Electrocatalytic determination of nitrite on a rigid disk electrode having cobalt phthalocyanine prepared in situ

This work reports an in situ cobalt(II) phthalocyanine (CoPc) synthesis on a SiO2/SnO2 (SiSn) matrix surface obtained by the sol-gel method and its electrocatalytic activity for oxidation of nitrite. A rigid disk electrode with SiSn/CoPc was used to study the electrooxidation of nitrite by the cyclic voltammetric, chronoamperometric techniques and differential pulse voltammetry (DPV). The adsorbed phthalocyanine electrocatalyzed nitrite oxidation at 0.73 V (versus SCE) using the DPV technique. The anodic peak current intensities, plotted from differential pulse voltammograms in 1 mol L-1 KCl for the concentration range 0.002 to 3.85 mmol L-1 of nitrite were linear, with a correlation coefficient of 0.998 and a detection limit of 0.95 mu mol L-1.20776577

SiO(2)/SnO(2)/Sb(2)O(5) microporous ceramic material for immobilization of Meldola's blue: Application as an electrochemical sensor for NADH

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)The mixed oxide SiO(2)/SnO(2), containing 25 wt% of SnO(2), determined by X-ray fluorescence, was prepared by the sol-gel method and the porous matrix obtained was then grafted with Sb (V), resulting the solid designated as (SiSnSb). XPS indicated 0.7% of Sb atoms on the surface. Sb grafted on the surface contains Bronsted acid centers (SbOH groups) that can immobilize Meldola's blue (MB(+)) cationic dye onto the surface by an ion exchange reaction, resulting the solid designated as (SiSnSb/MB). In the present case a surface concentration of MB(+) = 2.5 x 10(-11) mol cm(2) on the surface was obtained. A homogeneous mixture of the SiSnSb/MB with ultra pure graphite (99.99%) was pressed in disk format and used to fabricate a working electrode that displayed an excellent specific electrocatalytic response to NADH oxidation, with a formal potential of -0.05 Vat pH 7.3. The electrochemical properties of the resulting electrode were investigated thoroughly with cyclic voltammetric and chronoamperometry techniques. The proposed sensor showed a good linear response range for NADH concentrations between 8 x 10(-5) and 9.0 x 10(-4) mol L(-1), with a detection limit of 1.5 x 10(-7) mol L(-1). The presence of dopamine and ascorbic acid did not show any interference in the detection of NADH on this modified electrode surface. (C) 2010 Elsevier B.V. All rights reserved.26524022406Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)FAPESP [00/11103-5

Direct Synthesis of Ag Nanoparticles Incorporated on a Mesoporous Hybrid Material as a Sensitive Sensor for the Simultaneous Determination of Dihydroxybenzenes Isomers

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)This paper describes the synthesis, characterization, and applications of a mesoporous silica/ multiwalled carbon nanotube (SiO2/MWCNT) hybrid material, which was obtained by a sol-gel process and decorated with silver nanoparticles (AgNPs) ranging in size from 5 to 8 nm. The AgNPs were prepared directly on the surface of the SiO2/MWCNTs material by using N,N-dimethylformamide (DMF) as the reducing agent, and the resulting material was designated Ag/SiO2/MWCNT. The Ag/SiO2/MWCNT material was characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), high-resolution transmission electron microscopy (HR-TEM), and X-ray photoelectron spectroscopy (XPS). A glassy carbon electrode, modified with the Ag/SiO2/MWCNT material, was used in the development of a sensitive electrochemical sensor for the determination of hydroquinone and catechol in the presence of resorcinol by squarewave voltammetry. Well-defined and separate oxidation peaks were observed in phosphate buffer solution (PBS) at pH 7. The Ag/SiO2/MWCNT-modified electrode exhibited high sensitivity for the simultaneous determination of hydroquinone and catechol in the presence of resorcinol, and the limits of detection for hydroquinone and catechol are 0.0117 and 0.0121 M, respectively. No significant interference was seen for 2,6-dichloroindophenol, phenol, 4-nitrophenol, and nitrite ions in the detection of dihydroxybenzenes. Our study demonstrates that the resultant Ag/SiO2/MWCNT-modified electrode can be used for hydroquinone and catechol detection in the presence of resorcinol and other potentially interfering materials in river water samples.20133357465754Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)FAPESP [2011/23047-7, 2012/17689-9

Activity of SiDbCl in the Electrooxidation of Ascorbic Acid, Dopamine, and Uric Acid

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Selective electroanalytical responses for ascorbic acid, dopamine and uric acid at a carbon modified electrode based on 3-n-propyl-1-azonia-4-azabicyclo[2.2.2]octane silsesquioxane chloride (SiDbCl) is reported. The overlapped peaks observed at an unmodified electrode are resolved into three well defined voltammetric peaks allowing the simultaneous determination of the three species. Detection limits of 37, 0.3 and 0.1 mu moL(-1) of ascorbic acid, dopamine and uric acid, respectively, were calculated from calibration curves based on differential pulse voltammetric experiments performed in Britton-Robinson buffer solution at pH 7.04.232334338Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Simultaneous electroanalytical determination of hydroquinone and catechol in the presence of resorcinol at an SiO2/C electrode spin-coated with a thin film of Nb2O5

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)This paper describes the development, characterization and application of an Nb2O5 film formed on the surface of a carbon ceramic material, SiO2/C, obtained by a sol-gel method, using the spin-coating technique. The working electrode using this material will be designated as SiCNb. Hydroquinone and catechol can be oxidized at this electrode in the presence of resorcinol, allowing their simultaneous detection. The electrochemical properties of the resulting electrode were investigated using cyclic and differential pulse voltammetry techniques. Well-defined and separated oxidation peaks were observed by differential pulse voltammetry in Tris-HCl buffer solution at pH 7 containing 1 mol L-1 KCl in the supporting electrolyte solution. The SiCNb electrode exhibited high sensitivity in the simultaneous determination of hydroquinone and catechol in the presence of resorcinol, with the limits of detection for hydroquinone and catechol being 1.6 mu mol L-1 and 0.8 mu mol L-1, respectively. Theoretical calculations were performed to determine the ionization energies of hydroquinone, catechol and resorcinol; the results were used to explain the simultaneous determination of species by differential pulse voltammetry. The presence of resorcinol did not produce any interference in the simultaneous detection of hydroquinone and catechol on the surface of the modified electrode.1381315324Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)FAPESP [00/11103-5

Sol-gel thin-film based mesoporous silica and carbon nanotubes for the determination of dopamine, uric acid and paracetamol in urine

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)This work describes the preparation, characterization and application of a hybrid material composed of disordered mesoporous silica (SiO2) modified with multiwalled carbon nanotubes (MWCNTs), obtained by the sol-gel process using HF as the catalyst. This hybrid material was characterized by N-2 adsorption-desorption isotherms, X-ray powder diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission microscopy (HR-TEM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). This new hybrid material was used for the construction of a thin film on a glassy carbon electrode. The modified electrode using this material was designated SiO2/MWCNT/GCE. The electrocatalytic properties of the electrode toward dopamine, uric acid and paracetamol oxidation were studied by differential pulse voltammetry. Well-defined and separated oxidation peaks were observed in phosphate buffer solution at pH 7.0, in contrast with the ill-defined peaks observed with unmodified glassy carbon electrodes. The electrode had high sensitivity for the determination of dopamine, uric acid and paracetamol, with the limits of detection obtained using statistical methods, at 0.014, 0.068 and 0.098 mu mol L-1, respectively. The electrode presented some important advantages, including enhanced physical rigidity, surface renewability by polishing and high sensitivity, allowing the simultaneous determination of these three analytes in a human urine sample. Crown Copyright (C) 2013 Published by Elsevier B.V. All rights reserved.116726735Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)FAPERGSFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)FAPESP [2011/23047-7, 2012/17689-9

Variational Analysis of Nematic Shells

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