (n=10) e frequência analítica de 47 determinações por hora. Recuperações entre 89 e 109% foram obtidas para adição de V(V) nas amostras de águas. O procedimento para a determinação de estanho em alimentos foi desenvolvido empregando bomba de multi-seringa como unidade de propulsão de fluidos, cela de fluxo com caminho óptico de 200 mm e parada de fluxo de 50 s. Baseado na reação do Sn(IV) com o violeta de pirocatecol (PCV) na presença de surfactantes, o sistema apresentou resposta linear de 0,10 a 1,25 mg L-1, limite de detecção estimado em 0,04 mg L-1, coeficiente de variação de 1,30% (n=10) e frequência analítica de 49 determinações por hora. Recuperações entre 95 e 115% foram obtidas com a adição de Sn(IV) às amostras de alimentos. / Automatic analytical procedures for photometric determinations of vanadium in water and tin in foods were developed using the multicommutation flow analysis process. A microcontroller of the PIC family and a software written in Visual Basic 6.0 language were used for devices control and data acquisition. Detection unit was designed to use high brightness LED and long optical pathlength flow cells (50-200 mm) to improve sensitivity. The flow analysis module using solenoid mini-pumps as fluid propelling devices and the photometer were integrated in order to form a compact unit. The determination of vanadium in mineral and river waters was based on the reduction of V(V) to V(IV) with ascorbic acid and subsequent complexation with Eriochrome Cyanine R (ECR). Employing flow cell of 150 mm, the system presented linear response between 0.02 and 1.00 mg L-1, detection limit of 13 ?g L-1, variation coefficient of 0.87% (n=10) and sampling throughput of 47 determinations per hour. Recoveries between 89 and 109% were attained for vanadium spiked to mineral and river water. The procedure for determination of tin in foods was development employing a multi-syringe pump as fluid propelling device, a flow cell with optical pathlength of 200 mm and stop flow of 50 s. The procedure was based on the reaction of Sn(IV) with pyrocatechol violet (PCV) in the presence of surfactants, presented linear response between 0.10 and 1.25 mg L-1, detection limit of 0.04 mg L-1, variation coefficient of 1.30% (n=10) and sampling throughput of 49 determination per hour. Recoveries between 95 and 115% were attained for tin spiked samples

Für die Reinigungseffizienz ist die Kenntnis des Wirkzusammenhangs zwischen Schmutzbeschaffenheit und Reinigungsverhalten bedeutsam, da der Reinigungsbedarf von den Schmutzeigenschaften bestimmt wird. Bisher ist jedoch unzureichend dokumentiert, worauf der Reinigungsbedarf von kohäsiven Lebensmittelrückständen im immergierten System zurückgeführt werden kann. Anhand von Reinigungsuntersuchungen in einer Fließzelle werden die Auswirkungen physikochemischer Schmutzparameter (z.B. elektrisches Potential, energetischer Zustand, Molekülgröße) von Proteinen und Stärken getestet, um Empfehlungen für eine ressourceneffiziente Reinigungspraxis abzuleiten. Die Vielfalt der physikochemischen Eigenschaften von Lebensmittelinhaltsstoffen wird durch gezielte Modifizierung (physikalisch, chemisch, enzymatisch) simuliert und unter Anwendung verschiedener Analysetechniken charakterisiert. Die vorgestellte Durchflusszelle ermöglicht vergleichende Untersuchungen zum Abtragsverhalten an einer Vielzahl von Verschmutzungen in verschiedenen Messkonfigurationen. Es konnten Prozessbedingungen (Fließrate, Temperatur) identifiziert werden und die Genauigkeit der Fließmethode durch Vergleich von spektroskopisch und gravimetrisch ermittelten Abtragswerten gezeigt werden. Die Reinigungsuntersuchungen an Polymerverschmutzungen zeigten eine deutliche Differenzierung hinsichtlich Polymerart und pH der Modifizierung und können auf Lifschitz van der Waals- oder elektrostatische Wechselwirkungen zurückgeführt werden. Die Auswirkungen hitzeinduzierter Strukturveränderungen und der Proteinvernetzung waren nicht signifikant. Der Grad der enzymatischen Stärkehydrolyse wurde über rheologische Messungen und den DE-Wert charakterisiert, wobei mit zunehmender Inkubationsdauer die Reinigungseffizienz in ähnlicher Weise zur Löslichkeit steigt. Die Anwendung eines Enzymreinigers aus Diastase verbesserte signifikant die Reinigungseffizienz von Stärke- sowie Dextrinverschmutzungen und es wurde eine Modellvorstellung abgeleitet, nach der geringer kationisch geladene, niederenergetische und niedermolekulare Rückstände einen kleineren Reinigungsbedarf erfordern.

No description available.

Ce travail porte sur la destruction quantitative et d'une manière respectueuse pour l'environnement de solutions concentrées en nitrates par deux procédés différents. Dans les deux cas, la solution de nitrates est d'abord réduite électrochimiquement en ammoniums sur électrode de cuivre avec une sélectivité élevée, ceci quel que soit le pH de la solution d'électrolyse. Dans le premier procédé, l'ammonium est ensuite oxydé en azote à l'aide d'ions hypochlorites générés électrochimiquement. Une excellente sélectivité réactionnelle en azote de 91,5% est obtenue avec des rendements chimiques et faradiques élevés pour la réaction de réduction des nitrates en azote, accompagnée d'une consommation énergétique basse. Le deuxième procédé est un couplage électrochimique / biologique où les solutions d'ammonium seront utilisées comme substrat azoté pour produire du biohydrogène via des boues traitées thermiquement. Une consommation complète de la solution d'ammonium provenant de la réduction des nitrates est obtenue. Un rendement maximal de 0,35 mole H2/mole de glucose est atteint en utilisant des boues activées collectées d'un bassin d'aération contre 1,1 mole H2/mole de glucose produit dans le cas des boues prélevées d'un digesteur anaérobie. / This work deals with the quantitative and environmentally friendly destruction of concentrated nitrates solutions using two different processes. In both cases, the nitrates solution was firstly reduced electrochemically into ammonium on a porous copper electrode. Whatever the initial pH of the electrolytic solution, a high ammonium selectivity was obtained. In the first process, the ammonium was subsequently oxidized to nitrogen gas by hypochlorite ions generated electrochemically. An excellent selectivity of 91.5% with high current efficiency and high chemical yield toward the nitrogen formation was recorded, with a low power consumption. The second method is an electrochemical / biological coupling process where the obtained ammonium solution will be used as a nitrogen source to produce biohydrogen (H2) via heat-treated sludge cultures. A complete assimilation of the ammonium solution resulting from the electroreduction of nitrate was obtained. A maximum hydrogen yield of 0.35 mol H2/mole glucose was achieved using activated sludge collected from an aeration tank versus 1.1 mole H2/mole glucose produced in the case of sludge taken from an anaerobic digester.