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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Preparation and characterization of a metal hydride electrode / Tillverkning och karakterisering av en metallhydridelektrod

Tammela, Petter January 2012 (has links)
Metal hydrides are used as anode material in nickel metal hydride batteries and are of particular interest because of the potential to be a part of energy systems completely involving renewable sources (e.g. solar power, wind power etc.). Preparation and electrochemical characterization of metal hydride electrodes have not previously been performed at the Department of Chemistry – Ångström Laboratory. Two basic techniques that are desired to be used in the characterization are cyclic voltammetry and chronopotentiometry. This thesis work is aimed at preparation and electrochemical characterization of a metal hydride electrode and, as a complement, study the electrode with X-ray diffraction. LaNi3.55Co0.75Mn0.4Al0.3, a standard material for metal hydride electrodes previously studied by Khaldi et al. was chosen, to ensure that electrochemical absorption of hydrogen was possible, and to be able to compare electrochemical results [1-3]. LaNi3.55Co0.75Mn0.4Al0.3 was synthesized with arc melting, with additional annealing at 900˚C for five days, ground in a cemented carbide ball mill and sieved to less than 56 µm. Electrodes were prepared containing 90 wt.-% of LaNi3.55Co0.75Mn0.4Al0.3 powder, 5 wt.-% of polytetrafluoroethylene and 5 wt.-% of carbon black. The hydrogen absorption and desorption capabilities of the electrode were studied electrochemically with cyclic voltammetry and chronopotentiometry, and the structural changes associated with absorption of hydrogen was studied with X-ray diffraction. The capacity increased, probably from activation of the material, during initial cycling up to the maximum capacity of 294 mAh/g, obtained after 9 cycles, followed by a small decrease, probably caused by corrosion and passivation of the material, in capacity of the remaining 11 cycles. Activation of the material causes the charge and the discharge potential to shift to a more positive and a more negative value, respectively. The final values for the charge potential and the discharge potential were -841mV and -945 mV vs. Hg/HgO, respectively, after 16 cycles. Khalid et al. [1-3]reported a maximum capacity of 300 mAh/g, a charge potential of about -960 mV and a discharge potential of about -840 mV after 16 cycles the results obtained in this study are considered to be in good agreement with those reported. X-ray diffraction of the electrodes revealed, as expected, a cell volume change of the charged electrode compared to the discharged electrode. The change in cell volume corresponds to an estimated capacity of 303 mAh/g, which is very close to the, above mentioned, electrochemically obtained maximum capacity of 294 mAh/g.
2

Determinacao do coeficiente de difusao do acido oxalico em meio sulfurico pelos metodos da cronopotenciometria e do diafragma poroso

CHIERICE, GILBERTO O. 09 October 2014 (has links)
Made available in DSpace on 2014-10-09T12:23:45Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:57:00Z (GMT). No. of bitstreams: 1 00886.pdf: 3186592 bytes, checksum: 02aa449d230c78ebeaa2a6f79a1c56d9 (MD5) / Dissertacao (Mestrado) / IEA/D / Instituto de Quimica, Universidade de Sao Paulo - IQ/USP
3

Avaliação da influência de íons metálicos sobre o potencial de evolução do hidrogênio utilizando soluções recicladas de baterias automotivas.

OLIVEIRA, Aglailson Glêdson Cabral de. 21 August 2018 (has links)
Submitted by Maria Medeiros (maria.dilva1@ufcg.edu.br) on 2018-08-21T11:57:47Z No. of bitstreams: 1 AGLAILSON GLÊDSON CABRAL DE OLIVEIRA - TESE (PPGEP) 2018.pdf: 3433485 bytes, checksum: bf80f16a0a475dc40815db32282d5cc5 (MD5) / Made available in DSpace on 2018-08-21T11:57:47Z (GMT). No. of bitstreams: 1 AGLAILSON GLÊDSON CABRAL DE OLIVEIRA - TESE (PPGEP) 2018.pdf: 3433485 bytes, checksum: bf80f16a0a475dc40815db32282d5cc5 (MD5) Previous issue date: 2018-02 / O crescimento da produção de baterias automotivas nos últimos anos refletiu no processo de aquisição de matérias-primas, assim como no processo de reutilização das baterias descartadas. Cada vez mais, as empresas do setor e os centros de pesquisa investem no estudo do processo de reciclagem dos componentes das baterias chumbo-ácido. A reciclagem do chumbo já é bem conhecida em todo o mundo, entretanto, para a reciclagem da solução eletrolítica (solução aquosa de ácido sulfúrico - H2SO4) temos poucas pesquisas e o processo de reciclagem ainda não se demonstrou economicamente viável. As indústrias de baterias MOURA S.A., através do seu centro de pesquisa, vem desenvolvendo estudos sobre o processo de reciclagem da solução eletrolítica para reutilizar essas soluções no seu processo de produção de novas baterias. Provocado por esta empresa, este estudo teve o objetivo de analisar a influência de íons metálicos presentes na solução eletrolítica ao final do ciclo de uma bateria chumbo-ácido sobre o potencial de evolução de gás hidrogênio (H2), com a perspectiva de determinar parâmetros destes íons na solução reciclada. A metodologia foi baseada na utilização de técnicas eletroquímicas como a polarização linear, curvas de Tafel, cronopotenciometria e voltametria cíclica. Após o estudo individual de cada contaminante e com a aplicação do planejamento experimental de mistura foi possível desenvolver o estudo sinérgico para um grupo de íons presentes na solução eletrolítica e verificar os resultados demonstraram ser possível utilizar a metodologia e avaliar a influência de íons contaminantes no potencial de evolução de gás hidrogênio. Os íons que demonstraram ter maior influência nas concentrações utilizadas nos experimentos foram cobre, ferro e manganês. Podemos concluir que a aplicação desta metodologia criada nesta pesquisa e com o avanço no estudo de outros fatores que podem estar associados à utilização da solução eletrolítica reciclada será possível tornar esse processo economicamente viável. / The growth in the production of automotive batteries in recent years has reflected in the process of acquiring raw materials, as well as in the reuse process of discarded batteries. Increasingly, companies in the industry and research centers are investing in the study of the recycling process of lead-acid battery components. Recycling of lead is already well known worldwide, however, for the recycling of the electrolytic solution (aqueous solution of sulfuric acid - H2SO4) we have little research and the recycling process has not yet proven economically viable. The battery industries MOURA S.A., through its research center, has been developing studies on the recycling process of the electrolytic solution to reuse these solutions in its process of producing new batteries. This study aimed to analyze the influence of metal ions present in the electrolytic solution at the end of the cycle of a lead-acid battery on the evolution potential of hydrogen gas (H2), with the perspective of determining parameters of these ions in the recycled solution. The methodology was based on the use of electrochemical techniques such as linear polarization, Tafel curves, chronopotentiometry and cyclic voltammetry. After the individual study of each contaminant and the application of the experimental planning of the mixture it was possible to develop the synergic study for a group of ions present in the electrolytic solution and verify the results demonstrated that it is possible to use the methodology and to evaluate the influence of contaminant ions on the potential evolution of hydrogen gas. The ions that demonstrated to have greater influence in the concentrations used in the experiments were copper, iron and manganese. We can conclude that the application of this methodology created in this research and with the advancement in the study of other factors that may be associated to the use of the recycled electrolytic solution will be possible to make this process economically feasible.
4

Determinacao do coeficiente de difusao do acido oxalico em meio sulfurico pelos metodos da cronopotenciometria e do diafragma poroso

CHIERICE, GILBERTO O. 09 October 2014 (has links)
Made available in DSpace on 2014-10-09T12:23:45Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:57:00Z (GMT). No. of bitstreams: 1 00886.pdf: 3186592 bytes, checksum: 02aa449d230c78ebeaa2a6f79a1c56d9 (MD5) / Dissertacao (Mestrado) / IEA/D / Instituto de Quimica, Universidade de Sao Paulo - IQ/USP
5

Využití chronopotenciometrické titrace v huminovém výzkumu / Utilization of chronopotentiometric titration in humic research

Viktorinová, Jana January 2013 (has links)
Humic acids are natural substances belonging to the group of humic substances. They arise mainly decomposition of plant residues. They are contained in soils, peat, sediments, young coal, water and even in the air. Humic acids are only partially soluble in water with increasing pH increases their solubility. Diploma thesis focuses on the use of chronopotentiometric titration of humic research. This method is mainly used for the determination of trace concentrations of analytes. This work is focused on the determination of acidity by potentiometric titration and the determination of dissociation constants using chronopotentiometry with measurement of pH of prepared samples.
6

Određivanje vitamina B1, B2 i B3 primenom hronopotenciometrije i hronopotenciometrijske striping analize / Determination of vitamin B1, B2 and B3 by means of chronopotentiometry and chronopotentiometric stripping analysis

Brezo-Borjan Tanja 14 October 2019 (has links)
<p>U okviru ove doktorske disertacije razvijene su elektroanalitičke metode za određivanje pojedinih vitamina B grupe. Za određivanje vitamina B<sub>1</sub> i B<sub>3</sub> primenjena je adsorpciona hronopotenciometrijska striping analiza (AdHSA) na tankoslojnoj živinoj elektrodi kao radnoj elektrodi, dok je za određivanje vitamina B2 primenjena hronopotenciometrijska analiza (HA) na dvema geometrijski različitim elektrodama od staklastog ugljenika: planarnoj disk elektrodi i elektrodi u vidu procesne posude. U cilju optimizacije metoda ispitan je uticaj najznačajnijih eksperimentalnih faktora. Optimalni eksperimentalni uslovi za određivanje vitamina B<sub>1</sub> su podrazumevali primenu 0,2 mol/l citratnog pufera vrednosti pH 6 kao pomoćnog elektrolita, potencijala i vremena akumulacije od -1,313 V i 50 s, redom, i struje rastvaranja depozita od 1,9 &ndash; 6,1 &mu;A. Odgovarajući eksperimentalni faktori za određivanje vitamina B<sub>2</sub> su bili: 0,025 mol/l HCl kao pomoćni elektrolit, inicijalni potencijal od 0,023 V i struja redukcije od 0,8 &ndash; 4,2 &mu;A, dok su optimalni radni uslovi za određivanje vitamina B<sub>3</sub> obuhvatali primenu 0,05 mol/l citratnog pufera pH 6, potencijala akumulacije od -1,405 V pri vremenu akumulacije od 15 s, i struji rastvaranja u intervalu od 1,4 &ndash; 15,1 &mu;A. U slučaju određivanja vitamina B<sub>2</sub> primenom radne elektrode u vidu procesne posude ispitan je i uticaj aktivne povr&scaron;ine radne elektrode na analitički signal vitamina B<sub>2</sub>. Optimalna vrednost aktivne povr&scaron;ine radne elektrode iznosila je 13,4 cm<sup>2</sup>. Pod optimalnim eksperimentalnim uslovima, dolazilo je do elektrooksidacije molekula vitamina B<sub>1</sub> i B<sub>3</sub> na tankoslojnoj živinoj elektrodi u analitičkom koraku, dok se vitamin B<sub>2</sub> redukovao na elektrodama od staklastog ugljenika. U okviru validacije metoda definisani su opsezi linearnosti, određene su vrednosti granice detekcije i granice kvantitativnog određivanja, ocenjena je preciznost i ispitane su interferencije. Uz odgovarajuće uslove rada, dobijena je dobra linearnost analitičkog signala od sadržaja za sva tri ispitivana vitamina. Ostvarene su granice detekcije od 1,64 mg/l za vitamin B<sub>1</sub>, 0,076 mg/l za vitamin B<sub>2</sub> uz primenu planarne disk elektrode i 0,018 mg/l (vitamin B<sub>2</sub>) uz primenu procesne posude od staklastog ugljenika kao radne elektrode. Ostvarena granica detekcije za vitamin B<sub>3</sub> je iznosila 2,20 mg/l. Nakon optimizacije i validacije, razvijene metode HA i AdHSA primenjene su za određivanje vitamina B<sub>1</sub>, B<sub>2</sub> i B<sub>3</sub> u komercijalnim multivitaminskim dodacima ishrani i multivitaminskim instant napicima. Tačnost razvijenih metoda je potvrđena paralelnim analizama izvedenim primenom visokopritisne tečne hromatografije.</p> / <p>Within the scope of this doctoral dissertation, electroanalytical methods for the determination of several vitamins of the B-complex are developed. For the determination of vitamin B1 and B3 adsorptive chronopotentiometric stripping analysis was applied, with mercury film electrode as the working electrode. For vitamin B2 determination, the chronopotentiometric analysis was performed on two geometrically different glassy carbon working electrodes: the planar disc electrode and the process vessel electrode. The most important experimental parameters of the analysis were investigated and optimized. For vitamin B<sub>1</sub> determination, the optimized experimental conditions were: 0,2 mol/l citrate buffer pH 6 as the supporting electrolyte, accumulation potential of -1,313 V, accumulation time of 15 s and the oxidation current between 1,9 &mu;A and 6,1 &mu;A. The appropriate experimental factors for vitamin B<sub>2</sub> determination included 0,025 mol/l HCl solution (supporting electrolyte), initial potential of 0,023 V and reduction current in the range from 0,8 &ndash; 4,2 &mu;A, whereas the optimal working parameters for vitamin B3 determination were as follows:0,05 mol/l citrate buffer pH 6, accumulation potential of -1,405 V, accumulation time of 15 s and dissolution current from 1.4 &ndash; 15.1 &mu;A. When the process vessel was used as the working electrode, the optimal volume of the analyzed solution i.e. the active surface area of the electrode was optimized. The optimal value of the active surface area was 13,4 cm2. As well, under the optimal experimental conditions, vitamin B<sub>1</sub> and vitamin B3 underwent electrooxidation process in the analytical step, whereas vitamin B<sub>2</sub> was electrochemically reduced on glassy carbon electrodes. A validation procedure of the optimized methods was performed by evaluation of the following parameters: linearity, the limit of detection (LOD), the limit of quantitation (LOQ), precision, selectivity, and accuracy. Under optimal working conditions, the linearity of the proposed methods was very good. The achieved limits of detection were 1.64 mg/l for vitamin B<sub>1</sub>, 0,076 mg/l for vitamin B<sub>2</sub> (planar disc electrode) and 0,018 mg/l (process vessel electrode) and 2,2 mg/l for vitamin B<sub>3</sub>.<br />After optimization and validation procedures, the developed methods were applied for vitamin B<sub>1</sub>, B<sub>2</sub>, and vitamin B<sub>3</sub> determination in commercially available multivitamin supplements and instant multivitamin beverages. The accuracy of the proposed methods was tested by parallel HPLC analyses of the same samples.</p>
7

Élaboration par mécano-synthèse d'alliages à base Ti-Fe : caractérisation de leurs propriétés de stockage électrochimique d'hydrogène / Elaboration of Ti-Fe based alloys using ball milling : characterization of their electrochemical hydrogen storage properties

Hosni, Bilel 17 July 2018 (has links)
L’hydrogène est la solution potentielle pour réussir la transition énergétique d’un système actuel basé en grande partie sur les combustibles fossiles vers un système non émetteur de gaz toxiques et respectueux de l’environnement. Cependant, le stockage de l’hydrogène est un grand défi qui freine son application pratique dans les différents domaines. Les hydrures métalliques permettent de stocker une grande quantité d’hydrogène de façon réversible dans de bonnes conditions (Température, pression, sécurité…) comparée aux autres modes de stockage (gazeux et liquide). En plus, ces mêmes matériaux sont utilisés comme électrode négative dans les batteries Nickel-Métal Hydrure.Dans la première partie de cette thèse, les alliages Ti-Fe ont été synthétisés parmécanosynthèse pour différents temps de broyage et différents rapports massiquesbilles/poudre. Afin d’optimiser les paramètres d’élaboration, ces alliages ont été caractérisés par différentes techniques telles que la diffraction des rayons X, la microscopie électronique à balayage, la chronopotentiométrie, la chronoampérométrie et la voltamétrie cyclique.Dans une seconde partie, les alliages TiFe+4%MWNTs, TiFe0.95-xMx, TiFe0.90M0.10 etTiFe0.90Mn0.05V0.05 (x=0.05, 0.15) (M : Mn ou V) ont été élaborés selon les paramètres optimaux déterminés précédemment. L’influence de l’additif Nanotubes de Carbone à multiparois (MWNTs), de la substitution partielle du Fe par Mn et/ou V et de l’excès de Titane sur les propriétés structurales, morphologiques et électrochimiques telles que l’activation, la capacité de décharge électrochimique, la réversibilité, la tenue au cyclage, le coefficient de diffusion ont ensuite été étudiés. Les propriétés redox des électrodes, le potentiel de Nernst et la densité du courant d’échange, ont été déterminés, en se basant sur la première loi de Sternet le modèle théorique de Bulter -Volmer.Les résultats électrochimiques obtenus montrent que l’alliage TiFe+4 wt.% MWNTs présente les meilleures performances : une activation rapide (au 1er cycle) et une meilleure capacité maximale de décharge (266 mAh g-1) avec une réversibilité qui reste inchangée. / Hydrogen is the potential solution to make a success of the energy transition of a current system basically based on fossil fuels towards a system friendly to environment. However, the storage of hydrogen is a big challenge that hinders its practical application in different areas.. Metal hydrides can store a large amount of hydrogen reversibly under good conditions (temperature, pressure, safety ...) compared to other storage modes (gaseous and liquid). In addition, these same materials are used as negative electrode in Nickel-Metal Hydride batteriesIn the first part of this thesis, Ti-Fe alloys were synthesized using mechanical alloying (MA) under argon atmosphere at room temperature, with different ball to powder weight ratio and at different milling times. In order to determine the optimal parameters of the elaboration the metallic composite were investigated using different techniques such as X-ray diffraction, scanning electron microscopy (EDS support), chronopotentiometry, chronoamperometry and cyclic voltammetry,In the second part, the metallic compounds, TiFe+4%MWNTs, TiFe0.95-xMx, TiFe0.90M0.10 and TiFe0.90Mn0.05V0.05 (x=0.05, 0.15) (M : Mn or V), which are used as the negative electrode material for Ni-MH secondary batteries, were synthesized by mechanical alloying according to optimal parameters, previously determined.The effect of MWNT addition, the Mn and/or V partial substitution for Fe and the excess of titanium on the structural, morphological and electrochemical parameters such as activation, electrochemical discharge capacity, reversibility, cycle life time and hydrogen diffusion coefficient were investigated.The redox properties of the electrodes such as the Nernst potential and the exchange current density were studied based on Stern’s first law and the theoretical model of Bulter-Volmer.The electrochemical properties of studied samples show the best performance for TiFe+4% MWNTs alloy. Indeed, this alloy presents a rapid activation (1st cycle) and a best discharge capacity (266 mAhg-1) with a reversibility remaining unchanged
8

Sorpční schopnosti huminových kyselin / Sorption ability of humic acids

Pokorná, Markéta January 2011 (has links)
The Diploma thesis deals with humic acids and their ability to adsorb metal ions on their surface. Humic acids are aromatic polycyclic compounds which contain carboxylic and fenolic functional groups on their sidechains. Thanks to these functional groups humic acids can form complexes with metal ions of different stability and assist the partial immobilization of pollutants in the nature. In this thesis, the sorption of Pb2+ and Zn2+ ions on humic acids was studied by relatively new electroanalytic method called galvanostatic stripping chronopotentiometry. Experimental data were described by Freundlich and Langmuir isotherms. The results show that the amount of examined metal ions increases with their increasing concentration. Furthermore it was determined that Pb2+ ions are adsorbed better on humic acids than Zn2+ ions. Both metals are adsorbed better from solution containing only one metal ion than in presence of four metals at the same time (Cd, Cu, Zn and Pb) where the sorption of these metals is not influenced by the presence of other metals.
9

Elektrohemijsko određivanje histamina / Electrochemical determination of histamine

Stojanović Zorica 23 September 2011 (has links)
<p>U ovom radu su razvijene elektrohemijske metode za određivanje histamina. U svim<br />elektrohemijskim ispitivanjima kori&scaron;ćena je hronopotenciometrija. Istraživanja su obuhvatila optimizaciju uslova elektroanalitičkih tehnika i upoređivanje mehanizama generisanja analitičkog signala primenom različitih radnih elektroda, razvoj odgovarajućeg postupka pripreme uzoraka za analizu i samo određivanje histamina u hrani i piću. Ispitana je mogućnost primene čvrste zlatne elektrode, tankoslojne živine i tankoslojne niklove elektrode za elektrohemijsko određivanje histamina. U slučaju elektrooksidacije histamina, razja&scaron;njeni su mehanizmi generisanja signala na primenjenim elektrodama. Optimizacija uslova elektroanalitičkih tehnika obuhvatila je odabir odgovarajućeg pomoćnog elektrolita i njegove koncentracije, ispitivanje uticaja početnog potencijala i struje oksidacije na analitički signal analita. Pored toga, za svaki elektrohemijski sistem definisana su osetljivost i reproduktivnost, selektivnost, kao i opseg linearnosti. Primenom tankoslojne niklove elektrode uočena je pojava adsorpcionog koncentrovanja analita, te su u slučaju ovog elektrohemijskog sistema ispitani i uticaji vremena adsorpcije i temperature ispitivanog medijuma na analitički signal histamina. Na tankoslojnoj živinoj elektrodi analitički signal se generisao usled direktne oksidacije histamina primenom konstantne struje. Na ostale dve elektrode, pored elektrodnih reakcija odvijale su se i hemijske reakcije, tako da se oksidacija histamina u oba slučaja odigravala po ECE mehanizmu (elektrodna reakcija &ndash; hemijska reakcija &ndash; elektrodna reakcija). Na čvrstoj zlatnoj elektrodi, generisanje signala je bilo posledica oksidacije histamina elektrogenerisanim hlorom, dok se u slučaju tankoslojne niklove elektrode radilo o kombinovanoj katalitičko‐adsorpcionoj hronopotenciometriji. Tankoslojna živina elektroda je pokazala dobru selektivnost pri koncentracijama aminokiselina i histamina nižim od 5 mg/dm<sup>3</sup>, dok je pri vi&scaron;im koncentracijama dolazilo do preklapanja analitičkih signala. Ostali elektrohemijski sistemi nisu pokazali odgovarajuću selektivnost. Najveća osteljivost je ostvarena primenom tankoslojne niklove elektrode (LOD = 0,11 mg/dm<sup>3</sup>), zatim sledi čvrsta zlatna elektroda (LOD = 0,27 mg/dm<sup>3</sup>) i na kraju tankoslojna živina elektroda (LOD = 1,31 mg/dm<sup>3</sup>). U okviru definisanja postupka pripreme uzoraka, ispitana je efikasnost različitih ekstrakcionih tehnika i različitih ekstragenasa u pogledu izdvajanja histamina iz uzoraka. Pored toga razvijeni su odgovarajući postupci preči&scaron;ćavanja ekstrakata primenom preparativnih hromatografskih tehnika, i to na tankom sloju i na stubu adsorbensa. Po definisanju optimalnih uslova elektrohemijskog određivanje histamina, kao i razvijanja postupka pripreme uzoraka, histamin je određen u različitoj hrani i piću.</p> / <p>In this work, the electrochemical methods for the determination of histamine were<br />developed. All electrochemical investigations were carried out by chronopotentiometry. The research included optimization of the experimental parameters of electroanalytical techniques and comparison of the mechanism of the analytical signal generation by using the different working electrodes. Upon the development of sample preparation procedure, histamine was determined in different food and beverages. The possibility of applying solid gold electrodes, thin film mercury electrode and thin film nickel electrode for electrochemical determination of histamine was examined. The mechanisms of histamine electrooxidation on different working electrodes were explained and elaborated. Optimization of the experimental parameters of electroanalytical techniques included the selection of appropriate supporting electrolyte and its concentration, and investigation of the influence of initial potential and oxidation current on histamine analytical signal. Beside this, for each electrochemical system sensitivity and reproducibility, selectivity as well as linearity range were defined. The use of thin nickel film electrode resulted in adsorptive accumulation, and in that case the effects of accumulation time and medium temperature on histamine analytical signal were defined. On thin film mercury electrode, histamine analytical signal was generated<br />due to direct oxidation of histamine by a constant current. On other two electrodes, electrode reactions were coupled with chemical reaction, and histamine oxidation was by ECE mechanism (electrode reaction &ndash; chemical reaction &ndash; electrode reaction). On solid gold electrode histamine was oxidized indirectly by electrogenerated chlorine, while in the case of thin film nickel electrode combination of catalytic and adsorptive chronopotentiomety was responsible for signal generation. Thin film mercury electrode showed good selectivity for histamine and amino acids concentrations below 5 mg/dm<sup>3</sup>, but higher concentrations caused the overlapping of analytical signals. Other electrochemical systems did not show adequate selectivity. The best sensitivity was achived by thin film nickel electrode (LOD = 0.11 mg/dm<sup>3</sup>),<br />followed by a solid gold electrode (LOD = 0.27 mg/dm<sup>3</sup>), and by thin film mercury electrode (LOD = 1.31 mg/dm<sup>3</sup>). In order to define adequate sample preparation procedure, the efficiency of different extraction techniques and different solvents were tested for histamine extraction from the samples. Appropriate procedures for purification of extracts were defined as well, by applying preparative thin layer and column chromatography. After optimization of the electrochemical methods for histamine determination, as well as the procedure of sample preparation, developed methods were applied for histamine determination in various food and beverages.</p>
10

STUDY OF THE TRANSPORT OF HEAVY METAL IONS THROUGH CATION-EXCHANGE MEMBRANES APPLIED TO THE TREATMENT OF INDUSTRIAL EFFLUENTS

Martí Calatayud, Manuel César 12 January 2015 (has links)
La presente Tesis Doctoral consiste en la determinación de las propiedades de transporte de diferentes especies catiónicas a través de membranas de intercambio catiónico. Las membranas de intercambio iónico son un componente clave de los reactores electroquímicos y de los sistemas de electrodiálisis, puesto que determinan el consumo energético y la eficiencia del proceso. La utilización de este tipo de membranas para el tratamiento de efluentes industriales no es muy extendida debido a los requisitos de elevada resistencia química y durabilidad que deben cumplir las membranas. Otro asunto importante radica en la eficiencia en el transporte de los iones que se quieren eliminar a través de la membrana. Normalmente, existe una competencia por el paso a través de las membranas entre diferentes especies debido al carácter multicomponente de los efluentes a tratar. Sin embargo, una mejora en las propiedades de las membranas de intercambio iónico permitiría la implantación del tratamiento mediante reactores electroquímicos de efluentes industriales con un contenido importante en compuestos metálicos, tales como los baños agotados de las industrias de cromado. La utilización de una tecnología limpia como la electrodiálisis conllevaría diferentes ventajas, entre las cuales destacan la recuperación de los efluentes para su reutilización en el proceso industrial, el ahorro en el consumo de agua y la disminución de la descarga de contaminantes al medio ambiente. La determinación de las condiciones de operación óptimas así como la mejora de las propiedades de transporte de las membranas constituye el principal tema de la presente investigación. Para ello, se emplearán diferentes tipos de membrana. En primer lugar, se estudiará el comportamiento de las membranas poliméricas comerciales que poseen unas propiedades de resistencia química elevadas, las cuales se tomarán como referencia. De forma paralela, se producirán membranas conductoras de iones a partir de materiales cerámicos económicos, ya que la resistencia de los materiales cerámicos a sustancias oxidantes y muy ácidas es mayor que la de los materiales poliméricos. Este punto constituye la parte más innovadora de la investigación, puesto que la mayoría de las membranas de intercambio iónico comerciales están basadas en materiales poliméricos que no pueden resistir las condiciones específicas de los efluentes industriales. Una vez determinadas las condiciones de operación óptimas, se realizarán ensayos en plantas piloto con el fin de confirmar los resultados obtenidos mediante las técnicas de caracterización y determinar el grado de recuperación y coste energético asociado a los procesos electrodialíticos de tratamiento de efluentes industriales. / Martí Calatayud, MC. (2014). STUDY OF THE TRANSPORT OF HEAVY METAL IONS THROUGH CATION-EXCHANGE MEMBRANES APPLIED TO THE TREATMENT OF INDUSTRIAL EFFLUENTS [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/46004 / TESIS / Premios Extraordinarios de tesis doctorales

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