Transmission IR Spectra Research Articles

Determination of melt flow index and polymer additives in polyethylene based on IR spectra and multivariate modeling

Protection against degradation is essential for preserving the favorable physical and chemical properties of polymers. There are several types of stabilizers employed as antioxidants, but the latest studies showed that artificial stabilizers spark environmental and healthcare concern. Here, we have used multivariate modeling based on ATR and transmission infrared spectra to provide information about the degradation and the applied additive stabilizer for polyethylene samples. The classification of samples based on the used additives was successful in single and combined additive groups as well, with accuracies over 0.9 in each case. ATR-IR combined with principal component analysis (PCA) and correlation and regression tree (CART) methods yielded the best classification model. Melt flow index values (MFI), which can correlate with the degradation and stability of the polymers, were predicted with partial least squares (PLS) regression and artificial neural network (ANN) models. The best combination for regression modeling was the transmission IR spectra with the ANN algorithm. The ANN model could predict the MFI values remarkably well, with an R2 value of 0.95, even for the test validation. Infrared spectroscopy coupled with chemometrics is suitable to be integrated into the quality control of polymers.

Modification of Cellulose from water hyacinth (Eichhornia crassipes) for nanocomposite materials

The effects of temperature, time, alkalinity and solid/liquid ratio on separation of lignin, hemicellulose to obtain cellulose from water hyacinth (Eichhornia crassipes) were investigated. Microcrystalline cellulose fibers were examined by microscope and infrared spectroscopy IR. The results showed that lignin and hemicellulose were removed by alkaline treatment. The obtained cellulose fibers were modified by esterification reaction with acetic anhydride in acetic acid, sulfuric acid with the aid of ultrasound. The cellulose acetate was investigated using transmission electron microscopy (TEM) and IR spectra. The synthesized nano fibers were in the diameter range of 50 - 100 nm from the TEM with even arrangement. The IR spectrum also showed that the -OH group was replaced by the -OCOCH3 group, thus, reducing the polarization and hygroscopic ability of cellulose, suitable for using as the reinforcing phase in biodegradable composite materials.

Dipolar coupling and molecular vibrations in ionic liquids.

It is often the case that intense, non-degenerate bands appear asymmetric in transmission IR spectra of ionic liquids, with a high-frequency shoulder adjacent to the dominant band. Moreover, the band shape is temperature dependent with lower temperatures producing greater amounts of asymmetry. The 1-alkyl-3-methylimidazolium trifluoromethanesulfonate family of ionic liquids provides an excellent illustration of this phenomenon, wherein the νs(SO3) mode of the anion is split into two components whose frequencies change with temperature. In this article, a new theoretical model is derived to explain temperature-dependent trends in the infrared spectra of these materials. According to the model, vibrationally-induced dipole moments couple with one another across the charge-organized liquid structure inherent to ionic liquids to produce transverse optical (TO) and longitudinal optical (LO) phonons. The temperature dependence of the resulting TO-LO band splitting originates from two distinct sources. First, the interaction strength between vibrationally-induced dipole moments depends on the distance separating the ions, which in turn, is directly related to the ionic liquid's density. Second, TO-LO splitting requires a significant amount of angular correlation among the ions to facilitate the propagation of optical phonons. Elevated temperatures produce smaller densities and increased amounts of disorder, both of which lead to decreased amounts of TO-LO splitting. Although the model is developed in the context of ionic liquids, the equations are broadly applicable to other materials that possess long-range structure but are not fully crystalline, such as molten salts, plastic crystalline compounds, glasses, and disordered solids.

Catalytic performance of silicalite-1 modified HY zeolite in the hydrolysis of cellulose

A core-shell composite zeolite (HY/silicalite-1) was prepared by modifying HY zeolite with silicalite-1 and characterized by X-ray diffraction (XRD), Scanning electron microscope (SEM), Transmission electron microscope (TEM), N2 sorption and IR spectra of pyridine adsorption (Py-FTIR); the catalytic performance of HY/silicalite-1 composite zeolite in the hydrolysis of cellulose was then investigated in comparison with that of HY. The results show that the crystallization time has a significant influence on the crystal growth of the HY/silicalite-1 composite zeolite and the relative content of two components. With the optimum crystallization time of 16–24 h, a core-shell structure for the HY/silicalite-1 composite zeolite is achieved, where the silicalite-1 crystal grows over the surface of HY zeolite; with the prolongation of the crystallization time, the morphology of the composite zeolite changes from rough turbid to smooth and eventually to scale-like surface. The amount of Brönsted acid sites decreases first and then increases with the increase of the crystallization time, whereas the amount of Lewis acid sites changes in the opposite direction. In particular, the HY/silicalite-1 composite zeolite obtained with a crystallization time of 24 h exhibits excellent catalytic performance in the hydrolysis of cellulose to glucose; over it, the yield of glucose reaches 45.8% at 130°C, much higher than the value of 28.0% over the HY zeolite.

Dominant Role of Entropy in Stabilizing Sugar Isomerization Transition States within Hydrophobic Zeolite Pores

Lewis acid sites in zeolites catalyze aqueous-phase sugar isomerization at higher turnover rates when confined within hydrophobic rather than within hydrophilic micropores; however, relative contributions of competitive water adsorption at active sites and preferential stabilization of isomerization transition states have remained unclear. Here, we employ a suite of experimental and theoretical techniques to elucidate the effects of coadsorbed water on glucose isomerization reaction coordinate free energy landscapes. Transmission IR spectra provide evidence that water forms extended hydrogen-bonding networks within hydrophilic but not hydrophobic micropores of Beta zeolites. Aqueous-phase glucose isomerization turnover rates measured on Ti-Beta zeolites transition from first-order to zero-order dependence on glucose thermodynamic activity, as Lewis acidic Ti sites transition from water-covered to glucose-covered, consistent with intermediates identified from modulation excitation spectroscopy during in situ attenuated total reflectance IR experiments. First-order and zero-order isomerization rate constants are systematically higher (by 3-12×, 368-383 K) when Ti sites are confined within hydrophobic micropores. Apparent activation enthalpies and entropies reveal that glucose and water competitive adsorption at Ti sites depend weakly on confining environment polarity, while Gibbs free energies of hydride-shift isomerization transition states are lower when confined within hydrophobic micropores. DFT calculations suggest that interactions between intraporous water and isomerization transition states increase effective transition state sizes through second-shell solvation spheres, reducing primary solvation sphere flexibility. These findings clarify the effects of hydrophobic pockets on the stability of coadsorbed water and isomerization transition states and suggest design strategies that modify micropore polarity to influence turnover rates in liquid water.

Synthesis and luminescent properties of GdNbO4:Bi3+ phosphors via high temperature high pressure

This work reports the high-pressure and high-temperature (HP-HT) synthesis of pure monoclinic phase of GdNbO4:Bi3+ phosphors. X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, photoluminescence, and IR spectra were utilized to characterize the synthesized phosphors. The crystal structure distortions operated by the pressure leads to tunable emission varying from blue to yellow. A small increase of the probability of non-radiative energy transfer with increase of pressure is observed. It is shown that the efficiency of the energy transfer process is dependent on pressure. The calculations of CIE chromaticity coordinates were performed.

Temperature-induced release of crystal water in the Co, Mo and Pt complexes of N,N-diacetatedithiocarbamate. FTIR spectroscopy and quantum chemical study

We describe temperature-induced water release from the complexes of triammonium N,N-diacetatedithiocarbamate (dadtc) with Co(III) (1), Mo(VI) (2) and Pt(II) (3), by the combination of temperature-dependent IR spectroscopy and quantum chemical calculations. Transmission IR spectra show that in the compounds 1 and 2, where water molecules are hydrogen-bonded with complex moieties, water release occurs at about 80 °C. In the compound 3 water most probably exist as non-hydrogen-bonded and remains within the sample above 100 °C. The influence of an inert salt in maintaining the water and consequently bringing up the artefacts in spectra is eliminated by recording the spectra in the internal reflection regime (ATR). Possible interplay of water release from the samples 1 and 2 and samples phase transition is presumed and indicated by the baseline analysis of temperature-dependent transmission IR spectra.

Study of a Magnetic Photocatalyst Based on Hemin with Axial Ligand and its Degradation under Visible Light

An investigation was conducted on hemin modified with axial ligand loaded onto magnetic carriers which created a kind of visible-light activated photocatalyst with good magnetic property. This photocatalyst exhibits excellent photo-degradation performance and can be readily reclaimed in the degradation of bis-phenol A (BPA) in aqueous solution under visible light. The catalysts were characterized by thermal gravimetric analysis (TG), transmission electron microscopy (TEM), magnetometer (VSM) and IR spectra. The effects of different operation parameters on the photocatalytic reaction have also been investigated. The highest degradation ratio reached up to 94.75% after 6 hours under optimized operation conditions. Moreover, the photocatalyst could be readily reclaimed by magnetic separation with an external magnetic field and when it was reused for 5 times under the same conditions, the degradation ratio of BPA solution during the last time was still higher than 90%. Possible mechanism on BPA degradation was also investigated based on a series of control experiments. The main intermediate of BPA degradation was monitored by GC/MS analysis.

FTIR microspectroscopy of Ediacaran phosphatized microfossils from the Doushantuo Formation, Weng'an, South China

Phosphatized microfossils from ca. 580Ma from the Doushantuo Formation in the Weng'an region of South China were analyzed by Fourier transform infrared (FTIR) microspectroscopy for their chemical characterization. Two morpho-types of phosphatized embryo-like fossils (Megasphaera and Megaclonophycus) were analyzed, together with algal fossils. Transmission IR spectra of the microfossils have absorption bands of around 2960cm−1 and 2925cm−1, indicating the presence of aliphatic hydrocarbon (anti-symmetric aliphatic CH3 and aliphatic CH2), and have an additional band of around 1595cm−1, probably derived from aromatic moieties (aromatic CC). In addition, IR microscopic mapping shows that aliphatic hydrocarbon and aromatics are distributed inside the embryo-like fossils. The embryo-like fossils appear to show three types of CH3/CH2 peak height ratios (R3/2) and aromatic CC/CH2 peak height ratios (RCC/2 values): (1) high-R3/2/low-RCC/2 type (R3/2=~0.2–1.0 and RCC/2~0–2), (2) low-R3/2/medium-RCC/2 type (R3/2=~0.2–0.6 and RCC/2=~1–4); and (3) low-R3/2/high-RCC/2 type (R3/2=~0.2–0.6 and RCC/2~1–8). All three types are contained in both Megasphaera and Megaclonophycus. Raman spectra for the carbonaceous matter within the rock sample show a similar degree of thermal alteration, indicating that the organics were embedded in situ prior to thermal maturation. The IR spectroscopic differences might reflect differences in original organic compositions of microorganisms, and/or immediate post-mortem alteration. This suggests that the origins of phosphatized embryo-like fossils are more diverse than was previously recognized on the basis of their morphology. A comparison of R3/2 and RCC/2 values in the embryo-like fossils with those of the algal fossils and the extant microorganisms indicates the possible interpretation that some of the embryo-like fossils belong to animal embryo, others are algae, but none of them originate from bacteria.

Ordered mesoporous carbons supported wacker‐type catalyst for catalytic oxidative carbonylation

Ordered mesoporous carbons (OMCs) were used as supports to prepare Wacker‐type catalysts for diethyl carbonate (DEC) synthesis by oxidative carbonylation of ethanol in a gas‐phase reaction. The effect of support structure on the dispersion of the active species and catalytic properties were investigated. Nitrogen sorption, X‐ray diffraction (XRD) and transmission electron microscopy (TEM) results revealed that the active components have encapsulated in pore channels of OMCs. Characterizations of the catalysts, such as TEM, scanning electron microscope (SEM) and XRD, indicated that active components supported on OMCs have better dispersion compared to activated carbon (AC). The ethanol conversion of the catalysts was improved by ∼65% using OMCs as the catalyst support than AC. The stability of the catalytic activity can also be enhanced through surface modification of OMCs. Surface oxygen‐containing groups (OCGs) on OMCs before and after surface modification were characterized by transmission IR spectra and the Beohm titration. The relationship between surface OCGs and anchor ability of OMCs was studied. © 2013 American Institute of Chemical Engineers AIChE J, 59: 3797–3805, 2013

Quantitative Analysis of IR Intensities of Alkanes Adsorbed on Solid Acid Catalysts

The goal of this work was to determine the integrated molar absorption coefficients of adsorbate vibrations and to use them as a measure of the activation of chemical bonds by the catalyst surface. For this purpose, an apparatus was built for the simultaneous measurement of transmission IR spectra of the adsorbate and the corresponding adsorption isotherm; the adsorbed amount was determined by a volumetric–barometric method. The adsorption of n-butane and 2,2-dimethylpropane on self-supporting wafers of mordenite and sulfated zirconia samples was investigated at temperatures of 298–308 K and alkane pressures of 0–100 hPa. The linear range of plots of the IR band intensities vs coverage was used to determine absorption coefficients of C–H stretching vibrations. The coefficients were found to depend on particle size and morphology, and it is shown that they are overestimated because the path length is enhanced through strong scattering in the wafers. The results reveal the limitations of quantitative analysis by transmission IR spectra when fine powders (such as catalysts) are investigated.

Fabrication of Silica/PDMS Hybrid Nanoparticles by a Novel Solvent Adjustment Route

The silica/polydimethylsilane (PDMS) hybrid nanoparticles were successfully synthesized by a novel solvent adjustment route. The as-prepared hybrid nanoparticles were characterized by transmission electron microscopy, UV-vis spectra, and IR spectra. The possible mechanism for the formation of silica/PDMS nanoparticles was discussed. The adjustment of solvents is a very important factor since it could tune the surface ligands and improve the coordination ability. On the other hand, it could also tune the interaction between precursors, intermediate or the target hybrid materials and guarantee the monodispersion of prepared nanoparticles. With the merits of PDMS and silica, the as-prepared SiO2-PDMS hybrid nanoparticles have a good application in hard coating material.

Molecular Orientation of the Decyl Monolayer Chemically Bonded to Si(111) Determined by Angle-Dependent Transmission Infrared Spectroscopy

We applied angle-dependent transmission infrared spectroscopy for determination of the molecular orientation of a decyl monolayer chemically bonded to the Si(111) surface. The peak intensities for CH2 symmetric and antisymmetric stretching modes show similar variations as a function of incident angle. CH3 antisymmetric in-plane stretching mode shows a prominent increase in proportion to incident angle, but CH3 out-of-plane stretching mode decreases. By analyzing these experimental data, we estimated the orientation angles of dynamic dipole moments for these modes. We have evaluated the tilt angle of a carbon framework from the surface normal to be 27–30°, when the multireflection in a Si wafer is taken into account. However, without considering multireflection, the tilt angle becomes 15–20°. We conclude that the multireflection in the Si substrate should be considered in the analysis of angle dependent transmission IR spectra.

Molecular Orientation of the Decyl Monolayer Chemically Bonded to Si(111) Determined by Angle-Dependent Transmission Infrared Spectroscopy

We applied angle-dependent transmission infrared spectroscopy for determination of the molecular orientation of a decyl monolayer chemically bonded to the Si(111) surface. The peak intensities for CH2 symmetric and antisymmetric stretching modes show similar variations as a function of incident angle. CH3 antisymmetric in-plane stretching mode shows a prominent increase in proportion to incident angle, but CH3 out-of-plane stretching mode decreases. By analyzing these experimental data, we estimated the orientation angles of dynamic dipole moments for these modes. We have evaluated the tilt angle of a carbon framework from the surface normal to be 27–30°, when the multireflection in a Si wafer is taken into account. However, without considering multireflection, the tilt angle becomes 15–20°. We conclude that the multireflection in the Si substrate should be considered in the analysis of angle dependent transmission IR spectra.

Rapid, Low‐Temperature Synthesis of β‐SiC Nanowires from Si and Graphite

β‐SiC nanowires were synthesized at a temperature as low as 150°C by the reaction of Si and graphite induced by an additional reaction between Na and S. Characterization by X‐ray diffraction, high‐resolution transmission electron microscopy, IR spectra, and Raman spectra demonstrates the formation of curly β‐SiC nanowires with several millimeters in length and 50–70 nm in diameter. Also, a prominent peak at 387 nm is observed in the visible photoluminescence emission. Besides the temperature, the molar ratio of S to Si (or graphite) has significant influence on the synthesis of SiC at relatively low temperatures.

Self-assembled monolayers of benzylmercaptan and para-cyanobenzylmercaptan on gold: surface infrared spectroscopic characterization

Self-assembled monolayers (SAMs) on gold substrates were prepared from benzylmercaptan (BM) and para-cyanobenzylmercaptan (pCBM), and the resulting surfaces were investigated using conventional infrared reflection-absorption spectroscopy (IRRAS) as well as polarization modulation infrared reflection-absorption spectroscopy (PM-IRRAS). IRRAS data are analyzed by comparison with transmission IR spectra and theoretical (DFT) simulations. The spectroscopic results indicate the presence of well-ordered monolayers of BM and pCBM with an orientation perpendicular to the surface. IRRAS and PM-IRRAS data are compared to each other and the respective merits of both methods are discussed.

In vitro photothermal study of gold nanoshells functionalized with small targeting peptides to liver cancer cells

Gold nanoshells functionalized with a small peptide as a targeting agent were designed and synthesized for photothermal therapy of hepatocarcinoma. The nanoshells exhibited high absorption in the near-infrared (NIR) range, 800-1,100 nm, and were functionalized with 12-amino acid sequence peptides for targeting liver cancer cells. The nanoshells were characterized by Dynamic Light Scattering (DLS), Transmission Electron Microscope (TEM) and IR spectra. The functionalized gold nanoshells showed good targeting ability to liver cancer cells BEL-7404 and BEL-7402 while not to the normal healthy liver cell HL-7702, and also had a low cytotoxic activity. The fluorescence images showed that the gold nanoshells caused death to the liver cancer cells efficiently after being treated with a NIR light in vitro. These simple, stable, low cytotoxic, cancer-cell targeting gold nanoshells present a great promise as delivery agents for the selective photothermal treatment of liver cancer cells.

Reduction of Nanostructured CuO Bundles: Correlation between Microstructure and Reduction Properties

A high yield of nanostructured CuO bundles with different building blocks is successfully prepared through simple hydrothermal and thermal treatment methods. The microstructure of the as-synthesized samples is characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), N2 physisorption, and IR spectra. The results show that the microstructure of the CuO bundles, such as different grain sizes, BET surface areas, pore sizes, defects and morphologies of building blocks can be obtained by different synthetic methods. Moreover, H2-TPR and in situ XRD experiments are used to investigate the reduction properties of the nanostructured CuO bundles. It is found that there are two different reduction pathways involved in the reduction processes at 30 mL/min of 10 vol. % H2/N2: for the sample synthesized through the hydrothermal method (CuO-HT), all of the CuO is reduced directly to metallic Cu; however, for the sample synthesized through the thermal treatment method (CuO-TT), all of the CuO is ...

Langmuir−Blodgett Films of a Novel Cellulose Derivative with Dihydrophytyl Group: The Ability to Anchor β-Carotene Molecules

A novel cellulose derivative, 6-O-dihydrophytylcellulose (DHPC), was first synthesized via a ring-opening polymerization and allowed to self-assemble onto an air-water interface. Langmuir-Blodgett (LB) films were characterized with atomic force microscope (AFM), UV-vis spectroscopy, and Fourier transform infrared spectroscopy. The surface pressure-area (pi-A) isotherms for DHPC and beta-carotene (betaC) mixture indicated strong interaction between these compounds to pack well. Thus, DHPC has the ability to anchor betaC in the monolayer. It was proved that a betaC-DHPC monolayer was transferred successfully onto a substrate, yielding Y-type LB films by UV spectroscopic analysis. The transmission and reflection-absorption IR spectra (RAS) indicated that the dihydrophytyl chains had almost trans-zigzag conformation and were oriented nearly perpendicular to the substrate. AFM section analysis revealed the thickness per layer to be 2.32 nm. Consequently, DHPC was found to be an appropriate matrix to fabricate the mixed LB films containing betaC.

Structure and Deposition Mechanism of 10-Undecenoic Acid Self-Assembled Layers on H-Si (111) Surfaces Studied by Atomic Force Microscopy and Fourier-Transform Infrared

Ten-undecenoic acid self-assembled multilayers were deposited on H-Si(111) surfaces and the surface morphology was investigated by atomic force microscopy (AFM). Namely, we studied the H-Si(111) surface modification of –COOH terminal functional groups. Characteristic islands of almost the same height are observed. From AFM images and transmission IR spectra, it was confirmed that multilayer deposition easily occurs through weak intermolecular interactions such as the Van der Waals force and hydrogen bond interactions. The growth mechanism and film structure were discussed.