Home About us Contact
|
Home About us Contact | ||
|
|
||
Electrochemical Characterization (electrochemical + characterization)
Selected AbstractsSelf-Assembled Multilayers of Polyethylenimine and DNA: Spectrophotometric and Electrochemical Characterization and Application for the Determination of Acridine Orange InteractionELECTROANALYSIS, Issue 15 2009F. Ferreyra Abstract This work deals with the study of the interaction between acridine orange (AO) and calf-thymus double stranded DNA (dsDNA) present in supramolecular architectures built on gold electrodes modified with mercapto-1-propanesulfonic acid (MPS) by self-assembling of polyethylenimine and dsDNA. The optimal conditions for building the supramolecular architecture were obtained from UV-vis spectrophotometric experiments. The electrochemical studies were performed by adsorptive transfer square wave voltammetry from the evaluation of the oxidation signal of AO accumulated within the multistructure. The effect of the number of PEI-dsDNA bilayers (Au/MPS/(PEI-dsDNA)n) on the accumulation and electrooxidation of AO is also discussed. [source] Electrochemical Characterization of In Situ Functionalized Gold Cysteamine Self-Assembled Monolayer with 4-Formylphenylboronic Acid for Detection of DopamineELECTROANALYSIS, Issue 5 2008Karimi Shervedani Abstract Functionalization of gold cysteamine (AuCA) self-assembled monolayer with 4-formylphenylboronic acid (BA) via Schiff's base formation, through in situ method to fabricate Au-CA-BA electrode is presented and described. The fabricated electrode was used as a novel sensor for accumulation and determination of dopamine (DA). The accumulation of DA as a diol on the topside of Au-CA-BA as a Lewis acid, was performed via esterification (AuCABADA), and followed for determination of DA. Functionalization, characterization, and determination steps were probed by electrochemical methods like cyclic voltammetry and electrochemical impedance spectroscopy. The data will be presented and discussed from which a new sensor for DA is introduced. [source] Synthesis of Nanohole-Structured Single-Crystalline Platinum Nanosheets Using Surfactant-Liquid-Crystals and their Electrochemical CharacterizationADVANCED FUNCTIONAL MATERIALS, Issue 4 2009Tsuyoshi Kijima Abstract Nanohole-structured single-crystalline Pt nanosheets have been synthesized by the borohydride reduction of Na2PtCl6 confined to the lyotropic liquid crystals (LLCs) of polyoxyethylene (20) sorbitan monooleate (Tween 80) with or without nonaethylene-glycol (C12EO9). The Pt nanosheets of around 4,10,nm in central thickness and up to 500,nm or above in diameter have a number of hexagonal-shaped nanoholes ,1.8,nm wide. High-resolution electron microscope images of the nanosheets showed atomic fringes with a spacing of 0.22,nm indicating that the nanosheets are crystallographically continuous through the nanoholed and non-holed areas. The inner-angle distributions for the hexagonal nanoholes indicate that the six sides of the nanoholes are walled with each two Pt (111), Pt (11) and Pt (010) planes. The formation mechanism of nanoholed Pt nanosheets is discussed on the basis of structural and compositional data for the resulting solids and their precursory LLCs, with the aid of similar nanohole growth observed for a Tween 80 free but oleic acid-incorporated system. It is also demonstrated that the nanoholed Pt nanostructures loaded on carbon exhibit fairly high electrocatalytic activity for oxygen reduction reaction and a high performance as a cathode material for polymer-electrolyte fuel cells, along with their extremely high thermostability revealed through the effect of electron-irradiation. [source] Raspberry-like Gold Microspheres: Preparation and Electrochemical Characterization,ADVANCED FUNCTIONAL MATERIALS, Issue 4 2007Z. Li Abstract A straightforward method to synthesize quasi-monodisperse gold microspheres from a commercial gold plating solution is reported. The size and the surface roughness of the obtained particles can easily be tuned. In particular, raspberry-like particles with a high active surface area are obtained. The microspheres are assembled on indium tin oxide (ITO) electrodes using the layer-by-layer technique and the overall electroactive surface area is increased, as characterized by cyclic voltammetry. The as-prepared products were characterized by scanning electron microscopy (SEM), powder X-ray diffraction (XRD), cyclic voltammetry, and light microscopy. [source] Synthesis, Structure, and Electrochemical Characterization of Nanocrystalline Tantalum and Tungsten NitridesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2007Daiwon Choi Nanocrystalline tantalum and tungsten nitrides were synthesized by a two-step ammonolysis reaction of transition metal chlorides. The first step involves ammonolysis of tantalum and tungsten chlorides at room temperature using anhydrous chloroform as the solvent. A second step consists of heat treatment of these as-prepared powders under anhydrous NH3 atmosphere leading to the formation of tantalum and tungsten nitride nanocrystallites at relatively low temperature (600°,675°C). The ammonolysis, nitridation, structure, morphology, surface area, density, and electronic conductivity of the nitrides obtained were studied and characterized. The electrochemical responses of these nitrides were also measured by cyclic voltammetry using 1M KOH electrolyte. [source] Electrochemical Characterization of a Single Electricity-Producing Bacterial Cell of Shewanella by Using Optical Tweezers,ANGEWANDTE CHEMIE, Issue 37 2010Huan Liu Dr. Leitend verbunden: Gram-negative Shewanella -Bakterien können feste Metalloxide als Netto-Elektronenakzeptoren der Atmungskette nutzen. Einzelne Zellen in direktem elektrischen Kontakt mit einer Mikroelektrode wurden mithilfe optischer Pinzetten charakterisiert (siehe Bild; ITO=Indiumzinnoxid). [source] Structural, Compositional and Electrochemical Characterization of Pt,Co Oxygen-Reduction CatalystsCHEMPHYSCHEM, Issue 7 2010S. Axnanda Abstract Pt,Co thin-film electrocatalysts have been characterized using low-energy ion-scattering spectroscopy (LEISS), X-ray photoelectron spectroscopy (XPS), low-energy electron diffraction (LEED), temperature-programmed desorption (TPD) and electrochemistry (EC). For comparative purposes, LEISS and EC were also carried out on a bulk Pt3Co(111) single crystal. The extensive experimental work resulted in the establishment of the surface phase diagram of the alloy film marked by a substantial divergence between the composition at the interface and that in the interior. When a dual-layer deposit of Pt and Co was annealed at high temperatures, alloy formation transpired in which the outermost layer became single-crystalline and enriched in Pt. The preferential surface segregation of Pt, however, was not sufficient to generate a platinum-only overlayer or "skin". Invariably, Co was found to co-exist with Pt, independent of the substrate [Mo(110) or Ru(0001)] employed; Pt3Co was the most favored composition. The same result, the absence of a Pt skin, was likewise indicated at the post-thermally-annealed surface of the bulk Pt3Co(111) monocrystal. For alloy-film surfaces more enriched in Pt than Pt3Co, the topmost layer was constituted primarily, but not exclusively, of Pt(111) domains. The proclivities of the alloys towards enhanced catalysis of the oxygen-reduction reaction were assessed in terms of their voltage efficiencies, as manifested by the open-circuit potential (OCP) in O2 -saturated sulfuric acid electrolyte. The Pt3Co surface, whether from the thin film or the bulk single crystal, exhibited the highest OCP, a significant improvement over pure Pt but still appreciably lower than the thermodynamic limit. The degradation of the Pt3Co thin-film surface was predominantly due to Co corrosion. A minimal amount was spontaneously dissolved upon simple immersion in solution; slightly higher dissolution occurred at potentials above the OCP. The fraction that was not immediately corroded proved to be stable even after prolonged periods at potentials more positive than the OCP. [source] Electrochemical Characterization of (ZnO/dsDNA)n Layer-by-layer Films and Detection of Natural DNA Oxidative DamageCHINESE JOURNAL OF CHEMISTRY, Issue 10 2009Meng Du Abstract The positively charged nano-ZnO and negatively charged natural DNA were alternately adsorbed on the surface of a gold electrode, forming (ZnO/dsDNA)nlayer-by-layer films. Valuable dynamic information for controlling the formation and growth of the films was obtained by cyclic voltammetry and electrochemical impedance spectroscopy. Differential pulse voltammetric (DPV) measurements showed that the electroactive probe methylene blue (MB) could be loaded in the (ZnO/dsDNA)nfilms from its solution, and then released from the films into Britton-Robinson (B-R) buffer. The complete reloading of MB in the films could be realized by immersing the films in MB solution again. However, after incubation in the solution of carcinogenic metal nickel, the damaged (ZnO/dsDNA)n films could not return to their original and fully-loaded state, and showed smaller DPV peak currents. The results demonstrated that the DNA damage induced by the hydroxyl radical could be achieved by electrochemistry. [source] Gravity-induced convective flow in microfluidic systems: Electrochemical characterization and application to enzyme-linked immunosorbent assay testsELECTROPHORESIS, Issue 21-22 2004Patrick Morier Abstract A way of using gravity flow to induce a linear convection within a microfluidic system is presented. It is shown and mathematically supported that tilting a 1 cm long covered microchannel is enough to generate flow rates up to 1000 nL·min -1, which represents a linear velocity of 2.4 mm·s -1. This paper also presents a method to monitor the microfluidic events occurring in a covered microchannel when a difference of pressure is applied to force a solution to flow in said covered microchannel, thanks to electrodes inserted in the microfluidic device. Gravity-induced flow monitored electrochemically is applied to the performance of a parallel-microchannel enzyme-linked immunosorbent assay (ELISA) of the thyroid-stimulating hormone (TSH) with electrochemical detection. A simple method for generating and monitoring fluid flows is described, which can, for instance, be used for controlling parallel assays in microsystems. [source] A New Indirect Electroanalytical Method to Monitor the Contamination of Natural Waters with 4-Nitrophenol Using Multiwall Carbon NanotubesELECTROANALYSIS, Issue 9 2009Cruz Moraes, Fernando Abstract The electrochemical detection of the hazardous pollutant 4-nitrophenol (4-NP) at low potentials, in order to avoid matrix interferences, is an important research challenge. This study describes the development, electrochemical characterization and utilization of a multiwall carbon nanotube (MWCNT) film electrode for the quantitative determination of 4-NP in natural water. Electrochemical impedance spectroscopy measurements showed that the modified surface exhibits a decrease of ca. 13 times in the charge transfer resistance when compared with a bare glassy carbon (GC) surface. Voltammetric experiments showed the possibility to oxidize a hydroxylamine layer (produced by the electrochemical reduction of 4-NP on the GC/MWNCT surface) in a potential region which is approximately 700,mV less positive than that needed to oxidize 4-NP, thus minimizing the interference of matrix components. The limit of detection for 4-NP obtained using square-wave voltammetry (0.12,,mol L,1) was lower than the value advised by EPA. A natural water sample from a dam located in Săo Carlos (Brazil) was spiked with 4-NP and analyzed by the standard addition method using the GC/MWCNT electrode, without any further purification step. The recovery procedure yielded a value of 96.5% for such sample, thus confirming the suitability of the developed method to determine 4-NP in natural water samples. The electrochemical determination was compared with that obtained by HPLC with UV-vis detection. [source] Photophysical and electrochemical characterization of new poly(arylene vinylene) copolymers containing quinoline or bisquinoline segmentsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 13 2009John A. Mikroyannidis Abstract Four new fluorescent conjugated vinylene-copolymers incorporating quinoline or bisquinoline segments along the backbone were synthesized by Heck coupling. Three of them were fluorenevinylene-copolymers and contained quinoline (PQFV, PQFVT) or bisquinoline segments (PBQFV). One of them (PBQPV) was phenylenevinylene-copolymer and contained bisquinoline segments. All the copolymers were soluble in common organic solvents and had relatively low glass transition temperature (Tg = 50,56 °C for fluorenevinylenes and Tg < 25 °C for phenylenevinylene). In THF solutions, the quinoline-containing copolymers showed absorption maxima at 411,420 nm while the bisquinoline-containing ones exhibited maxima at 357,361 nm. The emission maxima of solutions were 465,490 nm. The copolymers showed high quantum yields up to 64%. The films exhibited absorption and emission maxima in the range of 371,437 nm and 480,521 nm, respectively. All copolymers revealed reversible reduction with electron affinity of 2.66,3.53 eV and irreversible oxidation scans with ionization potential of 5.39,5.53 eV. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3370,3379, 2009 [source] Top-down processed silicon nanowire transistor arrays for biosensingPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 3 2009Xuan Thang Vu Abstract We describe the fabrication, electrical and electrochemical characterization of silicon nanowire arrays, which were processed in a top-down approach using combined nanoimprint lithography and wet chemical etching. We used the top silicon layer as contact line and observed an influence of implantation and subsequent annealing of these lines to the device performance. In addition we found a subthreshold slope dependence on wire size. When operated in a liquid environment, wires can be utilized as pH sensors. We characterized the pH sensitivity in the linear range and in the subthreshold operation regime. As a first proof-of-principle experiment for the later use of the sensors in bioassays, we monitored the buildup of polyelectrolyte multilayers on the wire surface. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Different nanostructure cathode catalysts application for direct methanol fuel cellPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 12 2007Sharmin Sultana Dipti Abstract Direct methanol fuel cell (DMFC) belongs to the same family of energy conversion device and the application of new hydrogen storage nanomaterials such as carbon nanotube (CNTs) supported catalysts is being addressed in an increasing industrial approach. In this present study, multiwall carbon nanotube supported Pt and Pt-Ni nanoparticles were prepared as cathode catalysts for direct methanol fuel cell application. Transmission electron microscopy and X-ray diffraction analyses indicated the formation of well-dispersed Pt and Pt-Ni nanoparticles having sizes of around 2 , 4 nm on carbon nanotube. Furthermore, the electrochemical characterization by the cyclic voltammetry (CV) demonstrated that these catalysts have higher catalytic activity and the methanol oxidation reaction of the Pt-Ni/CNTs is respectively almost similar and slightly higher than Pt/CNTs electrocatalysts. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Effect of Cyanato, Azido, Carboxylato, and Carbonato Ligands on the Formation of Cobalt(II) Polyoxometalates: Characterization, Magnetic, and Electrochemical Studies of Multinuclear Cobalt ClustersCHEMISTRY - A EUROPEAN JOURNAL, Issue 12 2007Laurent Lisnard Dr. Abstract Five CoII silicotungstate complexes are reported. The centrosymmetric heptanuclear compound K20[{(B-,-SiW9O33(OH))(,-SiW8O29(OH)2)Co3(H2O)}2Co(H2O)2],47,H2O (1) consists of two {(B-,-SiW9O33(OH))(,-SiW8O29(OH)2)Co3(H2O)} units connected by a {CoO4(H2O)2} group. In the chiral species K7[Co1.5(H2O)7)][(,-SiW10O36)(,-SiW8O30(OH))Co4(OH)(H2O)7],36,H2O (2), a {,-SiW10O36} and a {,-SiW8O30(OH)} unit enclose a mononuclear {CoO4(H2O)2} group and a {Co3O7(OH)(H2O)5} fragment. The two trinuclear CoII clusters present in 1 enclose a ,4 -O atom, while in 2 a ,3 -OH bridging group connects the three paramagnetic centers of the trinuclear unit, inducing significantly larger Co-L-Co (L=,4 -O (1), ,3 -OH (2)) bridging angles in 2 (,av(Co-L-Co)=99.1°) than in 1 (,av(Co-L-Co)=92.8°). Weaker ferromagnetic interactions were found in 2 than in 1, in agreement with larger Co-L-Co angles in 2. The electrochemistry of 1 was studied in detail. The two chemically reversible redox couples observed in the positive potential domain were attributed to the redox processes of CoII centers, and indicated that two types of CoII centers in the structure were oxidized in separate waves. Redox activity of the seventh CoII center was not detected. Preliminary experiments indicated that 1 catalyzes the reduction of nitrite and NO. Remarkably, a reversible interaction exists with NO or related species. The hybrid tetranuclear complexes K5Na3[(A-,-SiW9O34)Co4(OH)3(CH3COO)3],18,H2O (3) and K5Na3[(A-,-SiW9O34)Co4(OH)(N3)2(CH3COO)3],18,H2O (4) were characterized: in both, a tetrahedral {Co4(L1)(L2)2(CH3COO)3} (3: L1=L2=OH; 4: L1=OH, L2=N3) unit capped the [A-,-SiW9O34]10, trivacant polyanion. The octanuclear complex K8Na8[(A-,-SiW9O34)2Co8(OH)6(H2O)2(CO3)3],52,H2O (5), containing two {Co4O9(OH)3(H2O)} units, was also obtained. Compounds 2, 3, 4, and 5 were less stable than 1, but their partial electrochemical characterization was possible; the electronic effect expected for 3 and 4 was observed. [source] Efficient Light-Emitting Devices Based on Phosphorescent Polyhedral Oligomeric Silsesquioxane MaterialsADVANCED FUNCTIONAL MATERIALS, Issue 16 2009Xiaohui Yang Abstract Synthesis, photophysical, and electrochemical characterizations of iridium-complex anchored polyhedral oligomeric silsesquioxane (POSS) macromolecules are reported. Monochromatic organic light-emitting devices based on these phosphorescent POSS materials show peak external quantum efficiencies in the range of 5,9%, which can be driven at a voltage less than 10,V for a luminance of 1000,cd m,2. The white-emitting devices with POSS emitters show an external quantum efficiency of 8%, a power efficiency of 8.1,lm W,1, and Commission International de'lÉclairage coordinates of (0.36, 0.39) at 1000,cd m,2. Encouraging efficiency is achieved in the devices based on hole-transporting and Ir-complex moieties dual-functionalized POSS materials without using host materials, demonstrating that triplet-dye and carrier-transporting moieties functionalized POSS material is a viable approach for the development of solution-processable electrophosphorescent devices. [source] Physicochemical and electrochemical characterizations of organic montmorillonite (OMMT)/sulfonated poly(ether ether ketone) (SPEEK) composite membranesASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2010R. Gosalawit Abstract Physicochemical and electrochemical properties of the organic montmorillonite (OMMT)/sulfonated poly(ether ether ketone) (SPEEK) composite membranes are considered for their use as proton conducting membranes. The paper presents the preparation and characterization of SPEEK and its composite membranes with OMMT as well as their comparison to the reference Nafion® 117 membrane. Water uptake and thermal property (Td1) are improved when the OMMT loading content increases. Methanol permeability decreases as OMMT loading content increases up to as high as 53% (5 wt% OMMT/SPEEK composite membrane). For proton conductivity, all membranes show improvement when the operating temperature increases from 25 to 90 °C. The proton conductivity at 100 °C of 3 wt% OMMT/SPEEK composite membrane (5.6 × 10,2 S/cm) is one order of magnitude higher than that of Nafion® 117 (2 × 10,3 S/cm). Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] | |||||||||||||