Electrochemical Oxidation of N - p -Toluenesulfinamides

Contrasting and interesting electrochemical behavior is observed in anodic oxidation of N-substituted p-toluenesulfinamides under controlled current conditions. For sulfinamides derived from secondary alkylamines and primary arylamines, the N-sulfinyl group is removed and the corresponding amines are formed; for sulfinamides derived from primary alkylamines, sulfur oxidation yields the corresponding sulfonamides in good yields.

Ultrasound-assisted electrochemical treatment of wastewaters containing organic pollutants by using novel Ti/Ta2O5-SnO2 electrodes

Advanced oxidation processes (AOPs) are modern methods using reactive hydroxyl radicals for the mineralization of organic pollutants into simple inorganic compounds, such as CO2 and H2O. Among AOPs electrochemical oxidation (EO) is a method suitable for coloured and turbid wastewaters. The degradation of pollutants occurs on electrocatalytic electrodes. The majority of electrodes contain in their structure either expensive materials (diamond and Pt-group metals) or are toxic for the environment compounds (Sb or Pb). One of the main disadvantages of electrochemical method is the polarization and contamination of electrodes due to the deposition of reaction products on their surface, which results in diminishing of the process efficiency. Ultrasound combined with the electrochemical degradation process eliminates electrode contamination because of the continuous mechanical cleaning effect produced by the formation and collapse of acoustic cavitation bubbles near to the electrode surface. Moreover, high frequency ultrasound generates hydroxyl radicals at water sonolysis. Ultrasound-assisted EO is a non-selective method for oxidation of different organic compounds with high degradation efficiencies. The aim of this research was to develop novel sustainable and cost-effective electrodes working as electrocatalysts and test their activity in electrocatalytic oxidation of organic compounds such as dyes and organic acids. Moreover, the goal of the research was to enhance the efficiency of electrocatalytic degradation processes by assisting it with ultrasound in order to eliminate the main drawbacks of a single electrochemical oxidation such as electrodes polarization and passivation. Novel Ti/Ta2O5-SnO2 electrodes were developed and found to be electrocatalytically active towards water (with 5% Ta content, 10 oxide film layers) and organic compounds oxidation (with 7.5% Ta content, 8 oxide film layers) and therefore these electrodes can be applicable in both environmental and energy fields. The synergetic effect of combined electrolysis and sonication was shown while conducting sonoelectrochemical (EO/US) degradation of methylene blue (MB) and formic acid (FA). Complete degradation of MB and FA was achieved after 45 and 120 min of EO/US process respectively in neutral media. Mineralization efficiency of FA over 95% was obtained after 2 h of degradation using high frequency ultrasound (381, 863, 1176 kHz) combined with 9.1 mA/cm2 current density. EO/US degradation of MB provided over 75% mineralization in 8 h. High degradation kinetic rates and mineralization efficiencies of model pollutants obtained in EO/US experiments provide the preconditions for further extrapolation of this treatment method to pilot scale studies with industrial wastewaters.

Improving the stability of an oxime based electrochemical microsensor for organo-phosphate vapor detection

A micro gas sensor has been developed by our group for the detection of organo-phosphate vapors using an aqueous oxime solution. The analyte diffuses from the high flow rate gas stream through a porous membrane to the low flow rate aqueous phase. It reacts with the oxime PBO (1-Phenyl-1,2,3,-butanetrione 2-oxime) to produce cyanide ions, which are then detected electrochemically from the change in solution potential. Previous work on this oxime based electrochemistry indicated that the optimal buffer pH for the aqueous solution was approximately 10. A basic environment is needed for the oxime anion to form and the detection reaction to take place. At this specific pH, the potential response of the sensor to an analyte (such as acetic anhydride) is maximized. However, sensor response slowly decreases as the aqueous oxime solution ages, by as much as 80% in first 24 hours. The decrease in sensor response is due to cyanide which is produced during the oxime degradation process, as evidenced by the cyanide selective electrode. Solid phase micro-extraction carried out on the oxime solution found several other possible degradation products, including acetic acid, N-hydroxy benzamide, benzoic acid, benzoyl cyanide, 1-Phenyl 1,3-butadione, 2-isonitrosoacetophenone and an imine derived from the oxime. It was concluded that degradation occurred through nucleophilic attack by a hydroxide or oxime anion to produce cyanide, as well as a nitrogen atom rearrangement similar to Beckmann rearrangement. The stability of the oxime in organic solvents is most likely due to the lack of water, and specifically hydroxide ions. The reaction between oxime and organo-phosphate to produce cyanide ions requires hydroxide ions, and therefore pure organic solvents are not compatible with the current micro-sensor electrochemistry. By combining a concentrated organic oxime solution with the basic aqueous buffer just prior to being used in the detection process, oxime degradation can be avoided while preserving the original electrochemical detection scheme. Based on beaker cell experiments with selective cyanide sensitive electrodes, ethanol was chosen as the best organic solvent due to its stabilizing effect on the oxime, minimal interference with the aqueous electrochemistry, and compatibility with the current microsensor material (PMMA). Further studies showed that ethanol had a small effect on micro-sensor performance by reducing the rate of cyanide production and decreasing the overall response time. To avoid incomplete mixing of the aqueous and organic solutions, they were pre-mixed externally at a 10:1 ratio, respectively. To adapt the microsensor design to allow for mixing to take place within the device, a small serpentine channel component was fabricated with the same dimensions and material as the original sensor. This allowed for seamless integration of the microsensor with the serpentine mixing channel. Mixing in the serpentine microchannel takes place via diffusion. Both detector potential response and diffusional mixing improve with increased liquid residence time, and thus decreased liquid flowrate. Micromixer performance was studies at a 10:1 aqueous buffer to organic solution flow rate ratio, for a total rate of 5.5 μL/min. It was found that the sensor response utilizing the integrated micromixer was nearly identical to the response when the solutions were premixed and fed at the same rate.

An electrochemical process for the production of synthetic fuels at low temperatures [Resumo]

Following work exploring the low temperature electrolysis in alkaline media, using graphite consumable anodes, from which syngas was obtained1, laboratory studies have been conducted in acid media pursuing higher efficiency in the production of hydrogen and synthetic fuels. Experiments were conducted in an own designed undivided planar cell with 25 cm2 geometrical area electrodes using a 0.5 M H2SO4 solution with and without Fe(II) additions. Fe2+ oxidizes to Fe3+ at the anode surface. The redox couple Fe3+/ Fe2+ acts as an oxidation mediator not only oxidizing the bulk and detached graphite but also the surface functional groups. The practical experimental potential for graphite oxidation is within the range for the electroxidation of the Fe redox couple giving as a result a 4-fold increase in the amount of produced CO2 at near room temperature, when using 0.025 M FeSO4.

New design of electrostatic mirror actuators for application in high-precision interferometry

We describe a new geometry for electrostatic actuators to be used in sensitive laser interferometers, suited for prototype and table top experiments related to gravitational wave detection with mirrors of 100 g or less. The arrangement consists of two plates at the sides of the mirror (test mass), and therefore does not reduce its clear aperture as a conventional electrostatic drive (ESD) would do. Using the sample case of the AEI-10 m prototype interferometer, we investigate the actuation range and the influence of the relative misalignment of the ESD plates with respect to the test mass. We find that in the case of the AEI-10 m prototype interferometer, this new kind of ESD could provide a range of 0.28 mu m when operated at a voltage of 1 kV. In addition, the geometry presented is shown to provide a reduction factor of about 100 in the magnitude of the actuator motion coupling to the test mass displacement. We show that therefore in the specific case of the AEI-10 m interferometer, it is possible to mount the ESD actuators directly on the optical table without spoiling the seismic isolation performance of the triple stage suspension of the main test masses.

A study of electrochemical transport and diffuse charge dynamics using a Langevin equation

This thesis aims to develop new numerical and computational tools to study electrochemical transport and diffuse charge dynamics at small scales. Previous efforts at modeling electrokinetic phenomena at scales where the noncontinuum effects become significant have included continuum models based on the Poisson-Nernst-Planck equations and atomic simulations using molecular dynamics algorithms. Neither of them is easy to use or conducive to electrokinetic transport modeling in strong confinement or over long time scales. This work introduces a new approach based on a Langevin equation for diffuse charge dynamics in nanofluidic devices, which incorporates features from both continuum and atomistic methods. The model is then extended to include steric effects resulting from finite ion size, and applied to the phenomenon of double layer charging in a symmetric binary electrolyte between parallel-plate blocking electrodes, between which a voltage is applied. Finally, the results of this approach are compared to those of the continuum model based on the Poisson-Nernst-Planck equations.

Development of an electrochemical biosensor for the detection of miRNA-155 in Breast Cancer

Breast cancer is one of the most prevalent forms of cancer in women. Despite all recent advances in early diagnosis and therapy, mortality data is not decreasing. This is an outcome of the inexistence of validated serum biomarkers allowing an early prognosis, out coming from the limited understanding of the natural history of the disease. In this context, miRNAs have been attracting a special interest throughout the scientific community as promising biomarkers in the early diagnosis of cancer. In breast cancer, several miRNAs and their levels of expression are significantly different between normal tissue and tissue with neoplasia, as well as between different molecular subtypes of breast cancer, also associated with prognosis. Thus, this these presents a meta-analysis that allows identifying a reliable miRNA biomarker for the early detection of breast cancer. In this, miRNA-155 was identified as the best one and an electrochemical biosensor was developed for its detection in serum samples. The biosensor was assembled by following three button-up stages: (1) the complementary miRNA sequence thiol terminated (anti-miRNA-155) was immobilized on a commercial gold screen-printed electrode (Au-SPE), followed by (2) blocking non-specific binding with mercaptosuccinic acid and by (3) miRNA hybridization. The biosensor was able to detect miRNA concentrations lying in the 10-18 mol/L (aM) range, displaying a linear response from 10 aM to 1nM. The device showed a limit of detection of 5.7 aM in human serum samples and good selectivity against other biomolecules in serum, such as cancer antigen CA-15.3 and bovine serum albumin (BSA). Overall, this simple and sensitive strategy is a promising approach for the quantitative and/or simultaneous analysis of multiple miRNA in physiological fluids, aiming at further biomedical research devoted to biomarker monitoring and point-of-care diagnosis.