885 resultados para TG-FTIR spectroscopy


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FTIR spectroscopy was used to verify the presence of intermolecular hydrogen bond (inter-H-bond) between poly-(3-hydroxybutyrate co-3-hydroxyvalerate) (PHBV) and bisphenol A (BPA). By monitoring the spectral changes during PHBV crystallization and blends dissociation, the absorptivity ratio of C=O bonds in crystalline and amorphous regions in PHBV and that of H-bonded and free C=O in PHBV/BPA blends were experimentally determined as 1.40 and 1.68, respectively. Using curve-fitting program, the C=O absorptions in spectra of blends were ascribed to three types of bonds: amorphous, crystalline and H-bonded C=O. The crystallinity of PHBV and the fraction of H-bonded C=O were calculated. These results indicated that the H-bond clearly suppressed the PHBV crystallization. Furthermore, the fraction of BPA molecules that simultaneously formed two hydrogen bonds (H-bonds) with C=O was estimated. It revealed that there existed a H-bond network in PHBV/BPA blends. This network was compared with the covalent network by estimating the number of atoms between every two adjacent crosslink points in chain. Up to the high density of H-bond discussed in this paper, there was always a certain part in PHBV that crystallized due to the dynamic character of hydrogen bonds; however, the hydrogen bonds significantly reduced the crystallization rate of PHBV.

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Cobalt(II)-cyanoferrate polymeric film has been electrochemically deposited on a glassy carbon electrode and investigated by cyclic voltammetry and in-situ reflection FTIR spectroscopy. A reorientation of the terminal C=N groups upon redox reactions was proposed. The stretching vibration mode of the terminal C=N groups associated with Fe(III) was observed at 2122 cm(-1), however, the stretching vibration mode for terminal groups associated with Fe(II) did not appear. This process could result in a switch between lattice-closed and lattice-opened surface structure. (C) 1997 Elsevier Science B.V.

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Miscibility in blends of three styrene-butadiene-styrene and one styrene-isoprene-styrene triblock copolymers containing 28%, 30%, 48%, and 14% by weight of polystyrene, respectively, with poly(vinyl methyl ether) (PVME) were investigated by FTIR spectroscopy and differential scanning calorimetry (DSC). It was found from the optical clarity and the glass transition temperature behavior that the blends show miscibility for each kind of triblock copolymers below a certain concentration of PVME. The concentration range to show miscibility becomes wider as the polystyrene content and molecular weight of PS segment in the triblock copolymers increase. From the FTIR results, the relative peak intensity of the 1100 cm-1 region due to COCH3 band of PVME and peak position of 698 cm-1 region due to phenyl ring are sensitive to the miscibility of SBS(SIS)/PVME blends. The results show that the miscibility in SBS(SIS)/PVME blends is greatly affected by the composition of the copolymers and the polystyrene content in the triblock copolymers. Molecular weights of polystyrene segments have also affected the miscibility of the blends. (C) 1995 John Wiley & Sons, Inc.

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In this study, a novel sol-gel method is used to synthesize amorphous silica-alumina materials with a narrow mesoporous distribution and various Si/Al molar ratios without using any templates and pore-regulating agents. During the preparation procedure, only inexpensive inorganic salts were used as raw materials, instead of expensive and harmful alkoxides. The precursor sol was dried at room temperature in a vacuum box kept at 60 mmHg until it began to form the gel. The results of a nitrogen sorption experiment indicate that the synthesized materials with different Si/Al molar ratios have similar mesoporous distributions (within 2-12 nm). Moreover, it was found that the material's pore size distribution remains at a similar value during the heat treatment from room temperature to 550 degreesC. On the basis of the nitrogen sorption, TEM, and AFM characterization results, a formation mechanism of mesopores which accounts for the experimental data is also suggested. This suggested mechanism involves rearrangement of the primary particles during the drying process to form the precursors of the similarly sized mesopores. The synthesized materials were characterized by XRD, thermal analysis (TG/DTA), Al-27 and Si-29 MAS NMR spectroscopy, SEM, TEM, and AFM. The results of Al-27 and 29Si MAS NMR indicate that the distribution of silicon and aluminum in the synthesized materials is more uniform and homogeneous than that in the mixed oxides prepared via the traditional sol-gel method even at high alumina contents. The type and density of the acid sites were studied using pyridine adsorption-desorption FTIR spectroscopy. It was shown that the acidity of the synthesized materials is higher than that of the silica-alumina materials prepared by conventional methods.

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The behaviour of a self-assembled monolayer of 2-mercaptobenzimidazole (MBI) at the Au(111) electrode has been examined using cyclic voltammetry and in situ FTIR spectroscopy. The charge associated with the reductive desorption is pH independent while the oxidative partial redeposition charge increases when the pH is lowered. This is due to differences between the nature and the solubility of the MBI desorption product. In alkaline and neutral media MBI desorbs as the thiolate. In contrast, in acidic solutions the thiol is the desorbed product. Subtractively normalized interfacial reflection Fourier transform absorption spectroscopy (SNIFTIRS) has been applied to investigate the MBI monolayer in contact with aqueous solutions of different pH. The SNIFTIRS data are in agreement with the electrochemical results. Moreover, quantitative analysis of the IR data provided evidence that adsorbed MBI molecules assume a tilted orientation with an angle of 60±5° between the C2 axis of the molecule and the direction normal to the gold surface. © 2003 Elsevier B.V. All rights reserved.

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Solid molecular dispersions of bicalutamide (BL) and polyvinylpyrrolidone (PVP) were prepared by hot melt extrusion technology at drug-to-polymer ratios of 1:10, 2:10, and 3:10 (w/w). The solid-state properties of BL, physical mixtures of BL/PVP, and hot melt extrudates were characterized using differential scanning calorimetry (DSC), powder X-ray diffractometry (PXRD), Raman, and Fourier transform infrared (FTIR) spectroscopy. Drug dissolution studies were subsequently conducted on hot melt extruded solid dispersions and physical mixtures. All hot melt extrudates had a single Tg between theTg of amorphous BL and PVP indicating miscibility of BL with PVP and the formation of solid molecular dispersions. PXRD con?rmed the presence of the amorphous form of BL within the extrudates. Conversely, PXRD patterns recorded for physical mixtures showed sharp bands characteristic of crystalline BL, whereas DSC traces had a distinct endotherm at 1968C corresponding to melting of crystalline BL. Further investigations using DSC con?rmed solid-state plasticization of PVP by amorphous BL and hence antiplasticization of amorphous BL by PVP. Experimentally observed Tg values of physical mixtures were shown to be signi?cantly higher than those calculated using the Gordon–Taylor equation suggesting the formation of strong intermolecular interactions between BL and PVP. FTIR and Raman spectroscopy were used to investigate these interactions and strongly suggested the presence of secondary interaction between PVP and BL within the hot melt extrudates. The drug dissolution properties of hot melt extrudates were enhanced signi?cantly in comparison to crystalline BL and physical mixtures. Moreover, the rate and extent of BL release were highly dependent on the amount of PVP present within the extrudate. Storage of the extrudates con?rmed the stability of amorphous BL for up to 12 months at 208C, 40% RH whereas stability was reduced under highly humid conditions (208C, 65% RH). Interestingly, BL recrystallization after storage under these conditions had no effect on the dissolution properties of the extrudates.

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A comparative study of CO electrooxidation on different catalysts using in situ FTIR spectroscopy is presented. As electrode materials, polycrystalline Pt and Ru and a PtRu (50:50) alloy are used. The latter is one of the well-known active alloys for CO oxidation. The potential dependence of the band frequencies for the CO stretch indicates the formation of relatively compact islands at pure Pt and Ru, and a loose adlayer structure at the alloy. This loose structure has a positive effect on the rate of oxidative desorption. CO submonolayer coverages are obtained by integrating the absorption bands for CO produced upon oxidation of adsorbed CO. The band intensities measured at Pt, Ru, and PtRu indicate an influence of the substrate on the absorption coefficient of the CO stretch. It is shown that for a correct description of the catalyst properties toward CO electrooxidation, it must be distinguished between bulk and adsorbed CO. In contrast to the statement of most of the recent papers that a PtRu alloy (50:50) is the material with the highest activity for CO oxidation, it is demonstrated and rationalized in the present paper that for bulk CO oxidation pure Ru is the best catalyst. © 1999 American Chemical Society.

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The adsorption and electrooxidation of CO at a Ru(0001) electrode in perchloric acid solution have been investigated as a function of temperature, potential and time using in situ FTIR spectroscopy. This builds upon and extends previous work on the same system carried out at room temperature. As was observed at room temperature, both linear (CO) and 3-fold-hollow (CO) binding CO adsorbates (bands at 2000-2045 cm and 1768-1805 cm, respectively) were detected on the Ru(0001) electrode at 10°C and 50°C. However, the temperature of the Ru(0001) electrode had a significant effect upon the structure and behavior of the CO adlayer. At 10°C, the in-situ FTIR data showed that the adsorbed CO species still remain in rather compact islands up to ca. 1100 mV vs Ag/AgCl as the CO oxidation reaction proceeds, with oxidation occurring only at the boundaries between the CO and active surface oxide/hydroxide domains. However, the IR data collected at 50°C strongly suggest that the adsorbed CO species are present as relatively looser and weaker structures, which are more easily electro-oxidized. The temperature-, potential-, and coverage-dependent relaxation and compression of the CO adlayer at low coverages are also discussed.

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This paper reports the first observation, using in situ FTIR spectroscopy, of the oxidation of CO adsorbates on the Ru(0001) electrode to CO under open circuit (oc) conditions in both perchloric acid and sulphuric acid solution at 20 and 55 °C. While the significant oc oxidation of the adsorbed CO on the Ru(0001) electrode was observed in perchloric acid solution, much less oc oxidation took place in sulfuric acid solution due to the specific adsorption of bisulfate at the Ru surface which inhibits the surface oxidation and reduces the reactivity of the surface towards the oxidation of CO . The oc oxidation of the CO depends strongly on the oxygen concentration in the solution and the temperature. The data so obtained are compared to those observed at the gas|solid interface, as well as to those obtained from the electro-oxidation of CO , and possible new catalytic oxidation reaction mechanisms are discussed. In addition, it is shown that the C-O frequency of the adsorbed CO may be used as an effective probe of the open circuit potential. © 2003 Elsevier B.V. All rights reserved.

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The adsorption and electro-oxidation of formaldehyde, formic acid and methanol at the Ru(0001) electrode in perchloric acid solution have been studied as a function of temperature, potential and time using in situ FTIR spectroscopy, and the results interpreted in terms of the surface chemistry of the Ru(0001) electrode and compared to those obtained during our previous studies on the adsorption of CO under the same conditions. It was found that no dissociative adsorption or electro-oxidation of methanol takes place at Ru(0001) at potentials 1000 mV, both the oxidation of formic acid to CO and the oxidation of formaldehyde to both CO and formic acid were significantly increased, and the oxidation of methanol to CO and methyl formate was observed, all of which were attributed to the formation of an active RuO phase on the Ru(0001) surface.

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The electro-oxidations of methanol and formic acid at a Ru(0001) electrode in perchloric acid solution have been investigated as functions of temperature, potential and time using in-situ FTIR spectroscopy, and the results compared to those obtained during our previous studies on the adsorption and electro-oxidation of CO under the same conditions. It was found that no dissociative adsorption or electro-oxidation of methanol takes place at the Ru(0001) at potentials 1000 mV, the oxidation of formic acid to CO was significantly increased, and the oxidation of methanol to CO and methyl formate was observed, both of which were attributed to the formation of an active RuO phase on the Ru(0001) surface.

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The adsorption of water and deuterium oxide on TiO2 surfaces was investigated in the dark as well as under UV(A) irradiation using in situ ATR-FTIR spectroscopy under oxygen and oxygen free conditions. Adsorption of H2O-D2O mixtures revealed an isotopic exchange reaction occurring onto the surface of TiO2 in the dark. Under UV(A) irradiation, the amount of both OH and OD groups was found to be increased by the presence of molecular oxygen. Furthermore, the photocatalytic formation of hydroperoxide under oxygenated condition has been recorded utilizing Attenuated Total Reflection Fourier Transformed Infrared (ATR-FTIR) spectroscopy which appeared as new band at 3483 cm-1. Different possible mechanisms are discussed in terms of the source of hydroxyl groups formed and/or hydration water on the TiO2 surface for the photocatalytic reaction and photoinduced hydrophilicity.

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The vibrational structure of C---H stretching states in gas-phase cyclobutene was studied using FTIR spectroscopy in the range 700–9000 cm−1. The structure was modelled using two effective vibrational Hamiltonians, one for each type of C---H bond present, consisting of local mode basis functions subject to coupling with symmetrically equivalent bonds and to Fermi resonances with suitable low frequency vibrations. Best-fit model parameters were determined using least-squares routines and the model predictions are compared to the observed band positions and intensities. Some discussion is given of the relevance of the observed couplings to intramolecular vibrational redistribution (IVR) which results in the observation of statistical behaviour in cyclobutene isomerization induced by excitation of C---H stretching overtones in the visible region.

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The self-assembly of proteins and peptides into b-sheet-rich amyloid fibers is a process that has gained notoriety because of its association with human diseases and disorders. Spontaneous self-assembly of peptides into nonfibrillar supramolecular structures can also provide a versatile and convenient mechanism for the bottom-up design of biocompatible materials with functional properties favoring a wide range of practical applications.[1] One subset of these fascinating and potentially useful nanoscale constructions are the peptide nanotubes, elongated cylindrical structures with a hollow center bounded by a thin wall of peptide molecules.[2] A formidable challenge in optimizing and harnessing the properties of nanotube assemblies is to gain atomistic insight into their architecture, and to elucidate precisely how the tubular morphology is constructed from the peptide building blocks. Some of these fine details have been elucidated recently with the use of magic-angle-spinning (MAS) solidstate NMR (SSNMR) spectroscopy.[3] MAS SSNMR measurements of chemical shifts and through-space interatomic distances provide constraints on peptide conformation (e.g., b-strands and turns) and quaternary packing. We describe here a new application of a straightforward SSNMR technique which, when combined with FTIR spectroscopy, reports quantitatively on the orientation of the peptide molecules within the nanotube structure, thereby providing an additional structural constraint not accessible to MAS SSNMR.

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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.