Showing papers on "Infrared spectroscopy published in 2009"
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16 Mar 2009TL;DR: In this paper, the authors present a combination table of C NMR Spectroscopy, H NMR and Heteronuclear NMR spectroscopy with IR and Mass Spectrometry.
Abstract: Summary Tables.- Combination Tables.- C NMR Spectroscopy.- H NMR Spectroscopy.- Heteronuclear NMR Spectroscopy.- IR Spectroscopy.- Mass Spectrometry.- UV/Vis Spectroscopy.
2,180 citations
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TL;DR: In this article, the results of the elemental analysis with that obtained by different spectroscopic techniques (infrared and Raman spectroscopy, and XPS) have been inferred that, from a chemical point of view, the solid product consists of small clusters of condensed benzene rings that form stable groups with oxygen in the core.
1,526 citations
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TL;DR: In this article, the synthesis and Fourier Transform Infrared spectroscopy characterization results dealing with the surface modification of silica aerogels obtained via a two-step sol-gel process where various silicon precursors and co-precursors were used.
715 citations
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TL;DR: In this article, a study of the structure and bonding configuration of sol-gel silicate glasses by Raman and infrared spectroscopies is presented, and a review of the Raman lines and infrared bands assignment, the identification of the non-bridging silicon-oxygen groups and the ring structures are also demonstrated.
Abstract: A study of the structure and bonding configuration of sol–gel silicate glasses by Raman and infrared spectroscopies is presented. Moreover, a review of the Raman lines and infrared bands assignment, the identification of the non-bridging silicon–oxygen groups and the ring structures are also demonstrated. The evolution of the changes of the bonding configuration in the composition and the stabilization temperature of the bioactive glasses is discussed in terms of the structural and textural characteristics of the glasses. Raman and infrared analyses contribute to the improvement in understanding of the local symmetry for sol–gel silicate glasses. infrared spectroscopy has allowed to identify the vibration bands of the hydroxyl groups associated with various configurations of the terminal silanol bonds on the glass surface and the free molecular water in the glass matrix. Raman analysis has provided an alternative method of quantifying the network connectivity grade and predicting the textural properties of the sol–gel silicate glasses.
495 citations
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TL;DR: In this article, the gamma, delta, theta and alpha-Al{sub 2}O{sub 3} phases, prepared by dehydration of aluminium oxihydroxide AlOOH (boehmite), were measured by XRD and IR spectroscopy on all samples.
428 citations
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TL;DR: In this paper, the thermal stability of graphite oxides to heat treatment under ambient argon gas was investigated using X-ray diffraction, and it was found that the interlayer distances dropped off in a stepwise manner by approximately 0.1nm in relation to the annealing time.
416 citations
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TL;DR: It will be shown that IR spectroscopy of mass-selected (bio)molecular systems is now well-placed to address specific questions on the individual effect of charge carriers (protons and metal ions), as well as solvent molecules on the overall structure.
Abstract: The low density of ions in mass spectrometers generally precludes direct infrared (IR) absorption measurements. The IR spectrum of an ion can nonetheless be obtained by inducing photodissociation of the ion using a high-intensity tunable laser. The emergence of free electron lasers (FELs) and recent breakthroughs in bench-top lasers based on nonlinear optics have now made it possible to routinely record IR spectra of gas-phase ions. As the energy of one IR photon is insufficient to cause dissociation of molecules and strongly bound complexes, two main experimental strategies have been developed to effect photodissociation. In infrared multiple-photon dissociation (IR-MPD) many photons are absorbed resonantly and their energy is stored in the bath of vibrational modes, leading to dissociation. In the "messenger" technique a weakly bound van der Waals atom is detached upon absorption of a single photon. Fundamental, historical, and practical aspects of these methods will be presented. Both of these approaches make use of very different methods of ion preparation and manipulation. While in IR-MPD ions are irradiated in trapping mass spectrometers, the "messenger" technique is generally carried out in molecular beam instruments. The main focus of this review is the application of IR spectroscopy to biologically relevant molecular systems (amino acids, peptides, proteins). Particular issues that will be addressed here include gas-phase zwitterions, the (chemical) structures of peptides and their collision-induced dissociation (CID) products, IR spectra of gas-phase proteins, and the chelation of metal-ligand complexes. Another growing area of research is IR spectroscopy on solvated clusters, which offer a bridge between the gas-phase and solution environments. The development of state-of-the-art computational approaches has gone hand-in-hand with advances in experimental techniques. The main advantage of gas-phase cluster research, as opposed to condensed-phase experiments, is that the systems of interest can be understood in detail and structural effects can be studied in isolation. It will be shown that IR spectroscopy of mass-selected (bio)molecular systems is now well-placed to address specific questions on the individual effect of charge carriers (protons and metal ions), as well as solvent molecules on the overall structure.
395 citations
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TL;DR: In this paper, a nonlinear optical (NLO) crystal BaGa4S7 for the mid-infrared (IR) has been grown by a Bridgman-Stockbarger technique.
Abstract: The new nonlinear optical (NLO) crystal BaGa4S7 for the mid-infrared (IR) has been grown by a Bridgman-Stockbarger technique. Polycrystalline materials with stoichiometric composition were synthesized from BaS, Ga, and S as the initial materials by solid-state reactions. The ultraviolet (UV) and IR transmittance of the crystal was determined with polished crystal pieces. The UV and IR optical absorption edges were found to be at 350 nm and 13.7 μm, respectively. From optical measurements of second harmonic generation on powders, the NLO coefficient d33 was determined to be 12.6 pm/V. The laser damage threshold of a single crystal reached about 1.2 J/cm2 at 1.064 μm. The Vickers-hardness value of the crystal is 327.5 HV5, which is equivalent to Mohs’ hardness of about 5.
314 citations
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TL;DR: In this article, the authors used laser frequency combs as the light source of Fourier transform spectroscopy (FTS) to record well-resolved broadband absorption and dispersion spectra in a single experiment.
Abstract: Molecular fingerprinting using absorption spectroscopy is a powerful analytical method, particularly in the infrared, the region of intense spectral signatures Fourier transform spectroscopy—the widely used and essential tool for broadband spectroscopy—enables the recording of multi-octave-spanning spectra, exhibiting 100 MHz resolution with an accuracy of 1 × 10−9 and 1 × 10−2 in wavenumber and intensity determination, respectively Typically, 1 × 106 independent spectral elements may be measured simultaneously within a few hours, with only average sensitivity Here, we show that by using laser frequency combs as the light source of Fourier transform spectroscopy it is possible to record well-resolved broadband absorption and dispersion spectra in a single experiment, from the beating signatures of neighbouring comb lines in the interferogram The sensitivity is thus expected to increase by several orders of magnitude Experimental proof of principle is here carried out on the 15-µm overtone bands of acetylene, spanning 80 nm with a resolution of 15 GHz Consequently, without any optical modification, the performance of Fourier spectrometers may be drastically boosted By using an optical frequency comb as the light source for Fourier transform spectroscopy, scientists show that well-resolved broadband absorption and dispersion spectra can be recorded in a single experiment, providing sensitive detection of multiple molecular species over a broad spectral window
292 citations
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TL;DR: In this article, the effect of oxygen mobility on the bio-ethanol steam reforming of ZrO2-supported cobalt catalysts was investigated, and it was found that the addition of ceria was found to improve the catalytic stability as well as activity.
270 citations
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TL;DR: Graphene nanoplatelets were self-assembled through the layer-by-layer (LBL) method through electrostatic interaction and Ultraviolet-visible spectroscopy confirmed that the adsorption technique resulted in uniform film growth.
Abstract: In this report, graphene nanoplatelets were self-assembled through the layer-by-layer (LBL) method The graphene surface was modified with poly(acrylic acid) and poly(acryl amide) by covalent bonding, which introduced negative and positive charge on the surface of graphene, respectively Through electrostatic interaction, the positively and negatively charged graphene nanoplatelets assembled together to form a multilayer structure Thermogravimetric analysis, Raman spectroscopy, scanning electron microscopy (SEM), and atomic force microscopy were used to demonstrate the modification of graphene nanoplatelets Fourier transform infrared spectroscopy and SEM proved this method is feasible for preparing graphene-containing films Ultraviolet−visible spectroscopy confirmed that the adsorption technique resulted in uniform film growth
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TL;DR: This short review of vibrational spectroscopic advances in microbial identification of yeast and bacterial cells for bulk environment and single‐cell analysis is discussed.
Abstract: Rapid microbial detection and identification with a high grade of sensitivity and selectivity is a great and challenging issue in many fields, primarily in clinical diagnosis, pharmaceutical, or food processing technology. The tedious and time-consuming processes of current microbiological approaches call for faster ideally on-line identification techniques. The vibrational spectroscopic techniques IR absorption and Raman spectroscopy are noninvasive methods yielding molecular fingerprint information; thus, allowing for a fast and reliable analysis of complex biological systems such as bacterial or yeast cells. In this short review, we discuss recent vibrational spectroscopic advances in microbial identification of yeast and bacterial cells for bulk environment and single-cell analysis. IR absorption spectroscopy enables a bulk analysis whereas micro-Raman-spectroscopy with excitation in the near infrared or visible range has the potential for the analysis of single bacterial and yeast cells. The inherently weak Raman signal can be increased up to several orders of magnitude by applying Raman signal enhancement methods such as UV-resonance Raman spectroscopy with excitation in the deep UV region, surface enhanced Raman scattering, or tip-enhanced Raman scattering. © 2008 International Society for Advancement of Cytometry
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TL;DR: The infrared spectra (IR) of pure liquid light and heavy water were obtained with attenuated total reflection (ATR) and transmission measurements in the mid-IR and far-IR with new optical properties (n and k) that can now be used as standards for liquid H(2)O and D( 2)O.
Abstract: The infrared spectra (IR) of pure liquid light (H(2)O) and heavy (D(2)O) water were obtained with attenuated total reflection (ATR) and transmission measurements in the mid-IR and far-IR. With these and with other values obtained from the literature, the real (n) and imaginary parts (k) of the refractive index were meticulously derived in the complete IR region from 6000 to 0 cm(-1). The reliability of the results resides in the critical comparison of our experimental data with that obtained from other laboratories and between calculated and experimental spectra, obtained by ATR and transmission techniques. The new optical properties (n and k) can now be used as standards for liquid H(2)O and D(2)O. To these we have added the water (H and D) absorption coefficients (K) that are derived from the k values. These can be used as references for spectra obtained by transmission with an absorbance intensity scale because they are almost the same.
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TL;DR: In this paper, the catalytic properties of Au nanoclusters deposited on a 1-D nanorod and CeO2-nanoparticles have been investigated during CO oxidation at ambient temperatures.
Abstract: Catalytic properties of Au nanoclusters deposited on a one-dimensional CeO2 (1-D) nanorod and CeO2-nanoparticles have been investigated during CO oxidation at ambient temperatures. The kinetic data showed that the activity of Au catalysts could be remarkably improved by using CeO2-nanorods as support compared to the CeO2-nanoparticles. The measured specific rate and apparent activation energy (Ea) at 278 K were 4.02 molCO gAu−1 h−1 and 15.9 kJ mol−1, respectively, for the Au/CeO2-nanorods (Au-CR) catalyst, while those for the Au/CeO2-nanoparticles (Au-CP) catalyst were 0.15 molCO gAu−1 h−1 and 28.4 kJ mol−1, respectively. Characterization by X-ray diffraction (XRD), transmission electron microscopy (TEM), hydrogen temperature-programmed reduction (H2-TPR), X-ray photoelectron spectroscopy (XPS), diffuse reflectance UV–Vis spectroscopy (DR UV–Vis) and in situ diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) of CO adsorption reveal that the predominantly exposed {1 0 0}/{1 1 0}-dominated surface structures of ceria nanorods show great superiority for anchoring and dispersing of gold nanoclusters, which in turn leads to a higher reducibility and activity of the Au-CeO2 surface for CO oxidation. It is also confirmed that, arising from the strong metal–support interaction (SMSI), the presence of gold nanoclusters has a strong influence on the electronic state of the CeO2 substrates.
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TL;DR: In this article, the structure of the organic capping layers of platinum colloid nanoparticles and their removal by UV-ozone exposure were reported, and the overall shape of the nanoparticles was preserved after the removal of capping layer.
Abstract: We report the structure of the organic capping layers of platinum colloid nanoparticles and their removal by UV-ozone exposure. Sum frequency generation vibrational spectroscopy (SFGVS) studies identify the carbon-hydrogen stretching modes on poly(vinylpyrrolidone) (PVP) and tetradecyl tributylammonium bromide (TTAB)-capped platinum nanoparticles. We found that the UV-ozone treatment technique effectively removes the capping layer on the basis of several analytical measurements including SFGVS, X-ray photoelectron spectroscopy, and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The overall shape of the nanoparticles was preserved after the removal of capping layers, as confirmed by transmission electron microscopy (TEM). SFGVS of ethylene hydrogenation on the clean platinum nanoparticles demonstrates the existence of ethylidyne and di-σ-bonded species, indicating the similarity between single-crystal and nanoparticle systems.
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TL;DR: This compound is isostructural to the MIL-53 type, previously observed with the trivalent cations Cr, Fe, Al, In and exhibits a three-dimensional metal-organic framework built up from infinite chains of trans corner-sharing GaO(4)(OH)(2) octahedra (viamu(2)-hydroxo bonds) linked to each other through the terephthalate linkers.
Abstract: The gallium terephthalate Ga(OH)[O2C-C6H4-CO2]·xA (A = HO2C–C6H4–CO2H) was hydrothermally synthesized in water under mild conditions (210 °C, 3½ h) in the presence of terephthalic acid. The compound was characterized by powder X-ray diffraction, TGA, IR and BET method. This compound is isostructural to the MIL-53 type, previously observed with the trivalent cations Cr, Fe, Al, In. It exhibits a three-dimensional metal–organic framework built up from infinite chains of trans corner-sharing GaO4(OH)2 octahedra (viaμ2-hydroxo bonds) linked to each other through the terephthalate linkers. It results in the formation of lozenge-shape channels structure running parallel to the infinite files of gallium-centered octahedra. After activation, the compound is able to adsorb one molar equivalent of water at room temperature under ambient air (MIL-53(Ga){H2O}). Different hydrogen bond interactions are observed for the encapsulated water within the channels. In one tunnel, pairs of water species with strong hydrogen-bond interactions were observed whereas in the adjacent tunnel, only a continuous linear and weakly hydrogen bonded network occurs. The dehydrated form is obtained upon heating the MIL-53(Ga) solid at 80 °C together with the shrinkage of the channels (MIL-53(Ga)_lt. This form is stable up to 220 °C and then the open structure MIL-53(Ga)_ht is visible, but starts to decompose from 350 °C. Such a breathing effect was previously reported with cations such as Cr or Al but in the case of Ga, the stability domain of the narrow pore structure MIL-53(Ga)_lt is larger (160 °C instead of 20–30 °C for Al, for instance). The BET surface area was 1140 ± 114 m2.g−1. The phase transitions were characterized by IR spectroscopy at different temperatures, which confirms the stability domain of the narrow close form (specific band at 1016 cm−1) of MIL-53(Ga) and then the pore opening (shifted band toward 1024 cm−1) together with the structure collapse. An identical behaviour is also discussed for the aluminum MIL-53 analogue. A comparison between the behaviour of the Al, Ga and Fe samples is presented.
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TL;DR: In this article, the role of divalent cations in the structure of B2O3 glasses has been investigated using sound velocity measurements at 4 MHz and IR spectroscopic analysis of IR spectra.
Abstract: Studies on xRO · 30Bi2O3 · (70−x)B2O3 glasses have been carried out (0 ⩽ x ⩽ 30 mol%, R = Zn, Ba). Elastic properties and Debye temperature have been investigated using sound velocity measurements at 4 MHz. The ultrasonic parameters along with the IR spectroscopic studies have been employed to explore the role of divalent cations in the structure of the studied glasses. Analysis of infrared spectra indicates that RO is preferentially incorporated into the borate network, forming BO4 units. It is assumed that Bi2O3 enters the structure in the form of BiO6 only. The change of density and molar volume with RO content reveals that BO4 units linked to R2+ cations are denser than those linked to positive sites in the Bi2O3 network. Predicted values of four co-ordinated boron put forward questions about the reliability of assignment of structural units that Bi2O3 may form.
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TL;DR: The new and exciting techniques of infrared consequence spectroscopy of gaseous ions are reviewed and this review mainly covers the topics with which the author has been directly involved in research: structures of proton-bound dimers, protonated amino acids and DNA bases, amino acid andDNA bases bound to metal ions and, more recently, solvated ionic complexes.
Abstract: In this article, the new and exciting techniques of infrared consequence spectroscopy (sometimes called action spectroscopy) of gaseous ions are reviewed. These techniques include vibrational predissociation spectroscopy and infrared multiple photon dissociation spectroscopy and they typically complement one another in the systems studied and the information gained. In recent years infrared consequence spectroscopy has provided long-awaited direct evidence into the structures of gaseous ions from organometallic species to strong ionic hydrogen bonded structures to large biomolecules. Much is being learned with respect to the structures of ions without their stabilizing solvent which can be used to better understand the effect of solvent on their structures. This review mainly covers the topics with which the author has been directly involved in research: structures of proton-bound dimers, protonated amino acids and DNA bases, amino acid and DNA bases bound to metal ions and, more recently, solvated ionic complexes. It is hoped that this review reveals the impact that infrared consequence spectroscopy has had on the field of gaseous ion chemistry.
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TL;DR: In this paper, the catalytic acids were synthesized at room temperature and characterized by atomic absorption spectrometry (AAS), thermal analysis (TG/DTA), X-ray diffraction (XRD), nitrogen absorption (BET/BJH), infrared spectroscopy (IR), scanning electron microscopy (SEM) and transmission electron microscope (TEM).
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TL;DR: A significant asymmetry in the optical conductivity upon electrostatic doping of electrons and holes arises from a marked asymmetry between the valence and conduction bands, which is mainly due to the inequivalence of the two sublattices within the graphene layer and the next-nearest-neighbor interlayer coupling.
Abstract: We report on infrared spectroscopy of bilayer graphene integrated in gated structures. We observe a significant asymmetry in the optical conductivity upon electrostatic doping of electrons and holes. We show that this finding arises from a marked asymmetry between the valence and conduction bands, which is mainly due to the inequivalence of the two sublattices within the graphene layer and the next-nearest-neighbor interlayer coupling. From the conductivity data, the energy difference of the two sublattices and the interlayer coupling energy are directly determined.
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TL;DR: The onset of extensive water-water hydrogen bonding is observed starting with four water molecules and persists in the larger clusters, indicating an ion with a highly symmetric solvation shell.
Abstract: We present infrared photodissociation spectra of the microhydrated nitrate ions NO3−(H2O)1−6, measured from 600 to 1800 cm−1. The assignment of the spectra is aided by comparison with calculated B3LYP/aug-cc-pVDZ harmonic frequencies, as well as with higher-level calculations. The IR spectra are dominated by the antisymmetric stretching mode of NO3−, which is doubly degenerate in the bare ion but splits into its two components for most microhydrated ions studied here due to asymmetric solvation of the nitrate core. However, for NO3−(H2O)3, the spectrum reveals no lifting of this degeneracy, indicating an ion with a highly symmetric solvation shell. The first three water molecules bind in a bidentate fashion to the terminal oxygen atoms of the nitrate ion, keeping the planar symmetry. The onset of extensive water−water hydrogen bonding is observed starting with four water molecules and persists in the larger clusters.
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TL;DR: The information content of resonance Raman spectra of chlorophyll and carotenoid molecules is described in this review, together with the experiments which helped in determining which structural parameter each Raman band is sensitive to.
Abstract: Resonance Raman spectroscopy may yield precise information on the conformation of, and on the interactions assumed by, the chromophores involved in the first steps of the photosynthetic process, whether isolated in solvents, embedded in soluble or membrane proteins, or, as shown recently, in vivo. By making use of this technique, it is possible, for instance, to relate the electronic properties of these molecules to their structure and/or the physical properties of their environment, or to determine subtle changes of their conformation associated with regulatory processes. After a short introduction to the physical principles that govern resonance Raman spectroscopy, the information content of resonance Raman spectra of chlorophyll and carotenoid molecules is described in this review, together with the experiments which helped in determining which structural parameter each Raman band is sensitive to. A selection of applications of this technique is then presented, in order to give a fair and precise idea of which type of information can be obtained from its use in the field of photosynthesis.
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TL;DR: Five silica samples (four precipitated silicas provided by commercial suppliers and one with the MCM-41 structure) have been studied by infrared spectroscopy and by a homemade thermogravimetry-infrared spectrum (TG-IR) setup to determine the integrated molar absorption coefficient of the (nu+delta)OH band and the amount of water adsorbed on silicas through the intensity of the deltaH2O band.
Abstract: Five silica samples (four precipitated silicas provided by commercial suppliers and one with the MCM-41 structure) have been studied by infrared spectroscopy and by a homemade thermogravimetry−infr...
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TL;DR: In this paper, the composition, morphology, crystal microstructure, specific surface area, infrared spectra, and particle size distribution of product were analyzed by using X-ray diffraction (XRD), transmission electron microscopy (TEM) and corresponding selected area electron diffraction, Fourier transform infrared (FTIR) spectrum, and Brunauer-Emmett-Teller (BET) N2 adsorption.
Abstract: NiO nanoparticles with average particle size of 25 nm were successfully prepared by anodic arc plasma method. The composition, morphology, crystal microstructure, specific surface area, infrared spectra, and particle size distribution of product were analyzed by using X-ray diffraction (XRD), transmission electron microscopy (TEM) and the corresponding selected area electron diffraction (SAED), Fourier transform infrared (FTIR) spectrum, and Brunauer-Emmett-Teller (BET) N2 adsorption. The experiment results show that the NiO nanoparticles are bcc structure with spherical shape and well dispersed, the particle size distribution ranging from 15 to 45nm with the average particle size is about 25 nm, and the specific surface area is 33m2/g. The infrared absorption band of NiO nanoparticles shows blue shifts compared with that of bulk NiO.
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TL;DR: In this paper, a series of Fe3−xTixO4 (0.78) was synthesized using a new soft chemical method using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Mossbauer Spectroscopy, thermogravimetric and differential scanning calorimetry (TG-DSC) analyses.
Abstract: In this work, a series of Fe3−xTixO4 (0 ≤ x ≤ 0.78) was synthesized using a new soft chemical method. The synthetic Fe3−xTixO4 were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Mossbauer spectroscopy, thermogravimetric and differential scanning calorimetry (TG–DSC) analyses. The results showed that they were spinel structures and Ti was introduced into their structures. Then, decolorization of methylene blue (MB) by Fe3−xTixO4 in the presence of H2O2 at neutral pH values was studied using UV–vis spectra, dissolved organic carbon (DOC) and element C analyses. Furthermore, the degradation products remained in reaction solution after the decolorization were identified using ionic chromatography (IC), 13C nuclear magnetic resonance spectra (NMR), liquid chromatography and mass spectrometry (LC–MS). Although small amounts of MB were mineralized, the aromatic rings in MB were destroyed completely after the decolorization. Decolorization of MB by Fe3−xTixO4 in the presence of H2O2 was promoted remarkably with the increase of Ti content in Fe3−xTixO4 due to the enhancement of both adsorption and degradation of MB on Fe3−xTixO4.
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TL;DR: In this paper, the Mars and van Krevelen mechanism for CO and H2 oxidation was proposed and supported by comparing the model to the experimental data, and the results showed that the mechanism was able to achieve high selectivity.
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TL;DR: The transient absorption of nanocrystalline TiO2 films in the visible-to-IR wavelength region was measured under UV excitation at 266 nm in order to purposely generate plural electron−hole pairs in this paper.
Abstract: The transient absorption of nanocrystalline TiO2 films in the visible-to-IR wavelength region was measured under UV excitation at 266 nm in order to purposely generate plural electron−hole pairs in...
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TL;DR: In this article, a microwave assisted combustion method was used to synthesize nanocrystalline ZnxNi1−xFe2O4 from a stoichiometric mixture of corresponding metal nitrates and urea powders.
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TL;DR: In this article, gas-phase infrared multiple photon dissociation (IRMPD) spectra have been recorded for the conjugate bases of a series of amino acids (Asp, Cys, Glu, Phe, Ser, Trp, Tyr) and showed strong symmetric and antisymmetric carboxylate stretching modes around 1300 and 1600 cm−1, respectively.
Abstract: Gas-phase infrared multiple photon dissociation (IRMPD) spectra have been recorded for the conjugate bases of a series of amino acids (Asp, Cys, Glu, Phe, Ser, Trp, Tyr). The spectra are dominated by strong symmetric and antisymmetric carboxylate stretching modes around 1300 and 1600 cm−1, respectively. Comparison of the experimental spectra with spectra calculated at the DFT level suggests a carboxylate structure for all species investigated, which is in contrast with what has recently been suggested in this journal for deprotonated cysteine [J. Am. Chem. Soc. 2007, 129, 5403−5407]. In addition, the IR spectrum of the conjugate base of tyrosine is also unambiguously that of a carboxylate ion and not that of a phenoxide ion. In sharp contrast with the conjugate bases of other amino acids investigated here, the aspartate and glutamate anions show very broad, hardly resolved spectral features. We present qualitative experimental evidence indicating that this can be attributed to the formation of a proton br...
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TL;DR: In this paper, a detailed infrared study of the insulator-to-metal transition IMT in vanadium dioxide VO2 thin films is presented, and it is shown that the phase transition is percolative with cooling across the IMT.
Abstract: We present a detailed infrared study of the insulator-to-metal transition IMT in vanadium dioxide VO2 thin films. Conventional infrared spectroscopy was employed to investigate the IMT in the far field. Scanning near-field infrared microscopy directly revealed the percolative IMT with increasing temperature. We confirmed that the phase transition is also percolative with cooling across the IMT. We present extensive near-field infrared images of phase coexistence in the IMT regime in VO2. We find that the coexisting insulating and metallic regions at a fixed temperature are static on the time scale of our measurements. A distinctive approach for analyzing the far-field and near-field infrared data within the Bruggeman effective medium theory was employed to extract the optical constants of the incipient metallic puddles at the onset of the IMT. We found divergent effective carrier mass in the metallic puddles that demonstrates the importance of electronic correlations to the IMT in VO2. We employ the extended dipole model for a quantitative analysis of the observed near-field infrared amplitude contrast and compare the results with those obtained with the basic dipole model.