Different level of fluorescence in Raman spectra of montmorillonites

The paper presents the study of selected montmorillonite standards by Raman spectroscopy and microscopy supported by elemental analysis, X-ray powder diffraction analysis and thermal analysis. Dispersive Raman spectroscopy with excitation lasers of 532 nm and 780 nm, dispersive Raman microscopy with excitation laser of 532 nm and 100× magnifying lens, and Fourier Transform-Raman spectroscopy with excitation laser of 1064 nm were used for the analysis of four montmorillonites (Kunipia-F, SWy-2, STx-1b and SAz-2). These mineral standards differed mainly in the type of interlayer cation and substitution of octahedral aluminium by magnesium or iron. A comparison of measured Raman spectra of montmorillonite with regard to their level of fluorescence and the presence of characteristic spectral bands was carried out. Almost all measured spectra of montmorillonites were significantly affected by fluorescence and only one sample was influenced by fluorescence slightly or not at all. In the spectra of tested montmorillonites, several characteristic Raman bands were found. The most intensive band at 96 cm⁻¹ belongs to deformation vibrations of interlayer cations. The band at 200 cm⁻¹ corresponds to deformation vibrations of the AlO₆ octahedron and at 710 cm⁻¹ can be assigned to deformation vibrations of the SiO₄ tetrahedron. The band at 3620 cm⁻¹ corresponds to the stretching vibration of structural OH groups in montmorillonites.     

Construction of a universal model for non-invasive identification of penicillins for injection using near-infrared diffuse reflectance spectroscopy

A universal NIR model for identification of 24 types of penicillins for injection has been developed. A total of 194 batches of 24 products from 87 manufacturers in China were used in the study. The classification model is a principal component analysis (PCA) based model consisting of a primary identification library with four sub-libraries. The spectral frequency regions used were 6000–6400 cm⁻¹ and 8400–8900 cm⁻¹ in the main library, 6000–6800 cm⁻¹ in sub-library 1, 4100–12,000 cm⁻¹ in sub-libraries 2 and 3, and 6200–6400 cm⁻¹ and 4700–5000 cm⁻¹ in sub-library 4. The data preprocessing method is the first derivative with nine-point smoothing followed by vector normalization. The distances between spectra were calculated using factors 2–5 for the primary identification library, factors 4–7 for sub-library 1, and factor 2 for sub-libraries 2–4. The specificity of the model was validated, and it had a correct identification rate of approximately 99%. This study has not only confirmed, but also improved the strategy described in our early report (Chong et al. (2009) [11]) to build such a library for the identification of different medicines by NIR.     

A combined laser-induced breakdown and Raman spectroscopy Echelle system for elemental and molecular microanalysis

Raman and laser-induced breakdown spectroscopy is integrated into a single system for molecular and elemental microanalyses. Both analyses are performed on the same ~ 0.002 mm² sample spot allowing the assessment of sample heterogeneity on a micrometric scale through mapping and scanning. The core of the spectrometer system is a novel high resolution dual arm Echelle spectrograph utilized for both techniques. In contrast to scanning Raman spectroscopy systems, the Echelle–Raman spectrograph provides a high resolution spectrum in a broad spectral range of 200–6000 cm^? 1 without moving the dispersive element. The system displays comparable or better sensitivity and spectral resolution in comparison to a state-of-the-art scanning Raman microscope and allows short analysis times for both Raman and laser induced breakdown spectroscopy. The laser-induced breakdown spectroscopy performance of the system is characterized by ppm detection limits, high spectral resolving power (15,000), and broad spectral range (290–945 nm). The capability of the system is demonstrated with the mapping of heterogeneous mineral samples and layer by layer analysis of pigments revealing the advantages of combining the techniques in a single unified set-up.     

Near-infrared spectroscopy as an effective tool for monitoring the conformation of alkylammonium surfactants in montmorillonite interlayers

Application of near-infrared (NIR) spectroscopy to probing the arrangement of trimethylalkylammonium cations in montmorillonite interlayers has been demonstrated. Detailed analysis of the mid-IR (MIR) and NIR spectra of montmorillonite from Jelšový Potok (JP, Slovakia) saturated with surfactants with varying alkyl chain length (even numbers of carbon atoms from C6 to C18) was performed to show the advantages of the NIR region in characterizing surfactant conformations. The position of the ν_as(CH₂), (∼2930–2920 cm⁻¹), ν_s(CH₂) (∼2860–2850 cm⁻¹), 2ν_as(CH₂) (∼5810–5785 cm⁻¹), (ν + δ)_as(CH₂) (∼4340–4330 cm⁻¹) and (ν + δ)_s(CH₂) (∼4270–4250 cm⁻¹) signals was used as an indicator of the gauche/trans conformer ratio. For all bands, a shift toward lower wavenumber on increasing the alkyl chain length from 6 to 18 carbons suggests a transition from disordered liquid-like to more ordered solid-like structures of the surfactants. The magnitude of the shift was significantly higher for 2ν_as(CH₂) (28 cm⁻¹) than for ν_as(CH₂) (8 cm⁻¹) or ν_s(CH₂) (10 cm⁻¹), showing the NIR region to be a useful tool for examining this issue. Comparison of the IR spectra of crystalline alkylammonium salts and the corresponding organo-montmorillonites demonstrated a confining effect of montmorillonite layers on surfactant ordering. For each alkyl chain length the CH₂ bands of the organo-montmorillonites appeared at higher wavenumbers than for the unconfined surfactant, thus indicating a higher disorder of the alkyl chains. The wavenumber difference between corresponding samples was always higher in the NIR than in the MIR region. All these findings show NIR spectroscopy to be useful for conformational studies.     

Vibrational spectroscopic study of syngenite formed during the treatment of liquid manure with sulphuric acid

Syngenite (K₂Ca(SO₄)₂·H₂O), formed during treatment of manure with sulphuric acid, was studied by infrared, near-infrared (NIR) and Raman spectroscopy. C_s site symmetry was determined for the two sulphate groups in syngenite (P2₁/m), so all bands are both infrared and Raman active. The split ν₁ (two Raman+two infrared bands) was observed at 981 and 1000 cm⁻¹. The split ν₂ (four Raman+four infrared bands) was observed in the Raman spectrum at 424, 441, 471 and 491 cm⁻¹. In the infrared spectrum, only one band was observed at 439 cm⁻¹. From the split ν₃ (six Raman+six infrared) bands three 298 K Raman bands were observed at 1117, 1138 and 1166 cm⁻¹. Cooling to 77 K resulted in four bands at 1119, 1136, 1144 and 1167 cm⁻¹. In the infrared spectrum, five bands were observed at 1110, 1125, 1136, 1148 and 1193 cm⁻¹. From the split ν₄ (six infrared+six Raman bands) four bands were observed in the infrared spectrum at 604, 617, 644 and 657 cm⁻¹. The 298 K Raman spectrum showed one band at 641 cm⁻¹, while at 77 K four bands were observed at 607, 621, 634 and 643 cm⁻¹. Crystal water is observed in the infrared spectrum by the OH-liberation mode at 754 cm⁻¹, OH-bending mode at 1631 cm⁻¹, OH-stretching modes at 3248 (symmetric) and 3377 cm⁻¹ (antisymmetric) and a combination band at 3510 cm⁻¹ of the H-bonded OH-mode plus the OH-stretching mode. The near-infrared spectrum gave information about the crystal water resulting in overtone and combination bands of OH-liberation, OH-bending and OH-stretching modes.     

Preparation of monodisperse carbon nanospheres for electrochemical capacitors

The efficiently hydrothermal route using sucrose without any catalysts is employed to prepare the uniform carbon spheres. The monodisperse 100–150 nm carbon spheres are obtained with the activation treatment in molten KOH. The carbon spheres are characterized by transmission electron microscope, X-ray diffraction, N₂ adsorption, Raman spectroscopy and electrochemical techniques. The relationships of specific capacitance and surface properties of carbon spheres are investigated. A single electrode of carbon nanosphere materials performs excellent specific capacitance (328 F g⁻¹), area capacitance (19.2 μF cm⁻²) and volumetric capacitance (383 F cm⁻³).     

The spectroscopic characterization of the sulphate mineral ettringite from Kuruman manganese deposits,South Africa

The mineral ettringite has been studied using a number of techniques, including XRD, SEM with EDX, thermogravimetry and vibrational spectroscopy. The mineral proved to be composed of 53% of ettringite and 47% of thaumasite in a solid solution. Thermogravimetry shows a mass loss of 46.2% up to 1000 °C. Raman spectroscopy identifies multiple sulphate symmetric stretching modes in line with the three sulphate crystallographically different sites. Raman spectroscopy also identifies a band at 1072 cm⁻¹ attributed to a carbonate symmetric stretching mode, confirming the presence of thaumasite. The observation of multiple bands in the ν₄ spectral region between 700 and 550 cm⁻¹ offers evidence for the reduction in symmetry of the sulphate anion from T_d to C_2v or even lower symmetry. The Raman band at 3629 cm⁻¹ is assigned to the OH unit stretching vibration and the broad feature at around 3487 cm⁻¹ to water stretching bands. Vibrational spectroscopy enables an assessment of the molecular structure of natural ettringite to be made.     

Polarized Raman study on the lattice structure of BiFeO3 films prepared by pulsed laser deposition

Polarized Raman spectroscopy was used to study the lattice structure of BiFeO₃ films on different substrates prepared by pulsed laser deposition. Interestingly, the Raman spectra of BiFeO₃ films exhibit distinct polarization dependences. The symmetries of the fundamental Raman modes in 50–700 cm⁻¹ were identified based on group theory. The symmetries of the high order Raman modes in 900–1500 cm⁻¹ of BiFeO₃ are determined for the first time, which can provide strong clarifications to the symmetry of the fundamental peaks in 400–700 cm⁻¹ in return. Moreover, the lattice structures of BiFeO₃ films are identified consequently on the basis of Raman spectroscopy. BiFeO₃ films on SrRuO₃ coated SrTiO₃ (0 0 1) substrate, CaRuO₃ coated SrTiO₃ (0 0 1) substrate and tin-doped indium oxide substrate are found to be in the rhombohedral structure, while BiFeO₃ film on SrRuO₃ coated Nb: SrTiO₃ (0 0 1) substrate is in the monoclinic structure. Our results suggest that polarized Raman spectroscopy would be a feasible tool to study the lattice structure of BiFeO₃ films.     

A Raman spectroscopy study of cerium oxide in a cerium–5 wt.% lanthanum alloy

This paper describes a study of a cerium–5 wt.% lanthanum (Ce–5 wt.% La) alloy using Raman spectroscopy and X-ray diffraction (XRD). Examination of the alloy microstructure by optical microscopy and Raman spectroscopy revealed the presence of inclusions which were identified as cerium oxide (CeO₂). The study also highlighted the need to avoid excessive laser power during acquisition of the Raman spectra as this appeared to cause the oxidation of the region being analysed where previously no cerium oxide peak had been detected. The propensity of cerium to oxidise in air results in the formation of a CeO₂ layer on the surface of the alloy. Raman spectroscopy of the oxide layer formed on the alloy after exposure to air for 21 days found that the Raman peak denoting cerium oxide was seen at between 5 and 7 cm⁻¹ lower than the value for CeO₂ (465 cm⁻¹). This is attributed to a combination of a sub-stoichiometric oxide layer and the presence of La in the alloy.     

Infrared and Raman spectroscopic characterization of the hydrogen-bonding network in l-serine crystal

The IR spectra (4000–400 cm⁻¹) of neat and isotopically substituted (ND/OD ≤ 10% D and ≅30% D) polycrystalline l-serine (α-amino-β-hydroxypropionic acid; HO–CH₂–CH(NH₃)⁺–COO⁻) were recorded in the temperature range 300–10 K and assigned. The isotopic-doping/low-temperature methodology, which allows for decoupling of individual proton vibrational modes from the crystal bulk vibrations, was used for estimating the lengths and energies of the different H-bonds present in l-serine crystal. To this end, the frequency shifts observed in both the NH/OH stretching and out-of-plane bending spectral regions (relatively to reference values for these vibrations in non-hydrogen-bonded l-serine molecules) were used, together with previously developed empirical correlations between these spectral parameters and the H-bond properties. In addition, the room-temperature Raman spectrum (4000–150 cm⁻¹) of a single crystal of neat l-serine was also recorded and interpreted. A systematic comparison was made between the spectroscopic data obtained currently for l-serine and previously for dl-serine, revealing that the vibrational spectra of the two crystals reflect well the different characteristics of their hydrogen-bond networks, and also correlate accurately with the different susceptibility of the two crystals to pressure-induced strain.     

Vibrational spectroscopy of lapachol, α- and β-lapachone: Theoretical and experimental elucidation of the Raman and infrared spectra

Raman and infrared spectroscopy were applied for the vibrational characterization of lapachol and its pyran derivatives, α-lapachone and β-lapachone. Experimental spectra of solid state samples were acquired between 4000 and 100 cm⁻¹ in Raman experiments, and between 4000 and 600 cm⁻¹ (mid-infrared) and 600–100 cm⁻¹ (far-infrared) with FTIR spectroscopy, respectively. Full structure optimization and theoretical vibrational wavenumbers were calculated at the B3LYP/6-31 + + G(d,p) level. Detailed assignments of vibrational modes in an experimental and theoretical spectra were based on potential energy distribution analyses, using Veda 4.1 software. Clear differentiation between the three compounds was verified in the region between 1725 and 1525 cm⁻¹, in which the ν(CO) and ν(CC) modes of the quinone moiety were assigned.     

Vibrational spectroscopic characterization of the phosphate mineral series eosphorite–childrenite–(Mn,Fe)Al(PO4)(OH)2·(H2O)

The phosphate mineral series eosphorite–childrenite–(Mn,Fe)Al(PO₄)(OH)₂·(H₂O) has been studied using a combination of electron probe analysis and vibrational spectroscopy. Eosphorite is the manganese rich mineral with lower iron content in comparison with the childrenite which has higher iron and lower manganese content. The determined formulae of the two studied minerals are: (Mn_0.72,Fe_0.13,Ca_0.01)(Al)_1.04(PO₄, OHPO₃)_1.07(OH_1.89,F_0.02)·0.94(H₂O) for SAA-090 and (Fe_0.49,Mn_0.35,Mg_0.06,Ca_0.04)(Al)_1.03(PO₄, OHPO₃)_1.05(OH)_1.90·0.95(H₂O) for SAA-072. Raman spectroscopy enabled the observation of bands at 970 cm⁻¹ and 1011 cm⁻¹ assigned to monohydrogen phosphate, phosphate and dihydrogen phosphate units. Differences are observed in the area of the peaks between the two eosphorite minerals. Raman bands at 562 cm⁻¹, 595 cm⁻¹, and 608 cm⁻¹ are assigned to the ν₄ bending modes of the PO₄, HPO₄ and H₂PO₄ units; Raman bands at 405 cm⁻¹, 427 cm⁻¹ and 466 cm⁻¹ are attributed to the ν₂ modes of these units. Raman bands of the hydroxyl and water stretching modes are observed. Vibrational spectroscopy enabled details of the molecular structure of the eosphorite mineral series to be determined.     

Vibrational and electronic properties of single-walled and double-walled boron nitride nanotubes

We calculated IR, nonresonance Raman spectra and vertical electronic transitions of the zigzag single-walled and double-walled boron nitride nanotubes ((0,n)-SWBNNTs and (0,n)@(0,2n)-DWBNNTs). In the low frequency range below 600 cm⁻¹, the calculated Raman spectra of the nanotubes showed that RBMs (radial breathing modes) are strongly diameter-dependent, and in addition the RBMs of the DWBNNTs are blue-shifted reference to their corresponding one in the Raman spectra of the isolated (0,n)-SWBNNTs. In the high frequency range above ∼1200 cm⁻¹, two proximate Raman features with symmetries of the A_1g (∼1355 ± 10 cm⁻¹) and E_2g (∼1330 ± 25 cm⁻¹) first increase in frequency then approach a constant value of ∼1365 and ∼1356 cm⁻¹, respectively, with increasing tubes’ diameter, which is in excellent agreement with experimental observations. The calculated IR spectra exhibited IR features in the range of 1200–1550 cm⁻¹ and in mid-frequency region are consistent with experiments. The calculated dipole allowed singlet–singlet and triplet–triplet electronic transitions suggesting a charge transfer process between the outer- and inner-shells of the DWBNNTs as well as, upon irradiation, the possibility of a system that can undergo internal conversion (IC) and intersystem crossing (ISC) processes, besides the photochemical and other photophysical processes.     

Raman spectroscopy of the Pb-Sb sulfosalts minerals: Boulangerite,jamesonite, robinsonite and zinkenite

Raman spectroscopy was used to investigate the lead–antimony sulfosalts minerals: boulangerite (Pb₅Sb₄S₁₁), jamesonite (FePb₄Sb₆S₁₄), robinsonite (Pb₄Sb₆S_l3) and zinkenite (Pb₉Sb₂₂S₄₂). Raman bands of the investigated minerals that have interconnected SbS₃ pyramids are found between 375 and 50 cm⁻¹. The stretching and bending modes of SbS₃ groups occur between 375 and 175 cm⁻¹ in boulangerite, 350 and 180 cm⁻¹ in jamesonite, 350 and 175 cm⁻¹ in robinsonite and zinkenite. The investigated minerals show approximate similarities in their spectral features with those of minerals containing pyramidal SbS₃ groups.     

FTIR investigation of spray-dried milk protein concentrate powders

Fourier transform infrared (FTIR) spectroscopy was used to examine the conformation of proteins in spray-dried milk protein concentrate (MPC) powders and to determine if the spectral changes could be related to nitrogen solubility of these powders. MPC samples (83–92% protein, dry basis) were prepared using a range of processing conditions and stored for 4 weeks at 21 °C. FTIR spectra were collected in the mid infrared (MIR) region between 4000 and 600 cm⁻¹. FTIR data was pre-processed to remove physical effects causing discrimination between samples using firstly second derivatives and normalization and secondly the extended multiplicative scatter correction (EMSC) technique. The FTIR spectral changes were subsequently assessed using second derivative spectroscopy and principal components analysis (PCA) in the amide I and II regions (1700–1400 cm⁻¹) and the fingerprint region (1800–700 cm⁻¹). PCA analysis showed that the different powder preparations could be separated on scores plots but the separation was not related to nitrogen solubility per se. However, changes in nitrogen solubility of individual MPC powders during storage could be correlated to changes in FTIR spectra. PCA analysis of FTIR spectra could generally discriminate between MPC powders that had lost significant nitrogen solubility (9–20%) and those in which nitrogen solubility was preserved on storage. There were changes in intensity and/or position of bands at 1630 cm⁻¹ when the solubility of a stored sample decreased substantially. The results of this work also show that EMSC data pre-processing for these samples gives comparable results when compared with more complicated data pre-processing for the removal of physical effects.     

High pressure Raman spectra of DL-lysine hydrochloride

DL-lysine hydrochloride crystals were studied by Raman spectroscopy under hydrostatic pressure using a diamond anvil cell from ambient pressure up to 9.8 GPa in the spectral range from 1150 to 40 cm⁻¹. Changes in the Raman spectrum were observed in all spectral regions analyzed. In particular, modifications in the lattice modes indicate that the crystal undergoes a phase transition. The classification of the vibrational modes, the behavior of their band wavenumber as a function of the pressure and the reversibility of the phase transitions are also discussed.     

Influence of crystal size on the electron–phonon coupling in ZnO nanocrystals investigated by Raman spectroscopy

We have synthesized ZnO nanocrystals of different sizes (25–41 nm) using the sol–gel method and characterized them using different techniques such as: transmission electron microscopy (TEM) and X-ray diffraction (XRD). Raman spectra of different sizes of ZnO nanocrystals were recorded at two excitation wavelengths, 514 and 647 nm, in the spectral range 300–1200 cm⁻¹. The vibrational modes were assigned on the basis of group theory analysis. The influence of mean crystallite size on the strength of the electron–phonon coupling is experimentally estimated by the variation of relative intensities of second order Raman band and the first order Raman band for ZnO nanocrystals of different sizes. We found that the intensity ratio of the 2E₂ and 1E₂ Raman bands decreases almost linearly for both excitation wavelengths with decreasing crystallite size, which reveals that the Fröhlich interaction plays a dominant role in the electron–phonon coupling of the ZnO nanocrystals.     

NIR-SERS studies of DNA and DNA bases attached on polyvinyl alcohol (PVA) protected silver grass-like nanostructures

In this work, polyvinyl alcohol (PVA) protected silver grass-like nanostructure (PVA–Ag–GNS) with near infrared surface-enhanced Raman scattering (NIR-SERS) activity was prepared and employed to detect DNA and DNA bases. The PVA–Ag–GNS demonstrated high NIR-SERS activity and good optical reproducibility in the detection of adsorbates such as the case of crystal violet, DNA and DNA bases. By using of the tested molecule of thymine, the PVA–Ag–GNS shows a high enhancement factor (EF) of ∼10⁸. For NIR-SERS detection of DNA molecules, Raman signals from the DNA bases of guanine (630 cm⁻¹) and adenine (720 cm⁻¹) are greatly enhanced. For DNA molecules NIR-SERS detection, Raman signals from the DNA bases of guanine (630 cm⁻¹), adenine (720 cm⁻¹) and cytosine (1010 cm⁻¹) are greatly enhanced. The experimental results show that the NIR-SERS spectrum of DNA is dominated by guanine mode, which is followed by adenine and cytosine modes, respectively. Meanwhile, the NIR-SERS signal intensities of the DNA bases increase in the order of thymine (T) < cytosine (C) < adenine (A) < guanine (G). One can conclude that the adsorption strength of the DNA bases in DNA molecule with the silver surface is in the order T < C < A < G, which is different from that of the four DNA bases in individual molecule adsorbed on silver surface (T < A < G < C). On the other hand, the geometry optimization and calculated wavenumber of the complexes of adenine–Ag, guanine–Ag, cytosine–Ag and thymine–Ag for the ground states are performed with DFT, B3LYP functional and the LanL2DZ basis set. The calculated wavenumbers match well with the experimental results. According to our experiment and calculations, DNA base molecules adsorbed on silver surface via the intra-annular nitrogen atom which is adsorbed on the silver nanoparticle and formed metal–molecule complexes by the available lone pair.     

In-plane chemical pressure in (U1−yCey)O2 studied by Raman spectroscopy

We investigate the nature of bonding and charge states in (U_1−yCe_y)O₂ (y = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) by Raman spectroscopy. Raman spectrum of UO₂ exhibits two prominent bands below 1000 cm⁻¹, a F_2g mode at 446 cm⁻¹ and a F_1u LO mode at 578 cm⁻¹. As y is increased from 0 to 0.6, the F_1u exhibits a large blue shift of 90 cm⁻¹, and from y = 0.6 to 1.0, a red shift of 54 cm⁻¹. We show that our results can be interpreted as arising from anisotropic compression/relaxation of the lattice under Ce substitution and this can give an indication of its charge states. Alternate interpretations have been given in the literature on the effect of substituents and dopants to the Raman spectra of UO₂ and CeO₂. The present interpretation of chemical stress effects can be taken as another plausible explanation.     

Application of laser-induced plasma spectroscopy to the measurement of Stark broadening parameters

In this work, we have studied the main conditions that a laser-induced plasma must fulfill in order to be considered as adequate for the measurement of Stark broadening parameters. We investigated the effect of the temporal window, the self-absorption, the crater size, and the effect of the spatial inhomogeneity on the emission profiles coming from a laser-induced plasma. Starting from the spatially resolved values of the plasma parameters, obtained by emission spectroscopy, the error in the determination of the Stark electron width due to the spatial inhomogeneity has been estimated and, for the present experimental conditions, was found to be lower than 7%. As a test of the method, the Stark electron broadening constant of Fe I 381.58 nm has been measured using the Fe I 538.34 nm emission line as the reference to determine the electron density. The plasma was produced under a controlled atmosphere of argon at atmospheric pressure, on an iron–nickel alloy sample. The emission was collected by a system with high spectral resolution, for different temporal windows after the laser pulse. For time delays between 2.75 and 21 μs, the electron density showed an evolution in the range 2.0–0.13 × 10¹⁷ cm^− 3, while the temperature varied from 11 100 to 7100 K. The representation of the Stark electron width of Fe I 381.58 nm, measured for each temporal window, versus the Stark electron width of the reference line showed a linear behavior with a high correlation coefficient. From the slope of this linear fit and the Stark electron broadening constant of the reference line, the Stark width of Fe I 381.58 nm was obtained to be 1.10 ± 0.07 × 10^− 2 nm for an electron density of 10¹⁷ cm^− 3.