thermo-Raman Spectroscopy Research Articles

Frankamenite: Relationship between the Crystal–Chemical and Vibrational Properties

The study provides novel insights into the crystal–chemical and optical characteristics of frankamenite. Frankamenite belongs to a special group (canasite group) of the complex alkaline Ca-(K)-(Na) silicates, and it was found in charoitites from the only known location, Murun Massif, Eastern Siberia, Russia. The crystal–chemical, vibrational, and optical properties of frankamenite were investigated by combining electron probe microanalysis (EPMA), single-crystal X-ray diffraction (SCXRD), infrared (IR) absorption, Raman, UV-Visible absorption, and electron spin resonance (ESR) spectroscopy. The behavior of the peaks in the IR spectra was also studied using ab initio calculations. Detailed characteristics of the internal composition and structure of the mineral species were described, and vibrational and optical properties based on these peculiarities were interpreted. The thermally stimulated reorientation of the H2O molecules and OH− groups was studied by thermo-Raman spectroscopy. Octahedral cationic positions can be readily doped with transition metal and lanthanide ions that provide a promising opportunity to adjust the Ce3+ luminescence. Hence, frankamenite is a potential material for ion exchange, novel phosphors, and luminophores.

Optimisation and characterisation of bio-adsorbent based on barley straw and coconut shell

Cost efficiency and environmental friendliness of biomass-derived adsorbents for wastewater treatment are explored. Preparation of bio-adsorbents that are economically and environmentally sustainable has achieved an enormous interest in water treatment. A single-step method for preparing a high-capacity adsorbent is shown in this study by refluxing barley straw (BS) and coconut shell (CS) in concentrated sulfuric acid. Using response surface methodology predicts the optimum parameters for production of the bio-adsorbent based on the yield and the adsorption capacity for methylene blue dye. Optimal conditions for the sulfuric acid refluxing stage were obtained at 94% sulfuric acid, 10 liquid/solid (L/S) ratio for 2 h and 98% sulfuric acid, 4 L/S ratio for 2.5 h for BS and CS, respectively. The produced bio-adsorbent was characterised by scanning electron microscopy coupled with energy dispersive X-ray scattering, X-ray diffraction, Fourier transform infrared spectroscopy, thermo gravimetric analysis, Raman spectroscopy, and Brunauer–Emmett–Teller specific surface area, analysis. The detailed analysis showed that the bio-adsorbent produced from BS and CS has good adsorptive properties – thermal stability and high specific surface area, which are 11.759 and 1.165 m2/g, respectively. The results indicate that BS and CS are critical and potential low-cost raw materials for the production of bio-adsorbents.

Controlling the carbon nanotube type with processing parameters synthesized by floating catalyst chemical vapour deposition

Abstract Single and multi-walled carbon nanotubes have been synthesized by floating catalyst chemical vapour deposition technique. Methane, argon, ferrocene and sulphur were used as carbon source, inert gas, catalyst and promoter, respectively. The types of carbon nanotubes (single or multi-walled) were governed by a variety of experimental factors: the ferrocene flow rate, methane flow rate, sulfur flow rate, argon flow rate and reaction temperature. The optimization of the process parameters was carried out to find the parameter 'islands' for the selective formation of single or multiwalled carbon nanotubes. The characterization was carried out by transmission electron microscopy, thermo gravimetric analysis and Raman spectroscopy. A high hydrogen flow rate, low methane flow rate and high sulfur flow rate were crucial factors for selective synthesis of single walled carbon nanotubes. This work provides methodology for optimization of processing parameters for synthesizing high purity single or multi walled carbon nanotubes

Alkali incorporation into Cu(In,Ga)Se2 determined by crystal orientation of Mo back contact: Implications for highly efficient photovoltaic devices

The structural, optical, and electrical properties of molybdenum (Mo) layers play a major role in Cu(In,Ga)Se2 (CIGS) solar cell performance. The Mo layer works as a transport gate for diffusion of alkali ion from the soda-lime glass substrate to the back contact in CIGS solar cells. In the present work, Mo back contacts are controlled to exhibit two different orientations: (110)-oriented and randomly oriented. The influence of these orientations on CIGS absorbers and resulting solar cells is investigated. In situ thermo-Raman spectroscopy and secondary ion mass spectrometry results indicate that the greater amount of alkali ions are found in the CIGS absorber with randomly oriented Mo back contact than in the (110)-orientated Mo back contact. The resulting different Na incorporations significantly affect the performance of the resulting devices. Devices with the randomly oriented Mo back contact exhibit superior device performances to the devices with (110)-oriented Mo back contact. With comprehensive device characterizations, an alkali ion release determined by the orientation of the Mo back contact affects the recombination mechanism in the CIGS bulk and the back contact properties at the CIGS/Mo interface.

Vibrational spectroscopic study of the natural layered double hydroxide manasseite now defined as hydrotalcite-2H – Mg6Al2(OH)16[CO3]⋅4H2O

Raman and thermo-Raman spectroscopy have been applied to study the mineral formerly known as manasseite now simply renamed as hydrotalcite-2H Mg6Al2(OH)16[CO3]⋅4H2O. The mineral is a member of the homonymous hydrotalcite supergroup. Hydrogen bond distances calculated using a Libowitzky-type empirical function varied between 2.61 and 3.00Å. Stronger hydrogen bonds were formed by water units as compared to the hydroxyl units. Raman spectroscopy enabled the identification of bands attributed to the hydroxyl units. Two Raman bands at 1059 and 1064cm−1 are assigned to symmetric stretching modes of the carbonate anion. Thermal treatment shifts these bands to higher wavenumbers indicating a change in the strength of the carbonate bonding.

Temperature‐dependent Raman spectroscopy of BaTiO3 nanorods synthesized by using a template‐assisted sol–gel procedure

In the present work, multiphase polycrystalline BTO nanorods were synthesized using template‐assisted sol–gel deposition and their structural evolution was studied using thermo Raman spectroscopy, X‐ray diffractometry and high‐resolution transmission electron microscopy (HRTEM). In the BTO nanorods, the tetragonal phase was the dominant one, while both Raman and HRTEM indicated a coexistence with the high‐temperature hexagonal polymorph. This phase was stable across the whole of the investigated temperature range (from −95 °C to 200 °C). The investigated nanorods underwent a diffuse phase transition from tetragonal to cubic with respect to the temperature, whereas the final phase‐transition temperature was shifted to higher values compared to that expected for BTO. The low‐temperature orthorhombic‐to‐rhombohedral phase transition was also shifted to higher temperatures. These differences could be explained by the strain induced by the presence of hexagonal nanolamellas intergrown within the tetragonal nanocrystals. This result indicates that the temperature of the ferroelectric phase transition in polycrystalline BTO nanorods can be manipulated by introducing a stable hexagonal phase. Copyright © 2012 John Wiley & Sons, Ltd.

Role of the residual Na + ions on the dispersion of WO x species on titania nanotubes by in situ thermo-Raman study

Titania nanotubes synthesized by alkali hydrothermal method were used to support 5–20 wt.% of WO x by wet impregnation method. Samples were characterized by in situ thermo-Raman spectroscopy, electronic microscopy and X-ray diffraction. Initially and below 400 °C, WO x species have octahedral coordination as isolated species. After annealing at 500 °C, the nanotubular support collapsed and transformed into anatase. This event released Na + ions that reacted with surface WO x species converting into sub-nanometric sodium tungstate (Na 2WO 4) particles, homogeneously dispersed on the support. At higher temperature, that is at 700 °C and 800 °C, Na 2WO 4 nanoparticles were detected on samples with W content ≤10 wt.%, whereas a mixture of Na 2WO 4 and Na 2W 2 O 7 was obtained on samples with W content above 15 wt.%. A very thin layer of sodium tungstate covered the titania (anatase or rutile, depending on W loading) support after annealing at 800 °C yielding core–shell particles, with titania phase in the core and Na 2WO 4 and/or Na 2W 2O 7 on the shell.

Thermo-Raman spectroscopy in situ monitoring study of solid-state synthesis of NiO–Al 2O 3 nanoparticles and its characterization

Hyphenation of thermogravimetric analyzer (TGA) and thermo-Raman spectrophotometer for in situ monitoring of solid-state reaction in oxygen atmosphere forming NiO–Al 2O 3 catalyst nanoparticles is investigated. In situ thermo-Raman spectra in the range from 200 to 1400 cm −1 were recorded at every degree interval from 25 to 800 °C. Thermo-Raman spectroscopic studies reveal that, although the onset of formation is around 600 °C, the bulk NiAl 2O 4 forms at temperatures above 800 °C. The X-ray diffraction (XRD) spectra and the scanning electron microscopy (SEM) images of the reaction mixtures were recorded at regular temperature intervals of 100 °C, in the temperature range from 400 to 1000 °C, which could provide information on structural and morphological evolution of NiO–Al 2O 3. Slow controlled heating of the sample enabled better control over morphology and particle size distribution (∼20–30 nm diameter). The observed results were supported by complementary characterizations using TGA, XRD, SEM, transmission electron microscopy, and energy dispersive X-ray analysis.

Use of thermo‐Raman spectroscopy and chemometric analysis to identify dehydration steps of hydrated inorganic samples—application to copper sulfate pentahydrate

AbstractIn situ thermo‐Raman spectroscopy (TRS) measurements were performed in order to investigate solid‐phase transformation of the copper sulfate pentahydrate from room temperature up to 300 °C. Band‐target entropy minimization (BTEM), a blind‐source separation algorithm, was employed in order to identify and reconstruct the pure component spectra of the species involved in the dehydration process. In spite of low signal‐to‐noise ratio and elevated baseline spectral data, BTEM was successfully utilized to identify and reconstruct four pure component spectra of copper sulfate pentahydrate, trihydrate, monohydrate, and anhydrate, which were formed during this thermally induced process. Subsequent mapping of these four pure component spectral estimates back onto the preprocessed spectra yielded the relative concentrations of each individual species. Finally, the transition temperatures of each dehydration step could be unambiguously deduced from the obtained concentration profile. The current study shows that combined thermo‐Raman spectroscopy and chemometric analysis provides an effective tool to determine the dehydration temperatures as well as to identify the structures of each individual species involved in a solid‐phase dehydration process. Copyright © 2009 John Wiley & Sons, Ltd.

In situ monitoring of NiO–Al 2O 3 nanoparticles synthesis by thermo-Raman spectroscopy

Simultaneous thermogravimetric analysis and thermo-Raman spectroscopy (TRS) measurements for in situ monitoring of wet chemical reaction of Ni(OH) 2·4H 2O and Al(OH) 3 forming NiO–Al 2O 3 nanoparticles is studied and compared with the solid-state reaction. Herein, a different approach of synthesis and monitoring of NiO–Al 2O 3 by TRS is presented, in which, in situ thermo-Raman spectra are recorded at every degree interval from 25 to 800 °C to understand the structural and compositional changes in NiO–Al 2O 3 as a function of temperature. Slow controlled heating of the sample as in TRS, enables better control over morphology and particle size distribution (∼10–20 nm diameter). The X-ray diffraction (XRD) shows that smaller particle size is obtained using wet chemical reaction than the solid-state reaction (∼25 nm diameter). TRS studies also reveal that, the bulk NiAl 2O 4 forms at temperatures above 800 °C, although, the onset of formation is around 600 °C. Condensation of Al(OH) 3 forming Al 2O 3 is also monitored, wherein, presence of hydrocarbon is found to contribute to the observed fluorescence background. Based on the TRS and complementary characterizations using XRD, scanning electron microscopy, transmission electron microscopy, and energy-dispersive X-ray analysis, the formation of supported NiO–Al 2O 3 is discussed.

Evolution of titania nanotubes-supported WO x species by in situ thermo-Raman spectroscopy, X-ray diffraction and high resolution transmission electron microscopy

Structural evolution of WO x species on the surface of titania nanotubes was followed by in situ thermo-Raman spectroscopy. A total of 15 wt% of W atoms were loaded on the surface of a hydroxylated titania nanotubes by impregnation with ammonium metatungstate solution and then, the sample was thermally treated in a Linkam cell at different temperatures in nitrogen flow. The band characteristic of the W O bond was observed at 962 cm −1 in the dried sample, which vanished between 300 and 700 °C, and reappear again after annealing at 800 °C, along with a broad band centered at 935 cm −1, attributed to the v 1 vibration of W O in tetrahedral coordination. At 900 and 1000 °C, the broad band decomposed into four bands at 923, 934, 940 and 950 cm −1, corresponding to the symmetric and asymmetric vibration of W O bonds in Na 2WO 4 and Na 2W 2O 7 phases as determined by X-ray diffraction and High resolution transmission electron microscopy (HRTEM). The structure of the nanotubular support was kept at temperatures below 450 °C, thereafter, it transformed into anatase being stabilized at temperatures as high as 900 °C. At 1000 °C, anatase phase partially converted into rutile. After annealing at 1000 °C, a core–shell model material was obtained, with a shell of ca. 5 nm thickness, composed of sodium tungstate nanoclusters, and a core composed mainly of rutile TiO 2 phase.

Narrow Diameter Carbon Nanotubes (CNTs) for Polymer Composite Reinforcement

Strong and versatile carbon nanotubes are finding new applications in improving conventional polymer-based fibers. Nanotube-reinforced composites could ultimately provide the foundation for a new class of strong and lightweight fibers with properties such as electrical and thermal conductivity unavailable in current fibers. A recent research has discovered that the best type of nanotube for polymer composite reinforcement is the small diameter multiwalled nanotubes (MWNTs). Here, a catalytic technique has been developed to produce narrow diameter bulk multiwalled carbon nanotubes of less than 38 nm. Structural characterizations including scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), thermo gravimetric analysis (TGA) and Raman spectroscopy conducted on CNTs grown on three different catalysts, namely iron, cobalt and nickel have indicated that the catalyst used affects their sizes and crystallinity. Results showed that the smallest CNTs could be obtained by catalytic growth on Ni catalyst. The study has proven that with the skillful use of catalyst, a range of narrow sized nanotubes could be produced, providing the material needed to investigate the optimum diameter for the best mechanical reinforcement of polymer composites.

Thermo-Raman spectroscopic study of the natural layered double hydroxide manasseite

Raman and thermo-Raman spectroscopy have been applied to study the natural hydrotalcite manasseite Mg6Al2(OH)16(CO3)·4H2O. Hydrogen bond distances calculated using a Libowitzky-type empirical function varied between 2.61 and 3.00Å. Stronger hydrogen bonds were formed by water units as compared to the hydroxyl units. Thermo-Raman spectroscopy enabled the identification of bands attributed to the hydroxyl units. Two Raman bands at 1062 and 1058cm−1 are assigned to symmetric stretching modes of the carbonate anion. Thermal treatment shifts these bands to higher wavenumbers indicating a change in the carbonate bonding.

Molecular structure of segnitite: A Raman spectroscopic study

ThermoRaman spectroscopy has been used to study the mineral segnitite PbFe 3(AsO 4) 2(OH) 6, a member of the jarosite mineral group. The hot stage Raman spectroscopic technique identifies the temperatures for the dehydration and dehydroxylation as 200 and 400 °C. No changes are observed in the spectra attributed to the arsenate unit until after dehydroxylation. The results of Raman spectroscopy are in agreement with the results of thermogravimetric analyses coupled to evolved gas mass spectrometry. The Raman spectrum of segnitite is characterised by an intense band at 860 cm −1 and bands at 848 and 811 cm −1 attributed to the arsenate ν 1 and ν 3 modes. Bands observed at 998 and 931 cm −1 are assigned to ν 1 symmetric stretching vibration of the sulphate and phosphate units. Thermal treatment causes the ν 1 band to shift to 850 cm −1 at 400 °C. Hydroxyl stretching bands are observed at 3216, 2982, 3467 and 3440 cm −1. These bands are attributed to OH units each coordinating the Fe 3+ in octahedral FeO 2(OH) 4 building blocks. The ν 2 and ν 4 modes are split for segnitite indicating a lowering of the symmetry of the (AsO 4) 3− unit.

ThermoRaman spectroscopic study of kintoreite

ThermoRaman spectroscopy has been used to study the molecular structure and thermal decomposition of kintoreite, a phosphated jarosite PbFe 3(PO 4) 2(OH,H 2O) 6. Infrared spectroscopy shows the presence of significant amounts of water in the structure as well as hydroxyl units. In contrast, no water was observed for segnitite (the arsenojarosite) as determined by infrared spectroscopy. The Raman spectra at 77 K exhibit bands at 974.6, 1003.2 and 866.5 cm −1. These bands are attributed to the symmetric stretching vibrations of (PO 4) 3−, (SO 4) 3− and (AsO 4) 3− units. Raman spectroscopy confirms the presence of both arsenate and phosphate in the structure. Bands at 583.7 and 558.1 cm −1 in the 77 K spectrum are assigned to the ν 4 (PO 4) 3− bending modes. ThermoRaman spectroscopy of kintoreite identifies the temperature range of dehydration and dehydroxylation.

Synthesis and Monitoring of α‐Bi2Mo3O12 Catalyst Formation Using Thermo‐Raman Spectroscopy.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Investigations on temperature dependent structural evolution of NaPO3glass

The understanding of molecular level structural information of phosphate glasses is very much essential. The unique microwave-absorbing ability of NaH2PO4·2H2O was found to be very useful for preparing crystal and glassy sodium super ionic conductors (Nasicon's) as a component of batch mixtures. In this work NaPO3 glass was prepared by both conventional melt quench and microwave heating from NaH2PO4·2H2O as a starting material. The structure of NaPO3 glass and their structural evolution upon heating through glass transition were probed by combination of complementary techniques like differential scanning calorimetry (DSC), powder X-ray diffraction (PXRD), Fourier transform infrared (FT-IR) and thermo-Raman spectroscopy.

Phase transformation studies of Na 3PO 4 by thermo-Raman and conductivity measurements

In this work, phase transformations of anhydrous Na 3PO 4 prepared by two methods have been studied by thermo-Raman spectroscopy (TRS). For dehydrated Na 3PO 4, four characteristic spectra were found corresponding to four phases and the transformation temperatures were 229, 262 and 356 °C, respectively. Differential scanning calorimeter (DSC) showed endotherms at around 228, 247 and 358 °C, whereas differential thermal analyzer (DTA) showed them at around 274, 339 and 438 °C, respectively. Probably, these phase transformations observed during heating process might be unreported and are tentatively assigned as phases IV, III, II and I, respectively. During cooling of the same sample, only one phase transformation was detected in the temperature range from 342 to 320 °C from phase I to phase II. For Na 3PO 4 preheated to 600 °C, only one phase transformation was observed at 339 °C by thermo-Raman spectroscopy during heating process. This should be the phase transformation from α phase (tetragonal) to γ phase (cubic). Reversed transformation from γ to α phase during cooling of the same sample was observed at 313 °C. The band width for the band at 934 cm −1 also showed that the phase transformation was of order–disorder type. DSC and DTA for preheated Na 3PO 4 during heating showed an endotherm at 320 and 316 °C, respectively. The conductivity study supported the phase transformation to be in the range from 316 to 360 °C and was clearly evident from the increase in conductivity during the phase transformation. Further coupling of LCR meter to thermo-Raman spectrometer ensured the transformation and the temperature range measured by both conductivity and thermo-Raman spectroscopy simultaneously and its nature to be of order–disorder type.

Monitoring dehydration and condensation processes of Na 2HPO 4 · 12H 2O using thermo-Raman spectroscopy

Thermal dehydration and condensation processes of disodium hydrogen phosphate dodecahydrate (Na 2HPO 4 · 12H 2O) were monitored by thermo-Raman spectroscopy (TRS). Various hydrated forms Na 2HPO 4 · 12H 2O, Na 2HPO 4 · 8H 2O, Na 2HPO 4 · 7H 2O, Na 2HPO 4 · 2H 2O, Na 2HPO 4 · H 2O and Na 2HPO 4 were observed, followed by condensation of Na 2HPO 4 to sodium pyrophosphate (Na 4P 2O 7) in a dynamic thermal process. Representative Raman spectra of all the hydrated forms Na 2HPO 4 · 12H 2O, Na 2HPO 4 · 8H 2O, Na 2HPO 4 · 7H 2O, Na 2HPO 4 · 2H 2O, Na 2HPO 4 · H 2O and Na 2HPO 4 were detected in both H 2O and PO 4 3− regions are reported. The thermo-Raman intensity (TRI) thermogram also showed systematic loss of water in five steps of dehydration, with the differential TRI thermogram in agreement shows five dips corresponding to the five steps of dehydration, respectively. Thermogravimetry (TG) and differential thermogravimetry (DTG) are in harmony with the results of TRS, though, the two could not resolve the steps involved.

Phase transformation studies of ceramic BaTiO3 using thermo-Raman and dielectric constant measurements

Ferroelectric phase transformation characteristics of ceramic BaTiO3 have been studied by combined thermo-Raman and dielectric measurements. The temperature dependence of Raman bands at 311 and 721 cm−1 shows that tetragonal to cubic (T–C) phase transformation occurs over a range of temperature. The increase in the bandwidths of these bands indicates that this transformation is an order-disorder transformation. The differential thermo-Raman intensity thermograms show a dip at a temperature corresponding to the maximum rate of phase transformation and this temperature can be defined as phase transformation temperature Tp. The ferroelectric transformation temperature Tm corresponding to the peak in the ε(T) obtained from the temperature dependence of dielectric constant is found to coincide with Tp. This indicates that maximum in dielectric constant occurs at the maximum rate of T–C phase transformation. Both Tp and Tm exhibit thermal hysteresis. The Curie temperature TC obtained from the intersection of tangential of inverse dielectric constant to the temperature axis and is found to be less than Tm and Tp in agreement with O. G. Vendik and S. P. Zubko [J. Appl. Phys. 88, 5343 (2000)] calculations. Thermo-Raman spectroscopy coupled with dielectric constant measurement is shown to be an effective technique to investigate the phase transformation in ferroelectric materials.