Fourier Transform Far-infrared Research Articles

Innovatively identifying naringin and hesperidin by using terahertz spectroscopy and evaluating flavonoids extracts from waste orange peels by coupling with multivariate analysis

Fourier transform far-infrared (FT-FIR) was exploited to evaluate the flavonoids content of orange extracts using Soxhlet extraction. The absorbance fingerprint spectra of hesperidin and naringin were identified in the range of 0.5–7 THz. The absorption peaks of hesperidin were obtained at 1.53, 1.85, 2.46, 3.36, 4.51, 5.35, 6.51, and 7.55 THz, respectively. For naringin, the absorption peaks were observed at 0.75, 1.50, 2.29, 3.76, 5.18, 6.48, and 8.36 THz, respectively. The perceptible absorption peaks at 3.76, 4.40, and 5.18 THz can be observed from fingerprint spectra of naringin whilst those peaks cannot be detected from the hesperidin THz spectrum. The noticeable absorption peaks at 3.36, 4.51, 5.35, and 8.19 THz can be obtained from fingerprint spectra of hesperidin whereas they are indiscernible from the naringin THz spectrum. Pre-treatments such as normalization, standard normal variate (SNV), multiplicative scatter correction (MSC), 1st and 2nd derivation were employed to enhance the robustness of the model performance. Partial least squares regression model performed well to explain the relationship between THz spectra and concentrations of hesperidin and naringin, with the determination coefficients of prediction up to 0.99 (pre-treated by 1st deviation) for hesperidin and 0.97 for naringin, respectively. This study addressed the detection of hesperidin and naringin by using terahertz spectroscopy, which could potentially simplify the procedures to detect the flavonoids of orange extracts from waste orange peels.

Blackbody-like infrared radiation in stacked graphene P–N junction diode

The electrical and optical properties of a stacked graphene p–n junction were investigated. N-type and p-type graphene films epitaxially grown on a SiC substrate were directly bonded to each other in a face-to-face manner. The current–voltage characteristics of the graphene junction diode exhibited an Ohmic behavior below 20 V. The conductance increased in the bias range above 20 V and had a peak around 65 V. The emission spectrum and temperature of the graphene p–n junction were measured using Fourier-transform far-infrared (FTIR) spectroscopy and infrared bolometer array. An electrically induced blackbody-like radiation with a peak wavelength of 10.2 μm was observed. Although the temperature change estimated using the bolometer results was 66 K at a power of 1.2 W, the peak wavelength of the FTIR spectrum was constant. An electrically induced blackbody-like far-infrared emission diode with a defined peak wavelength was successfully realized using the stacked graphene p–n junctions.

Blends of Cyanate Ester and Phthalonitrile⁻Polyhedral Oligomeric Silsesquioxane Copolymers: Cure Behavior and Properties.

Blends of cyanate ester and phthalonitrile–polyhedral oligomeric silsesquioxane copolymers were prepared, and their cure behavior and properties were compared via differential scanning calorimetry (DSC) analysis, thermogravimetric (TG) analysis, dynamic mechanical analysis, Fourier-transform far-infrared (FTIR) spectroscopy, and rheometric studies. The copolymer blends showed high chemical reactivity, low viscosity, and good thermal stability (TG temperatures were above 400 °C). The glass-transition temperature of the blends increased by at least 140 °C compared to cyanate ester resin. The blends are suitable for preparing carbon-fiber-reinforced composite materials via a winding process and a prepreg lay-up process with a molding technique. The FTIR data showed that the polymerization products contained triazine-ring structures that were responsible for the superior thermal properties.

Cure Behavior and Thermomechanical Properties of Phthalonitrile⁻Polyhedral Oligomeric Silsesquioxane Copolymers.

Phthalonitrile–polyhedral oligomeric silsesquioxane (POSS) copolymers were prepared by adding two different POSS cage mixtures: epoxycyclohexyl POSS (EP0408) and N-phenylaminopropyl POSS (AM0281). The cure behavior and properties of these polymers were analyzed and compared using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), Fourier transform far infrared (FTIR) measurements, and rheometric studies. The POSS-containing polymers showed higher chemical reactivity, better thermal stability and better mechanical performance in comparison to their unmodified counterparts. All the polymers showed water absorption below 1.5%. As revealed by FTIR measurements, the polymerization products contained triazine ring structures that were responsible for the superior thermal properties exhibited by these POSS-containing polymers.

Crystal structure characteristics, dielectric loss, and vibrational spectra of Zn-rich non-stoichiometric Ba[(Zn1/3Nb2/3)1−xZnx]O3 ceramics

Zn-Rich non-stoichiometric Ba(Zn1/3Nb2/3)1−xZnxO3 (BZNZ) (x = 0.01, 0.02, 0.03, 0.04) ceramics were prepared by the solid-state reaction method at 1500 °C for 2 h. The crystal structures and morphologies were analyzed by x-ray diffraction (XRD) and scanning electron microscopy. The vibration modes were obtained by Raman scattering spectroscopy and Fourier transform far-infrared (FTIR) reflectance spectroscopy. Rietveld refinement was performed for the XRD data. The relationship between crystal structures, dielectric properties, and phonon modes was analyzed in detail. XRD results show that the main phase is Ba(Zn1/3Nb2/3)O3. The Raman results displayed that the ordering structure of BZNZ transformed from 1:2 to 1:1 when x changed from 0.02 to 0.04, and the dielectric losses have a positive correlation with the full width at half maximum values of the A1g(O) and Eg(O) modes. The FTIR spectra were analyzed by the Kramers–Krönig method to obtain the real parts (ε′) and the imaginary parts (ε″) of the dielectric constant. When x = 0.02, the sample possesses uniform grains with clear boundaries and the lowest dielectric loss value (tanδ = 5.5 × 10‒4) due to the largest packing fraction.

Investigation of the crystal structure, lattice vibration and dielectric property of SrZrO3 ceramic

Abstract

Palladium(II) and N,N′-dimethyl-N,N′-dicyclohexylthiodiglycolamide – The extracted species from concentrated chloride solutions

The present article focuses on the systematic investigation of the palladium(II) extraction reactions from concentrated chloride media by N,N′-dimethyl-N,N′-dicyclohexylthiodiglycolamide (DMDCHTDGA) in toluene, relying both on equilibrium and spectroscopic data. The equilibrium results collected have been cautiously assessed by the analysis of the effects caused by the variation of the extractant, hydrogen and chloride ions concentrations on the Pd(II) distribution ratio. UV–visible, 1H nuclear magnetic resonance (NMR), Fourier-transform far infrared (FIR) and Raman spectroscopic results contributed for the clarification of the Pd(II) extraction reactions by DMDCHTDGA as well. The overall information suggests that inner-sphere complexes [PdCl2·L2] (L = DMDCHTDGA) should form, with the likely co-extraction of HCl traces. The determination of the apparent molar volumes indicates that DMDCHTDGA is essentially monomeric in toluene in the concentration range tested.

Haloaluminate Ionic Liquid Based Electrolytes for Secondary Magnesium Batteries: Ab-Initio and Experimental Vibrational Analysis

A critical roadblock toward practical Mg-based energy storage technologies is the lack of reversible electrolytes that are safe and electrochemically stable. Ionic liquids (ILs) are possible candidates for the electrolytes because in addition to being endowed with high thermal and electrochemical stability, they exhibit negligible vapor pressure and are non-flammable. High-performance electrolytes based on 1-ethyl-3-methylimidazolium halide (EMImX, X = Cl or I) doped with AlX3 and highly amorphous δ-MgX2 salt have recently been developed for application in secondary magnesium batteries [1,2]. Using a magnesium anode in conjunction with the chloride-based electrolytes the coin cells are cyclically discharged at a high rate (35 mA/g) exhibiting an initial capacity of 80 mAh/g and a steady-state voltage of 2.3 V [1]. This development seems very promising, however the key to the improvement of these new materials is the structural identification as it directly determines the properties and behavior of the electrolyte. This work presents the coupling between experimental and computational vibrational frequency investigations that characterizes a family of electrolytes with the general formula [EMImX/(AlX3)m]/(δ-MgX2)n. Experimental Raman and Fourier Transform Far Infrared (FT-FIR) spectra were measured for the electrolyte systems at various Mg salt concentrations. The spectra reveals new peaks indicative of the formation of new species and structural changes over the pristine IL. Hence, molecular-level investigations are necessary to assign the spectra and understand the ionic structure of these new materials. High-level density functional theory (DFT) calculations implementing the B3LYP functional were undertaken to determine the local structure and vibrational modes of the EMIm+ cation interacting with AlX4 −, Al2X7 −, and MgX2 (X = Cl or I). The analysis of the calculated and experimental vibrational spectra suggests that the pristine IL, i.e., EMImX/(AlX3)m, contains both AlX4 − and Al2X7 − anionic species. Addition of the buffering δ-MgX2 salt to the pristine IL increases the ratio of the AlX4 − to Al2X7 − anions in both chloride- and iodide-based electrolytes as shown in Figure 1. The experimental spectra reveal differences in the structure of the dissolved salt between the two halide-based electrolytes. The presence of vibrational peaks associated with the vibration of (MgCl2)n>1 species in the chloride-based electrolytes reveals that the dissolved salt can be found in the dimeric and polymeric forms. However, the corresponding vibrations are absent in the experimental spectra of the iodide-based material, indicating that the magnesium salt interacts with the IL in the form of a monomer rather than either a dimer or trimer (in contrast to the chloride-based).

Formulations for microprojection/microneedle vaccine delivery: Structure, strength and release profiles

To develop novel methods for vaccine delivery, the skin is viewed as a high potential target, due to the abundance of immune cells that reside therein. One method, the use of dissolving microneedle technologies, has the potential to achieve this, with a range of formulations now being employed. Within this paper we assemble a range of methods (including FT-FIR using synchrotron radiation, nanoindentation and skin delivery assays) to systematically examine the effect of key bulking agents/excipients – sugars/polyols – on the material form, structure, strength, failure properties, diffusion and dissolution for dissolving microdevices. We investigated concentrations of mannitol, sucrose, trehalose and sorbitol from 1:1 to 30:1 with carboxymethylcellulose (CMC), although mannitol did not form our micro-structures so was discounted early in the study. The other formulations showed a variety of crystalline (sorbitol) and amorphous (sucrose, trehalose) structures, when investigated using Fourier transform far infra-red (FT-FIR) with synchrotron radiation. The crystalline structures had a higher elastic modulus than the amorphous formulations (8–12GPa compared to 0.05–11GPa), with sorbitol formulations showing a bimodal distribution of results including both amorphous and crystalline behaviour. In skin, diffusion properties were similar among all formulations with dissolution occurring within 5s for our small projection array structures (~100μm in length). Overall, slight variations in formulation can significantly change the ability of our projections to perform their required function, making the choice of bulking/vaccine stabilising agents of great importance for these devices.

Heavy metal behavior and dissolved organic matter (DOM) characterization of vermicomposted pig manure amended with rice straw.

Vermicomposting is an eco-friendly method for disposing of livestock and poultry manure. In addition, dissolved organic matter (DOM) can serve as a carrier that enhances the migration and transformation of heavy metals. Here, pig manure amended with rice straw was vermicomposted with Eisenia fetida. The DOM content, molecular weight distribution, and spectroscopic properties of the amended pig manure were measured before and after vermicomposting. The Cu and Zn concentrations in the earthworms increased from 8.24 and 17.63 to 40.75 and 362.78 mg/kg separately after vermicomposting, and the earthworms also increased the heavy metal availability in the vermicompost. Relative to the DOM properties of conventional compost, the DOM molecular weight decreased and varied widely following vermicomposting, and the C/N ratio of the DOM in the vermicompost treatments decreased from 10.37 to 8.60. The Fourier transform far-infrared (FTIR) and fluorescence spectra of the DOM indicated that the amounts of oxygen-containing structures increased while the ratio of humic acid to fulvic acid decreased following vermicomposting. Accordingly, the earthworms augmented the heavy metal mitigation risk in the pig manure. This augment potentially resulted from the decreased humic acid-to-fulvic acid (HA/FA) ratio from DOM structural changes.

Sol–gel transition of organogels observed by terahertz spectroscopy

Terahertz (THz) absorption spectra of organogels consisting of (1R,2R)-1,2-bis(dodecanoylamino)cyclohexane/2-nitrophenyl octyl ether (RR-BDC/NPOE) and RR-BDC/n-dodecane were measured by Fourier-transform far-infrared (FT-FIR) spectroscopy. The vibrational peaks of the gels were observed at the same frequencies as those of the pure gelator, suggesting that the intermolecular structure around the NH⋯OC hydrogen bond is maintained in the gel phase. Temperature-dependent spectroscopy showed a drastic spectral change at the sol–gel transition temperature, in which the vibrational peak at 3.5THz disappears and a new peak appears at 2.9THz. The change in THz vibrational frequency is indicative of the structural collapse of the hydrogen-bonded fibrous architecture in the sol phase.

First‐Principle Calculation and Assignment for Vibrational Spectra of Ba(Mg1/2W1/2)O3 Microwave Dielectric Ceramic

Ba(Mg1/2W1/2)O3 ceramic was synthesized using a conventional solid‐state reaction method at 1500°C for 4 h. The face‐centered cubic crystal structure of the material was confirmed by Rietveld refinement of X‐ray diffraction (XRD) data, and vibrational modes were obtained by Raman and Fourier transform far‐infrared (FTIR) reflection spectroscopies. First‐principle calculations based on density functional theory with local density approximation were used to calculate Gamma‐point modes and dielectric properties of Ba(Mg1/2W1/2)O3. The Raman spectrum with nine active modes can be fitted with Lorentzian function, and the modes were assigned as F2g(1) (126 cm−1), F2g(2) (441 cm−1), Eg(O) (538 cm−1), and A1g(O) (812 cm−1). Far‐infrared spectrum with 12 infrared active modes was fitted using both the Lorenz three‐parameter classical and four‐parameter semiquantum models. Consequently, the modes were assigned as F1u(1) (144 cm−1), F1u(2) (284 cm−1), F1u(3) (330–468 cm−1), and F1u(4) (593–678 cm−1). The active modes were represented by linear combinations of symmetry coordinates that were obtained by group theory analyses. The Raman mode A1g, which has the highest wave number (812 cm−1) is dominated by the breath vibration of the MgO6 octahedron. The infrared modes F1u(2), that can be described as the inverted vibrations of Mg atoms in the MgO6 octahedron along the xi, yi, and zi axes have the most contributions to the microwave permittivity and dielectric loss.

Terahertz and far-infrared synchrotron spectroscopy and global modeling of methyl mercaptan, CH332SH

In this work, terahertz and Fourier transform far-infrared (FTFIR) synchrotron spectra of methyl mercaptan, CH(3)SH, have been investigated in order to provide new laboratory information for enhanced observations of this species in interstellar molecular clouds and star-forming regions. Like its methanol cousin, methyl mercaptan has particularly rich spectra associated with its large-amplitude internal rotation that extend throughout the THz and FIR regions. We have recorded new spectra for CH(3)SH from 1.1-1.5 and 1.790-1.808 THz at the University of Cologne as well as high-resolution FTFIR synchrotron spectra from 50-550 cm(-1) at 0.001 cm(-1) resolution on the far-IR beam-line at the Canadian Light Source. Assignments are reported for rotational quantum numbers up to J ≈ 40 and K ≈ 15, and torsional states up to v(t) = 2 for the THz measurements and v(t) = 3 for the FTFIR observations. The THz and FTFIR measurements together with literature results have been combined in a global analysis of a dataset comprising a total of 1725 microwave and THz frequencies together with ~18000 FTFIR transitions, ranging up to v(t) = 2 and J(max) = 30 for MW∕THz and 40 for FTFIR. The global fit employs 78 torsion-rotation parameters and has achieved a weighted standard deviation of ~1.1. A prediction list (v(t) ≤ 2, J ≤ 45 and K ≤ 20) has been generated from the model giving essentially complete coverage of observable CH(3)(32)SH transitions within the bandwidths of major new astronomical facilities such as HIFI (Heterodyne Instrument for the Far Infrared) on the Herschel Space Observatory, ALMA (Atacama Large Millimeter Array), SOFIA (Stratospheric Observatory For Infrared Astronomy) and APEX (Atacama Pathfinder Experiment) to close to spectroscopic accuracy.

Measurement and analysis of new terahertz and far-infrared spectra of high temperature water

Terahertz absorption spectroscopy and far infrared Fourier transform (FIR-FT) emission spectroscopy were employed to measure new rotational and ro-vibrational spectra and validate existing datasets for high temperature water, with the goal to improve the accuracy of predictions for pure rotation in the (020), (100) and (001) vibrational states. A total of 104 new rotational transitions in (000), (010), (020), (100) and (001) were observed in the 293–2723GHz region with MW accuracy and with observed J(Max)=18, 11, 10, 14, 10; Ka(Max)=10, 7, 7, 7, 4; E″(Max)=4178, 3771, 4996, 5430, 4939 cm−1, respectively. A total of 4194 new FIR-FT transitions were assigned in the 50–600cm−1 region to the same five vibrational states with estimated experimental uncertainty of 0.0008–0.002cm−1 and with J(Max)=27; Ka(Max)=21, 18, 18, 17, 17, respectively. Together with previous high-resolution observations, these new data were fitted with the Bending–Rotation approach and the Euler Hamiltonian. The new measurements and predictions reported here will support the analyses of astronomical observations by high-resolution spectroscopy telescopes such as Herschel, SOFIA, and ALMA.

Interplay between structural and electrochemical properties of Pt-Rh carbon nitride electrocatalysts for the oxygen reduction reaction

This report describes a new family of bimetal carbon nitride (CN) electrocatalysts for the oxygen reduction reaction (ORR) for application in polymer electrolyte membrane fuel cells (PEMFCs). The materials, which bear active sites based on Pt and Rh, are prepared with a three-step protocol consisting of: (1) the synthesis of a homogeneous zeolitic inorganic–organic polymer electrolyte (Z-IOPE) precursor; (2) the pyrolysis of the precursor at a temperature T f = 400, 500, 600, 700 or 900 °C; (3) the activation, yielding the final product. It is found that T f has a major effect on the structure and the electrochemical properties of these electrocatalysts, as determined from a wide array of independent characterization techniques including: high-resolution thermogravimetry (HR-TGA); Fourier-transform medium infrared (FT-MIR), Fourier-transform far infrared (FT-FIR) and confocal micro-Raman spectroscopies; powder X-ray diffraction (powder XRD); X-ray photoelectron spectroscopy (XPS); and electrochemical investigations carried out with the cyclic voltammetry thin-film rotating disk electrode (CV-TF-RDE) method. All the information is integrated to propose a comprehensive model correlating the effect of T f on the structure of the materials with the corresponding electrochemical performance. The best results in the ORR are obtained with materials prepared at 600 ≤ T f ≤ 700 °C. These systems present the optimal compromise between the size of the metal-rich nanoparticles, the degree of graphitization of the carbon nitride support and the concentration of ligands blocking the active sites. The best Pt-Rh electrocatalysts exhibit an ORR activity very similar to the Pt/C reference. In addition, the peculiar structure of the proposed materials, which are characterized by active sites supported on the carbon nitride bulky materials, results in a better tolerance toward typical contaminants in the ORR process such as chloride anions with respect to the Pt/C reference.

Terahertz absorption spectra of nitromethane

Nitromethane, with its heavy frame and internal rotator, readily evaporates into the atmosphere making it an ideal candidate for remote sensing. Here we present the absorption spectra of gas-phase nitromethane between 9 and 50 cm −1. Measurements were taken using a Bruker IFS 66v Fourier transform far-infrared (FTIR) spectrometer at a resolution of 0.12 cm −1 (0.0036 THz) from 9 to 40 cm −1 and a Bruker Vertex 80v FTIR spectrometer with a resolution of 0.0075 cm −1 (0.00226 THz) from 10 to 50 cm −1. The absorption spectra were measured at multiple pathlengths ranging from 2 to 6 m. These measurements were used to calculate the absorption coefficient of nitromethane as a function of wavenumber.

Polarization and temperature dependent spectra of poly(3-hydroxyalkanoate)s measured at terahertz frequencies

Temperature-dependent terahertz (THz) absorption spectra of poly(3-hydroxyalkanoate)s (PHAs) were measured by using a Fourier transform far-infrared (FT-FIR) spectrometer and a THz time-domain spectrometer over a temperature range of 10 K to 465 K with a liquid helium cryostat and a heating cell. Clear differences were observed between the spectra of crystalline and amorphous polyhydroxybutyrate (PHB), indicating that the absorption peaks observed in the THz spectra originated in the higher-order conformation of PHB. The polarization spectra of a stretched PHB sample were measured, and the direction of the vibrational transition moment was determined. The temperature dependences of the spectra reveal frequency shifts and broadening of the absorption peaks with temperature, suggesting large anharmonicity of the vibrational potential. The temperature shift behaviour is quite different in each transition. Some of the transitions show a blue shift, which cannot be explained by a simple anharmonic potential model. Frequency shifts of the peaks were mainly observed below 10 THz, which suggests a large anharmonicity of the vibrational potential at lower frequencies.

Measurement of the Soft-Mode Dispersion in SrTiO3 by Terahertz Time-Domain Spectroscopic Ellipsometry

We have measured the soft-mode dispersion of SrTiO3 bulk single crystals by terahertz time-domain spectroscopic ellipsometry (THz-TDSE). The real and imaginary parts of the dielectric function of the sample are independently derived from the complex amplitude reflectivities of p- and s-polarized terahertz pulses. The TO1 soft-mode resonance is clearly observed at 2.62 THz (87 cm-1). The spectra of the complex dielectric function agree well with those predicted using the general harmonic oscillator model with parameters obtained from conventional Fourier-transform far-infrared (FT-FIR) reflection measurements. THz-TDSE developed in this study can be employed to investigate low-frequency dielectric dispersions.

Analysis of Dielectric Response of TiO2 in Terahertz Frequency Region by General Harmonic Oscillator Model

The terahertz range dielectric response of polycrystalline TiO2 (rutile) ceramics and rutile single crystals were investigated by analyzing infrared-active phonons by both Fourier-transform far-infrared (FT-FIR) reflectivity measurement and terahertz time-domain spectroscopy (THz-TDS). The dielectric functions at room temperature measured by THz-TDS are well expressed using the general harmonic oscillator model. We found that the imaginary part of the dielectric permittivity of the TiO2 ceramic is threefold higher than that of the rutile single crystal at 300 K. The large dielectric loss is attributed to the additional damping of the A2u mode or/and an increase in the phonon damping. The low-temperature dielectric loss of the rutile single crystals is exceedingly low. However, TiO2 ceramics shows little temperature dependence. These results indicate that extrinsic scattering significantly affects the dielectric loss of the TiO2 ceramics in the THz region.

Torsion–rotation global analysis of the first three torsional states ( νt = 0, 1, 2) and terahertz database for methanol

Stimulated by recent THz measurements of the methanol spectrum in one of our laboratories, undertaken in support of NASA programs related to the Herschel Space Observatory (HSO) and the Atacama Large Millimeter Array (ALMA), we have carried out a global analysis of available microwave and high-resolution infrared data for the first three torsional states ( ν t = 0, 1, 2), and for J values up to 30. This global fit of approximately 5600 frequency measurements and 19 000 Fourier transform far infrared (FTFIR) wavenumber measurements to 119 parameters reaches the estimated experimental measurement accuracy for the FTFIR transitions, and about twice the estimated experimental measurement accuracy for the microwave, submillimeter-wave, and terahertz transitions. The present fit is essentially a continuation of our earlier work, but we have greatly expanded our previous data set and have added a large number of new torsion–rotation interaction terms to the Hamiltonian in our previously used computer program. The results, together with a number of calculated (but unmeasured) transitions, including their line strength, estimated uncertainty, and lower state energy, are made available in the supplementary material as a database formatted to be useful for astronomical searches. Some discussion of several open spectroscopic problems, e.g., (i) an improved notation for the numerous parameters in the torsion–rotation Hamiltonian, (ii) possible causes of the failure to fit frequency measurements to the estimated measurement uncertainty, and (iii) pitfalls to be avoided when intercomparing apparently identical parameters from the internal axis method and the rho axis method are also given.