Synthesis and Characterization of Ordered Intermetallic Nanostructured PtSn/C and PtSb/C and Evaluation as Electrodes for Alcohol Oxidation

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Thermolysis of octa (hydridodimethylsiloxyl) octasilsesquioxane in pyridine media and subsequent toluidine blue O adsorption

This work describes the synthesis of octa (hydridodimethylsiloxyl) octasilsesquioxane, (Q(8)M(8)(H)) and its thermolysis in pyridine media. The new compound called CPy was characterized by FTIR, NMR-MAS, XRD, MEV spectroscopies and TGA analyses. These results indicate that silsesquioxanes cages (octanion) are maintained after thermal treatment. A cleavage of vertex siloxy groups yielding a nanocomposite with polymeric nature is proposed. Its structure and morphology allows the adsorption/inclusion of electrochemical mediator, toluidine blue O. The square wave voltammetry analysis of resulting composite (CPyTBO) exhibits two redox couple with a formal potential (E-0') 0.1 V and 0.26 V to I and II redox couples respectively, (Britton-Robinson (BR) buffer pH 3, v = 10 Hz versus SCE) ascribed to a monomer and dimmer of the toluidine blue species. This paper opens the use of spherosiloxane derived materials a's host for small molecules in the electrochemical field. (C) 2004 Elsevier B.V. All rights reserved.

Preparation, characterization and application of a nanostructured composite: Octakis(cyanopropyldimethylsiloxy)octasilsesquioxane

Octakis(cyanopropyldimethylsiloxy)octasilsesquioxane was prepared and characterized by C-13, Si-29 NMR (MAS), SEM, FF-IR, XRD and thermogravimetric techniques. The four groups alpha, beta, gamma, kappa (to the terminal silicon atom), associated with an acrylonitrile, were clearly seen in the C-13 NMR (alpha-CH2 at 17.9; P-CH2 at 31.3; gamma-CH, at 50.4; K-C N at 59.0 ppm). The Si-29 NMR spectrum of the final product, exhibits only Q type silicon signal, ascribed to Q(4) (-118.0 ppm). The presence of acrylonittile substituted for octameric cube confers a relative change phase and thermal stability to the material. With regard to the applications for this new material, it was intended, in this case, to react with Na-2[Fe(CN)(5)NH3] by chemical substitution. This composite was incorporated into a carbon paste electrode and the electrochemical studies were performed by cyclic voltammetry. The cyclic voltammogram of the modified graphite paste electrode, showed one redox couples with formal potential (E-1/2(ox)) = 0.24 V versus SCE. (c) 2006 Elsevier B.V. All rights reserved.

Adsorção de Mn (II) e Zn (II) em soluções aquosas usando perlita expandida revestida com quitosana

In this work, chitosan was used as a coating of pure perlite in order to increase the accessibility of the groups OH- e NH2+the adsorptionof ions Mn2+ e Zn2+.The characterization results of the expanded perlite classified as microporous and whose surface area 3,176 m2 g-1after the change resulted in 4,664 m2g-1.From the thermogravimetry(TG) it was found that the percentage of coating was34,3%.The infrared analysis can prove the presence of groups Si-OH, Si-O e Al-O-Siresulting from the perlite and C=O, NH2and OH characterization of chitosan. The experiments on experiments on the adsorption of Mn and Zn were performed in the concentration range of10 a 50 mgL-1and the adsorption capacity inpH 5,8 e 5,2 was 19,49 and 23,09 mgg-1to 25 oC,respectively.The adsorption data were best fitted to Langmuir adsorption model to Langmuir adsorption model for both metalionsisindicative of monolayer adsorption. The kinetics of adsorption were calculated from the equation of Lagergren fitting the model pseudo-second-order for all initial concentrations, suggesting that adsorption of ions Mn2+ and Zn2+ follows the kinetics of pseudo-second-order and whose constant Speedk2(g/mg.min) are 0,105 e 3,98 and capacity and maximum removal qe 4,326 e 3,348,respectively.In this study we used a square wave voltammetry cathodic stripping voltammetry to quantify the adsorbed ions, and the working electrode glassy carbon, reference electrode silver / silver chloride and a platinum auxiliary electrode. The attainment of the peaks corresponding to ions Mn2+ and Zn2+ was evaluated in and electrochemical cell with a capacity of 30 mL using a buffer system (Na2HPO4/NaH2PO4)at pH 4 and was adjusted with solutionsH3PO4 0,1molL-1and NaOH 0,1 molL-1and addition of the analyte has been a cathodic peak in- 0,873 Vand detection limit of2,55x10-6molL-1para Zn.The dough used for obtaining the adsorption isotherm was 150 mg and reached in 120 min time of equilibrium for both metal ions.The maximum adsorption for 120 min with Mn concentration 20 mgL-1 and Zn 10 mgL-1,was91, 09 e 94, 34%, respectively

Electrochemical study of o-toluidine blue impregnated in mesoporous silica channels

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Desenvolvimento de um novo complexo macrocíclico do sistema cobalto cyclam

In this work were synthesized and studied the spectroscopic and electrochemical characteristics of the coordination compounds trans-[Co (cyclam)Cl2]Cl, trans- Na[Co(cyclam)(tios)2], trans-[Co(en)2Cl2]Cl and trans-Na[Co(en)2(tios)2], where tios = thiosulfate and en = ethylenediamine. The compounds were characterized by: Elemental Analysis (CHN), Absorption Spectroscopy in the Infrared (IR), Uv-Visible Absorption Spectroscopy, Luminescence Spectroscopy and Electrochemistry (cyclic voltammetry). Elemental Analysis (CHN) suggests the following structures for the complex: trans- [Co(cyclam)Cl2]Cl.6H2O and trans-Na[Co(cyclam)(tios)2].7H2O. The electrochemical analysis, when compared the cathodic potential (Ec) processes of the complexes trans- [Co(cyclam)Cl2]Cl and trans-[Co(en)2Cl2]Cl, indicated a more negative value (-655 mV) for the second complex, suggesting a greater electron donation to the metal center in this complex which can be attributed to a greater proximity of the nitrogen atoms of ethylenediamine in relation to metal-nitrogen cyclam. Due to the effect of setting macrocyclic ring to the metal center, the metal-nitrogen bound in the cyclam are not as close as the ethylenediamine, this fact became these two ligands different. Similar behavior is also observed for complexes in which the chlorides are replaced by thiosulfate ligand, trans-Na[Co(en)2(tios)2] (-640 mV) and trans-Na[Co(cyclam)(tios)2] (-376 mV). In absorption spectroscopy in the UV-visible, there is the band of charge transfer LMCT (ligand p d* the metal) in the trans-Na[Co(cyclam)(tios)2] (350 nm, p tios  d* Co3+) and in the trans-Na[Co(en)2(tios)2] (333 nm, p tios d* Co3+), that present higher wavelength compared to complex precursor trans- [Co(cyclam)Cl2]Cl (318 nm, pCl  d* Co3+), indicating a facility of electron density transfer for the metal in the complex with the thiosulfate ligand. The infrared analysis showed the coordination of the thiosulfate ligand to the metal by bands in the region (620-635 cm-1), features that prove the monodentate coordination via the sulfur atom. The νN-H bands of the complexes with ethylenediamine are (3283 and 3267 cm-1) and the complex with cyclam bands are (3213 and 3133 cm-1). The luminescence spectrum of the trans-Na[Co(cyclam)(tios)2] present charge transfer band at 397 nm and bands dd at 438, 450, 467, 481 and 492 nm.

Adsorption and electropolymerization of toluidine blue on the nano structured octakis(hydridodimethylsiloxy)-octasilsesquioxane surface

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)

Copper Hexacyanoferrate Formation on the Modified Silica Surface with DAB-Am-16 Dendrimer

The third generation (G-3) polypropylenimine hexadecaamine dendrimer (DAB-Am-16) was grafted onto the silica gel surface. The modified silica interacts easily with Cu(2+) and then with potassium ferrocyanide to form copper hexacyanoferrate. The modified silica was characterized by the following techniques: Nuclear Magnetic Resonance (NMR), FTIR spectroscopy, Energy Dispersive X-ray (EDX) and Cyclic Voltammetry. The modified silica containing copper hexacyanoferrate (CuHCFSD) was tested for a voltammetric determination of nitrite using a modified graphite paste electrode.

Investigation about the copper adsorption on the chloropropylsilica gel surface modified with a nanostructured dendrimer DAB-Am-16: an analytical application for determination of copper in different samples

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

Voltammetric determination of total iron in fuel ethanol using a 1,10 fenantroline/nafion carbon paste-modified electrode

This work presents a methodology for iron determination in fuel ethanol using a modified carbon paste electrode with 1.10 fenantroline/nafion. The electrochemical parameters were optimized for the proposed system and the voltammetric technique of square wave was employed for iron determination. An accumulation time of 5 minutes, such as a 100 mV of pulse magnitude (E(sw)) and frequency (f) of 25 Hz were used as optimized experimental conditions. The modified carbon paste electrode presented linear dependence of amperometric signal with iron concentration in a work range from 6.0x10(-6) until 2.0x10(-5) mol L(-1) of iron, exhibiting a linear correlation coefficient of 0.9884, a detection limit of 2.4 x10(-6) mol L(-1) (n = 3) and amperometric sensibility of 4.5x10(5) mu A/mol L(-1). Analytical curve method was used for iron determination at a commercial fuel sample. Flame atomic absorption spectroscopy was employed as comparative technique.

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)

Preparation and Voltammetric Studies of Titanium (IV) Phosphate Modified with Silver Hexacyanoferrate to a Voltammetric Determination of L-Cysteine

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

Aplicação da técnica eletroanalítica de pulso diferencial usando o eletrodo de carbono vítreo modificado com cisteína para monitorar a degradação eletroquímica de ácido oxálico

In this paper, the technique of differential pulse voltammetry (DPV) has been studied for monitoring the concentration of oxalic acid (OA) during their electrochemical oxidation (EO) in acidic medium using platinum anode supported on titanium (Ti / Pt). The DPV was standardized and optimized using a glassy carbon electrode modified with cysteine. The modification with cysteine was developed electrochemically, forming a polymeric film on the surface of the glassy carbon electrode. The formation of the polymer film was confirmed by analysis of scanning electron microscope and atomic force microscope, confirming the modification of the electrode. The electrochemical degradation was developed using different current densities 10, 20 30 and 40 mA cm -2 electrode with Ti / Pt observing the degradation of oxalic acid, and monitored using the method of KMnO4 titration. However, the analyzes with DPV showed the same behavior elimination of oxalic acid titration. Compared with the titration method classical observed and DPV could be a good fit, confidence limits of detection and confirming the applicability of the technique electroanalytical for monitoring the degradation of oxalic acid