Kinetics of NiO reduction and morphological changes in composite anodes of solid oxide fuel cells: Estimate using Raman scattering technique

The kinetics of nickel reduction and morphological changes in Ni–10Sc1CeSZ composite anodes in intermediate-temperature solid oxide fuel cells (SOFC) are studied using the Raman spectroscopy technique with the help of application of optically transparent single crystal solid electrolyte membranes and also the thermogravimetric analysis technique. It is shown that the first reduction cycle differs considerably from all the further ones, which is related to morphological changes of nickel grains occurring during the first reduction cycle. A general scheme of occurrence of the process is suggested in studies of model cells using the Raman spectroscopy technique and also in the case of thermogravimetric analysis of powders; it explains the causes for significant differences between the total duration of the process as measured using different techniques. The results of the work can be used for optimization of the mode of initial reduction of the anodic SOFC electrode.     

Methods for extracting biochemical information from bacterial Raman spectra: focus on a group of structurally similar biomolecules--fatty acids

In this paper we explore the possibilities of Raman spectroscopy in order to deduce information on the fatty acid composition of bacterial cells. Therefore, representative strains of two bacterial taxa were each cultured in different conditions and in parallel analyzed by Raman spectroscopy and gaschromatographic FAME analysis. Raman spectra of pure fatty acids were recorded and used as reference spectra. The culturing conditions for each strain could be easily distinguished by the fatty acid information retrieved from bacterial Raman spectra. Chemometric techniques such as EMSC and PCA allowed to extract information about groups of fatty acids, that was consistent with the results from FAME analysis. Although the information retrieved from Raman spectroscopy is not as refined as that from FAME analysis, the presented methods could be useful to obtain basic information on the fatty acid present in bacteria when performing Raman spectroscopic analysis for fast whole cell profiling, which provides information for different types of cell components (fatty acids, amino acids, primary metabolites, etc.).     

Synthesis and characterization of non-transformable tetragonal YSZ nanopowder by means of Pechini method for thermal barrier coatings (TBCs) applications

A simple soft chemical method of synthesizing tetragonal yttria stabilized zirconia nanopowders is described here. Zirconium oxy-chloride octahydrate and yttrium nitrate hexahydrate were taken as a source of zirconium, citric acid was taken as a chelating agent, and ethylene glycol was used as a polysterification agent. The synthesized powders were characterized by X-ray diffraction, thermogravimetric analysis and differential scanning calorimetry, transmission electron microscopy, field emission scanning electron microscope, Fourier transform infrared spectroscopy and Raman spectroscopy. Furthermore, precise cell parameters were calculated in order to exactly determine non-transformable tetragonal crystal structure, which was the best zirconia phase for thermal barrier coatings applications. In this process, tetragonal yttria stabilized zirconia nanopowders could be prepared at a temperature of 1,000 °C and the process was simple and cost-effective.     

A Raman spectroscopic study of thermally treated glushinskite--the natural magnesium oxalate dihydrate

Raman spectroscopy has been used to study the thermal transformations of natural magnesium oxalate dihydrate known in mineralogy as glushinskite. The data obtained by Raman spectroscopy was supplemented with that of infrared emission spectroscopy. The vibrational spectroscopic data was complimented with high resolution thermogravimetric analysis combined with evolved gas mass spectrometry. TG-MS identified two mass loss steps at 146 and 397 degrees C. In the first mass loss step water is evolved only, in the second step carbon dioxide is evolved. The combination of Raman microscopy and a thermal stage clearly identifies the changes in the molecular structure with thermal treatment. Glushinskite is the dihydrate phase in the temperature range up to the pre-dehydration temperature of 146 degrees C. Above 397 degrees C, magnesium oxide is formed. Infrared emission spectroscopy shows that this mineral decomposes at around 400 degrees C. Changes in the position and intensity of the CO and CC stretching vibrations in the Raman spectra indicate the temperature range at which these phase changes occur.     

3,4,9,10-Perylene Tetracarboxylic Acid Noncovalently Modified Multiwalled Carbon Nanotubes: Synthesis,Characterization, and Application for Electrochemical Determination of 2-Aminonaphthalene

Carbon nanotubes have been intensively studied for their diverse applications but are insoluble in water. In this paper, 3,4,9,10-perylene tetracarboxylic acid noncovalently modified multiwalled carbon nanotubes were prepared by a facile approach and applied successfully for electrochemical determination of 2-aminonaphthalene. Infrared spectroscopy, Raman spectroscopy, thermogravimetric analysis, and electrochemical methods were used to characterize the hybridized nanotubes. The results reveal that the hybrids exhibit high dispersibility in water, and a glassy carbon electrode modified by the hybrids displayed a higher electrochemical response toward 2-aminonaphthalene than bare glassy carbon and multiwalled carbon nanotube–glassy carbon electrodes with a linear dynamic range of 15.0–500.0 nM and a detection limit of 4.5 nM. The modified hybrid electrode was successfully applied for the determination of 2-aminonaphthalene in water.     

Role of graphene in structural transformation of zirconium oxide

Fine powders of zirconium oxide (ZrO₂) were prepared using zirconium oxychloride by combustion method. The crystalline size of pure ZrO₂ was in range of 14–45 nm. Graphene was incorporated in ZrO₂ using graphene oxide as precursor and reducing it with hydrazine hydrate. X-Ray diffraction, Fourier transform infra-red spectroscopy, thermogravimetric analysis and Raman spectroscopy methods were used to characterize the samples. The role of graphene in structural transformation of ZrO₂ to monoclinic phase was clearly observed.     

Determination of glucose and ethanol after enzymatic hydrolysis and fermentation of biomass using Raman spectroscopy

Raman spectroscopy has been used for the quantitative determination of the conversion efficiency at each step in the production of ethanol from biomass. The method requires little sample preparation; therefore, it is suitable for screening large numbers of biomass samples and reaction conditions in a complex sample matrix. Dilute acid or ammonia-pretreated corn stover was used as a model biomass for these studies. Ammonia pretreatment was suitable for subsequent measurements with Raman spectroscopy, but dilute acid-pretreated corn stover generated a large background signal that surpassed the Raman signal. The background signal is attributed to lignin, which remains in the plant tissue after dilute acid pretreatment. A commercial enzyme mixture was used for the enzymatic hydrolysis of corn stover, and glucose levels were measured with a dispersive 785 nm Raman spectrometer. The glucose detection limit in hydrolysis liquor by Raman spectroscopy was 8 g L⁻¹. The mean hydrolysis efficiency for three replicate measurements obtained with Raman spectroscopy (86 ± 4%) was compared to the result obtained using an enzymatic reaction with UV-vis spectrophotometry detection (78 ± 8%). The results indicate good accuracy, as determined using a Student's t-test, and better precision for the Raman spectroscopy measurement relative to the enzymatic detection assay. The detection of glucose in hydrolysis broth by Raman spectroscopy showed no spectral interference, provided the sample was filtered to remove insoluble cellulose prior to analysis. The hydrolysate was further subjected to fermentation to yield ethanol. The detection limit for ethanol in fermentation broth by Raman spectroscopy was found to be 6 g L⁻¹. Comparison of the fermentation efficiencies measured by Raman spectroscopy (80 ± 10%) and gas chromatrography-mass spectrometry (87 ± 9%) were statistically the same. The work demonstrates the utility of Raman spectroscopy for screening the entire conversion process to generate lignocellulosic ethanol.     

Rapid monitoring of antibiotics using Raman and surface enhanced Raman spectroscopy

Comparatively few studies have explored the ability of Raman spectroscopy for the quantitative analysis of microbial secondary metabolites in fermentation broths. In this study we investigated the ability of Raman spectroscopy to differentiate between different penicillins and to quantify the level of penicillin in fermentation broths. However, the Raman signal is rather weak, therefore the Raman signal was enhanced using surface enhanced Raman spectroscopy (SERS) employing silver colloids. It was difficult by eye to differentiate between the five different penicillin molecules studied using Raman and SERS spectra, therefore the spectra were analysed by multivariate cluster analysis. Principal components analysis (PCA) clearly showed that SERS rather than the Raman spectra produced reproducible enough spectra to allow for the recovery of each of the different penicillins into their respective five groups. To highlight this further the first five principal components were used to construct a dendrogram using agglomerative clustering, and this again clearly showed that SERS can be used to identify which penicillin molecule was being analysed, despite their molecular similarities. With respect to the quantification of penicillin G it was shown that Raman spectroscopy could be used to quantify the amount of penicillin present in solution when relatively high levels of penicillin were analysed (>50 mM). By contrast, the SERS spectra showed reduced fluorescence, and improved signal to noise ratios from considerably lower concentrations of the antibiotic. This could prove to be advantageous in industry for monitoring low levels of penicillin in the early stages of antibiotic production. In addition, SERS may have advantages for quantifying low levels of high value, low yield, secondary metabolites in microbial processes.     

Micro-Raman spectroscopy of natural and synthetic indigo samples

In this work indigo samples from three different sources are studied by using Raman spectroscopy: the synthetic pigment and pigments from the woad (Isatis tinctoria) and the indigo plant (Indigofera tinctoria). 21 samples were obtained from 8 suppliers; for each sample 5 Raman spectra were recorded and used for further chemometrical analysis. Principal components analysis (PCA) was performed as data reduction method before applying hierarchical cluster analysis. Linear discriminant analysis (LDA) was implemented as a non-hierarchical supervised pattern recognition method to build a classification model. In order to avoid broad-shaped interferences from the fluorescence background, the influence of 1st and 2nd derivatives on the classification was studied by using cross-validation. Although chemically identical, it is shown that Raman spectroscopy in combination with suitable chemometric methods has the potential to discriminate between synthetic and natural indigo samples.     

An expeditious synthesis of 2,3-dihydroquinozoline-4(1H)-ones using graphene-supported sulfonic acid

Graphene-supported sulfonic acid (Gr@SO₃H) has been prepared by covalent grafting of (3-mercaptopropyl)trimethoxysilane in the matrix of graphene followed by treatment with sulfuric acid and hydrogen peroxide. Gr@SO₃H has been successfully characterized by Fourier transform infrared (FT-IR) spectroscopy, Fourier transform Raman (FT-Raman) spectroscopy, CP-MAS ¹³C NMR spectroscopy, thermogravimetric analysis (TGA), energy dispersive X-ray analysis (EDX), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET) analysis, and X-ray diffractometer (XRD) analysis. Gr@SO₃H served as a robust heterogeneous catalyst for the synthesis of bioactive 2,3-dihydroquinazolin-4(1H)-ones from anthranilamide and aryl aldehydes in ethanol. Recyclability experiments were executed successfully for six consecutive runs.     

Kubas-type hydrogen storage in V(III) polymers using tri- and tetradentate bridging ligands

Oxalic acid, oxamide, glycolic acid, and glycolamide were employed as 2-carbon linkers to synthesize a series of one-dimensional V(III) polymers from trismesityl vanadium(III)·THF containing a high concentration of low-valent metal sites that can be exploited for Kubas binding in hydrogen storage. Synthesized materials were characterized by powder X-ray diffraction (PXRD), nitrogen adsorption (BET), X-ray photoelectron spectroscopy (XPS), infrared spectroscopy (IR), Raman spectroscopy, thermogravimetric analysis, and elemental analysis. Because each of these organic linkers possesses a different number of protons and coordinating atoms, the products in each case were expected to have different stoichiometries with respect to the number of mesityl groups eliminated and also a different geometry about the V(III) centers. For example, the oxalate and glycolate polymers contained residual mesityl groups; however, these could be exchanged with hydride via hydrogenolysis. The highest adsorption capacity was recorded on the product of trismesityl vanadium(III)·THF with oxamide (3.49 wt % at 77 K and 85 bar). As suggested by the high enthalpy of adsorption (17.9 kJ/mol H(2)), a substantial degree of performance of the vanadium metal centers was retained at room temperature (25%), corresponding to a gravimetric adsorption of 0.87 wt % at 85 bar, close to the performance of MOF-177 at this temperature and pressure. This is remarkable given the BET surface area of this material is only 9 m(2)/g. A calculation on the basis of thermogravimetric results provides 0.88 hydrogen molecule per vanadium center under these conditions. Raman studies with H(2) and D(2) showed the first unequivocal evidence for Kubas binding on a framework metal in an extended solid, and IR studies demonstrated H(D) exchange of the vanadium hydride with coordinated D(2). These spectroscopic observations are sufficient to assign the rising trends in isosteric heats of hydrogen adsorption observed previously by our group in several classes of materials containing low-valent transition metals to the Kubas interaction.     

Overview of Popular Techniques of Raman Spectroscopy and Their Potential in the Study of Plant Tissues

Raman spectroscopy is one of the main analytical techniques used in optical metrology. It is a vibration, marker-free technique that provides insight into the structure and composition of tissues and cells at the molecular level. Raman spectroscopy is an outstanding material identification technique. It provides spatial information of vibrations from complex biological samples which renders it a very accurate tool for the analysis of highly complex plant tissues. Raman spectra can be used as a fingerprint tool for a very wide range of compounds. Raman spectroscopy enables all the polymers that build the cell walls of plants to be tracked simultaneously; it facilitates the analysis of both the molecular composition and the molecular structure of cell walls. Due to its high sensitivity to even minute structural changes, this method is used for comparative tests. The introduction of new and improved Raman techniques by scientists as well as the constant technological development of the apparatus has resulted in an increased importance of Raman spectroscopy in the discovery and defining of tissues and the processes taking place in them.     

Preparation of Hydroxypropyl-β-cyclodextrin Cross-linked Multi-walled Carbon Nanotubes and Their Application in Enantioseparation of Clenbuterol

A method of cross‐linking multi‐walled carbon nanotubes by a nucleophilic substitution of brominated multi‐walled carbon nanotubes using hydroxypropyl‐β‐cyclodextrin anions was studied. The modified multi‐walled carbon nanotube samples were characterized using thermogravimetric analysis, energy‐dispersive X‐ray spectroscopy, transmission electron microscopy, scanning electron microscopy, Raman spectroscopy and Fourier transform infrared spectroscopy. The hydroxypropyl‐β‐cyclodextrin modified multi‐walled carbon nanotubes were used as a chiral stationary phase additive for thin‐layer chromatography to separate clenbuterol enantiomers, and the chiral separation factor was increased.     

Effect of acid-treated multi-walled carbon nanotubes on thermo-oxidative stability and degradation behavior of silicone rubber

The effect of acid-treated multi-walled carbon nanotubes (MWCNTs) on thermo-oxidative stability and degradation behavior of silicone rubber (SR) was evaluated. Raman microscopy, Fourier transformed infrared spectroscopy, X-ray photoelectron spectroscopy and thermogravimetric (TG) analysis were performed to characterize the surface states of MWCNTs samples. The results demonstrated that after acid treatment the nanodefects and surface oxygen-containing groups (mainly hydroxyl and carboxyl groups) were formed and the number of them was gradually increased by increasing the treatment time. Then these MWCNTs were embedded into SR matrix. Furthermore, the thermo-oxidative stability and degradation behavior of MWCNTs/SR composites were studied using thermogravimetric/infrared spectrometry (TG-IR). Thermo-oxidative stability test in air revealed that the degradation of SR, at relatively low temperature, was mainly due to the oxidation of Si-CH₃ side groups and the generation of free radicals. This behavior was hindered by the MWCNTs’ surface nanodefects and hydroxyl groups, as proved by TG-IR study which revealed that the amount of carbonyl compounds was reduced more than 60%, compared with that of neat SR. Therefore, acid treatment led a better thermo-oxidative stability of MWCNTs/SR. For 4hAT-MWCNTs/SR, with maximum hydroxyl groups on MWCNTs surface, the T_i (defined as the temperature for 5% mass loss) of it is increased by 34.8 °C compared to that of neat SR, and even increased by 18.5 °C compared with that of raw-MWCNTs/SR.     

Spectroscopic analysis of triflusal impregnated into PMMA from supercritical CO2 solution

The applicability of supercritical carbon dioxide (scCO₂) as a solvent instead of organics has already been demonstrated for the impregnation of biopolymers with pharmaceuticals. This specific process enables the dispersion of a drug in a polymer and leads to further control of drug release. In this work, scCO₂ technology was employed to impregnate triflusal active agent and its hydrolysis metabolite 4-(trifluoromethyl) salicylic acid (HTB) into PMMA bars. Confocal Raman spectroscopy and high-pressure liquid chromatography were the main analysis techniques employed to characterize the degree of dispersion of the drug inside of the polymer. In the Raman analysis, obtained spectra were decomposed with several Gaussians functions. Hence, by using the decomposition of each spectrum it was possible to study the evolution of the concentration of the drug and its metabolite in hundreds of different positions along the radius of the polymer bar. Raman spectroscopy was also used to detect water in the PMMA matrix and to analyze its influence in the formation of the HTB. Finally, spectroscopic analysis showed that scCO₂ impregnation process resulted in triflusal and its metabolite being molecularly dispersed in the polymer matrix. Drug molecules interaction with PMMA chains was detected for the metabolite HTB, but not for triflusal.     

Near-edge X-ray absorption fine structure spectroscopy-assisted purification of single-walled carbon nanotubes

Single-walled carbon nanotubes were produced by the conventional arc discharge method, and purified with a two-step treatment. First, the raw soot containing single-walled carbon nanotubes was burned up at ca. 350 °C in air to remove amorphous carbon, and then it was treated by strong acidic solvents to remove metal catalysts. Near-edge X-ray absorption fine structure spectroscopy was applied to analyze the defects on single-walled carbon nanotubes in whole purification process, so the experimental conditions can be optimized, and finally high-purity single-walled carbon nanotubes were obtained as revealed by various spectroscopic characterizations such as scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, and Raman spectroscopy.     

A Novel Synthesis and Characterization of Titanium Superoxide and its Application in Organic Oxidative Processes

A novel, exceptionally stable titanium superoxide radical ion was prepared and its structure determined by FTIR, ESR, Raman spectroscopy, X-ray diffraction, thermogravimetric/differential thermal analysis and elemental analysis. This heterogeneous catalyst has been found to be effective for the selective oxidation of aromatic amines and phenols to the corresponding nitro aromatics and p-quinones, respectively. In addition, this non-toxic, inexpensive and reusable catalyst has also been used in aminobromination of olefins, which proceed to give the 1, 2-bromoaminated anti-Markovnikov product. A brief account of these results is summarized in this review.     

Allyloxyporphyrin‐Functionalized Multiwalled Carbon Nanotubes: Synthesis by Radical Polymerization and Enhanced Optical‐Limiting Properties

Allyloxyporphyrin‐functionalized multiwalled carbon nanotubes (MWCNT‐TPP) were synthesized by radical polymerization and characterized by FTIR, UV/Vis absorption, and X‐ray photoelectron spectroscopy; elemental analysis; TEM; and thermogravimetric analysis. Z‐scan studies revealed that this nanohybrid exhibits enhanced nonlinear optical (NLO) properties compared to a control sample consisting of a covalently unattached physical blend of MWCNTs and porphyrin, as well as to the separate MWCNTs and porphyrin. At the wavelengths used, the mechanism of enhanced optical limiting likely involves reverse saturable absorption, nonlinear scattering, and photoinduced electron/energy transfer between the MWCNTs and the porphyrin. The role of electron/energy transfer in the NLO performance of MWCNT‐TPP was investigated by Raman and fluorescence spectroscopy.     

Analysis of 2-ethylhexyl-p-methoxycinnamate in sunscreen products by HPLC and Raman spectroscopy

The analyses of 2-ethylhexyl-p-methoxycinnamate (EHMC) using HPLC and Raman spectroscopy have been undertaken and compared. EHMC, which is one of the most widely used sunscreen agents in suncare products in the US, exhibits a strong Raman signal. This signal clearly appears in both ethanol solutions of EHMC as well as in commercial sunscreen lotions containing this sun screen agent. A method for the direct detection and analysis of EHMC has been developed using Raman spectroscopy. This was accomplished by correlating the Raman intensities with the HPLC assays for a series of prototype suncare formulations. Based upon this information, it would be possible to employ Raman spectroscopy as an in-process control method in the commercial production of suncare products containing EHMC. The possibility of applying surface-enhanced Raman scattering for trace analysis was discussed.     

Monitoring thermal,structural properties,methotrexate release and biological activity from biocompatible spray-dried microparticles

Boron phosphates (BPs) with different acidities were prepared by regulating the calcination temperatures for the reaction products of boric acid and phosphoric acid. The crystal structure, morphology, surface acidity, and thermal stability were characterized by X-ray diffraction, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), chemical absorbed apparatus, and thermogravimetric analysis (TG). The effects of BPs on the combustion behavior and catalyzing the carbonization of bisphenol-A epoxy resin (EP) were investigated by the limiting oxygen index (LOI) and cone calorimetry test. Upon loading 5 mass% BP prepared at 300 °C, the LOI value of the EP/BP composites increased to 29.6%, and moreover, the peak heat release rate and average specific extinction area decreased by 43 and 25%, respectively. A possible catalyzing carbonization mechanism was explored by TG coupled with Fourier transform infrared spectroscopy (TG–FTIR), TG, FTIR, SEM, Raman spectroscopy (Raman), and XPS. The results demonstrated that BP catalyzed EP to degrade at relatively low temperature, and the yield, compactness, and graphitization degree of the char residue were obviously enhanced with an increase in the ratio of Brønsted and Lewis acid sites (B/L value) and the total surface acid sites on the BP surface. Therefore, the catalyzing carbonization flame retardancy of the EP/BP composites can be improved through regulating the surface acidity of BP.