In situ infrared (FTIR) study of the mechanism of the borohydride oxidation reaction

Early reports stated that Au was a catalyst of choice for the BOR because it would yield a near complete faradaic efficiency. However, it has recently been suggested that gold could yield to some extent the heterogeneous hydrolysis of BH(4)(-),therefore lowering the electron count per BH(4)(-), especially at low potential. Actually, the blur will exist regarding the BOR mechanism on Au as long as no physical proof regarding the reaction intermediates is not put forward. In that frame, in situ physical techniques like FTIR exhibit some interest to study the BOR. Consequently, in situ infrared reflectance spectroscopy measurements (SPAIRS technique) have been performed in 1 M NaOH/1 M NaBH(4) on a gold electrode with the aim to detect the intermediate species. We monitored several bands in B-H ((nu) over bar similar to 1180,1080 and 972 cm(-1)) and B-O bond regions ((nu) over bar =1325 and similar to 1425cm(-1)), which appear sequentially as a function of the electrode polarization. These absorption bands are assigned to BH(3), BH(2) and BO(2)(-) species. At the light of the experimental results, possible initial elementary steps of the BOR on gold electrode have been proposed and discussed according to the relevant literature data.

Expedient, accurate methods for the determination of the degree of substitution of cellulose carboxylic esters: Application of UV-vis spectroscopy (dye solvatochromism) and FTIR

Two techniques, namely UV-vis- and FTIR spectroscopy, have been employed in order to calculate the degree of substitution (DS) of cellulose carboxylic esters, including acetates, CAs, butyrates, CBs, and hexanoates, CHs. Regarding UV-vis spectroscopy, we have employed a novel approach, based on measuring the dependence of lambda(max) of the intra-molecular charge-transfer bands of polarity probes adsorbed on DS of the ester films (solvatochromism). Additionally, we have revisited the use of FTIR for DS determination. Several methods have been used in order to plot Beer`s law graph, namely: Absorption of KBr pellets, pre-coated with CA: reflectance (DRIFTS) of CAs-KBr solid-solid mixtures with, or without the use of 1.4-dicyanobenzene as an internal reference; reflectance of KBr powder pre-coated with CA. The methods indicated are simple, fast, and accurate, requiring much less ester than the titration method. The probe method is independent of the experimental variables examined. (c) 2010 Published by Elsevier Ltd.

FT-Raman, FTIR and density functional theory studies of a hydrogen-bonded formamide: pyridine complex

Raman and IR experiments have been carried out on formamide (FA) and pyridine (Py) mixtures at different compositions. The appearance of a new Raman band at 996 cm(-1) (nu(1) region of Py), whose intensity depends on the FA concentration, is assigned to an FA: Py adduct and this result is in excellent agreement with those of other authors who employed noisy light-based coherent Raman scattering spectroscopy (I((2)) CARS). Another band at 1587 cm(-1) (nu(8) region of Py) has been observed for the first time by using Raman and IR spectroscopies. Its intensity shows the same dependence on the FA concentration and this fact allows us to also attribute it to an FA: Py adduct. The good relationship between the Raman and IR data demonstrates the potential of the vibrational spectroscopy for this kind of study. Owing to higher absolute Raman scattering cross section, the nu(1) region of Py has been chosen for the quantitative analysis and a stoichiometry of 1 : 1 FA: Py is reported. The experimental data are very well supported by the density functional theory (OFT) calculation, which was employed for the first time to the present system. Furthermore, the actual investigation shows an excellent agreement with those reported from computational calculations for similar systems. A comparison with our previous studies confirms that: the solvent dielectric constant determines the stoichiometry of a given Lewis acid-base adduct in the infinite dilution limit. Copyright (C) 2009 John Wiley & Sons, Ltd.

PtSnCe/C electrocatalysts for ethanol oxidation: DEFC and FTIR ""in-situ"" studies

The ethanol oxidation reaction (EOR) was investigated using PtSnCe/C electrocatalysts in different mass ratios (72:23:5, 68:22:10 and 64:21:15) that were prepared by the polymeric precursor method. Transmission electron microscopy (TEM) showed that the particles ranged in size from approximately 2 to 5 nm. Changes in the net parameters observed for Pt suggest the incorporation of Sn and Ce into the Pt crystalline network with the formation of an alloy between Pt, Sn and/or Ce. Among the PtSnCe catalysts investigated, the 68:22:10 composition showed the highest activity toward ethanol oxidation, and the current time curves obtained in the presence of ethanol in acidic media showed a current density 50% higher than that observed for commercial PtSn/C (E-Tek). During the experiments performed on single direct ethanol fuel cells, the power density for the PtSnCe/C 68:22:10 anode was nearly 40% higher than the one obtained using the commercial catalyst. Data from Fourier transform infrared (FTIR) spectroscopy showed that the observed behavior for ethanol oxidation may be explained in terms of a double mechanism. The presence of Sn and Ce seems to favor CO oxidation, since they produce an oxygen-containing species to oxidize acetaldehyde to acetic acid. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

In Situ Infrared (FTIR) Study of the Mechanism of the Borohydride Oxidation Reaction on Smooth Pt Electrode

Although Pt has been thoroughly studied regarding its activity for the borohydride oxidation reaction (BOR), the BOR mechanism at Pt remains unclear: Depending on the applied potential, spontaneous BH(4)(-) hydrolysis can compete with the direct BOR. The goal of the present work is to provide more insight into the behavior of smooth Pt electrodes toward the BOR, by coupling in situ infrared reflectance spectroscopy with electrochemistry. The measurements were performed on a Pt electrode in 1 M NaOH/1 M NaBH(4), so as to detect the reaction intermediate species generated as a function of the applied potential. Several bands were monitored in the B-H ((v) over bar approximate to 1180, 1080, and 972 cm(-1)) and B-O ((v) over bar = 1325 and similar to 1425 cm(-1)) bond regions upon increased electrode polarization. These absorption bands, which appear sequentially and were already detected for similar measurements on Au electrodes, are assigned to BH(3), BH(2), and BO(2)(-) species. In light of these experimental data and previous results obtained in our group for Pt- or Au-based electrodes, possible initial elementary steps of the BOR on platinum electrodes are proposed and discussed according to the relevant literature data.

Ethanol electro-oxidation over Pt(h k l): Comparative study on the reaction intermediates probed by FTIR and SFG spectroscopies

We have investigated the adsorbed intermediates of ethanol electro-oxidation at Pt(1 1 1), Pt(1 0 0) and Pt(1 1 0) using FTIR and SFG spectroscopies. Mainly, we focus on the CO formation. The aim of the present work is to compare the responses coming from two different surf, cc probes: a FTIR spectroscopy and SFG spectroscopy. Between 1800cm(-1) and 2300cm(-1), our MR and SFG results are in good agreement. Specifically in the case of the ethanol/Pt(1 1 1) interface, the SFG spectroscopy presents higher sensibility to the interface response compared to the FTIR spectroscopy. (c) 2008 Elsevier Ltd. All rights reserved.

Characterization of Polyurethane Resins by FTIR, TGA, and XRD

Fourier Transformed Infrared Spectroscopy, Thermogravimetric Analysis, and X-ray Diffractometry have been used to investigate the rigid, semi rigid, and soft polyurethane (PU) forms, which were developed by the Group of Analytic Chemistry and Technology of Polymers - USF - Sao Carlos. The -NCO/-OH ratios were 0.6, 0.5, and 0.3% for rigid, semi rigid, and soft PUs, respectively, showing that different ratios cause differences in thermal behaviors and crystalline structures of the synthesized PU resins. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115: 263-268, 2010

A novel bioactive glass-ceramic for treating dentin hypersensitivity

Dentin hypersensitivity (DH) is a painful response to stimulus applied to the open dentinal tubules of a vital tooth. It's a common oral condition, however, without an ideal treatment available yet. This work evaluated in vitro the effect of micron-sized particles from a novel bioactive glass-ceramic (Biosilicate) in occluding open dentinal tubules. A dentin disc model was employed to observe comparatively, using scanning electron microscopy (SEM), dentinal tubule occlusion by different products and deposition of hydroxyl carbonate apatite (HCA) on dentin surface by Biosilicate, after a single application: G1 - Dentifrice with potassium nitrate and fluoride; G2 - Two-step calcium phosphate precipitation treatment; G3 - Water-free gel containing Biosilicate particles (1%); G4 - Biosilicate particles mixed with distilled water in a 1:10 ratio; all of them after 1, 12 and 24 hours of immersion in artificial saliva. Fourier transform infrared spectroscopy (FTIR) was performed to detect HCA formation on dentin discs filled with Biosilicate after 2 minutes, 30 minutes and 12 hours of immersion in artificial saliva. SEM showed a layer of HCA formed on dentin surface after 24 hours by G4. G1, G2 and G3 promoted not total occlusion of open dentinal tubules after 24 hours. FTIR showed HCA precipitation on the dentin surface induced by Biosilicate after 30 minutes. The micron-sized particles from the bioactive glass-ceramic thus were able to induce HCA deposition in open dentinal tubules in vitro. This finding suggests that Biosilicate may provide a new option for treating DH.

Influência do grau de hidrólise do poli(vinil álcool) nas propriedades físicas de filmes à base de blendas de gelatina e poli(vinil álcool) plastificados com glicerol

O objetivo deste trabalho foi o estudo do efeito do Grau de Hidrólise (GH) do poli(vinil álcool) (PVA) nas propriedades dos filmes à base de blendas de gelatina suína e PVA com dois GH. Os filmes foram produzidos com soluções com 2 g de macromoléculas/100 g de solução, contendo 23,1 g de PVA.100 g-1 de macromoléculas e 25 g de glicerol/100 g de macromoléculas. As propriedades mecânicas e térmicas, cor, opacidade, umidade e solubilidade, além de espectros de infravermelho com transformada de Fourier (FTIR) dos filmes, foram estudadas. As soluções foram analisadas por reometria dinâmica. Os filmes produzidos com o PVA de menor GH foram mais higroscópicos e mais solúveis. Mas o tipo de PVA não afetou a cor, afetando a opacidade e o brilho dos filmes. O PVA com maior GH proporcionou filmes mais resistentes, e o PVA de menor GH produziu filmes mais resistentes à tração, embora menos deformáveis na perfuração. O GH do PVA não afetou a temperatura de transição vítrea dos filmes, determinada na primeira varredura, mas a afetou na segunda varredura. Os resultados das análises de FTIR corroborraram com esses resultados. As propriedades viscoelásticas das soluções não foram afetadas pelo GH do PVA, muito possivelmente por se tratar de soluções diluídas.

Obtaining high purity silica from rice hulls

Many routes for extracting silica from rice hulls are based on direct calcining. These methods, though, often produce silica contaminated with inorganic impurities. This work presents the study of a strategy for obtaining silica from rice hulls with a purity level adequate for applications in electronics. The technique is based on two leaching steps, using respectively aqua regia and Piranha solutions, which extract the organic matrix and inorganic impurities. The material was characterized by Fourier-transform infrared spectroscopy (FTIR), powder x-ray diffraction (XRD), x-ray fluorescence (XRF), scanning electron microscopy (SEM), particle size analysis by laser diffraction (LPSA) and thermal analysis.

Estudos termoanalíticos de sais de sódio e potássio de ditiocarbamatos em atmosfera oxidante

Thermoanalytical behavior of sodium and potassium salts of pyrrolidinedithiocarbamate (pyr), piperidineditiocarbamate (pip), morpholinedithiocarbamate (mor), hexametileneiminedithiocarbamate (hex), were investigated. In a first step the salts were synthesized and characterized by infrared spectroscopy (FTIR), ¹H and 13C nuclear magnetic resonance (NMR) and elementar analysis. Finally, thermal analytical (TG/DTG and DSC) studies were performed in order to evaluate the thermal stability, as well as the pathways of the thermal decomposition based in the intermediate and final decomposition products.

Caracterização mecânica e térmica da borracha natural formulada e vulcanizada dos clones: GT 1, IAN 873, PB 235 e RRIM 600

Neste trabalho estudou-se o desempenho mecânico e térmico de compostos de borracha natural (Hevea brasiliensis) de 4 diferentes clones (GT 1, IAN 873, PB 235 e RRIM 600) cultivados no Estado de São Paulo, assim como de uma mistura destes clones e de uma borracha comercial, GEB-1. Estas borrachas foram formuladas e vulcanizadas com tempos de 5, 7 e 9 minutos. A caracterização foi realizada por calorimetria exploratória diferencial, termogravimetria, ensaios de resistência à tração, análise dinâmico-mecânica, medidas de dureza Shore A, microscopia eletrônica de varredura e espectroscopia na região do infravermelho. Os resultados permitiram concluir que o tempo de vulcanização e o tipo de clone não influenciaram na temperatura de transição vítrea (Tg) dos compostos. Os valores de Tg obtidos por DMA foram de cerca de -62 °C, e os resultados ensaios de dureza apresentaram valores próximos de 60 para todos os compostos estudados. Os ensaios de resistência à tração mostraram que o melhor desempenho mecânico foi obtido pelo clone RRIM 600. De acordo com os resultados obtidos neste trabalho, todos os clones atingiram as propriedades reportadas na literatura, podendo ser utilizados, em princípio, nas indústrias de artefatos de borracha separadamente ou na forma de mistura.

Síntese de poli(1,1'-ferrocenilenovinileno) via acoplamento de McMurry

Com base nas grandes modificações das propriedades de materiais poliméricos resultantes da inclusão de unidades organometálicas, descrevem-se neste trabalho a síntese e a caracterização de um polímero organometálico conjugado com estrutura semelhante à de poli(p-fenilenovinileno) (PPV), o qual apresenta grupos 1,1'-ferrocenileno no lugar de 1,4fenileno em sua cadeia principal. Sintetizado por meio de reação de acoplamento de McMurry de 1,1'-ferrocenodialdeído, o poli(1,1'-ferrocenilenovinileno) (PFV) se apresentou na forma de um sólido de cor laranja, amorfo e insolúvel tanto em solventes polares quanto em apolares. Para caracterização do PFV, empregaram-se os métodos de espectroscopia no infravermelho (FTIR), espectroscopia Raman e análise termogravimétrica (TGA).

A theoretical study of the tautomerism and vibrational spectra of 4,5-diamine-2,6-dimercaptopyrimidine

The 4,5-diamine-2,6-dimercaptopyrimidine (DADMcP) compound is an interesting multifunctional species exhibiting a rather complex tautomerism, encompassing nine tautomeric forms. Investigation of tautomerism in this compound has been carried out by means of FTIR spectroscopy, in association with ab-initio HF/SCF and DFT calculations. According to this study three tautomers are energetically favored; the thione form being the most stable one. The theoretical vibrational spectra of such tautomeric forms have been successfully simulated by means of DFT calculations, allowing the elucidation and assignment of the complex composition of the vibrational bands observed for the mixture of isomers.

Knoop microhardness and FT-Raman evaluation of composite resins: influence of opacity and photoactivation source

The aim of this study was to evaluate the degree of conversion by Knoop microhardness (KHN) and FT-Raman spectroscopy (FTIR) of one nanofilled (Filtek Supreme-3M-ESPE [FS]) and one microhybrid composite (Charisma-Heraeus-Kulzer [CH]), each with different opacities, namely enamel, dentin, and translucent, which were photo-activated by a quartz-tungsten-halogen lamp (QTH) and a light-emitting diode (LED). Resin was bulk inserted into a disc-shaped mold that was 2.0 mm thick and 4 mm in diameter, obtaining 10 samples per group. KHN and FTIR values were analyzed by two-way ANOVA and Tukey's tests (α = 0.05). Nanofilled resin activated by a LED presented higher microhardness values than samples activated by a QTH for dentin opacity (p < 0.05). The microhybrid resin showed no differences in KHN or FTIR values with different activation sources or opacity. The nanofilled dentin and enamel resins showed lower FTIR values than the translucent resin. The KHN values of the translucent resins were not influenced by the light source.