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The palladium–salen complex was immobilized by electropolymerization onto a Pt disc electrode and applied as an electrocatalyst for the reduction of CO2 in an aqueous solution. Linear sweep voltammetry measurements and rotating disk experiments were carried out to study the electrochemical reduction of carbon dioxide. The onset overpotential for carbon dioxide reduction was approximately −0.22 V vs. NHE on the poly-Pd(salen) modified electrode. In addition, by combining the electrochemical study with a kinetic study, the rate-determining step of the electrochemical CO2 reduction reaction (CO2RR) was found to be the radial reduction of carbon dioxide to the CO adsorbed on the metal. [ABSTRACT FROM AUTHOR]

This work describes the photoelectrochemical properties of devices coated with poly(azo‐Bismarck Brown R) and the nanocomposite poly(azo‐Bismarck Brown R)/reduced graphene oxide. Chronoamperometric methods with pulsed light are applied to the polymer surfaces of poly(azo‐Bismarck R) and poly(azo‐Bismarck Brown R)/rGO nanocomposites at two applied potentials (corresponding to the reduced and oxidized polymer forms) to obtain information on the photocurrent in a short response time. The results indicate that the photoactivity of the nanomaterial depends on the oxidation state of the azo‐polymer and its chemical structure. The carrier mobility of the material is affected by the applied potential profile and consequently by the isomerism of the polymer backbone. This behavior explains the photoelectrochemical performance of the nanocomposite material. The photoresponsiveness of the semiconducting hybrid material with light‐switchable conductance is promising for applications in photoelectrochemical switches and molecular switching devices. [ABSTRACT FROM AUTHOR]

Copyright of Colloquium Exactarum is the property of Asociacao Prudentina de Educacao e Cultura (APEC) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Colloquium Exactarum is the property of Asociacao Prudentina de Educacao e Cultura (APEC) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The present paper describes the electrochemical activity of a Ni(II)‐Schiff base metallopolymer electrode for the oxidation of ethanol in alkaline media. The scanning electron microscope results show that the metallopolymer at the glassy carbon surface has a nanoflake‐like lamellar structure, and there is no molecular structural change after treatment with NaOH. Voltammetry measurements indicate that the metallopolymer acts as efficient material for the electrocatalytic oxidation of ethanol, where a high‐valent nickel(IV) was revealed as the reactive intermediate during the anodic scan. An isopotential point can be observed in rotating disk electrode voltammetry for ethanol oxidation. The electrode surface may be considered to consist of two independent electrochemical regions, one corresponding to the ethanol electro‐oxidation by nickel(IV) and the second corresponding to water oxidation. The Tafel slopes were found to be 246 mV dec−1 at low overpotentials and 44 mV dec−1 at high overpotentials, which suggest that the first electron transfer step is the rate controlling step. The specific activity of the metallopolymer‐modified electrode for the ethanol electro‐oxidation reaction was 6.66 mA cm−2 for 0.130 μmol cm−2 of electroactive species of metallopolymer at 0.6 V vs. SCE. The activity of a Ni(II)‐Schiff base metallopolymer electrodes for ethanol oxidation is investigated in alkaline media. Tafel slopes of 246 mV dec−1 at low overpotentials and 44 mV dec−1 at high overpotentials are found, suggesting that the first electron transfer step is rate controlling. An isopotential point is observed, revealing that the electrode surface may be considered to consist of two independent electrochemical regions. [ABSTRACT FROM AUTHOR]

Copyright of Colloquium Exactarum is the property of Asociacao Prudentina de Educacao e Cultura (APEC) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The mediation of electron-transfer by oxo-bridged dinuclear ruthenium ammine [(bpy)2(NH3)RuIII( µ-O)RuIII(NH3)(bpy)2]4+ for the oxidation of glucose was investigated by cyclic voltammetry. These ruthenium (III) complexes exhibit appropriate redox potentials of 0.131-0.09 V vs. SCE to act as electron-transfer mediators. The plot of anodic current vs. the glucose concentration was linear in the concentration range between 2.52×10−5 and 1.00×10−4 mol L−1. Moreover, the apparent Michaelis-Menten kinetic ( KMapp) and the catalytic ( Kcat) constants were 8.757×10−6 mol L−1 and 1,956 s−1, respectively, demonstrating the efficiency of the ruthenium dinuclear oxo-complex [(bpy)2(NH3)RuIII( µ-O)RuIII(NH3)(bpy)2]4+ as mediator of redox electron-transfer. [ABSTRACT FROM AUTHOR]

A simple and fast method based on electrochemical measurements was proposed for estimation of total polyphenols using a carbon paste modified electrode. The method was based on catalytic response exhibited by a ruthenium complex [(bpy)2(NH3)RuIII(µ-O)RuIII(NH3)(bpy)2]4+ in presence of gallic acid (GA). Calibration plots using chronoamperometry (CA) showed a linear response for GA concentrations ranging from 6.6×10−6 to 1.9×10−4 mol L−1 with a detection limit of 4.9×10−7 mol L−1. Comparative studies using the official method revealed a good agreement between methods suggesting that the proposed method can be applied for polyphenol estimation without any sample treatment. [ABSTRACT FROM AUTHOR]

A biomimetic sensor containing the oxo-bridged dinuclear manganese-phenanthroline complex incorporated into a cation-exchange polymeric film deposited onto glassy carbon electrode for detection of sulfite was studied. Cyclic voltammetry at the modified electrode in universal buffer showed a two electron oxidation/reduction of the couple MnIV(μ-O)2MnIV/MnIII(μ-O)2MnIII. The sensor exhibited electrocatalytic property toward sulfite oxidation with a decrease of the overpotential of 450 mV compared with the glassy carbon electrode. A plot of the anodic current versus the sulfite concentration for potential fixed (+0.15 V vs. SCE) at the sensor was linear in the 4.99×10−7 to 2.49×10−6 mol L−1 concentration range and the concentration limit was 1.33×10−7 mol L−1. The mediated mechanism was derived by MichaelisMenten kinetics. The calculated kinetics values were MichaelisMenten rate constant= ${K{{{\rm app}\hfill \atop {\rm M}\hfill}}}$=1.33 µmol L−1, catalytic rate constant=6.06×10−3 s−1 and heterogeneous electro-chemical rate constant=3.61×10−5 cm s−1. [ABSTRACT FROM AUTHOR]

An analytical method was developed for quantification of the fungicide thiram (tetramethylthiuram disulfide), based on its capacity to complex Cu2+ions. A solid-phase reactor (SPR) was coupled in a flow system containing a spectrophotometer as detector. The SPR consisted of a tube filled with finely ground resin, in which copper(II) phosphate was immobilised prior to polymerisation. Contact of thiram with the Cu2+ions immobilised in the resin resulted in the formation of a strongly coloured Cu2+/thiram complex. Maximum absorbance of the Cu2+/thiram complex was obtained at a wavelength of 439 nm. The usefulness of the methodology has been evidenced by the determination of thiram residues in corn and bean grains. Previously, a variety of transition metal cations which would form coloured complexes with tetramethylthiuram disulfide were tested. [ABSTRACT FROM PUBLISHER]

The participation of cations in redox reactions of manganese oxides provides an opportunity for development of chemical sensors for non-electroactive ions. A sensor based on a nanostructured hollandite-type manganese oxide was investigated for voltammetric detection of potassium ions. The detection is based on the measurement of anodic current generated by oxidation of Mn(III) to Mn(IV) at the surface of the electrode and the subsequent extraction of the potassium ions into the hollandite structure. In this work, an amperometric procedure at an operating potential of 0.80 V (versus SCE) is exploited for amperometric monitoring. The current signals are linearly proportional to potassium ion concentration in the range 4.97 × 10-5 to 9.05 × 10-4 mol L-1, with a correlation coefficient of 0.9997. [ABSTRACT FROM AUTHOR]

A carbon paste electrode modified with copper(II) phosphate immobilized in a polyester resin (CuP-Poly) is proposed for voltammetric determination of l -ascorbic acid in pharmaceutical formulations. The modified electrode allows the detection of l -ascorbic acid at lower anodic potentials than observed at unmodified electrodes. Several parameters that can influence the voltammetric response of the proposed electrode such as carbon paste composition, pH, scan rate, and possible interference were investigated. The peak current was proportional to the concentration of ascorbic acid in the range 2.0×10-5 to 3.2×10-3 mol L-1 with a detection limit of 1.0×10-5 mol L-1. The stability and repeatability of the electrode for the determination of l -ascorbic acid are also discussed. Amperometric response was also recorded for electrocatalytic oxidation of the l -ascorbic acid. Concentrations of the vitamin C in pharmaceutical formulations (tablets) measured using the modified electrode and a titrimetric method are in agreement at the 95% confidence level and within an acceptable range of error. [ABSTRACT FROM AUTHOR]

The construction and analytical evaluation of a PbO2-based graphite–epoxy electrode sensitive to H3O+, based on incorporation of lead(IV) oxide in a graphite– epoxy matrix, are described. The data obtained from a variety of acid–base titrations in aqueous and aqueous– ethanolic media were compared with those obtained by use of a glass electrode under the same conditions. The proposed electrode provides a linear response in the pH range from 1 to 11 with a slope of –58.7 ± 0.3 mV pH–1 and –60.8 ± 0.2 mV pH–1 in aqueous and ethanolic media, respectively. The response time was less than 15 s and the lifetime of the electrode was at least eight months (ca. 5000 determinations) and its performance is good in pH determination and end-point detection in potentiometric acid–base titrations in both aqueous and aqueous– ethanolic media. [ABSTRACT FROM AUTHOR]

The present study evaluated the spatiotemporal variation in concentration of cadmium, lead and copper ions in groundwater wells in the stratigraphic subdivision "Santo Anastácio" that belongs to the Bauru aquifer system in the western region of São Paulo State. Exploratory statistics methods were employed to investigate the response of the concentration of these metals in the aquifer through the pluviometric index of the region. The results show a direct dependence of the mean monthly flow of the metals in the groundwaters to the monthly rainfall flow. The observed behavior was cyclic with a gradual increase and decrease in the flow throughout time. Two groups of cyclic variation were identified. The seasonality of the mean monthly flow of Cd2+ and Pb2+ was inversely proportional to the magnitude of the pluviometric index of the region studied. Meanwhile, the seasonality of Cu2+ was directly correlated to the seasonable rainfall variability. These behaviors lead us to point out that cadmium and lead come from minerals present in the aquifer itself and the presence of copper in groundwater is associated with an anthropogenic action due to the region's agricultural activity. The study helps us better comprehend the behavior of the whole groundwater system through a comparison with temporal hydrogeochemistry. [ABSTRACT FROM AUTHOR]

The use of graphene and its derivatives in the development of electrochemical sensors has been growing in recent decades. Part of this success is due to the excellent characteristics of such materials, such as good electrical and mechanical properties and a large specific surface area. The formation of composites and nanocomposites with these two materials leads to better sensing performance compared to pure graphene and conductive polymers. The increased large specific surface area of the nanocomposites and the synergistic effect between graphene and conducting polymers is responsible for this interesting result. The most widely used methodologies for the synthesis of these materials are still based on chemical routes. However, electrochemical routes have emerged and are gaining space, affording advantages such as low cost and the promising possibility of modulation of the structural characteristics of composites. As a result, application in sensor devices can lead to increased sensitivity and decreased analysis cost. Thus, this review presents the main aspects for the construction of nanomaterials based on graphene oxide and conducting polymers, as well as the recent efforts made to apply this methodology in the development of sensors and biosensors. [ABSTRACT FROM AUTHOR]

A correction to the article "Electrochemical Properties of the Oxo-Manganese-Phenanthroline Complex Immobilized on Ion-Exchange Polymeric Film and Its Application as Biomimetic Sensor for Sulfite Ions," that was published in a previous issue is presented.