A novel nanostructured composite formed by interaction of copper octa(3-aminopropyl)octasilsesquioxane with azide ligands: Preparation, characterization and a voltammetric application

This study presents the preparation, characterization and application of copper octa(3-aminopropyl)octasilsesquioxane following its subsequent reaction with azide ions (ASCA). The precursor (AC) and the novel compound (ASCA) were characterized by Fourier transform infrared spectra (FTIR), nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR), scanning electronic microscopy (SEM), X-ray diffraction (XRD), Thermogravimetric analyses and voltammetric technique. The cyclic voltammogram of the modified graphite paste electrode with ASCA (GPE-ASCA), showed one redox couple with formal potential (E(1/2)(ox)) = 0.30 V and an irreversible process at 1.1 V (vs. Ag/AgCl; NaCl 1.0 M; v = 20 mV s(-1)). The material is very sensitive to nitrite concentrations. The modified graphite paste electrode (GPE-ASCA) gives a linear range from 1.0 x 10(-4) to 4.0 x 10(-3) mol L(-1) for the determination of nitrite, with a detection limit of 2.1 x 10(-4) mol L(-1) and the amperometric sensitivity of 8.04 mA/mol L(-1). (C) 2010 Elsevier Ltd. All rights reserved.

Nanogravimetric study of the complex voltammetric response in the electro-oxidation of methanol on platinum

Instead of a time-invariant voltammetric profile, many electrochemical systems display a cycle-dependent current-potential response. This phenomenon has been referred to as complex voltammetric response and it has been observed during the electro-oxidation of several molecules such as methanol, ethanol, propanol and hydrogen. There are currently two explanations for the surface mechanism underlying this behavior. In one scenario, the complex voltammogram would result from the specific kinetic pathway taken during the forward sweep. In the other explanation, the phenomenon is discussed in terms of the interplay among the surface roughening and subsequent relaxation, and the ohmic drop coupled to a negative differential resistance. We report in this paper a nanogravimetric investigation of the complex voltammetric response in the electro-oxidation of methanol on platinum electrode in both acidic and alkaline media. Different periodic patterns composed of intercalated small and large hysteresis cycles were observed as a function of the applied voltage and the series resistance between the working electrode and the potentiostat. Independently, nanogravimetric results indicated no detectable difference in the delta-frequency versus voltage profile between small and large hysteresis cycles. These findings were interpreted as experimental evidence of the secondary, if any, role played by the very electrochemical reaction on the emergence of complex voltammetric response. (C) 2009 Elsevier Ltd. All rights reserved.

Voltammetric characterization of stepped platinum single crystal surfaces vicinal to the (110) pole

Platinum stepped surfaces vicinal to the (1 1 0) crystallographic pole have been investigated voltammetrically in 0.1 M HClO(4) and 0.1 M H(2)SO(4) solutions. Changes in the voltammetric profile with the step density suggest the existence of two types of surface sites, that has been ascribed to linear and bidimensional domains. This result indicates the existence of important restructuring processes that separate the real surface distribution from the nominal one. The electronic properties of the surfaces have been characterized with the CO charge displacement method and the potential of zero total charge has been calculated as a function of the step density. (c) 2009 Elsevier B.V. All rights reserved.

Development and application of a microelectrode based scanning voltammetric detector

A large part of the work presented in this thesis describes the development and use of a novel electrochemical detector designed to allow the electrochemical characterisation of compounds in flowing solution by means of cyclic voltammetry. The detector was microprocessor controlled, which provides digital generation of the potential waveform and collection of data for subsequent analysis. Microdisk working electrodes are employed to permit both thermodynamic and kinetically controlled processes to be studied under steady-state conditions in flowing solutions without the distortion or hysteresis normally encountered with larger sized electrodes. The effect of electrode size, potential scan rate, and solution flow rate are studied extensively with the oxidation of ferrocene used as an example of a thermodynamically controlled process and a series of catecholamines as examples of a kinetically controlled process. The performance of the detector was best demonstrated when used as a HPLC post-column detector. The 3-dimensional chromatovoltammograms obtained allow on-line characterisation of each fraction as it elutes from the column. The rest of the work presented in this thesis involves the study of the oxidative degradation pathway of dithranol. The oxidative pathway was shown to involve a complex free radical mechanism, dependent on the presence of both oxygen and, in particular light. The pathway is further complicated by the fact that dithranol may exist in either a keto or enol form, the enol being most susceptible to oxidation. A likely mechanism is proposed from studies performed with cyclic voltammetry and controlled potential electrolysis, then defined by subsequent kinetic studies.

Direct electro-deposition of graphene from aqueous suspensions

We describe the direct electro-chemical reduction of graphene oxide to graphene from aqueous suspension by applying reduction voltages exceeding -1.0 to -1.2 V. The conductivity of the deposition medium is of crucial importance and only values between 4-25 mS cm^-1 result in deposition. Above 25 mS cm^-1 the suspension de-stabilises while conductivities below 4 mS cm_^-1 do not show a measurable deposition rate. Furthermore, we show that deposition can be carried out over a wide pH region ranging from 1.5 to 12.5. The electro-deposition process is characterised in terms of electro-chemical methods including cyclic voltammetry, quartz crystal microbalance, impedance spectroscopy, constant amperometry and potentiometric titrations, while the deposits are analysed via Raman spectroscopy, infra-red spectroscopy, X-ray photoelectron spectroscopy and X-ray diffractometry. The determined oxygen contents are similar to those of chemically reduced graphene oxide, and the conductivity of the deposits was found to be ~20 S cm ^-1.

Systematic approach to the quantitative voltammetric analysis of the Fe III /Fe II component of the [α 2 -Fe(OH 2 )P 2 W 17 O 61 ] 7-/8- reduction process in buffered and unbuffered aqueous media

The one-electron reduction of [α2-FeIII(OH2)P2W17O61]7- at a glassy carbon electrode was investigated using cyclic and rotating-disk-electrode voltammetry in buffered and unbuffered aqueous solutions over the pH range 3.45−7.50 with an ionic strength of approximately 0.6 M maintained. The behavior is well-described by a square-scheme mechanism P + e- ↔ Q (E10/ = −0.275 V, k10/ = 0.008 cm s-1, and α1 = 1/2), PH+ + e- ↔ QH+ (E20/ = −0.036 V, k20/ = 0.014 cm s-1, and α2 = 1/2), PH+ ↔ P + H+ (KP = 3.02 × 10-6 M), and QH+ ↔ Q + H+ (KQ = 2.35 × 10-10 M), where P, Q, PH+, and QH+ correspond to [α2-FeIII(OH)P2W17O61]8-, [α2-FeII(OH)P2W17O61]9-, [α2-FeIII(OH2)P2W17O61]7-, and [α2-FeII(OH2)P2W17O61]8-, respectively; E10‘ and E20‘ are the formal potentials, k10‘ and k20‘ are the formal (standard) rate constants, and KP and KQ are the acid dissociation constants for the relevant reactions. The analysis for the buffered media is based on the approach of Laviron who demonstrated that a square scheme with fully reversible protonations, reversible or quasi reversible electron transfers with the assumption that α1 = α2, can be well-described by the behavior of a simple redox couple, ox + e- ↔ red, whose formal potential, Eapp0‘, and standard rate constant, kapp0‘, are straightforwardly derived functions of pH, as are the values of E10‘, k10‘, E20‘, k20‘, and KP (only three of the four thermodynamic parameters in a square scheme can be specified). It was assumed that αapp = 1/2, and the simulation program DigiSim was used to determine the values of Eapp0‘ and kapp0‘, which are required to describe the cyclic voltammograms obtained in buffered media in the pH range from 3.45 to 7.52 (buffer-related reactions which effect general acid−base catalysis are included in the simulations). DigiSim simulations of cyclic voltammograms obtained in unbuffered media yielded the values of E10‘ and k10‘; KQ was then directly computed from thermodynamic constraints. These simulations included additional reactions between the redox species and H2O. The value of the diffusion coefficient of the [α2-FeIII(OH2)P2W17O61]7-, 2.92 × 10-6 cm2 s-1, was determined using DigiSim simulations of voltammograms at a rotating disk electrode in buffered and unbuffered media at pH 3.45. The diffusion coefficients of all redox species were assumed to be identical. When the pH is greater than 6, instability of P (i.e., [α2-FeIII(OH)P2W17O61]8-) led to the loss of the reactant and precluded lengthy experimentation.

Voltammetric determination of isoprenaline in pharmaceutical preparations using a copper(II) hexacyanoferrate(III) modified carbon paste electrode

The electroanalytical determination of isoprenaline in pharmaceutical preparations of a homemade carbon paste electrode modified with copper(II) hexacyanoferrate(III) (CuHCF) was studied by cyclic voltammetry. Several parameters were studied for the optimization of the sensor such as electrode composition, electrolytic solution, pH effect, potential scan rate and interferences in potential. The optimum conditions were found in an electrode composition (in mass) of 15% CuHCF, 60% graphite and 25% mineral oil in 0.5 mol l(-1) acetate buffer solution at pH 6.0. The analytical curve for isoprenaline was linear in the concentration range from 1.96 x 10(-4) to 1.07 x 10(-3) mol l(-1) with a detection limit of 8.0 x 10(-5) mol l(-1). The relative standard deviation was 1.2% for 1.96 x 10(-4) mol l(-1) isoprenaline solution (n=5). The procedure was successfully applied to the determination of isoprenaline in pharmaceutical preparations; the CuHCF modified carbon paste electrode gave comparable results to those results obtained using a UV spectrophotometric method. (C) 2004 Elsevier B.V. All rights reserved.

Determination of Analgesics (Dipyrone and Acetaminophen) in Pharmaceutical Preparations by Cyclic Voltammetry at a Copper(II) Hexacyanoferrate(III) Modified Carbon Paste Electrode

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Voltammetric performance and application of a sensor for sodium ions constructed with layered birnessite-type manganese oxide

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Caffeine Determination at a Carbon Fiber Ultramicroelectrodes by Fast-Scan Cyclic Voltammetry

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Voltammetric studies of titanium (IV) phosphate modified with copper hexacyanoferrate and electroanalytical determination of N-acetylcysteine

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

A novel nanostructured composite formed by interaction of copper octa(3-aminopropyl)octasilsesquioxane with azide ligands: Preparation, characterization and a voltammetric application

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Voltammetric Behavior of a Modified Electrode With Azide Copper Octa(3-Aminopropyl)Octasilsesquioxane Composite in the Oxidation of Ascorbic Acid

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Voltammetric Studies of Cobalt Hexacyanoferrate Formed on the Titanium (IV) Phosphate Surface and its Application to the Determination of Sulfite

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)