Enhanced Performance of Bioelectrodes Made with Amination-Modified Glucose Oxidase Immobilized on Carboxyl-Functionalized Ordered Mesoporous Carbon

This research reveals the improved performance of bioelectrodes made with amination-modified glucose oxidase (GOx-NH2) and carboxyl-functionalized mesoporous carbon (OMC-COOH). Results showed that when applied with 10 mM EDC amination, the functional groups of NH2 were successfully added to GOx, according to the analysis of 1H-NMR, elemental composition, and FTIR spectra. Moreover, after the aminated modification, increased enzyme immobilization (124.01 ± 1.49 mg GOx-NH2/g OMC-COOH; 2.77-fold increase) and enzyme activity (1.17-fold increase) were achieved, compared with those of non-modified GOx. Electrochemical analysis showed that aminated modification enhanced the peak current intensity of Nafion/GOx-NH2/OMC-COOH (1.32-fold increase), with increases in the charge transfer coefficient α (0.54), the apparent electron transfer rate constant ks (2.54 s−1), and the surface coverage Γ (2.91 × 10−9 mol·cm−2). Results showed that GOx-NH2/OMC-COOH exhibited impressive electro-activity and a favorable anodic reaction.

Influence of Thermomechanical Treatments on Corrosion of Carbon Steel in Synthetic Geopolymer Fly Ash Pore Solution

In this study the effect of thermomechanical treatments in chloride induced pitting corrosion is presented for carbon steel rebars exposed to synthetic fly ash (FA) pore solution. Due to the likely phase transformations that steel reinforcements in concrete experience during the event of a fire, the understanding of the corrosion behavior of such phases is key in predicting the stability of the structure. The motivation for this study arrives from the scarce literature regarding the corrosion behavior of thermomechanically treated steel reinforcements in FA environments and the need for further investigation to understand its mechanism. In order to better understand the effects on the corrosion behavior electrochemical measurements including cyclic potentiodynamic polarization curves (CPP) and electrochemical impedance spectroscopy (EIS) were used. It was found that quenched specimens showed enhanced corrosion kinetics as their icorr values were higher, being of 3.18 × 10−5 and 2.20 × 10−5 A/cm2 for water and oil quenched compared to 2.13 × 10−6 A/cm2 for the as-received. Furthermore, the effective capacitance of the double layer (Ceff,dl) showed the lower stability of the passive film for the quenched specimens, with values of 1.11 × 10−3 µF/cm2 for the as-receive sample that decreased to 8.12 × 10−4 µF/cm2 for the water quenched sample. The anodic charge transfer coefficient in the synthetic FA alkaline pore solution changes from 0.282 to 0.088, for the as-received and water quenched rebars specimens, respectively. These results indicate a lower energy barrier for the anodic dissolution reaction of quenched specimens, indicating that martensite and bainite microstructures promote corrosion process. Enhanced corrosion was found on quenched samples presenting martensite and bainite microstructure as showed by the increased pith depth, with values of 5 μm compared to 1 μm observed in the as-received samples.

Chlorate Electrochemical Removal from Aqueous Media Based on a Possible Autocatalytic Mechanism

The electrochemical chlorate reduction at the Pt electrode in 0.5 M H2SO4 deaerated solutions has been studied using potentiostatic steady-state voltammetry. The kinetics parameters (Tafel slope, charge transfer coefficient, current density, and reaction order) were evaluated in function of chlorate concentration (1x10-4 � 0.2 M KClO3). The process of chlorate reduction is a complex one that implies two charge transfer controlled steps with formation of free radicals and an extent potential region controlled by the concentration polarization. The current density dependence of chlorate concentration tends to an exponential growth at concentration � 0.1 M KClO3 and becomes exponential in the conditions of the catalyst system presence. In the second charge transfer, a surface reaction between free radical �Cl-2 and platinum electrode with formation of complex anions PtCL42- and PtCL62- is responsible for the rapid increase of the reaction rate.

Separating the Effects of Experimental Noise from Inherent System Variability in Voltammetry: The [Fe(CN)_6]^3−/4− Process

<div>Recently, we have introduced the use of techniques drawn from Bayesian statistics to recover kinetic and thermodynamic parameters from voltammetric data, and were able to show that the technique of large amplitude ac voltammetry yielded significantly more accurate parameter values than the equivalent dc approach. In this paper we build on this work to show that this approach allows us, for the first time, to separate the effects of random experimental noise and inherent system variability in voltammetric</div><div>experiments. We analyse ten repeated experimental data sets for the [Fe(CN) 6 ] 3−/4− process, again using large-amplitude ac cyclic voltammetry. In each of the ten cases</div><div>we are able to obtain an extremely good fit to the experimental data and obtain very narrow distributions of the recovered parameters governing both the faradaic (the reversible formal faradaic potential, E_0, the standard heterogeneous charge transfer rate constant k_0, and the charge transfer coefficient α) and non-faradaic terms (uncompensated resistance, R_u , and double layer capacitance, C_dl). We then employ hierarchical</div><div>Bayesian methods to recover the underlying “hyperdistribution” of the faradaic and non-faradaic parameters, showing that in general the variation between the experimental data sets is significantly greater than suggested by individual experiments, except for α where the inter-experiment variation was relatively minor. Correlations between pairs of parameters are provided, and for example, reveal a weak link between k_0 and C_dl (surface activity of a glassy carbon electrode surface). Finally, we discuss the</div><div>implications of our findings for voltammetric experiments more generally.</div>

Separating the Effects of Experimental Noise from Inherent System Variability in Voltammetry: The [Fe(CN)_6]^3−/4− Process

<div>Recently, we have introduced the use of techniques drawn from Bayesian statistics to recover kinetic and thermodynamic parameters from voltammetric data, and were able to show that the technique of large amplitude ac voltammetry yielded significantly more accurate parameter values than the equivalent dc approach. In this paper we build on this work to show that this approach allows us, for the first time, to separate the effects of random experimental noise and inherent system variability in voltammetric</div><div>experiments. We analyse ten repeated experimental data sets for the [Fe(CN) 6 ] 3−/4− process, again using large-amplitude ac cyclic voltammetry. In each of the ten cases</div><div>we are able to obtain an extremely good fit to the experimental data and obtain very narrow distributions of the recovered parameters governing both the faradaic (the reversible formal faradaic potential, E_0, the standard heterogeneous charge transfer rate constant k_0, and the charge transfer coefficient α) and non-faradaic terms (uncompensated resistance, R_u , and double layer capacitance, C_dl). We then employ hierarchical</div><div>Bayesian methods to recover the underlying “hyperdistribution” of the faradaic and non-faradaic parameters, showing that in general the variation between the experimental data sets is significantly greater than suggested by individual experiments, except for α where the inter-experiment variation was relatively minor. Correlations between pairs of parameters are provided, and for example, reveal a weak link between k_0 and C_dl (surface activity of a glassy carbon electrode surface). Finally, we discuss the</div><div>implications of our findings for voltammetric experiments more generally.</div>

Electrochemical detection of chlorpheniramine maleate in the presence of an anionic surfactant and its analytical applications

Improvement of methods for the detection of an analyte at a low concentration with high sensitivity has become an important point of interest. An effort has been made to know the electrochemical behavior of chlorpheniramine maleate in the presence of an anionic surfactant. Voltammograms were obtained in the range of 6.0–11.2 pH, and the maximum peak current (IP) was observed at pH 10.4. Various physicochemical parameters were estimated, including the process on the surface of the electrode, which was found to be diffusion controlled, heterogeneous rate constant, number of electrons transferred, and charge transfer coefficient. Square wave voltammetry of chlorpheniramine maleate at the modified electrode exhibited a linear calibration curve in the concentration range of 1.0–100 μmol/L, with a limit of detection of 28 nmol/L. The proposed technique was successfully used for the determination of chlorpheniramine maleate in pharmaceuticals, as well as in biological samples.