Infrared Emission Spectroscopy Research Articles

A combined FTIR and infrared emission spectroscopy investigation of layered double hydroxide as an effective electron donor

A novel method has been presented to characterize electron transfer in layered double hydroxides (LDHs) utilizing an investigation combing FTIR and infrared emission spectroscopy. At room temperature, electron could transfer to interlayer Fe3+ through monodentate ligand cyanide, and resulted in a reduction of 40% Fe3+ to Fe2+. When the environmental temperature increased from 25 to 300°C, reduction of Fe3+ and Ni2+ increased to 94% and 42%. Furthermore, electron also transferred to interlayer cation through multidentate ligand EDTA. As a result, LDHs has been proven to be an effective electron donor, and FTIR was a feasible tool in characterizing this property by monitoring the valence state of cations. It was also concluded that octahedral units with OH− groups in LDH layer functioned as electron donor centers. Driving force for electron transfer is attributed to the charge density difference between cation layer and probe anion. These results could help to explain the mechanism of various applications of LDHs in catalysis and photocatalysis.

The effect of graphene oxide and its oxidized debris on the cure chemistry and interphase structure of epoxy nanocomposites

The influence of graphene oxide (GO) and its surface oxidized debris (OD) on the cure chemistry of an amine cured epoxy resin has been investigated by Fourier Transform Infrared Emission Spectroscopy (FT-IES) and Differential Scanning Calorimetry (DSC). Spectral analysis of IR radiation emitted at the cure temperature from thin films of diglycidyl ether of bisphenol A epoxy resin (DGEBA) and 4,4'-diaminodiphenylmethane (DDM) curing agent with and without GO allowed the cure kinetics of the interphase between the bulk resin and GO to be monitored in real time, by measuring both the consumption of primary (1°) amine and epoxy groups, formation of ether groups as well as computing the profiles for formation of secondary (2°) and tertiary (3°) amines. OD was isolated from as-produced GO (aGO) by a simple autoclave method to give OD-free autoclaved GO (acGO). It has been found that the presence of OD on the GO prevents active sites on GO surfaces fully catalysing and participating in the reaction of DGEBA with DDM, which results in slower reaction and a lower crosslink density of the three-dimensional networks in the aGO-resin interphase compared to the acGO-resin interphase. We also determined that OD itself promoted DGEBA homopolymerization. A DSC study further confirmed that the aGO nanocomposite exhibited lower Tg while acGO nanocomposite showed higher Tg compared to neat resin because of the difference in crosslink densities of the matrix around the different GOs.

Toward a Working Mechanism of Fuel Oxidation in SOFCs: In Situ Optical Studies of Simulated Biogas and Methane

Solid-oxide fuel cells (SOFCs) have potential as highly efficient, clean, and sustainable electricity sources. However, the current, limited state of understanding of the complex electrochemical processes that occur at the anode in these systems, particularly those that lead to anode carbon formation and degradation, are roadblocks to effective cell design and operation. A suite of noninvasive, in situ optical techniques has been developed to help identify these processes. Vibrational Raman spectroscopy, Fourier-transform infrared emission spectroscopy (FTIRES), and near-infrared thermal (NIR) imaging, along with electrochemical measurements, provide surface and gas-phase molecular-specific diagnostics with the requisite temporal, spatial, and thermal resolution to correlate in operando observations with model chemical mechanisms associated with oxidation and carbon formation on Ni-based, anode-supported cells. This present work expands upon earlier in operando studies to fully assess the performance of commercially available Ni-YSZ anode SOFCs from 700 to 800 °C and to provide a more comprehensive description of the anode chemistry involved. Methane and simulated biogas (BG) are used as fuel. Raman measurements show that carbon grows minimally only at the lower operational temperatures for BG; however under methane, carbon formation occurs at all temperatures. Subsequent electrochemical oxidation of deposited carbon revealed that carbon formation under both fuels varies differently as a function of temperature. FTIRES measurements show that COx constituents increase with cell polarization only under methane fuel; this effect changes with temperature. NIR imaging indicates that the Ni anode surface cools significantly when cells are operated at 800 °C relative to 700 °C under BG, and only minimal cooling is observed when operating with methane.

Optical Studies of Dry and Wet Reformed Methane on Solid Oxide Fuel Cell Anodes

The presently limited understanding of solid oxide fuel cell (SOFC) anode mechanisms is due to a lack of experimental techniques that can probe species and component materials directly during operation, or in operando. Previous investigations on the efficiency of Ni-YSZ-based electrode materials in different reforming conditions have been performed using post-mortem and in situ electrochemical analyses with little information on specific mechanisms that lead to fuel oxidation and cell degradation. An ensemble of non-invasive optical methods consisting of near infrared thermal imaging (NIRTI), Raman spectroscopy, and Fourier-transform infrared emission spectroscopy (FTIRES) is utilized to correlate the chemistry of fuel oxidation and carbon formation with traditional electrochemical measurements for methane and simulated biogas fuels in operating SOFCs. Different reforming conditions for methane including plain, wet (steam), and dry (carbon dioxide) are investigated on anode- and electrolyte-supported cells. NIRTI results demonstrate that cooling on the anode surface due to endothermic hydrocarbon cracking for dry reforming or simulated biogas is significantly greater than for unreformed methane on both types of cells. Raman and FTIRES both show that more carbon is deposited with methane than with biogas. The small amount of carbon formed is limited to lower temperatures with simulated biogas whereas carbon formation occurs to a great extent at all temperatures with methane. Exhaust gas analysis with ex situ FTIR absorption measurements and mass spectrometry are combined with in operando measurements to further characterize and quantify the species involved. These findings serve as benchmark data for a better understanding of the mechanisms responsible for performance and degradation of SOFCs.

Communication: photodissociation of CH3CHO at 308 nm: observation of H-roaming, CH3-roaming, and transition state pathways together along the ground state surface.

Following photodissociation of acetaldehyde (CH3CHO) at 308 nm, the CO(v = 1-4) fragment is acquired using time-resolved Fourier-transform infrared emission spectroscopy. The CO(v = 1) rotational distribution shows a bimodal feature; the low- and high-J components result from H-roaming around CH3CO core and CH3-roaming around CHO radical, respectively, in consistency with a recent assignment by Kable and co-workers (Lee et al., Chem. Sci. 5, 4633 (2014)). The H-roaming pathway disappears at the CO(v ≥ 2) states, because of insufficient available energy following bond-breaking of H + CH3CO. By analyzing the CH4 emission spectrum, we obtained a bimodal vibrational distribution; the low-energy component is ascribed to the transition state (TS) pathway, consistent with prediction by quasiclassical trajectory calculations, while the high-energy component results from H- and CH3-roamings. A branching fraction of H-roaming/CH3-roaming/TS contribution is evaluated to be (8% ± 3%)/(68% ± 10%)/(25% ± 5%), in which the TS pathway was observed for the first time. The three pathways proceed concomitantly along the electronic ground state surface.

Roaming as the dominant mechanism for molecular products in the photodissociation of large aliphatic aldehydes.

Photodissociation of isobutyraldehyde (C3H7CHO) at 248 nm is investigated using time-resolved Fourier-transform infrared emission spectroscopy to demonstrate the growing importance of the roaming pathway with increasing molecular size of aliphatic aldehydes. Each acquired CO rotational distribution from v = 1 to 4 is well characterized by a single Boltzmann rotational temperature from 637 to 750 K, corresponding to an average rotational energy of 5.9 ± 0.6 kJ mol(-1). The roaming signature that shows a small fraction of CO rotational energy disposal accompanied by a vibrationally hot C3H8 co-fragment is supported by theoretical prediction. The energy difference between the tight transition state (TS) and the roaming saddle point (SP) is found to be -27, 4, 15, 22, and 30 kJ mol(-1) for formaldehyde, acetaldehyde, propionaldehyde, isobutyraldehyde, and 2,2-dimethyl propanal, respectively. The roaming SP is stabilized by a larger alkyl moiety. It is suggested that the roaming photodissociation rate of aldehydes increasingly exceeds those via the tight TS, resulting in the dominance of the CO + alkane products, as the size of aldehydes becomes larger. Along with formaldehyde, acetaldehyde, and propionaldehyde, in this work isobutyraldehyde is further demonstrated that this aldehyde family with special functional group is the first case in the organic compound to follow predominantly a roaming dissociation pathway, as the molecular size becomes larger.

Light-Induced Mid-Infrared Emission of Liquid Carbon Tetrachloride and Benzene

Light-induced infrared emission spectroscopy (LIRES) is a novel technique that permits to receive high-quality spectra in the mid-infrared region. Low-intensity visible light connected to a highly sensitive FTIR spectrometer is more advantageous for studying any samples, including biological samples without any damage. This technique permits obtaining unique information on the molecule structure via vibrational excitation fundamental frequencies, overtones, and combination modes. It also enables a direct observation of vibrational radiation transitions in vibrationally excited molecules as well as the channels of vibration energy redistribution, which is not allowed with any other method. In this work, the LIRES is being tested as a technique for studying of vibrationally-excited molecules of carbon tetrachloride and benzene in the liquid phase. On the other hand, using transparent liquids, we had tried to understand some of the physical phenomena that can drive emission in mid-IR. The characteristics of the infrared emission of both liquid species produced by different wavelength radiation from various types of light systems (100 - watt Xe-lamp and Nd:YAG laser; lambda = 1064 nm (8 mW) and lambda = 532 nm (4 mW)) are presented. We demonstrated that the IR-signal, as well as spectral properties of carbon tetrachloride and benzene, was dependent on the wavelength and power of excitation beam. Results obtained with different light sources show that the visible light produces a nonlinear IR-emission signal in transparent liquids. We believe that the visible light is the source of the nonlinear response and is producing the vibration excitation as well as photostimulated transformations of the molecules possessing the high activity for the nonlinear response.

Reaction dynamics of O(¹D) + HCOOD/DCOOH investigated with time-resolved Fourier-transform infrared emission spectroscopy.

We investigated the reaction dynamics of O((1)D) towards hydrogen atoms of two types in HCOOH. The reaction was initiated on irradiation of a flowing mixture of O3 and HCOOD or DCOOH at 248 nm. The relative vibration-rotational populations of OH and OD (1 ≦ v ≦ 4, J ≤ 15) states were determined from time-resolved IR emission recorded with a step-scan Fourier-transform spectrometer. In the reaction of O((1)D) + HCOOD, the rotational distribution of product OH is nearly Boltzmann, whereas that of OD is bimodal. The product ratio [OH]/[OD] is 0.16 ± 0.05. In the reaction of O((1)D) + DCOOH, the rotational distribution of product OH is bimodal, but the observed OD lines are too weak to provide reliable intensities. The three observed OH/OD channels agree with three major channels of production predicted with quantum-chemical calculations. In the case of O((1)D) + HCOOD, two intermediates HOC(O)OD and HC(O)OOD are produced in the initial C-H and O-D insertion, respectively. The former undergoes further decomposition of the newly formed OH or the original OD, whereas the latter produces OD via direct decomposition. Decomposition of HOC(O)OD produced OH and OD with similar vibrational excitation, indicating efficient intramolecular vibrational relaxation, IVR. Decomposition of HC(O)OOD produced OD with greater rotational excitation. The predicted [OH]/[OD] ratio is 0.20 for O((1)D) + HCOOD and 4.08 for O((1)D) + DCOOH; the former agrees satisfactorily with experiments. We also observed the v3 emission from the product CO2. This emission band is deconvoluted into two components corresponding to internal energies E = 317 and 96 kJ mol(-1) of CO2, predicted to be produced via direct dehydration of HOC(O)OH and secondary decomposition of HC(O)O that was produced via decomposition of HC(O)OOH, respectively.

Comment on “A spectroscopic comparison of selected Chinese kaolinite, coal bearing kaolinite and halloysite – A mid-infrared and near-infrared study” and “Infrared and infrared emission spectroscopic study of typical Chinese kaolinite and halloysite” by Hongfei Cheng et al. (2010)

In two papers Cheng et al. (2010) reported in this journal on the mid-infrared, near-infrared and infrared emission spectroscopy of a halloysite from Hunan Xianrenwan, China. This halloysite contains around 8% of quartz (SiO2) and nearly 9% gibbsite (Al(OH)3). In their interpretation of the spectra these impurities were completely ignored. Careful comparison with a phase pure halloysite from Southern Belgium, synthetic gibbsite, gibbsite from Minas Gerais, and quartz show that these impurities do have a marked influence on the mid-infrared and infrared emission spectra. In the near-infrared, the effect is much less pronounced. Quartz does not show bands in this region and the gibbsite bands will be very weak. Comparison still show that the presence of gibbsite does contribute to the overall spectrum and bands that were ascribed to the halloysite alone do coincide with those of gibbsite.

Fabrication of macro–mesoporous titania/alumina core–shell materials in oil/water interface

A series of macro–mesoporous TiO2/Al2O3 nanocomposites with different morphologies were synthesized. The materials were calcined at 723K and were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscope (TEM), N2 adsorption/desorption, Infrared Emission Spectroscopy (IES), X-ray photoelectron spectroscopy (XPS) and UV–visible spectroscopy (UV–visible). A modified approach was proposed for the synthesis of 1D (fibrous) nanocomposite with higher Ti/Al molar ratio (2:1) at lower temperature (<100°C), which makes it possible to synthesize such materials on industrial scale. The performance–morphology relationship of as-synthesized TiO2/Al2O3 nanocomposites was investigated by the photocatalytic degradation of a model organic pollutant under UV irradiation. The samples with 1D (fibrous) morphology exhibited superior catalytic performance than the samples without, such as titania microspheres.

ALMA OBSERVATIONS OF THE T TAURI BINARY SYSTEM AS 205: EVIDENCE FOR MOLECULAR WINDS AND/OR BINARY INTERACTIONS

In this study, we present high-resolution millimeter observations of the dust and gas disk of the T Tauri star AS 205 N and its companion, AS 205 S, obtained with the Atacama Large Millimeter Array. The gas disk around AS 205 N, for which infrared emission spectroscopy demonstrates significant deviations from Keplerian motion that has been interpreted as evidence for a disk wind (Pontoppidan et al. 2011; Bast et al. 2011), also displays significant deviations from Keplerian disk emission in the observations presented here. Detections near both AS 205 N and S are obtained in 1.3 mm continuum, 12CO 2-1, 13CO 2-1 and C18O 2-1. The 12CO emission is extended up to 2 arcsec from AS 205N, and both 12CO and 13CO display deviations from Keplerian rotation at all angular scales. Two possible explanations for these observations hold up best to close scrutiny - tidal interaction with AS 205 S or disk winds (or a combination of the two), and we discuss these possibilities in some detail.

Phase transformations of crystalline SiO2 versus dynamic disorder between room temperature and liquid state

The sequence of phase transitions of crystalline silica has been probed by infrared emission spectroscopy. The lattice dynamics, deeply impacted by the low frequency dynamic disorder, exhibit with increasing temperature signs of inhomogeneous broadening of the symmetry-allowed normal modes. High frequency supplementary components are also activated. The analysis with a causal Voigt dielectric function model within the framework of hard mode spectroscopy allowed a fine characterization of solid–solid phase transitions. We also report experimental evidence showing that the occurrence of the intermediate ill-defined region above 1300 K is concomitant with the reactivation of the low frequency dynamic disorder; a behavior change that on the way explains the appearance of the negative thermal expansion regime.

Elucidation of Intermediates and Mechanisms in Heterogeneous Catalysis Using Infrared Spectroscopy

Infrared spectroscopy has a long history as a tool for the identification of chemical compounds. More recently, various implementations of infrared spectroscopy have been successfully applied to studies of heterogeneous catalytic reactions with the objective of identifying intermediates and determining catalytic reaction mechanisms. We discuss selective applications of these techniques with a focus on several heterogeneous catalytic reactions, including hydrogenation, deNOx, water-gas shift, and reverse-water-gas shift. The utility of using isotopic substitutions and other techniques in tandem with infrared spectroscopy is discussed. We comment on the modes of implementation and the advantages and disadvantages of the various infrared techniques. We also note future trends and the role of computational calculations in such studies. The infrared techniques considered are transmission Fourier transform infrared spectroscopy, infrared reflection-absorption spectroscopy, polarization-modulation infrared reflection-absorption spectroscopy, sum-frequency generation, diffuse reflectance infrared Fourier transform spectroscopy, attenuated total reflectance, infrared emission spectroscopy, photoacoustic infrared spectroscopy, and surface-enhanced infrared absorption spectroscopy.

Photodissociation of CH3CHO at 248 nm by time-resolved Fourier-transform infrared emission spectroscopy: Verification of roaming and triple fragmentation

By using time-resolved Fourier-transform infrared emission spectroscopy, the HCO fragment dissociated from acetaldehyde (CH3CHO) at 248 nm is found to partially decompose to H and CO. The fragment yields are enhanced by the Ar addition that facilitates the collision-induced internal conversion. The channels to CH2CO + H2 and CH3CO + H are not detected significantly. The rotational population distribution of CO, after removing the Ar collision effect, shows a bimodal feature comprising both low- and high-rotational (J) components, sharing a fraction of 19% and 81%, respectively, for the vibrational state v = 1. The low-J component is ascribed to both roaming pathway and triple fragmentation. They are determined to have a branching ratio of <0.13 and >0.06, respectively, relative to the whole v = 1 population. The CO roaming is accompanied by a highly vibrational population of CH4 that yields a vibrational bimodality.

In situ optical studies of methane and simulated biogas oxidation on high temperature solid oxide fuel cell anodes

Novel integration of in situ near infrared (NIR) thermal imaging, vibrational Raman spectroscopy, and Fourier-transform infrared emission spectroscopy (FTIRES) coupled with traditional electrochemical measurements has been used to probe chemical and thermal properties of Ni-based, solid oxide fuel cell (SOFC) anodes operating with methane and simulated biogas fuel mixtures at 800 °C. Together, these three non-invasive optical techniques provide direct insight into the surface chemistry associated with device performance as a function of cell polarization. Specifically, data from these complementary methods measure with high spatial and temporal resolution thermal gradients and changes in material and gas phase composition in operando. NIR thermal images show that SOFC anodes operating with biogas undergo significant cooling (ΔT = -13 °C) relative to the same anodes operating with methane fuel (ΔT = -3 °C). This result is general regardless of cell polarization. Simultaneous Raman spectroscopic measurements are unable to detect carbon formation on anodes operating with biogas. Carbon deposition is observable during operation with methane as evidenced by a weak vibrational band at 1556 cm(-1). This feature is assigned to highly ordered graphite. In situ FTIRES corroborates these results by identifying relative amounts of CO2 and CO produced during electrochemical removal of anodic carbon previously formed from an incident fuel feed. Taken together, these three optical techniques illustrate the promise that complementary, in situ methods have for identifying electrochemical oxidation mechanisms and carbon-forming pathways in high temperature electrochemical devices.

Photodissociation of Propionaldehyde at 248 nm: Roaming Pathway as an Increasingly Important Role in Large Aliphatic Aldehydes.

Time-resolved Fourier transform infrared emission spectroscopy is employed in the photolysis of propionaldehyde (CH3CH2CHO) at 248 nm to characterize the role of the roaming pathway. High-resolution spectra of CO are analyzed to yield a single Boltzmann rotational distribution for each vibrational level (ν = 1-4) with small rotational and large vibrational energy disposals. A roaming saddle point is found containing two far separated moieties of HCO and CH3CH2 with a weak interaction between them. Quasiclassical trajectory calculations on this configuration yield the CO energy flow behavior, consistent with the findings. The rate constant along the roaming pathway is evaluated to be larger by >1-2 orders of magnitude than those along tight transition state or three-body dissociation pathways. This work implies that the roaming mechanism plays an increasingly important role in aliphatic aldehydes as the molecular size becomes larger.

Correlation between the Plasma Characteristics and the Surface Chemistry of Plasma-Treated Polymers through Partial Least-Squares Analysis

We investigated the effect of various plasma parameters (relative density of atomic N and H, plasma temperature, and vibrational temperature) and process conditions (pressure and H2/(N2 + H2) ratio) on the chemical composition of modified poly(tetrafluoroethylene) (PTFE). The plasma parameters were measured by means of near-infrared (NIR) and UV-visible emission spectroscopy with and without actinometry. The process conditions of the N2-H2 microwave discharges were set at various pressures ranging from 100 to 2000 mTorr and H2/(N2+H2) gas mixture ratios between 0 and 0.4. The surface chemical composition of the modified polymers was determined by X-ray photoelectron spectroscopy (XPS). A mathematical model was constructed using the partial least-squares regression algorithm to correlate the plasma information (process condition and plasma parameters as determined by emission spectroscopy) with the modified surface characteristics. To construct the model, a set of data input variables containing process conditions and plasma parameters were generated, as well as a response matrix containing the surface composition of the polymer. This model was used to predict the composition of PTFE surfaces subjected to N2-H2 plasma treatment. Contrary to what is generally accepted in the literature, the present data demonstrate that hydrogen is not directly involved in the defluorination of the surface but rather produces atomic nitrogen and/or NH radicals that are shown to be at the origin of fluorine atom removal from the polymer surface. The results show that process conditions alone do not suffice in predicting the surface chemical composition and that the plasma characteristics, which cannot be easily correlated with these conditions, should be considered. Process optimization and control would benefit from plasma diagnostics, particularly infrared emission spectroscopy.

Infrared and microwave properties of polypyrrole/multi-walled carbon nanotube composites

This study analyses the formation of polypyrrole/multi-walled carbon nanotube (PPy/MWCNT) composite materials using chemical oxidation with varying amounts of MWCNTs added. The samples are characterized by scanning electron microscopy, Fourier transform infrared emission spectroscopy, a four-probe method, and infrared thermal imaging using electromagnetic parameters. According to the test results, it is seen that the formation of PPy with the addition of MWCNTs can affect the material’s infrared properties and increase the material’s microwave return losses (up to −19dB). This production procedure can also make the peak frequency of the microwave return losses adjustable, and the composite’s infrared and microwave performance becomes compatible and adjustable.

Determination of the oxidative stability of biodiesel using near infrared emission spectroscopy

Oxidative stability is an important parameter for quality control of biodiesel samples. Autoxidation is the main cause of deterioration of this type of fuel, and yields hydroperoxides, peroxides and carboxylic acids as main products, in a similar way as in the raw materials employed for its manufacture (vegetable oils and animal fat). Usually, oxidative stability is determined by monitoring the formation of an autoxidation product until a significant change in its concentration can be detected. In this work, a near infrared emission (NIRES) method based on the hydroperoxide emission at 2900nm (3450cm−1) was evaluated for determining oxidative stability of biodiesel. A comparative study between the oxidative stability of biodiesel samples and their parent vegetable oils is also presented. Results show that the NIRES method provides oxidative stability values correlated to those obtained with the official Rancimat method (R2=0.88), and present equivalent precision. The photometer presents several advantages compared to the Rancimat method, including faster analysis, lower sample consumption and operational simplicity.

Near infrared emission photometer for measuring the oxidative stability of edible oils

Near infrared emission spectroscopy (NIRES) allows the determination of the induction time (IT) of edible oils in accelerated oxidation experiments by monitoring the emissivity of a band at 2900nm, which corresponds to the formation of hydroperoxides. In this work, a new near infrared emission photometer dedicated to the determination of oxidative stability is described. The photometer presents several advantages compared to the previously reported NIRES instrument, such as lower cost and extreme simplicity of design and maintenance. The results obtained in the evaluation of the proposed instrument were compared with the official Rancimat method and instrument. The significant advantages include: faster analysis, lower sample consumption and operational simplicity. It is demonstrated that the procedure for determination of oxidative stability of oils can be significantly simplified and performed by measuring the sample emission at only one spectral region centered at 2900nm. Also, the proposed instrument and method present precision equivalent to the Rancimat method (coefficient of variation=5.0%). A significant correlation between the methods has been found (R2=0.81).