Showing papers on "Fourier transform infrared spectroscopy published in 1998"

Genesis and Structure of WOx/ZrO2 Solid Acid Catalysts†

Abstract: Zirconia-supported tungsten oxide catalysts were prepared by suspending hydrous zirconium oxide in aqueous solutions of ammonium metatungstate at their natural pH. The suspensions were refluxed at 383 K followed by evaporation of the water, drying and calcination. The WO3 loadings were chosen between 3.6 and 32 wt % and the calcination temperatures were in the range 773 ≤ T ≤ 1273 K. The resulting materials were structurally characterized by X-ray diffraction, differential thermal analysis, and surface area measurements, by laser Raman and Fourier transform infrared (FTIR) spectroscopy, and by UV−vis diffuse reflectance spectroscopy. Their acidic properties were tested by FTIR spectroscopy using carbon monoxide as a probe molecule. The experimental results indicate that the presence of WOx retards the crystallization of the zirconia material and stabilizes the tetragonal ZrO2 phase and the intrinsic BET surface area. W−O−W linkages are detected even at the lowest WO3 loadings indicating that oligomeric WO...

A FT-IR Study of the Hydrolysis of Tetraethylorthosilicate (TEOS).

Abstract: The hydrolysis and polymerization of a non-catalyzed silica sol was investigated by Fourier Transform Infrared Spectroscopy (FT-IR) and deconvolution of the infrared spectra. The hydrolysis was followed by the 1168 and 812 cm−1 bands which have been observed that decrease continously with the reaction time, and they dissapear showing the complete hydrolysis. The bands located at 1200 and 1147 cm−1 are assigned to polymerization of Si-OH groups forming Si-O-Si bonds in cyclic or linear structures respectively. Both bands increase with time and are present simultaneously in the spectra showing that both kind of cross-linking of Si-OH groups are taking place in the sol to form the gel. In the gel the presence of Si-OH groups and Si-O− free broken bonds have been detected by means of the bonds located at 960 and 920 cm−1 respectively.

Spectroscopic determination of the structure of amorphous nitrogenated carbon films

Abstract: Studies on structure and electronic properties of amorphous nitrogenated carbon films prepared in dual electron cyclotron resonance–radio frequency plasma from a mixture of methane and nitrogen are presently reported. These films are characterized by Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, x-ray photoemission spectroscopy (XPS), ultraviolet photoemission spectroscopy (UPS), electrical conductivity measurement, and optical absorption spectroscopy. Symmetry breaking of aromatic rings are at a very small amount of nitrogen incorporation is understood from FTIR spectra. The relative contribution of C=N and C–N bonds is found to change with the variation of the nitrogen content in the samples, which shows a similar trend with the shift of the G peak to a higher wave number and the increase of the ID/IG ratio. From decomposition of XPS C 1s and N 1s peaks a three-phase model of CN bonds is proposed. UPS valence band spectra obtained by using a Helium II source, are decomposed into p-...

Gold and Silver Nanoparticles Functionalized by the Adsorption of Dialkyl Disulfides.

Abstract: The formation of three-dimensional self-assembled monolayers (3-D SAMs) generated by the adsorption of n-octadecyl disulfide onto colloidal gold and silver nanoparticles is described. The functionalized nanoparticles were characterized by solubility, transmission electron microscopy, ultraviolet−visible spectroscopy, 1H nuclear magnetic resonance spectroscopy, surface-enhanced Raman spectroscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. On gold nanoparticles, this new functionalization method affords crystalline 3-D SAMs that are indistinct from those prepared by the analogous adsorption of n-octadecanethiol. On silver nanoparticles, however, the films derived from n-octadecyl disulfide appear to be somewhat less crystalline than those prepared similarly from n-octadecanethiol. The origin of this difference is briefly explored and discussed.

Determination of Lignin Content of Eucalyptus globulus Wood Using FTIR Spectroscopy

Abstract: FTIR spectroscopy was used to quantitatively determine lignin in Eucalyptus globulus wood. A total of 40 wood samples from a 9 year old provenance trial was divided into two independent sets for calibration and validation. Lignin contents, as determined by the acetyl bromide method, ranged from 23 % to 34 % o.d. extractive-free wood. Spectra were recorded with the KBr pellet technique and twelve peaks between 1800cm -1 to 800cm -1 used for calibration by linear regression. The best calibration fit (R 2 =0.98) was obtained with the 1505 cm -1 peak from lignin and the 1157 cm -1 peak from polysaccharides as a reference. The standard error of calibration (SEC), and the standard error of prediction (SEP) calculated with the validation set, were very low. A linear regression of FTIR measurements proved strong enough to predict lignin content with a very high coefficient of determination. The accuracy of FTIR techniques allows its use in large scale breeding programmes to assess wood lignin content with considerable less effort and shorter time than using wet-lab methods, once a reliable calibration is performed for the species.

Molecular dynamics simulations of organically modified layered silicates

Abstract: Molecular dynamics (MD) simulations are used to study the static and dynamic properties of 2:1 layered silicates ion exchanged with alkyl-ammonium surfactants. These systems are in the form of oligomeric alkanes grafted by cationic groups on atomically smooth crystalline layers 10 A thick and several microns wide. The organically modified layers self-assemble parallel to each other to form alternating, well-ordered organic/inorganic multilayers. By studying the systems at the experimentally measured layer separations, computer modeling directly provides the structure and dynamics of the intercalated surfactant molecules. The grafted-chain conformations are also expressed through the trans-gauche conformer ratios and transition frequencies which compare well with Fourier transform infrared spectroscopy (FTIR) experiments.

Handbook of fourier transform raman and infrared spectra of polymers

Abstract: Chapter Headings Historical introduction The essential principles of infrared absorption and Raman scattering Important advantages of Raman spectroscopy Main stages in the development of Fourier transform infrared spectroscopy FTIR spectrometer - optical correlometer Fourier transform Raman spectroscopy Characterization of samples Polymer classification Polymer classification guide Experimental conditions Comments on data presentation References Appendix Spectral interpretation literature Spectral collections Acknowledgements Spectra Alphabetical compound name index Alphabetical synonym or TM index Alphabetical general formula index Chemical Abstracts Service registry index

Analysis of chemical structure of wood charcoal by X-ray photoelectron spectroscopy

Abstract: Wood charcoal carbonized at various temperatures was analyzed by X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffractometry to investigate the changes of chemical structures during the carbonization process. From the infrared spectra, the carbon double bonds and aromatic rings were seen to form at a carbonization temperature of about 600°C. From the XPS spectra, the ratio of aromatic carbons increased in the temperature range 800–1000°C and over 1800°C. The condensation of aromatic rings proceeded as carbonization progressed. The drastic reduction of electrical resistivity of charcoals was observed in almost the same temperature range. It was found that the condensation of aromatic rings had some relation to the decline in electrical resistivity. Wood charcoal carbonized at 1800°C was partly graphitized, a finding supported by the results of X-ray diffraction and XPS. The functional groups containing oxygen diminished with the increase in carbonization temperature.

Chemistry of a Chromate Conversion Coating on Aluminum Alloy AA2024‐T3 Probed by Vibrational Spectroscopy

Abstract: Infrared and Raman spectroscopy were used to characterize a chromate conversion coating (CCC) on 2024-T3 aluminum aircraft alloy with a long range objective of determining the anticorrosion mechanism of the CCC. Spectra were compared to those from synthetic mixed oxides of aluminum, Cr(III), and Cr(VI) made by treating pure reagents with NaOH. The Fourier transform infrared (FTIR) and Raman spectra of the CCC showed similar behavior to the chromium III/VI mixed oxide for both the initial materials and after heat-treatment. Analysis of the CCC and chromium mixed oxide by UV-vis spectroscopy indicated that both have a 3:1 ratio of Cr(III) to Cr(VI). When the chromium mixed oxide was immersed in pH 4 HNO 3 , the ratio of released H + to released Cr(VI) ranged from 0.98 to 1.07. In addition, a compound with a Raman spectrum very similar to that of a CCC was formed by a reaction of Cr(III) hydroxide with Cr 2 O 7 -2 , CrO 4 -2 , or the Alodine chromating bath. The results indicate a strong structural similarity between the Cr-mixed oxide and a major component of the CCC. A likely structure for this common material involves covalent bonding between polymeric Cr(III) hydroxide and Cr 2 O 7 -2 or CrO 4 2 , This mixed oxide structure may hydrolyze to release H + and soluble chromate.

Cancer grading by Fourier transform infrared spectroscopy.

Abstract: Thirty-nine freeze-dried tissue samples from 17 lymphoid tumors (nine malignant non-Hodgkin's lymphomas) were studied by Fourier transform infrared (FTIR) spectroscopy. The absorbance ratio A1121/A1020 increased, along with the emergence of an absorbance pulse at 1121 cm-1, with increasing clinicopathological grade of malignant lymphoma. An increasing A1121/A1020 ratio from benign to malignant is evident in literature spectra from several different tissues; however, the present study is the first to comment on this effect and to propose it as an index of the cellular RNA/DNA ratio after subtraction of overlapping absorbances, if present, due to collagen or glycogen. Absorbance attributable to collagen increased with lymphoma grade and was greater in benign inflammatory tumors than in low-grade lymphomas. The A1121/A1020 trend observed here may form the basis of a universal cancer-grading parameter to assist with cancer treatment decisions and may also be useful in the analysis of cellular growth perturbation induced by drugs or other therapies. Our spectral findings may potentially be applied to cell clusters and discrete areas of tumor tissue sections using the FTIR microscope, allowing correlation with morphology and a high degree of spatial resolution.

Self-assembled monolayers on oxidized metals. 4. superior n-alkanethiol monolayers on copper

Abstract: Self-assembly (SA) of long-chain alkanethiols on copper was studied. Two factors were found to have substantial influence on the SA process: (i) the chemical reactivity of Cu toward substances present in the adsorption solution, particularly the solvent, and (ii) surface pretreatment, which influences the amount of oxide and the surface morphology. Both factors are less important in the case of SA onto gold because of its chemical inertness. Monolayers of octadecanethiol (C18SH) were adsorbed from different solvents (ethanol, toluene, and bicyclohexyl) at various thiol concentrations onto Cu surfaces pretreated in several different ways. The monolayers were characterized by contact-angle measurements, grazing-incidence Fourier transform infrared spectroscopy, and scanning force microscopy. Ethanol, the most common solvent for alkanethiol SA, is found to have a negative effect on monolayer SA apparently because of its chemical reactivity toward copper. With toluene as a solvent, better oriented and more c...

Comparative Study on Structure of Solubilized Water in Reversed Micelles. 1. FT-IR Spectroscopic Evidence of Water/AOT/n-Heptane and Water/NaDEHP/n-Heptane Systems

Abstract: The interactions of water with the polar headgroups in the reversed micelles of sodium bis(2-ethylhexyl) sulfosuccinate (AOT) and sodium bis(2-ethylhexyl) phosphate (NaDEHP) have been studied by me...

Ageing of Starch Based Systems as Observed with FT‐IR and Solid State NMR Spectroscopy

Abstract: The retrogradation and physical ageing of model starch systems with respect to their glass transition temperatures Tg have been investigated by Fourier transform infrared Spectroscopy and solid state NMR spectroscopy. Diffuse reflectance Fourier transform infrared (DRIFT) spectra demonstrate the commencing retrogradation of starch materials stored above their Tg by changes in peak lineshapes and intensities in the characteristic area between 995 cm−1 and 1020 cm−1. Solid state NMR proton relaxation times in the rotating frame (proton T1ρ) show a characteristic course in relation to the storage conditions (time, humidity), for which a distinction is made between physical ageing which occurs below the Tg, and recrystallisation (retrogradation) which takes place above Tg. The proton T1ρ's of materials stored below Tg increase asymptotically in time due to physical ageing, whereas the proton T1ρ's of materials stored above Tg increase until a moisture content is reached that rises them above Tg, decrease due to further water absorption and then increase due to recrystallisation (retrogradation).

Increased lateral density in alkanethiolate films on gold by mercury adsorption

Abstract: We present a method for increasing the lateral chain density in self-assembled monolayers (SAMs) of alkanethiols on polycrystalline gold. This method relies on exposure of the alkanethiolate monolayers to mercury vapor and subsequent reimmersion into the thiol solution. Mercury adsorption on the gold surface induces a structural rearrangement in the alkanethiolate monolayers, as indicated by changes in dichroism in the Fourier transform infrared (FTIR) spectra, in line shape in the sum frequency generation (SFG) spectra, and in the macroscopic wetting behavior of the monolayers. X-ray photoelectron spectroscopy (XPS) data show that saturation of the thiolate samples with mercury occurs after 20−30 min of exposure to air saturated with mercury vapor. For 100 nm evaporated gold films a mercury bulk concentration of 14−16 atom % was determined by energy-dispersive X-ray analysis (EDX). Time-of-flight secondary ion mass spectroscopy (ToF-SIMS) data indicate that after mercury adsorption the monolayers consist...

Laser-induced chemical vapor deposition of nanostructured silicon carbonitride thin films

Abstract: Laser-induced chemical vapor deposition of silicon carbonitride thin films has been investigated using a continuous wave CO2 laser in parallel configuration with the substrate. The reactant gases in this process, hexamethyl disilazane and ammonia, are rapidly heated by CO2 laser radiation due to their absorption of the laser energy. Polymerlike silicon carbonitride films or agglomerated nanosized particles are formed depending on process conditions. Dense, smooth films or nanostructured deposits have been synthesized at low substrate temperatures (Ts<300 °C) on quartz, copper, and silicon and can be obtained with controlled microstructures. Surface morphology, composition, and type of chemical bonding have been studied with electron microscopy and spectroscopic analysis and are correlated to the most important laser process parameters. X-ray photoelectron spectroscopy and reflectance Fourier transform infrared spectroscopy show that the deposits consist of Si–N, Si–C, and Si–O bonds, linked together in a x-ray amorphous, polymerlike structure. The nitrogen content is about 40% and can be varied by adding ammonia to the reactant gas flow. The layers are readily contaminated with oxygen after exposure to air, caused by hydrolysis and/or oxidation.

Hydrothermal–electrochemical deposition of hydroxyapatite

Abstract: Hydroxyapatite crystals were formed on a titanium electrode using the hydrothermal-electrochemical method in an autoclave with two electrodes. The electrolyte dissolving NaCl, K 2 HPO 4 , CaCl 2 . 2H 2 O, trishydroxyaminomethane, and hydrochloric acid was maintained at 80°- 200°C. After loading of a constant current at 12.5 mA/cm 2 for 1 h, the deposited amounts were measured through the weight gain of the electrode. The deposits were characterized by X-ray diffractometry, Fourier transform infrared spectroscopy, field emission-type scanning electron microscopy, field emission-type transmission electron microscopy, and energy dispersive X-ray spectroscopy. The deposited amount increased with electrolyte temperatures up to 150°C and slightly decreased above that temperature. The deposits were identified as hydroxyapatite crystal rods grown along the c axis and perpendicular to the substrate. The crystallinity of the deposited hydroxyapatite increased continuously with the electrolyte temperature and closed to stoichiometric hydroxyapatite. At 150°-160°C, the hydroxyapatite rod grew very homogeneously perpendicular to the substrate, and the edge of the needle had a flat hexagonal plane. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 42, 387-395, 1998.

Predictions of protein secondary structures using factor analysis on Fourier transform infrared spectra: effect of Fourier self-deconvolution of the amide I and amide II bands.

Abstract: Fourier self-deconvolution (FSD) was performed on protein amide I and II Fourier transform infrared (FTIR) spectra to test if the resultant increased band shape variation would lead to improvements in protein secondary structure prediction with our factor analysis based restricted multiple regression (RMR) methods. FTIR spectra of 23 proteins dissolved in H2O were measured and normalized to a constant amide I peak absorbance. The deconvolved spectra were renormalized by area so that the deconvolved spectra sets had the same area as before. Principal component analysis of the deconvolved spectra sets was carried out, which was followed by a selective multiple linear regression (RMR) analysis of the principal component loadings with regard to the fractional components (FC) of secondary structure. As compared to analyses based on the original spectra set, helix and sheet predictions were not noticeably improved by FSD; but, if a very large number of component spectra (16) were retained in the pool to select which loadings to be used in the RMR optimization, better predictions of turn and “other” resulted. The prediction quality varied depending on the deconvolution parameters used. © 1998 John Wiley & Sons, Inc. Biospectroscopy 4: 93–106, 1998

Microstructure and properties of silicon nitride thin films deposited by reactive bias magnetron sputtering

Abstract: Silicon nitride (SiNx) thin films have been deposited by radio frequency (rf) magnetron sputtering of a silicon target in reactive nitrogen-argon atmospheres without intentional substrate heating. The influence of negative substrate bias Vs on the microstructural, compositional, chemical, mechanical, and optical properties of the SiNx films was systematically investigated. An extensive analysis of the films was carried out using ellipsometry, transmission electron microscopy (TEM), atomic force microscopy (AFM), Rutherford backscattering spectrometry, secondary ion mass spectrometry (SIMS), Fourier transform infrared (FTIR) spectroscopy, ultraviolet-visible spectroscopy, stress and chemical etch rate measurements. TEM and AFM studies revealed that films produced at low bias voltages had a porous columnar structure containing large void, typical of zone 1, but that films produced at higher bias voltages had relatively smooth surfaces with a highly condensed structure, typical of zone T. Both FTIR and SIMS ...