Reflectance Infrared Spectroscopy Techniques Research Articles

Understanding solvent effects on adsorption and protonation in porous catalysts

Solvent selection is a pressing challenge in developing efficient and selective liquid phase catalytic processes, as predictive understanding of the solvent effect remains lacking. In this work, an attenuated total reflection infrared spectroscopy technique is developed to quantitatively measure adsorption isotherms on porous materials in solvent and decouple the thermodynamic contributions of van der Waals interactions within zeolite pore walls from those of pore-phase proton transfer. While both the pore diameter and the solvent identity dramatically impact the confinement (adsorption) step, the solvent identity plays a dominant role in proton-transfer. Combined computational and experimental investigations show increasingly favorable pore-phase proton transfer to pyridine in the order: water < acetonitrile < 1,4 – dioxane. Equilibrium methods unaffected by mass transfer limitations are outlined for quantitatively estimating fundamental thermodynamic values using statistical thermodynamics.

Quantitative Analysis of Heave Mental Ion Based on Portable NIR Spectrometer

By virtue of the characters of rapid analysis and simple pretreatment, near infrared reflectance spectroscopy technique is widely used in agriculture, medicine, environment, petrochemical and other fields. To satisfy the rapid on-site identification and analysis, portable near-infrared spectrometers have gained more and more attention. Because near infrared reflectance spectroscopy technique also is a green tool for multi-component analysis, the paper aims at investigating the feasibility for simultaneous quantitative analysis of various heavy metal ions in dilute solution using portable near infrared spectrometer. First, amino modified polymerized starch was used as adsorbent to enrich nickel ions and copper ions in diluted solution. Then, the diffuse reflectance spectra of amino modified polymerized starch samples were measured directly by portable near-infrared spectrometer. Furthermore, with the help of spectral preprocessing methods and partial least-squares regression, quantitative models were built from the near infrared diffuse reflectance spectra of amino modified polymerized starch enriched with heavy metal ions and reference concentrations. At last, the stability of the models was proved through cross validation and external validation. The results show that nickel ions and copper ions in diluted solution can be efficiently enriched by amino modified polymerized starch in the presence of other interfering ions. The adsorption rates for nickel ions and copper ions are 99.5% and 99.8%, respectively. Two robust models can be achieved after spectra processing and partial least squares regression. The spectra processing methods contains Continuous wavelet transform and multiplicative scatter correction combined with Savitzky-Golay. The obtained corresponding correlation coefficients of the two robust models are 0.981 9 and 0.965 4, respectively. Thus, simultaneous quantitative analysis of nickel ions and copper ions in the mixed diluted solution was achieved, and the detectable concentrations of nickel ions and copper ions are both as low as 3.0 mg·L(-1). The method not only improves the sensitivity of near infrared reflectance spectroscopy technique, but also demonstrates the feasibility for simultaneous quantitative determination of various heavy metal ions by using portable near infrared spectrometer. Moreover, the method may be a useful exploration to further broaden the application of near infrared reflectance spectroscopy technique.

Beneficial effects of rhodium and tin oxide on carbon supported platinum catalysts for ethanol electrooxidation

This work investigates ethanol electrooxidation on Pt/C, PtxRhy/C, Pt-SnO2/C, and PtxRhy-SnO2/C catalysts synthesized by the Pechini and microwave-assisted polyol methods. The catalysts are characterized by energy dispersive X-ray analysis (EDX), transmission electron microscopy (TEM), and X-ray diffraction (XRD) techniques. The electrochemical properties of these electrode materials are examined by cyclic voltammetry and chronoamperometry experiments in acid medium. The products obtained during ethanol electrolysis are identified by high performance liquid chromatography (HPLC). The adsorbed intermediates are evaluated by an in situ reflectance Infrared Spectroscopy technique combined with cyclic voltammetry. Catalysts performance in a direct ethanol fuel cell (DEFC) is also assessed. The electrical performance of the electrocatalysts in a single DEFC at 80 °C decreases in the following order Pt70Rh30SnO2 > Pt80Rh20SnO2 > Pt60Rh40SnO2 ∼ PtSnO2 > PtxRhy ∼ Pt, showing that the presence of SnO2 enhances the ability of Pt to catalyze ethanol electrooxidation.

Raman and Infrared reflection spectroscopic study of pre-Columbian Mesoamerican pottery

Taking advantage of the recent development of Raman microprobe (RMP) and infrared reflection spectroscopy (IRS) techniques, we report for the first time the mineralogical composition of pre-Columbian Mesoamerican ceramic materials from two sites: Cuanalan (Teotihuacan, Mexico) and Kaminaljuyu area (Guatemala). The Raman spectra obtained from selected areas of the rough fragments from the Cuanalan ceramic materials show that these samples are characterized by the highly heterogeneous body matrix mineralogy due to the presence of a large variety of minerals such as alkali and plagioclase feldspars, diopside, magnetite and Ti-magnetite, and rutile. This mineralogical assemblage including a confirmed diopside is characteristic for the clays that start to crystallize at a temperature near to 800–900 °C. Representative FTIR reflection spectra of the ceramic matrix of Cuanalan pottery in the 1700–400 cm −1 were indicative of non-calcareous ceramic materials, showing strong SiO vibration of meta-clay. The RMP studies of the Mayan ceramics from Guatemala have shown their different mineralogy and chemistry. Due to the presence of calcite (characteristic Raman CO 2− 3 lines at 1089, 714 and 285 cm −1 were observed) and the absence of diopside and rutile in ceramic pottery from the Kaminaljuyu area, a firing temperature between 600 and 700 °C can be deduced. The IRS spectra indicate a weakly calcareous ceramic matrix with CO 3 2− vibration of microcrystalline calcite. The main CO 2− 3 reflection bands (at 1530, 1442, 880, and 726 cm −1 ) were obtained in the heterogeneous samples by using an infrared microscope capable of distinguishing small mineral inclusions and eliminating the characteristic bands of the silicate matrix in the range 1047–1055 cm −1 . The detection of anatase polymorph in the Kaminaljuyu pottery demonstrates the content of kaolinite in the raw material. The combined application of RMP and IRS improves the identification of the mineral phases in the composition of the pottery and makes it possible to analyze the structural degree of ordering of the principal amorphous phases that are formed during the firing of the clayey raw material to pottery. With the recent development of combined RMP and IRS techniques, these spectroscopic methods are emerging as an important tools in mineralogical research and, in particular, in the case of in situ studies of archaeological artifacts.

Optical spectroscopy and electronic structure of the face-centered icosahedral quasicrystals Zn-Mg-R(R=Y, Ho, Er)

Results of optical spectroscopy studies of the face-centered icosahedral (fci) single-grain Zn-Mg-Y, Zn-Mg-Ho, and Zn-Mg-Er quasicrystals (QCs) are presented. The dielectric function of the QCs was measured in the 0.01--6 eV spectral range by IR-UV spectroscopic ellipsometry and far infrared reflection spectroscopy techniques. A theoretical scheme of optical conductivity calculations is extended to account for the Fermi level positions within and below a pseudogap. The model of the QC electron energy spectrum, based on a band structure hypothesis, is suggested, which treats the electronic subsystem as a nearly free electron gas affected by intersections of the Fermi surface with several families of Bragg planes. The experimental optical spectra are reproduced in detail by theoretical calculations carried out within the framework of the model. The parameters of the electron energy spectrum deduced from an analysis of optical data are close to those previously determined in an analysis of fci Zn-Mg-$R$ valence band photoemission spectra.

Interaction of quercetin, genistein and its derivatives with lipid bilayers – An ATR IR-spectroscopic study

Genistein, a main soy isoflavone, is well known as phytoestrogen and antioxidant but details of its interactions with lipid membranes are poorly understood. The aim of this work was to elucidate the interaction of genistein, its derivatives and quercetin with lipid bilayers using attenuated total reflection infrared spectroscopy technique. Measurements performed mainly on liposomes and assistantly on dehydrated lipid films enabled us to find that studied flavonoids intercalate into phospholipid bilayers. The temperature of chain-melting phase transition for isoflavone-mixed DPPC liposomes was determined. The changes of population of the trans/gauche conformers of lipid chains were studied. They exert rigidifying effect in hydrophobic core of bilayer and due to the formation of hydrogen bonds induce a new spatial arrangement of lipid molecules.

Ferroelectric domains in epitaxial PbTiO3 films on LaAlO3 substrate investigated by piezoresponse force microscopy and far-infrared reflectance

Domain structures of 100–300 nm thin epitaxial films of ferroelectric PbTiO3 grown by metalorganic chemical vapor deposition technique on LaAlO3 perovskite substrate have been investigated by piezoresponse force microscopy and infrared reflectance spectroscopy techniques. Normal-incidence reflectance spectra reveal both E- and A1-symmetry modes of PbTiO3. The latter ones demonstrate the presence of a minor fraction of a-domains (with in-plane orientation of the spontaneous polarization) in the film. The piezoresponse force microscopy images allow to get local insight in the complex nanodomain architecture composed by few hundred nm large areas of primarily c/a/c/a but also a1/a2/a1/a2 domain pattern types, with participation of all six tetragonal ferroelectric domain states and both 180 ° and 90 ° ferroelectric walls.

Metallic pattern fabrication in organic Mott insulating crystal by local X-ray irradiation

We have fabricated a metallic structure in an organic Mott insulator κ-(BEDT-TTF) 2Cu[N(CN) 2]Cl. The periodic metallic domains of approximately 90×90 μm 2 obtained by X-ray irradiation through a molybdenum mesh mask are visualized by scanning microregion infrared reflectance spectroscopy technique. No deterioration by irradiation is found in a range of nanometer to micrometer scales. We demonstrate that the present processing method is applicable for the fabrication of molecular electronic devices.

“Ir-in-ceria”: A highly selective catalyst for preferential CO oxidation

An Ir-in-ceria catalyst has been developed, in which most of the iridium particles are embedded in the ceria matrix through the redox reaction between Ce 3+ and Ir 4+, which occurred during co-precipitation (CP). This Ir-CP catalyst exhibited high activity for preferential CO oxidation under excess hydrogen conditions, and the selectivity to CO 2 remained nearly constant, at around 70%, with increasing reaction temperature. Temperature-programmed reduction and in situ diffuse reflectance infrared spectroscopy techniques were used to explore the structure of the Ir-CP catalyst and to correlate it with the catalytic performance. It was found that the CeO 2 support was activated by iridium and formed on the surface the active sites for CO oxidation. Due to the absence of extensively exposed Ir species on the Ir-CP catalyst, H 2 oxidation occurring on the Ir species and the ceria support at high temperatures was significantly suppressed, thus keeping the selectivity to CO 2 at a high level.

In situ FTIRS studies of the electrocatalytic oxidation of ethanol on Pt alloy electrodes

Ethanol oxidation on Pt–Os and Pt–Ru–Os alloy electrodes was investigated by electrochemical and spectroelectrochemical techniques. Cyclic voltammetry and chronoamperometric results showed that the Pt–Os alloy has the highest current density at lower potentials. Linear COads, acetic acid, acetaldehyde, and CO2 were identified as reaction intermediates and/or products by single potential alteration infrared reflectance spectroscopy and subtractively normalized interfacial Fourier transform infrared reflectance spectroscopy techniques. The in situ Fourier transform infrared spectroscopy results showed that the electrooxidative adsorption of ethanol was dissociative providing COads at low potentials.

Effects of shear rate and forced convection residence time on asymmetric polysulfone membranes structure and gas separation performance

The objectives of this study are to illustrate the effects of shear rate and forced convection residence time on asymmetric polysulfone membrane structure and gas separation performance. The membranes were produced by a simple dry/wet phase inversion technique using a pneumatically-controlled flat sheet membrane casting system. Varying the casting speed varied shear rate. Rheologically induced molecular orientation in membranes during casting was measured directly using plane polarized reflectance infrared spectroscopy technique. The highly sheared asymmetric membranes tend to exhibit greater molecular orientation in the skin layer. Thus, a high pressure-normalized flux and selectivity were obtained. The mean pressure-normalized fluxes of O2 and CO2 were about 5.05 and 11.41 GPU, respectively. The selectivity of O2/N2 and CO2/CH4 were approximately 6.72 and 32.63, respectively, at shear rate of 367 s−1. However, increasing forced convection residence time in the dry phase inversion step resulted in lower pressure-normalized flux but higher selectivity membrane. The best membrane performance obtained based on the trade-off between pressure-normalized flux and selectivity was observed at forced convection residence time of 20 s and at 367 s−1 shear rate.

Characterizations of Nanostructured Films as Responsive Electrode Materials

AbstractNanostructured thin films were assembled as metal-responsive electrode materials from monolayer-capped gold nanoparticles (2 nm) and carboxylic acid functionalized alkyl thiol linkers via an exchange-crosslinking-precipitation reaction pathway. The network assemblies have open frameworks in which void space forms channels or chambers with the nanometer sized cores defining its size and the shell structures defining its chemical specificity. Such nanostructures were investigated as responsive materials for the detection of metal ion fluxes. Cyclic voltammetry, in-situ electrochemical quartz-crystal nanobalance, and surface infrared reflection spectroscopy techniques were used to characterize the interfacial redox reactivity and mass fluxes at the nanostructured electrode materials. The system showed remarkable reversible mass loading arising from incorporation of ionic species into the film. The diagnostic stretching bands of the carboxylic and carboxylate groups at the shell allowed the identification and assessment of the interfacial carboxylate-metal ion reactivity.

DIFFUSE REFLECTANCE INFRARED SPECTROSCOPIC CHARACTERIZATION OF SEDIMENTS DERIVED FROM VISBROKEN RESIDUAL OILS

ABSTRACT Diffuse reflectance infrared spectroscopy technique possesses a decided advantage to many classical transmission spectroscopic studies of petroleum fractions and related materials. where the solids are dispersed and encapsulated in a matrix. The detailed and comprehensive diffuse reflectance infrared spectroscopic study on the sediments derived from visbroken residues after prolonged storage at ambient aging conditions are reported. The technique provides a better degree of characterization and high quality data on the structure and chemistry of sediment formation during visbreaking and storage at ambient aging conditions. The study also provides a new insight into the visbreaking reactions, which especially influence the nature and extent of sediment formation.