Amorphous palladium-silicon alloys for the oxidation of formic acid and formaldehyde. A voltammetric investigation

The electrocatalytic oxidation of formic acid and formaldehyde on Pd and on amorphous Pd(Si) was studied by cyclic voltammetry and the results compared with the literature for similar systems. The oxidation of HCOOH on Pd occurs through direct catalytic dehydrogenation via (:C(OH)2)ads while on Pd(Si) this intermediate does not appear to be formed. This is a consequence of the presence of inert Si on the surface that diminishes the probability of adjacent free sites. At high HCOOH concentrations, that intermediate undergoes dehydration on the Pd surface and COads oxidation peak is observed. For HCHO, the oxidation mechanism on both electrode materials appears similar to that previously proposed for Pt. However, the oxides formed on the amorphous Pd(Si) alloy are more reactive than those on Pd thus affecting the overall kinetics of the process for both organic molecules, a fact revealed by the increase in anodic currents observed in the voltammograms

Picloram and Thiram: 2 pesticides acting as heavy metals carriers portrayed by DPASV

Comunicación presentada en el Program of the 59th Annual Meeting of the International Society of Electrochemistry, Seville, 2008, S10-P085:Page 141. Picloram (4-amino-3,5,6-trichloro-2-pyridinecarboxilic acid) is a herbicide widely used, alone or in combination with other herbicides to control of weeds in crops of sugar cane, rice, pasture and wheat1. It can stay active for long time, depending on the type of soil, moisture and temperature. Thiram (N,N-dimethildithiocabamate) is a fungicide used for a control of a variety diseases in the crops of fruits, vegetables and ornamentals2. From an electrochemical point of view, the study of the redox behaviour of both pesticides on modified electrodes has been reported recently3. However, few works reported the interactions between metallic ions and pesticides and their properties in the environment, although these molecules usually present functional groups that can act as ligands. In this work, we studied the interaction between heavy metals (Zn, Cu, Pb and Cd) and the pesticides (picloram and thiram) using the Differential Pulse Anodic Stripping Voltammetry technique on Hg electrode (DPASV) which has shown efficient in the evaluation of the formation of complexes in natural samples4 through the competing role of Hg for metals with respect to ligands. Electrochemical measurements provided a simple means to evaluate the stoichiometry of the complexes, and Scatchard and Langmuir algorithms allowed the calculation of the conditional complexation constants for both systems in an acetate pH 4 buffered solutions. Studies carried out for both Zn and Cu with Picloram have shown that 1:1 complexes were formed in all instances. Calculated conditional stability constants are quite close (log K’ ~ 6) for both metallic species, Cu consistently yielding highest values

Picloram and Thiram: 2 pesticides acting as heavy metals carriers portrayed by DPASV

Comunicación presentada en el Program of the 59th Annual Meeting of the International Society of Electrochemistry, Seville, 2008, S10-P085:Page 141. Picloram (4-amino-3,5,6-trichloro-2-pyridinecarboxilic acid) is a herbicide widely used, alone or in combination with other herbicides to control of weeds in crops of sugar cane, rice, pasture and wheat1. It can stay active for long time, depending on the type of soil, moisture and temperature. Thiram (N,N-dimethildithiocabamate) is a fungicide used for a control of a variety diseases in the crops of fruits, vegetables and ornamentals2. From an electrochemical point of view, the study of the redox behaviour of both pesticides on modified electrodes has been reported recently3. However, few works reported the interactions between metallic ions and pesticides and their properties in the environment, although these molecules usually present functional groups that can act as ligands. In this work, we studied the interaction between heavy metals (Zn, Cu, Pb and Cd) and the pesticides (picloram and thiram) using the Differential Pulse Anodic Stripping Voltammetry technique on Hg electrode (DPASV) which has shown efficient in the evaluation of the formation of complexes in natural samples4 through the competing role of Hg for metals with respect to ligands. Electrochemical measurements provided a simple means to evaluate the stoichiometry of the complexes, and Scatchard and Langmuir algorithms allowed the calculation of the conditional complexation constants for both systems in an acetate pH 4 buffered solutions. Studies carried out for both Zn and Cu with Picloram have shown that 1:1 complexes were formed in all instances. Calculated conditional stability constants are quite close (log K’ ~ 6) for both metallic species, Cu consistently yielding highest values

Adsorption Of Silanes Bearing Nitrogenated Lewis Bases On Sio 2/si (100) Model Surfaces

The present paper describes the one-pot procedure for the formation of self-assembled thin films of two silanes on the model oxidized silicon wafer, SiO2/Si. SiO2/Si is a model system for other surfaces, such as glass, quartz, aerosol, and silica gel. MALDI-TOF MS with and without a matrix, XPS, and AFM have confirmed the formation of self-assembled thin films of both 3-imidazolylpropyltrimethoxysilane (3-IPTS) and 4-(N- propyltriethoxysilane-imino)pyridine (4-PTSIP) on the SiO2/Si surface after 30 min. Longer adsorption times lead to the deposition of nonreacted 3-IPTS precursors and the formation of agglomerates on the 3-IPTS monolayer. The formation of 4-PTSIP self-assembled layers on SiO2/Si is also demonstrated. The present results for the flat SiO2/Si surface can lead to a better understanding of the formation of a stationary phase for affinity chromatography as well as transition-metal-supported catalysts on silica and their relationship with surface roughness and ordering. The 3-IPTS and 4-PTSIP modified SiO2/Si wafers can also be envisaged as possible built-on-silicon thin-layer chromatography (TLC) extraction devices for metal determination or N-heterocycle analytes, such as histidine and histamine, with "on-spot" MALDI-TOF MS detection. © 2005 Elsevier Inc. All rights reserved.2861303309Sagiv, J., (1980) J. Am. Chem. Soc., 102, p. 92Mirkhalaf, F., Whittaker, D., Schiffrin, D.J., (1998) J. Electroanal. Chem., 452, p. 203Cao, C., Fadeev, A.Y., McCarthy, T.J., (2001) Langmuir, 17, p. 757Tada, H., Nagayama, H., (1994) Langmuir, 10, p. 1472Sander, L.C., Wise, S.A., (1987) Crit. Rev. Anal. Chem., 18, p. 299Regnier, F.E., Unger, K.K., Majors, R.E., (1991) J. Chromatogr., 9, p. 544Stenger, D.A., Hickman, J.J., Calvert, J.M., (1992) J. Am. Chem. Soc., 114, p. 8435Zhang, M.Q., Desai, T., Ferrari, M., (1998) Biomaterials, 19, p. 953Allara, D.L., (1995) Biosens. Bioelectron., 10, p. 771Ross, C.B., Sun, L., Crooks, R.M., (1993) Langmuir, 9, p. 632Gushikem, Y., Moreira, J.C., (1985) J. Colloid Interface Sci., 107, p. 81Moreira, J.C., Gushikem, Y., (1985) Anal. Chim. Acta, 176, p. 263Rodrigues-Filho, U.P., Gushikem, Y., Fujiwara, F.Y., Stadler, E., Drago, V., (1994) Struct. Chem., 5, p. 129Andresa, J.S., Moreira, L.M., Magalhães, J.L., Gonzalez, E.P., Landers, R., Rodrigues-Filho, U.P., (2004) Surf. Interface Anal., 36 (8), p. 1214Magalhães, J.L., Moreira, L.M., Rodrigues-Filho, U.P., Giz, M.J., Pereira-Da-Silva, M.A., Landers, R., Vinhas, R.C.G., Nascente, P.A.P., (2002) Surf. Interface Anal., 33, p. 293Mouder, J.F., Sticke, W.F., Sobol, P.E., Bombem, K.D., (1992) Handbook of X-Ray Photoelectron Spectroscopy, , Perkin-Elmer Eden Prairie, MNLeclercq, G., Pireaux, J.-J., (1995) J. Electron Spectrosc. Relat. Phenom., 71, p. 141Santos, L.S., Haddad, R., Höehr, N.F., Pilli, R.A., Eberlin, M.N., (2004) Anal. Chem., 76 (7), p. 2144Dunaway, D.J., McCarley, B.L., (1994) Langmuir, 10, p. 3598Kornherr, A., Hansal, S., Hansal, W.E.G., Besenhard, J.O., Kronberger, H., Nauer, G.E., Zifferer, G., (2003) J. Chem. Phys., 119 (18), p. 9719Helsen, J.A., Breme, H.J., (1998) Metals As Biomaterials, , Wiley New YorkHorr, T.J., Arora, P.S., (1997) Colloids Surf. a Physicochem. Eng. Aspects, 126, p. 113Ferragina, C., Massucci, M., (1989) J. Inclus. Phenom. Mol. Recogn. Chem., 7, p. 529Beamson, G., Briggs, D., (1992) High Resolution XPS of Organic Polymers: The Scienta ESCA300 DatabaseBarber, M., Connor, J.A., Guest, M.F., Hillier, I.H., Schwarz, M., Stacey, M., (1973) J. Chem. Soc. Faraday Trans. II, 69, p. 551Karas, M., Hillenkamp, F., (1988) Anal. Chem., 60, p. 2299MacFarlane, R.D., Torgerson, D.F., (1976) Science, 191, p. 920Barber, M., Bordoli, R.S., Sedgwick, R.D., Tyler, A.N., (1981) Nature, 293, p. 270Zenobi, R., Knochenmuss, R., (1998) Mass Spectrom. Rev., 17, p. 337Zenobi, R., (1997) Chimia, 51, p. 801Shen, Z., Thomas, J.J., Averbuj, C., Broo, K.M., Engelhard, M., Crowell, J.E., Finn, M.G., Siuzdak, G., (2001) Anal. Chem., 33, p. 179Go, E.P., Prenni, J.E., Wei, J., Jones, A., Hall, S.C., Witkowska, H.E., Shen, Z., Siuzdak, G., (2003) Anal. Chem., 75, p. 250