Showing papers on "Infrared spectroscopy published in 2008"

Introduction to Spectroscopy

Abstract: 1. Molecular Formulas and What Can Be Learned from Them. 2. Infrared Spectroscopy. 3. Nuclear Magnetic Resonance Spectroscopy Part One: Basic Concepts. 4. Nuclear Magnetic Resonance Spectroscopy Part Two: Carbon-13 Spectra, Including Heteronuclear Coupling with Other Nuclei. 5. Nuclear Magnetic Resonance Spectroscopy Part Three: Spin-Spin Coupling. 6. Nuclear Magnetic Resonance Spectroscopy Part Four: Other Topics in One-Dimensional NMR. 7. Ultraviolet Spectroscopy. 8. Mass Spectrometry. 9. Combined Structure Problems. 10. Nuclear Magnetic Resonance Spectroscopy Part Five: Advanced NMR Techniques. Answers to Selected Problems. Appendix 1: Infrared Absorption Frequencies of Functional Groups. Appendix 2: Some Representative Chemical Shift Values for Various Types of Protons. Appendix 3: Typical Proton Coupling Constants. Appendix 4: Calculation of Proton (1H) Chemical Shifts. Appendix 5: Calculation of Carbon-13 Chemical Shifts. Appendix 6: 13C Coupling Constants. Appendix 7: Tables of Precise Masses and Isotopic Abundance Ratios for Molecular Ions Under Mass 100 Containing Carbon, Hydrogen, Nitrogen, and Oxygen. Appendix 8: Common Fragment Ions Under Mass 105. Appendix 9: Handy-Dandy Guide to Mass Spectral Fragmentation Patterns. Appendix 10: Index of Spectra.

Evidence of Graphitic AB Stacking Order of Graphite Oxides

Abstract: Graphite oxide (GO) samples were prepared by a simplified Brodie method. Hydroxyl, epoxide, carboxyl, and some alkyl functional groups are present in the GO, as identified by solid-state 13C NMR, Fourier-transform infrared spectroscopy, and X-ray photoemission spectroscopy. Starting with pyrolytic graphite (interlayer separation 3.36 A), the average interlayer distance after 1 h of reaction, as determined by X-ray diffraction, increased to 5.62 A and then increased with further oxidation to 7.37 A after 24 h. A smaller signal in 13C CPMAS NMR compared to that in 13C NMR suggests that carboxyl and alkyl groups are at the edges of the flakes of graphite oxide. Other aspects of the chemical bonding were assessed from the NMR and XPS data and are discussed. AB stacking of the layers in the GO was inferred from an electron diffraction study. The elemental composition of GO prepared using this simplified Brodie method is further discussed.

Diazonium Functionalization of Surfactant-Wrapped Chemically Converted Graphene Sheets

Abstract: Surfactant-wrapped chemically converted graphene sheets obtained from reduction of graphene oxide with hydrazine were functionalized by treatment with aryl diazonium salts. The nanosheets are characterized by X-ray photoelectron spectroscopy, attenuated total reflectance infrared spectroscopy, Raman spectroscopy, atomic force microscopy, and transmission electron microscopy. The resulting functionalized nanosheets disperse readily in polar aprotic solvents, allowing alternative avenues for simple incorporation into different polymer matrices.

High contrast in vitro and in vivo photoluminescence bioimaging using near infrared to near infrared up-conversion in Tm3+ and Yb3+ doped fluoride nanophosphors.

Abstract: A new approach for photoluminescence imaging in vitro and in vivo has been shown utilizing near infrared to near infrared (NIR-to-NIR) up-conversion in nanophosphors. This NIR-to-NIR up-conversion process provides deeper light penetration into biological specimen and results in high contrast optical imaging due to absence of an autofluorescence background and decreased light scattering. Aqueous dispersible fluoride (NaYF4) nanocrystals (20−30 nm size) co-doped with the rare earth ions, Tm3+ and Yb3+, were synthesized and characterized by TEM, XRD, and photoluminescence (PL) spectroscopy. In vitro cellular uptake was shown by the PL microscopy visualizing the characteristic emission of Tm3+ at ∼800 nm excited with 975 nm. No apparent cytotoxicity was observed. Subsequent animal imaging studies were performed using Balb-c mice injected intravenously with up-converting nanophosphors, demonstrating the high contrast PL imaging in vivo.

Amide I Two-Dimensional Infrared Spectroscopy of Proteins

Abstract: We review two-dimensional infrared (2D IR) spectroscopy of the amide I protein backbone vibration. Amide I modes are known for secondary structural sensitivity derived from their protein-wide delocalization. However, amide I FTIR spectra often display little variation for different proteins due to the broad and featureless line shape that arises from different structural motifs. 2D IR offers increased structural resolution by spreading the spectra over a second frequency dimension to reveal two-dimensional line shapes and cross-peaks. In addition, it carries picosecond time resolution, making it an excellent choice for understanding protein dynamics. In 2D IR spectra, cross peaks arise from anharmonic coupling between vibrations. For example, the spectra of ordered antiparallel beta sheets shows a cross peak between the strong nu perpendicular mode at approximately 1620 cm(-1) and the weaker nu parallel mode at approximately 1680 cm(-1). In proteins with beta-sheet content, disorder spreads the cross peaks into ridges, which gives rise to a "Z"-shaped contour profile. 2D IR spectra of alpha helices show a flattened "figure-8" line shape, and random coils give rise to unstructured, diagonally elongated bands. A distinguishing quality of 2D IR is the availability of accurate structure-based models to calculate spectra from atomistic structures and MD simulations. The amide I region is relatively isolated from other protein vibrations, which allows the spectra to be described by coupled anharmonic local amide I vibrations at each peptide unit. One of the most exciting applications of 2D IR is to study protein unfolding dynamics. While 2D IR has been used to study equilibrium structural changes, it has the time resolution to probe all changes resulting from photoinitiated dynamics. Transient 2D IR has been used to probe downhill protein unfolding and hydrogen bond dynamics in peptides. Because 2D IR spectra can be calculated from folding MD simulations, opportunities arise for making rigorous connections. By introduction of isotope labels, amide I 2D IR spectra can probe site-specific structure with picosecond time resolution. This has been used to reveal local information about picosecond fluctuations and disorder in beta hairpins and peptides. Multimode 2D IR spectroscopy has been used to correlate the structure sensitivity of amide I with amide II to report on solvent accessibility and structural stability in proteins.

Attachment of 3-(Aminopropyl)triethoxysilane on Silicon Oxide Surfaces: Dependence on Solution Temperature

Abstract: Parameters important to the self-assembly of 3-(aminopropyl)triethoxysilane (APTES) on chemically grown silicon oxide (SiO2) to form an aminopropyl silane (APS) film have been investigated using in situ infrared (IR) absorption spectroscopy. Preannealing to ∼70 °C produces significant improvements in the quality of the film: the APS film is denser, and the Si−O−Si bonds between the molecules and the SiO2 surface are more structured and ordered with only a limited number of remaining unreacted ethoxy groups. In contrast, post-annealing the functionalized SiO2 samples after room temperature reaction with APTES (i.e., ex situ annealing) does not lead to any spectral change, suggesting that post-annealing has no strong effect on the horizontal polymerization as suggested earlier. Both IR and ellipsometry data show that the higher the solution temperature, the denser and thinner the APS layer is for a given immersion time. Finally, the APS layer obtained by preannealing the solution at 70 °C exhibits a better ...

Preparation of polyaniline-modified TiO2 nanoparticles and their photocatalytic activity under visible light illumination

Abstract: Titanium dioxide nanoparticles were modified by polyaniline (PANI) using ‘in situ’ chemical oxidative polymerization method in hydrochloric acid solutions. Powder X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier-transform infrared spectra (FT-IR), X-ray photoelectron spectroscopy spectrum (XPS) and UV–vis spectra were carried out to characterize the composites with different PANI contents. The photocatalytic degradation of phenol was chosen as a model reaction to evaluate the photocatalytic activities of the modified catalysts. Results show that TiO2 nanoparticles are deposited by PANI to mitigate TiO2 particles agglomeration. The modification does not alter the crystalline structure of the TiO2 nanoparticles according to the X-ray diffraction patterns. UV–vis spectra reveal that PANI-modified TiO2 composites show stronger absorption than neat TiO2 under the whole range of visible light. The resulting PANI-modified TiO2 composites exhibit significantly higher photocatalytic activity than that of neat TiO2 on degradation of phenol aqueous solution under visible light irradiation (λ ≥ 400 nm). An optimum of the synergetic effect is found for an initial molar ratio of aniline to TiO2 equal to 1/100.

Ruthenium Nanoparticles inside Porous [Zn4O(bdc)3] by Hydrogenolysis of Adsorbed [Ru(cod)(cot)]: A Solid-State Reference System for Surfactant-Stabilized Ruthenium Colloids

Abstract: The gas-phase loading of [Zn4O(bdc)3] (MOF-5; bdc = 1,4-benzenedicarboxylate) with the volatile compound [Ru(cod)(cot)] (cod = 1,5-cyclooctadiene, cot = 1,3,5-cyclooctatriene) was followed by solid-state 13C magic angle spinning (MAS) NMR spectroscopy. Subsequent hydrogenolysis of the adsorbed complex inside the porous structure of MOF-5 at 3 bar and 150 °C was performed, yielding ruthenium nanoparticles in a typical size range of 1.5–1.7 nm, embedded in the intact MOF-5 matrix, as confirmed by transmission electron microscopy (TEM), selected area electron diffraction (SAED), powder X-ray diffraction (PXRD), and X-ray absorption spectroscopy (XAS). The adsorption of CO molecules on the obtained Ru@MOF-5 nanocomposite was followed by IR spectroscopy. Solid-state 2H NMR measurements indicated that MOF-5 was a stabilizing support with only weak interactions with the embedded particles, as deduced from the surprisingly high mobility of the surface Ru−D species in comparison to surfactant-stabilized colloidal ...

The identification of hydroxyl groups on ZnO nanoparticles by infrared spectroscopy

Abstract: The interaction of water with ZnO nanoparticles has been studied by means of diffuse reflectance infrared spectroscopy (DRIFTS) and ultra-high vacuum FTIR spectroscopy (UHV-FTIRS). Exposing clean ZnO powder to water at 323 K leads to both molecular and dissociative adsorption of H2O forming a number of hydroxyl species. All the OH bands are clearly identified by the adsorption of D2O showing the expected isotopic shifts. According to the vibrational and thermal stability data obtained from single crystal surfaces, the OH species observed on ZnO nanoparticles are identified as follows: (1) OH group (3620 cm−1) on the polar O–ZnO(000) surface formed via dissociation of water on oxygen vacancy sites; (2) partial dissociation of water on the mixed-terminated ZnO(100) surface yielding coexistent H2O (∼3150 and 3687 cm−1) and OH species (3672 cm−1), where the molecularly adsorbed H2O is further identified by the characteristic scissoring mode at 1617 cm−1; (3) isolated OH species (3639 and 3656 cm−1) formed on the mixed-terminated ZnO(100) surface; (4) interaction of water with defects forming hydroxyl (or O–H⋯O) species (3564 and 3448 cm−1).

Surface Phases of TiO2 Nanoparticles Studied by UV Raman Spectroscopy and FT-IR Spectroscopy

Abstract: Surface phases of TiO2 nanoparticles (30 ∼ 200 nm) were studied by UV Raman spectroscopy and FT-IR spectroscopy with CO and CO2 as probe molecules. UV Raman spectroscopy can differentiate the surface phase structure of TiO2 calcined at different temperatures. IR spectra of adsorbed CO and CO2 on TiO2 calcined at different temperatures are in good agreement with the results from UV Raman spectra. IR results evidently confirm that UV Raman spectroscopy is a surface-sensitive technique for TiO2. Both UV Raman and IR spectra indicate that the crystalline phase of TiO2 in the surface region is usually different from that in the bulk which is characterized by XRD. CO is weakly adsorbed on Ti4+ ions of anatase phase but is hardly adsorbed on those of rutile phase at room temperature. Adsorbed CO2 on anatase phase produces mainly bidentate carbonate, while on rutile phase produces mainly bicarbonate species. These results suggest that the surface Lewis acidity of anatase phase is stronger than that of rutile phas...

The Kagomé topology of the gallium and indium metal-organic framework types with a MIL-68 structure: synthesis, XRD, solid-state NMR characterizations, and hydrogen adsorption.

Abstract: The vanadium-based terephthalate analogs of MIL-68 have been obtained with gallium and indium (network composition: M(OH)(O2C−C6H4−CO2), M = Ga or In) by using a solvothermal synthesis technique using N,N-dimethylformamide as a solvent (10 and 48 h, for Ga and In, respectively, at 100 °C). They have been characterized by X-ray diffraction analysis; vibrational spectroscopy; and solid-state 1H and 1H−1H radio-frequency-driven dipolar recoupling (RFDR), 1H−1H double quantum correlation (DQ), and 13C{1H} cross polarization magic angle spinning (CPMAS) NMR spectroscopy. The three-dimensional network with a Kagome-like lattice is built up from the connection of infinite trans-connected chains of octahedral units MO4(OH)2 (M = Ga or In), linked to each other through the terephthalate ligands in order to generate triangular and hexagonal one-dimensional channels. The presence of DMF molecules with strong interactions within the channels as well as their departure upon calcination (150 °C under a primary vacuum) ...

Comparison between XPS- and FTIR-analysis of plasma-treated polypropylene film surfaces

Abstract: Plasma treatment is often used to modify the surface properties of polymer films, since it offers numerous advantages over the conventional surface modification techniques. In this paper, a polypropylene (PP) film is plasma-treated using a dielec. barrier discharge (DBD) operating in air at medium pressure (5.0 kPa). The modified polymer films are characterized using contact angle measurements, XPS-anal. and attenuated total reflectance-Fourier transform IR (ATR-FTIR) spectroscopy. Results show that plasma treatment leads to a remarkable decrease in contact angle owing to the implantation of oxygen-contg. functional groups. Using XPS and ATR-FTIR, these oxygen-contg. groups can be identified as C-O, C=O and O-C=O. In this paper, it is also shown that XPS is well-suited to provide quant. chem. anal. of the PP films, while ATR-FTIR can only give qual. information. To perform quant. ATR-FTIR measurements, chem. derivatization will be explored in the near future

Structure and reactivity of plasma treated Ni/Al2O3 catalyst for CO2 reforming of methane

Abstract: The glow discharge plasma treated Ni/Al2O3 catalyst showed an excellent anti-coke property for CO2 reforming of methane. Characterizations using X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature programmed reduction (TPR), transmission electron microscopy (TEM), and CO adsorbed infrared spectroscopy (IR) were conducted to investigate the structure and reactivity of the plasma treated Ni/Al2O3 catalyst for CO2 reforming of methane. It confirms that the plasma treatment of Ni precursor at room temperature followed by calcination thermally has a significant influence on the surface characteristics of the active phase. The plasma treated catalyst contains high concentration of close packed plane with improved Ni dispersion and enhanced Ni-alumina interaction, which lead to high catalytic activity and excellent resistance to formations of filamentous carbon and encapsulating carbon.

Determination of the electronic structure of bilayer graphene from infrared spectroscopy

Abstract: We present an experimental study of the infrared conductivity, transmission, and reflection of a gated bilayer graphene and their theoretical analysis within the Slonczewski-Weiss-McClure (SWMc) model. The infrared response is shown to be governed by the interplay of the interband and the intraband transitions among the four bands of the bilayer. The position of the main conductivity peak at the charge-neutrality point is determined by the interlayer tunneling frequency. The shift of this peak as a function of the gate voltage gives information about less known parameters of the SWMc model such as those responsible for the electron-hole and sublattice asymmetries. These parameter values are shown to be consistent with recent electronic structure calculations for the bilayer graphene and the SWMc parameters commonly used for the bulk graphite.

Structural, vibrational and electrical characterization of PVA–NH4Br polymer electrolyte system

Abstract: Polymer electrolyte based on PVA doped with different concentrations of NH 4 Br has been prepared by solution casting technique. The complexation of the prepared polymer electrolytes has been studied using X-ray diffraction (XRD) and Fourier transform infra red (FTIR) spectroscopy. The maximum ionic conductivity (5.7×10 −4 S cm −1 ) has been obtained for 25 mol% NH 4 Br-doped PVA polymer electrolyte. The temperature dependence of ionic conductivity of the prepared polymer electrolytes obeys Arrhenius law. The ionic transference number of mobile ions has been estimated by dc polarization method and the results reveal that the conducting species are predominantly ions. The dielectric behavior of the polymer electrolytes has been analyzed using dielectric permittivity and electric modulus spectra.

Visible light responsive pristine metal oxide photocatalyst: enhancement of activity by crystallization under hydrothermal treatment.

Abstract: Photocatalytic activities of amorphous and crystal bismuth tungstate (Bi2WO6) were investigated using oxidative decomposition of gaseous acetaldehyde under visible light irradiation (>400 nm). Here, for the first time, negligible photocatalytic activity of amorphous Bi2WO6 owing to the fast recombination of electron−hole pairs and the high quantum efficiency of Bi2WO6 crystallites under visible light were demonstrated by action spectrum analysis and time-resolved infrared absorption measurements. Crystallization of the amorphous phase provided a red shift of the photoabsorption edge and marked increase in the lifetime of photoexcited electrons, resulting in an increase of photocatalytic activity.

Structure of Water at the Electrified Platinum−Water Interface: A Study by Surface-Enhanced Infrared Absorption Spectroscopy

Abstract: Surface-enhanced infrared absorption spectroscopy in the attenuated total reflection mode is used to examine the structure of water on a polycrystalline Pt electrode in H2SO4 and HClO4 as a function of applied potential. The electrode surface covered with CO is used as the reference in recording spectra, which enables us to obtain the absolute infrared spectrum of the interfacial water layer (monolayer or bilayer) in contact with the surface with negligible interference from the bulk water. The spectrum of the interfacial water is largely different from that of bulk water and changes around the potential of zero charge of the electrode. The spectral changes are ascribed to the potential-dependent reorientation of water molecules from a weakly hydrogen-bonded oxygen-up orientation at the negatively charged surface to a strongly hydrogen-bonded nearly flat orientation at the positively charged surface in agreement with theoretical simulations reported in the literature. Clear experimental evidence of the fo...

Structural change of 1-butyl-3-methylimidazolium tetrafluoroborate + water mixtures studied by infrared vibrational spectroscopy.

Abstract: Mixtures of ionic liquid (IL, 1-butyl-3-methylimidazolium tetrafluoroborate, [BMIM][BF4]) and water with varying concentrations were studied by attenuated total reflection infrared absorption and Raman spectroscopy. Changes in the peak intensities and peak positions of CHx (x = 1, 2, 3) vibration modes of the cation of the IL and OH vibration modes of the water molecules were investigated. Peaks from normal-mode stretch vibrations of CH bonds belonging to the imidazolium ring of the cation did not change their positions, while those from the terminal methyl group of the butyl chain blueshifted by approximately 10 cm-1 with the addition of water. On the other hand, change in the spectral shape in the OH stretch vibration region shows hydrogen-bonding network of water molecules breaking down rapidly as the IL is added. Trends in the change of the peak positions and the peak intensities suggested qualitative change of the intermolecular structure in the [BMIM][BF4] + H2O mixture at 32 +/- 2 and 45 +/- 2 mol/L of water concentration.

Silver on PEG-PU-TiO2 Polymer Nanocomposite Films: An Excellent System for Antibacterial Applications

Abstract: Silver impregnated on polymer-titania nanocomposite films exhibit excellent antibacterial properties with the added advantage of repeated use. The polyethylene glycol-polyurethane-titania designated as PEG-PU-TiO2 polymer nanocomposite films were synthesized by simple solution casting technique. Silver has been incorporated into these films by photochemical reduction of silver nitrate solution. The TiO2 facilitated the UV photoreduction of AgNO3 to Ag, which is active as an antibacterial agent. Fourier Transformed Infrared Spectroscopy (FT-IR) confirms the formation of the polymer, polyurethane. X-ray Diffraction (XRD) determined the structure and scanning electron microscopy (SEM), the morphology of the films. XPS confirms the Ag to be in zero oxidation state and the amount of silver impregnated in the films as estimated by scanning electron microscopy−energy-dispersive X-ray analysis (SEM-EDAX), and atomic absorption spectroscopy (AAS) is about 2−4 at %. The antibacterial properties of these films were ...

Alkyl‐Functionalized Oxide‐Free Silicon Nanoparticles: Synthesis and Optical Properties

Abstract: Highly monodisperse silicon nanoparticles (1.57 +/- 0.21 nm) are synthesized with a covalently attached alkyl monolayer on a gram scale. Infrared spectroscopy shows that these silicon nanoparticles contain only a few oxygen atoms per nanoparticle. XPS spectra clearly show the presence of unoxidized Si and attached alkyl chains. Owing to the relatively efficient synthesis (yields approximately 100-fold higher than of those previously reported) the molar extinction coefficient epsilon can be measured: epsilon(max) = 1.7 x 10(-4) M(-1)cm(-1), only a factor of 4 lower than that of CdS and CdSe nanoparticles of that size. The quantum yield of emission ranges from 0.12 (C(10)H(21)-capping) to 0.23 (C(16)H(33)-capping). UV/Vis absorption and emission spectroscopy show clear vibrational progressions (974 +/- 14 cm(-1); up to five vibrational bands visible at room temperature), resembling bulk SiC phonons, which support the monodispersity observed by TEM. This was also confirmed by time-resolved fluorescence anisotropy measurements, which display a strictly monoexponential decay that can only be indicative of monodisperse, ball-shaped nanoparticles.