Spelling suggestions: "subject:"[een] CYCLIC VOLTAMMETRY"" "subject:"[enn] CYCLIC VOLTAMMETRY""
121 |
Spectroelectrochemistry of Substituted AnilinesJbarah, Abdel Aziz 24 November 2006 (has links) (PDF)
Die Elektrochemie und die Spektroelektrochemie von Nitroanilinen (ortho-, meta- und para- Isomere)
und deren entsprechenden Diaminoverbindungen (ortho-, meta- und para-Phenylendiamin)
wurden an zwei verschiedenen Elektroden (Platin und Gold) und in zwei Elektrolytlösungen (saure
und neutrale Perchloratlösung) untersucht. Die erhaltenen Messergebnisse wurden als Referenz für
die spektroelektrochemische Untersuchung von Polyvinylaminen mit o- oder p-
Nitroanilinsubstituenten verwendet. Es wurden außerdem spektroelektrochemische Untersuchungen
mit anderen Polyvinylaminen, die das Wurster Kationradikal oder Stilbene als Substituenten
enthalten, durchgeführt.
Die oxidative und reduktive Elektrochemie von drei Nitroanilinisomeren wurde in neutraler (0.1 M
KClO4) und saurer (0.1 M HClO4) wässriger Elektrolytlösung mit zyklischer Voltammetrie und
oberflächenverstärkter Ramanspektroskopie (Surface Enhanced Raman Spectroscopy SERS) untersucht.
Die zyklischen Voltammogramme, die mit einer Goldelektrode in saurer Elektrolytlösung
für o- und p-Nitroanilin aufgezeichnet wurden, zeigten die Bildung von o- und p-Phenylendiamin
beim Potenzialdurchlauf in kathodischer Richtung. In neutraler Elektrolytlösung ist die Situation
anders und die Endprodukte der elektrochemischen Reduktion dieser Isomere sind o- und p-
Amino-N-phenylhydroxylamin. Aus den zyklischen Voltammogrammen, die mit Gold- und Platinelektroden
bei anodischem Potenzialdurchlauf für diese Isomere in saurer und neutraler Elektrolytlösung
aufgezeichnet wurden, erhält man folgende Reihenfolge für die Lage der Oxidationspotentiale
m-Nitroanilin > p-Nitroanilin > o-Nitroanilin. Eine Sauerstoff-Gold-Adsorbat-
Streckschwingung wurde zwischen 400 und 430 cm-1 in den SER-Spektren der drei isomeren Nitroaniline
in beiden Elektrolytlösungen bei positiven Elektrodenpotenzialen beobachtet. Das SERS-Experiment
zeigte auch eine senkrechte Orientierung der adsorbierten Nitroaniline zur Oberfläche
der Goldelektrode. Für die isomeren Phenylendiamine wurde in beiden Elektrolytlösungen und mit
beiden Elektroden im anodischen Durchlauf das gleiche Verhalten beobachtet. Das beim Ein-
Elektronenübergang erhaltene Oxidationsprodukt (Radikalkation) reagiert im Fall von o- und m-
Phenylendiamin über eine C-N-Kopplung mit einem weiteren Radikal zum Dimer (1.Schritt der
Elektropolymerisation). p-Phenylendiamin wird nach dem ECE-Mechanismus (E = Elektronentransfer,
C = chemische Reaktion) oxidiert, wobei die Ladungsübertragung in zwei Schritten erfolgt,
gekoppelt mit Säure-Base-Reaktionen, was zur Bildung des Diimin führt. Aus den SERS-Messungen
kann man schlussfolgern, dass m- und p-Phenylendiamin waagerecht zur Metalloberfläche
über den Benzenring und die Stickstoffatome adsorbiert sind. Die Adsorption von o-Phenylendiamin erfolgt über die Stickstoffatome und mit schräger Orientierung zur Metalloberfläche.
Die zyklischen Voltammogramme, die mit einer Goldelektrode in saurer und neutraler Elektrolytlösung
von den Polyvinylaminen mit Nitroanilinsubstituenten aufgenommen wurden, zeigen dasselbe
Verhalten wie Nitroanilinmonomere beim Potenzialdurchlauf in kathodischer Richtung. Die
für diese Polymere im anodischen Durchlauf erhaltenen Zyklovoltammogramme unterscheiden
sich von denen für die Monomere. Die Zahl der Adsorptionsplätze und die Adsorptionsstärke der
Polyvinylamine verändern sich in Abhängigkeit vom Elektrodenpotential, vom Prozentsatz und der
Art des aromatischen Substituenten am Polymerrückgrat und vom pH-Wert der Lösung. / The electrochemistry and spectroelectrochemistry of nitroanilines (ortho, meta, and
para isomers) and their respective amino compounds (ortho-, meta- and paraphenylenediamines)
have been investigated at two different electrodes (platinum and gold)
and in two different electrolyte solutions (acidic and neutral perchlorate). The results of
these investigations were used as a reference for the spectroelectrochemistry of polyvinylamines
containing o- or p-nitroaniline substituents. Spectroelectrochemical investigations
of polyvinylamine containing Wurster radical cation or stilbene as a substituent were also
carried out.
The oxidative and reductive electrochemistry of the three isomeric nitroanilines has
been studied in neutral (0.1 M KClO4) and acidic (0.1 M HClO4) aqueous electrolyte solutions
with cyclic voltammetry and Surface Enhanced Raman Spectroscopy (SERS). The
cyclic voltammograms recorded with a gold electrode in acidic electrolyte solution showed
formation of o- and p-phenylenediamine in the negative going potential scan for o- and pnitroaniline
respectively. In neutral electrolyte solution the situation is different and the final
products of electrochemical reduction of these isomers are o- and p-amino-Nphenylhydroxylamine.
The order of increasing electrochemical oxidation potential is mnitroaniline
> p-nitroaniline > o-nitroaniline as observed from cyclic voltammograms recorded
with a gold and platinum electrodes and in the positive going potentials scan for
these isomers in acidic and neutral electrolyte solutions. An oxygen-gold adsorbate stretching
mode was detected between 400 to 430 cm-1 in SER-spectra of the three isomeric nitroanilines
in both electrolyte solutions at positive electrode potentials. The SERS experiments
showed also a perpendicular orientation of adsorbed nitroanilines on a gold electrode
with respect to the metal surface.
General trends are observed in the anodic scans of isomeric phenylenediamines at both
electrodes and in both electrolyte solutions. The one-electron electrochemical oxidation
product (radical cation) in case of o- and m-phenylenediamine go into fast C-N coupling
between radicals to form dimers (the first step of electropolymerization). The pphenylenediamine
is oxidized according to an ECE mechanism (E = electron transfer reaction,
C = chemical reaction), which involved two charge transfer steps coupled with acidbase
reactions to form diimine. As we deduced from SERS measurements, m- and p-phenylenediamine
adsorbed in flat orientation with respect to the metal surface via benzene
ring and nitrogen atoms, respectively. o-Phenylenediamine adsorption is taking place via
nitrogen atoms and with tilted orientation with respect to the metal surface.
The cyclic voltammograms recorded with a gold electrode in acidic and neutral electrolyte
solutions of polyvinylamines containing o- or p-nitroaniline substituents exhibit the
same features like nitroaniline monomers in the negative going potentials scan. The result
observed in the anodic scan for these polymers are different from those observed for monomers.
Adsorption site and strength of the polyvinylamine polymer varies according to the
applied electrode potential, percentage and type of the aromatic substituent at the polymer
backbone, and the pH of the medium.
|
122 |
Spectroelectrochemistry of Intrinsically Conducting Furan-Thiophenes CopolymersAlakhras, Fadi 06 October 2008 (has links) (PDF)
Die elektrochemische Copolymerisation von Furan und Thiophen oder 3-Chlorothiophen wurde
erfolgreich realisiert in einer Elektrolytlösung von Bortrifluorid-Diethylether + Ethylether (Verhältnis
1:2) bei konstantem Elektrodenpotenzial. Die Zugabe von Trifluoroessigsäure (TFA) (10 Vol-%) zu
Bortrifluorid-Diethylether + Ethylether (Verhältnis 1:2) erniedrigte das Oxidationspotenzial der
Monomere; die Polymerisationsgeschwindigkeit erhöhte sich, da TFA die Ionenleitfähigkeit des
Elektrolyts vergrößert.
Die Homopolymere zeigen nur einen Redoxpeak, verursacht durch Polymeroxidation und -
reduktion. Die elektrochemische Copolymerisation wird bei verschiedenen Potenzialen und mit
unterschiedlichen Thiophen- oder 3-Chlorothiophenkonzentrationen untersucht. Die Copolymere
zeigen ein Redoxpeakpaar, dessen Position sich wesentlich von der der Homopolymere unterscheidet.
Mit zunehmendem Polymerisationspotenzial und/oder zunehmender Konzentration an Thiophen- oder
3-Chlorothiophen werden auch mehr Thiophen- oder 3-Chlorothiopheneinheiten in den Copolymerfilm
eingebaut. Ein Elektropolymerisationmechanismus wird für die Copolymere vermutet und die
Copolymere weisen eine recht gute Langzeitstabilität der Redoxaktivität nach Zyklen in Acetonitril
auf.
In situ UV-Vis-Spektren der Homo- und Copolymerfilme wurden gemessen und λ1max, welches
dem π → π*- Übergang entspricht, wurde bestimmt. Der optische Übergang bei λ2max vom Valenzband
in das höhere Bipolaronband wurde ebenfalls bestimmt. Die Bandlücke für die Homo- und
Copolymerfilme beim direkten Übergang wurde von der Kante im Absorptionsspektrum abgeschätzt.
Die elektrochemische Thermodynamik für die Homo- und Copolymerfilme deutet darauf hin, dass
jeweils ein Elektron von den Polymersegmenten, bestehend aus 4 Monomereinheiten, entfernt wird.
Die untersuchten leitfähigen Filme zeigen einen Leitfähigkeitssprung mit einer stabilen
Leitfähigkeit bis EAg/AgCl= 2 V. Diese Leitfähigkeitsänderung ist reversibel. Polyfuran hat verglichen
mit Polythiophen eine geringere Leitfähigkeit und die Leitfähigkeit von Poly(3-chlorothiophen) ist
rund eine Zehnerpotenz niedriger als die von Polythiophen. Da das in situ Leitfähigkeitsverhalten der
Copolymere nicht die Summe der einzelnen Homopolymere bildet, kann man ausschließen, dass es
sich bei den abgeschiedenen Copolymeren um Blockcopolymere handelt.
Mit Hilfe der FTIR-Spektroskopie wurden Schwingungsspektren der Homo- und
Copolymerfilme aufgenommen. Die Ergebnisse zeigen, dass es zur α-α'-Verknüpfung zwischen den
Radikalkationen während der Copolymerisation kommt, was charakteristisch ist für α-substituierte
fünfgliedrige heterozyklische Verbindungen. Der Mechanismus der elektrochemischen Degradation
von Furan-Thiophen-Copolymeren wird ebenfalls mit Hilfe der gemessenen Spektren beschrieben.
Die in situ Resonanz-Raman-Spektroskopie ergab, dass die spektroskopischen Eigenschaften
der Copolymere zwischen denen der Homopolymere lagen. Bei höheren Polymerisationspotenzialen
und höheren Konzentrationen an Thiophen oder 3-Chlorothiophen werden mehr Thiophen- oder 3-
Chlorothiopheneinheiten in die Copolymerketten eingebaut. Es ist offensichtlich, dass die
Ramanspektren der Copolymere wesentlich komplexer sind als die der Homopolymere, wodurch die
Auswertung erschwert wird. Dennoch erinnern die Ramanspektren der Copolymere an die der
Homopolymere.
Die spektroelektrochemischen Eigenschaften der Copolymere haben bestätigt, dass deren
Charakteristika zwischen denen der Homopolymere liegen, was deutlich macht, dass die Oxidation von
Monomeren möglich ist und dass die Copolymerketten demnach aus Furan- und Thiophen- bzw. 3-
Chlorothiopheneinheiten bestehen können. / Electrochemical copolymerization of furan and thiophene or 3-chlorothiophene was successfully realized in a solvent system consisting of boron trifluoride ethyl ether (BFEE) + ethyl ether (EE) (ratio 1:2) at constant electrode potential. The addition of trifluoroacetic acid (TFA) (10 % by volume) to BFEE + EE (ratio 1:2) decreased the oxidation potential of the monomers; the polymerization rate was also accelerated because TFA increases the ionic conductivity of the electrolyte. The homopolymers have only one redox peak caused by polymer oxidation and reduction. Electrochemical copolymerization both at different potentials and with different thiophene or 3-chlorothiophene concentrations is investigated. The copolymers show one anodic/cathodic peak couple that appears at a position quite different from the positions observed with homopolymers. More thiophene or 3-chlorothiophene units are incorporated into the copolymer film with an increasing polymerization potential of the copolymer and/or with an increasing concentration of thiophene or 3- chlorothiophene in the feed. An electropolymerization mechanism of copolymers has been proposed, and the copolymers show a fairly good long-term stability of the redox activity after cycling in acetonitrile. In situ UV-Vis spectra of the homo- and copolymer films were measured and λ1max which corresponds to the π → π* transition is determined. The optical transition with λ2max from the valence band into the higher bipolaron band is also assigned. The band gap (Eg) for homo- and copolymer films from a direct interband transition is estimated from the absorption edge of the spectrum. The redox thermodynamics of the homo- and copolymer films suggest that one electron is removed from polymer segments containing four monomer units. The studied conducting films show a single conductivity change with a stable conductivity up to EAg/AgCl= 2 V. The conductivity of these films is almost restored when the potential shift direction is reversed. Polyfuran compared to polythiophene, has a lower conductivity and the conductivity of poly(3-chlorothiophene) is around one order of magnitude lower than that of polythiophene. The in situ conductivity properties of the copolymers are not the sum of those of the individual homopolymers. This result may eliminate the possibility that the copolymers can be considered as block copolymers. Vibrational spectra of homo- and copolymer films investigated in this study have been obtained using FTIR spectroscopy. The results indicate that α-α' coupling of radical cations has taken place in the copolymerization. This is a characteristic of α-substituted five-membered heterocyclic compounds. The electrochemical degradation mechanism of furan-thiophene copolymers is also described using the obtained spectra. The in situ resonance Raman spectroscopy of the copolymers shows spectroscopic properties intermediate between those of homopolymers. At higher polymerization potentials and at higher concentrations of thiophene or 3-chlorothiophene in the feed more thiophene or 3-chlorothiophene units are incorporated into the copolymer chains. It is obvious that the Raman spectra of the copolymers are more complex than those of homopolymers, which makes the assignment difficult. However, the in situ Raman spectra of the copolymers are reminiscent of those of the homopolymers. The spectroelectrochemical properties of the copolymers confirmed that the copolymers show intermediate characteristics between the homopolymers, implying that oxidation of monomers is possible and the copolymer chains may accordingly be composed of furan and thiophene or 3-chlorothiophene units.
|
123 |
A comparative study of the electrosorption of sulfur-containing aromatic compounds on copper and gold electrodes / Eine vergleichende Studie zur Elektrosorption von schwefelhaltigen Aromaten auf Gold- und KupferelektrodenSardary, Hamidreza 09 January 2014 (has links) (PDF)
Diese Arbeit beinhaltet unsere Studien an selbstorganisierenden Monoschichten (engl. SAM = self- assembled monolayer) einiger aromatischer Thiole auf Gold- und Kupferoberflächen. Die Bildung von Monoschichten von Thiophenol, 4-Mercaptophenol, 4-Nitrothiophenol, 4-Aminothiophenol, 1,4-Dithiobenzol, 4-Mercaptopyridin und 2-Mercaptopyridin auf Au und Cu wurde untersucht und charakterisiert. Das abschirmende Verhalten und die strukturelle Anordnung dieser Monoschichten wurden mit Hilfe elektrochemischer und spektroskopischer Methoden geprüft und bestimmt. Zyklische Voltammetrie und oberflächenverstärkte Raman Spektroskopie wurden intensiv zur Aufklärung von Elektronentransferreaktionen an diesen mit SAMs modifizierten Oberflächen genutzt.
Elektrochemische Studien von Monoschichten aus Thiophenol, 4-Mercaptophenol, 4-Nitrothiophenol, 4-Aminothiophenol, 1,4-Dithiobenzol, 4-Mercaptopyridin und 2-Mercaptopyridin in 0,1 M wässriger KClO4-Lösung lassen schlussfolgern, dass diese Moleküle schwefelseitig an die Substratoberfläche gebunden sind. In 0,1 M wässriger KClO4-Lösung aufgenommene zyklische Voltammogramme an Gold- und Kupferoberflächen, welche mit oben genannten, aromatischen Thiolen beschichtet wurden, legen nahe, dass Adsorptionsschichten von Thiophenol und 1,4-Dithiobenzol eine stärkere Tendenz zum Abschirmen besitzen als andere.
Durch das Einbringen von Kupferproben, welche mit genannten aromatischen Thiolen behandelt wurden, in 0,1 M Silbernitrat-Lösung können sehr leicht Silber-Nanodendritstrukturen erhalten werden. Abscheidezeit und Konzentration der Silbernitrat-Lösung haben einen großen Einfluss auf das Wachstum der Silber-Nanodendritstrukturen auf den modifizierten Kupferproben. Diese Silber-Nanodendritstrukturen besitzen eine hohe katalytische Aktivität hinsichtlich der Oxidation von Hydroquinon.
Untersuchungen zur Korrosion an polykristallinem Kupfer, welches mit obigen aromatischen Thiolen modifiziert wurde, in 0,1 M Silbernitrate-Lösung ließen vermuten, dass dieses Kupfersubstrat mehr anodisches Verhalten zeigte als reines Kupfer bei ähnlichen Bedingungen.
Zyklische Voltammetrie an wie oben behandeltem Kupfer in 0,1M wässriger KClO4-Lösung zeigte, dass die Geschwindigkeit der Kupferauflösung bei diesen Messungen erhöht war gegenüber anderen, in welchen reines Kupfer bei identischen Bedingungen eingesetzt wurde. / It deals with our studies on self-assembled monolayers of aromatic thiols on gold and copper surfaces. Monolayer formation of thiophenol, 4-mercaptophenol, 4-nitrothiophenol, 4-aminothiophenol, 1,4-dithiobenzene, 4-mer¬cap¬to¬pyridine and 2-mercaptopyridine on Au and Cu surfaces was studied and characterized. The blocking behaviour and structural arrange¬ments of these monolayers were evaluated and characterized using electrochemical and spec¬troscopic techniques. Cyclic voltammetry and surface enhanced Raman spectroscopy were extensively used for the study of electron transfer reactions on these SAM modified surfaces.
Electrochemical and spectroelectrochemical studies of thiophenol, 4-mercaptophenol, 4-nitrothiophenol, 4-aminothiophenol, 1,4-dithiobenzene, 4-mercaptopyridine and 2-mercaptopyridine monolayers in aqueous solution of 0.1 M KClO4 suggest that these molecules adsorbed to substrate. Cyclic voltammetry of gold and copper covered with these aromatic thiolates recorded in aqueous solution of 0.1 M KClO4 suggests that adlayers of thio¬phenol and 1,4-dithiobenzene exhibit more blocking behavior than the other ones.
Silver nanodendritic structures are easily produced by placing copper samples modified with these aromatic thiolates into 0.1 M silver nitrate solution. Deposition time and concentration of silver nitrate solution have great influence on growing up silver nanodendritic structures on the surface of modified copper samples. These silver nanodendritic structures exhibit electrocatalytic activity towards the oxidation of hydroquinone.
Corrosion investigation of polycrystalline copper modified with these aromatic thiolates in 0.1 M silver nitrate solution suggest that copper substrate might be more anodic compared to bare copper under identical condition. Cyclic voltammetry of copper modified with these aromatic thiolates suggests that the rate of dissolution copper in aqueous solution of 0.1 M KClO4 is higher than bare copper in the same condition.
|
124 |
Organic Electrochemical Transistors for Fast Scan Cyclic VoltammetryKollipara, Suresh Babu January 2013 (has links)
The work presented in the thesis is about the evaluation of Organic Electrochemical Transistors (OECTs) for fast scan cyclic voltammetry (FSCV). FSCV is a method which has been used for real time dopamine sensing both in vivo and in vitro. The method is sensitive to noise and could therefore benefit from signal preamplification at the point of sensing, which could be achieved by incorporation of OECTs. In this study the OECTs are based on the conductive polymer poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS). The gate consists of gold microelectrodes of different sizes to be used one at a time. When dopamine is reacted at the gate electrode, the redox state of the PEDOT:PSS OECT channel is modulated and the resulting change in drain current can be measured. The gate current, which contains the sensing information, is after filtering obtained by differentiating the channel potential with respect to time. The derived gate current is plotted in cyclic voltammogram for different dopamine concentrations and the amplitude of the oxidation/reduction peaks can be used to determine the dopamine concentration. In this thesis for the first time it is demonstrated that OECTs can be used for FSCV detection of dopamine. The results are discussed and an outlook on future work is given.
|
125 |
Synthesis and electrochemical characterisation of conducting polyaniline-fly ash matrix composites.Mavundla, Sipho Enos. January 2005 (has links)
<p>
<p>  / </p>
<p align="left">  / </p>
<p>  / </p>
</p>
<p align="left">The aim of this study was to produce useful composite materials from fly ash, a major waste product of coal combustion from power plants. Polyaniline-fly ash (PANI-FA) composites were prepared by in situ polymerisation of aniline in the presence of Fly Ash (FA) by two slightly different methods. In one case polystyrene sulphonic acid (PSSA) was used as a stabilizer and in another case the starting materials (aniline and FA) were aged before oxidation. The aging procedure formed nanotubes that have cross-sectional diameters of 50-110 nm. The other procedure produced nanotubes with a diameter of 100-500 nm and the length of up to 10&mu / m. The presence of metal oxides and silica in FA were responsible for the formation of nanorods in PANI-PSSA-FA.. The formation of the composites was confirmed by UV-Vis and FTIR. The UV-Vis showed maximum absorbance at 330-360 nm ( due to &pi / -&pi / * transition of benzoid rings) and 600-650 nm(due to charge transfer excitons of quinoid rings), which are characteristics of emaraldine base. The electrochemical analysis of the composites showed that the composites were conductive and electroactive. The Cyclic Voltammetry of PANI-PSSA-FA showed three redox couples which are characteristics of sulphonated PANI. The morphology of the composites was studied by Scanning Electron Microscopy (SEM) and showed that our methods gave composites with improved homogeneity as compared to other reported methods. Thermo Gravimetric analysis (TGA) showed that the presence of FA in the composites improves the thermal stability of the composites by up to 100 0C.<br />
  / </p>
|
126 |
Partículas de pentacianonitrosilferrato (III) de cádmio em diferentes meios : preparação, caracterização e aplicação eletroanalítica /Souza, Tamires Rocha January 2018 (has links)
Orientador: Devaney Ribeiro do Carmo / Resumo: O presente trabalho descreve a preparação de partículas formadas a partir de Pentacianonitrosilferrato (III) de sódio e Cloreto de cádmio. As partículas foram preparadas em quatro proporções empregando os solventes Água/Formamida (100:0; 80:20; 40:60; 0:100) com o objetivo de investigar a sua influência na morfologia, topologia e nas propriedades eletrocatalíticas das partículas. Os materiais foram caracterizados por técnicas espectroscópicas e eletroquímica tais como: Espectroscopia na região do infravermelho (FTIR), Espectroscopia Raman, Reflectância difusa (UV-visível), Difração de raios-X (DRX), Microscopia eletrônica de varredura (MEV), Espectrometria de energia dispersiva de raios-X (EDS), Microscopia eletrônica de transmissão (MET) e voltametria cíclica (VC). Após as caracterizações foram realizados estudos sobre as propriedades eletroquímicas dos materiais utilizando um eletrodo de pasta de grafite. Dos quatro sistemas estudados, apenas dois foram sensíveis à concentrações de isoniazida, a saber o CdNP-3 e CdNP-4. Ambos os sistemas apresentaram duas regiões lineares de sinal em função da concentração com limites de detecção de 6,80×10-5 mol L-1 e 7,07×10-4 mol L-1, e 2,18×10-4 mol L-1 e 1,16×10-3 mol L-1 para os sistemas CdNP-3 e CdNP-4, respectivamente. Para o sistema CdNP-3 observou-se uma sensibilidade amperométrica de 23,96 mA mol L-1 e 10, 83 mA mol L-1, já para CdNP-4 observou-se uma sensibilidade amperométrica de 17,80 mA mol L-1 e 5,79 mA mol L-1 para cada reg... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The present work describes the preparation of particles formed from Sodium Pentacyanonitrosylferrate (III) and Cadmium Chloride. The particles were prepared in four ratios using solvents Water / Formamide (100:0, 80:20, 40:60, 0:100) to investigate the influence on particle morphology, topology and electrocatalytic properties. The materials were characterized by spectroscopic and electrochemical techniques such as: Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, Diffuse reflectance (UV-Visible), X-ray diffraction (XRD), Scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDS), Transmission electron microscopy (TEM) and Cyclic voltammetry (CV). After the characterization studies, the electrochemical properties of materials were performed using a graphite paste electrode. Of the four systems studied, only two tests with concentrations of isoniazid, CdNP-3 and CdNP-4. Both systems presented two linear concentrations with detection limits of 6.80 × 10-5 mol L-1 and 7.07 × 10-4 mol L-1 and 2.18 × 10-4 mol L-1 and 1.16 × 10-3 mol L-1 for the CdNP-3 and CdNP-4 systems, respectively. For the CdNP-3 system, an amperometric sensitivity of 23.96 mA mol L-1 and 10.83 mA mol L-1 was observed, whereas for CdNP-4 an amperometric sensitivity of 17.80 mA mol L-1 and 5.79 mA mol L-1 for each linear region. / Mestre
|
127 |
Potencialidades eletroanalíticas de complexos binucleares de nitroprussiato de metais de transição suportado em 3-aminopropil sílica /Sá, Acelino Cardoso de. January 2010 (has links)
Orientador: Devaney Ribeiro do Carmo / Banca: Newton Luiz Dias Filho / Banca: Jeosadaque José de Sene / Resumo: O objetivo deste trabalho esta resumido através de três etapas. 1 - A primeira etapa consistiu em funcionalizar e caracterizar a sílica gel com grupos 3- aminopropiltrietoxisilano. Nesta etapa o material obtido (Si) foi caracterizado por técnicas de Ressonância Magnética Nuclear no estado sólido (24Si e 13C) e espectroscopia vibracional (FTIR). 2- Numa segunda etapa promoveu-se a adsorção de íons de cobre (II) e de cobalto (II) na superfície da sílica (Si). Os materiais obtidos (SiCu e SiCo) foram caracterizados por espectroscopia vibracional e voltametria cíclica. 3- Na terceira etapa reagiu-se os materiais preparados (SiCu e SiCo) com nitroprussiato de sódio para formar os complexos binucleares (SiCuNP e SiCoNP). Estes materiais também foram caracterizados por espectroscopia vibracional e voltametria cíclica. Estes materiais foram utilizados na construção do eletrodo de pasta de grafite e testados na oxidação eletrocatalítica de substâncias biologicamente importantes tais como a hidrazina e N-acetilcisteína sendo empregado para isto a técnica de voltametria cíclica. Observou-se que o eletrodo de SiCuNP apresentam dois pares redox nos potenciais (Em)1 = 0,34 V e (Em)2 = 0,76 V vs Ag/AgCl, O primeiro foi atribuído ao processo de oxidação do par Cu(I)/Cu(II) e o segundo ao processo de oxidação Fe(II)(CN)5NO / Fe(III)(CN)5NO do complexo binuclear. O sistema SiCoNP foram observados dois pares redox distintos com os seguintes potenciais médios (Em); (Em)1 = 0,29 V e (Em)2 = 0,56 V vs Ag/AgCl, o primeiro foi atribuído ao processo redox do par Co(II)/Co(III) e o segundo ao processo redox Fe(II)(CN)5NO / Fe(III)(CN)5NO do complexo binuclear formado. O sistema SiCuNP foi sensível a concentração de hidrazina apresentando um limite de detecção e sensibilidade amperométrica de 3,07×10-4 mol L-1 e 5,84×10-6 A / mol L-1... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The objective of this work is summarized in three stages. 1 - The first stage functionalizes and characterizes the silica gel with 3-aminopropyltriethoxysilane groups. At this stage the material obtained (Si) was characterized by solid state Nuclear Magnetic Resonance techniques (24Si and 13C) and vibrational spectroscopy (FTIR). 2 - The second stage promotes the adsorption of copper (II) and cobalt (II) ions on the surface of the silica (Si). The materials obtained (SiCu and SiCo) were characterized by vibrational spectroscopy and cyclic voltammetry. 3 - The third stage prepares the reaction of the materials (SiCu and SiCo) with sodium nitroprusside to form the binuclear complex (SiCuNP and SiCoNP). These materials were characterized by vibrational spectroscopy and cyclic voltammetry. These materials were used to construct the electrode carbon paste and were tested for electrocatalytic oxidation of biologically important substances such as hydrazine and N-acetylcysteine using the cyclic voltammetry technique. It was observed that the electrode SiCuNP has two redox pairs in the potential (Em)1 = 0.34 V and (Em)2 = 0.76 V vs. Ag/AgCl, the first was attributed to the oxidation process of the pair Cu(I)/Cu(II) and the second to the oxidation process Fe(II)(CN)5NO / Fe(III)(CN)5NO of the binuclear complex. For the SiCoNP system, two distinct redox couples were observed with the following mean potentials (Em); (Em)1 = 0.29 V and (Em)2 = 0.56 V vs Ag/AgCl, the first one was assigned to the redox process of the Co(II)/Co(III) pair and the second one to the redox process Fe(II)(CN)5NO / Fe(III)(CN)5NO of the binuclear complex formed. The SiCuNP system was sensitive to the hydrazine concentration, exhibiting a detection limit and amperometric sensitivity of 3.07×10-4 mol L-1 and 5.84×10-6 A / mol L-1 respectively and was also... (Summary complete electronic access click below) / Mestre
|
128 |
Synthesis and Luminescence of Zinc Oxide Nanorods-Blended Thiopheno-Organosilicon PolymersTyombo, Nolukholo January 2017 (has links)
Magister Scientiae - MSc (Chemistry) / The increasing cost of fossil fuel energy production and its implication in environmental
pollution and climate change created high demand for alternative and renewable sources of
energy. This has led to great interest in research in the field of photovoltaic or solar cells Due to
the abundance of sunlight, the technology is sustainable, non-polluting and can be implemented
at places where power demand is needed, for example in rural areas. Solar cell devices that have
been commercialized are currently based on silicon technology, involving the use of
monocrystalline, polycrystalline and amorphous silicon. Although they produce highly efficient
solar cells, the cost of Si solar cells is too high. Second generation solar cell materials such as
cadmium telluride and third generation materials such as perovskites and organic polymers have
been receiving much attention recently. However, they lack the efficiency of Si solar cells. This
research proposes the development of high energy conservation photovoltaic cells from novel
low-cost organosilicon polymers. The aim was to develop novel highly branched organosilane
polymers such as poly(3-hexythiophene), polydi(thien-2-yl)dimethylsilane, poly(3-hexyl-
[2,2'] bithiophenyl-5-yl)-dimethyl-thiophen-2yl-silane) as electron donors along with zinc oxide
nanorod as the electron acceptor which were able to bring the efficiency of the resultant
photovoltaic cell close to that of current Si solar cell. / 2021-08-31
|
129 |
Amperometric biosensor systems prepared on poly (aniline-ferrocenium hexafluorophosphate) composites doped with poly(vinyl sulfonic acid sodium salt)Ndangili, Peter Munyao January 2008 (has links)
Magister Scientiae - MSc / The main hypothesis in this study is the development of a nanocomposite mediated amperometric biosensor for detection of hydrogen peroxide. The aim is to combine the electrochemical properties of both polyaniline and ferrocenium hexafluorophosphate into highly conductive nano composites capable of exhibiting electrochemistry in non acidic media; shuttling electrons between HRP and GCE for biosensor applications. / South Africa
|
130 |
Polyamic acid composites for multiiple sensing applications in complex sample matricesHess, Euòdia Hallouise January 2013 (has links)
Philosophiae Doctor - PhD / Polyamic acid-polypyrrole (PAA/PPy) composite films were prepared and characterised for the use as conducting platforms in the design of biosensor systems. The thin films were synthesised by electrochemical method from a solution containing controlled molar ratio of chemically synthesised polyamic acid (PAA) and pyrrole monomer. Homogenous films were obtained incorporating PAA into electropolymerised polypyrrole (PPy) thin film. The concentration of PAA (1.37 × 10-6 M) was kept fixed throughout the composite ratio analysis, whilst the concentration of PPy was varied from 1.9 × 10-3 M to 9.9 × 10-3 M. The PAA/PPy
thin films were electrodeposited at a glassy carbon electrode (GCE) and characterised using Fourier Transform Infrared Spectroscopy (FTIR), Raman spectroscopy, Atomic Force microscopy (AFM), Scanning electron microscopy (SEM) and electrochemical (CV, SWV) techniques. The composition that best represented the homogenous incorporation of PAA into PPy matrix was observed at a PAA/PPy ratio of 1: 4.13 × 10-3. This composite was observed to have two sets of coupled peaks with formal potential 99 mV and 567 mV respectively. The
De determined from cyclic voltammetry using the anodic peak currents were found to be twice as high (5.82 × 10-4 cm2/s) as the De calculated using the cathodic peak currents (2.60 × 10-4 cm2/s), indicating that the composite favours anodic electron mobility. Surface morphology and spectroscopy data support the formation of a homogenous polymer blend at the synthesis ratio represented by composite 3. For the construction of a biosensor the spectroscopic and electrochemical properties of the enzyme, luciferase and the analytes i.e
naphthalene and fluoranthene were evaluated. Fluorescence spectroscopy studies were carried out to characterize the enzyme’s bioluminescence response in PBS at pH 7. Luciferase showed an absorption peak at 340 nm. The bioluminescence properties of the enzyme with the analytes were explored by fluorescence spectroscopy. The emmision peak at 340 nm gradually decreased as the concentration of each analyte was increased respectively.
|
Page generated in 0.0913 seconds