High-temperature thermal and X-ray diffraction studies,and room-temperature spectroscopic investigation of some inorganic pigments

Inorganic Cr- and Mn-containing pigments of different structural types were investigated by high-temperature and spectroscopic methods. The differential scanning calorimetry in the temperature interval 298–1723 K was applied to measure temperatures of phase transition and melting of the studied compounds. High-temperature X-ray diffraction in the range 298–1173 K was used for the determination of the thermal expansion coefficients for the first time. Factor group analysis was used to predict general vibration modes of pigments and determine the activity of these vibrations in Raman and IR spectra, the Assignment of bands in Raman, IR and diffuse reflectance spectra was undertaken.     

Synthesis of graphene-like nanosheets and their hydrogen adsorption capacity

Graphene-like nanosheets have been synthesized by the reduction of a colloidal suspension of exfoliated graphite oxide. The morphology and structure of the graphene powder sample was studied using scanning electron microscopy, transmission electron microscopy, X-ray diffraction and Raman spectroscopy. The graphene sheets are found to be in a highly agglomerated state, with many wrinkles. The sample has a BET surface area of 640 m²/g as measured by nitrogen adsorption at 77 K. Hydrogen adsorption-desorption isotherms were measured in the temperature range 77-298 K and at pressures of up to 10 bar. This gives hydrogen adsorption capacities of about 1.2 wt.% and 0.1 wt.% at 77 K and 298 K, respectively. The isosteric heat of adsorption is in the range of 5.9-4 kJ/mol, indicating a favourable interaction between hydrogen and surface of the graphene sheets. The estimated room temperature H₂ uptake capacity of 0.72 wt.% at 100 bar and the isosteric heat of adsorption of our sample are comparable to those of high surface area activated carbons, however significantly better than the recently reported values for graphene and a range of other carbon and nanoporous materials; single and multi walled carbon nanotubes, nanofibers, graphites and zeolites.     

Raman study of the temperature-induced decomposition of the two-dimensional rhombohedral polymer of C60 and the intermediate states formed

Raman spectra of single crystalline two-dimensional rhombohedral (2D-R) polymer of C₆₀ were measured at ambient conditions after its high temperature treatment (HTT) in order to study the polymer decomposition process. The data obtained indicate that the 2D-R polymer remains stable after 0.5 h treatment up to ∼503 K, while at higher temperatures a material transformation takes place. New Raman lines appear in the Raman spectrum after HTT in the range of 513-553 K, related to the A_g(2) pentagon pinch (PP) mode of 2D tetragonal-like (2D-T-like) and 1D orthorhombic-like (1D-O-like) oligomers as well as to C₆₀ dimers and monomers, typical for an intermediate state of partially decomposed 2D-R polymer. Above 553 K, the material changes completely and its new composition is dominated by C₆₀ monomers with some possible inclusion of C₆₀ dimers. The activation energy of the 2D-R polymer decomposition, obtained from the dependence of the decomposition time on the treatment temperature, is E_A = 1.76 ± 0.07 eV/molecule.     

Experimental measurements and computer simulation of methane adsorption on activated carbon fibers

Three activated carbon fibers (ACFs) with different BET specific surface areas (SSAs) were prepared. Experimental characterization and methane adsorption on the ACFs were measured by the intelligent gravimetric analyzer (IGA-003, Hiden) at 258 and 298 K. Correlations proposed between the methane adsorption capacity and SSA indicate that the SSA plays an important role on storage amount at a given temperature. A detailed experimental investigation was focused on the sample ACF3 of the highest SSF of 1511 m²/g at five temperatures, from 258 to 298 K. The temperature dependence for methane adsorption amount on ACF3 at 1.8 MPa is proposed. It shows that temperature is vital to methane storage capacity for ACF3, and adsorption storage at the temperatures below 280 K is recommended for favorite uptakes. To model ACF3, the pores are described as slit-shaped with a pore size distribution that was determined by molecular simulation and the statistics integral equation. Predictions of methane adsorption, carried out at 258 and 298 K and high pressures by molecular simulation, indicate that our sample ACF3 can reach the uptake of 14.99 wt% at 4.0 MPa and 298 K, which is comparable with the best result in the literature.     

Formation and stability of β-structure in biodegradable ultra-high-molecular-weight poly(3-hydroxybutyrate) by infrared, Raman, and quantum chemical calculation studies

Infrared (IR) and Raman spectra were measured for four kinds of ultra-high-molecular-weight poly[(R)-3-hydroxybutyrate] (UHMW-PHB) films: a solvent-cast film, a cold-drawn film, a two-step-drawn film, and a hot-drawn film. Quantum chemical calculations were made for octamer models of UHMW-PHB with a helix conformation (α-form) and a planar zigzag conformation (β-form). Comparison of the results between the Raman spectra of four kinds of films and the quantum chemical calculations of octamer models revealed that only two-step-drawn film yields additional bands at 1735, 966, 935, 908, and 858 cm⁻¹ assignable to the β-structure, suggesting that it contains the β-form as well as the α-form. Detailed comparison of the frequencies and intensities of Raman bands between the observed and calculated values for the β-form indicates that the amount of β-form is relatively small and that the β-structure has a less ordered structure. The infrared and Raman spectra of two-step-drawn film also indicate that it has more amorphous parts than other films. When the two-step-drawn film was further heated up to 130 °C and then cooled down to room temperature, the above additional bands due to the β-form disappeared in the Raman spectra, suggesting that the β-form is less stable than α-form.     

Online monitoring of synthesis and curing of phenol-formaldehyde resol resins by Raman spectroscopy

The synthesis and curing of phenol-formaldehyde resol resins were monitored online by Raman spectroscopy. The synthesis of the resins (F/P 2.0, alkalinity 4.5 wt%) was studied at rising temperature (40-90 °C) for 90 min and at constant temperatures (80 °C, 90 °C, 100 °C, and 110 °C) for 120 min. The progress of the curing was investigated isothermally (80 °C, 90 °C, 100 °C, and 110 °C) for 120 min for three resins with different degrees of condensation. The synthesis and curing of the resins were started in the reactor and the advancement of the methylolation and condensation reactions was followed through the window of the reactor in the wave number region of 2000-400 cm⁻¹ with use of a fiber optic probe for the data collection. The Raman spectra of six model compounds (formaldehyde, phenol, 2-hydroxybenzyl alcohol, 4-hydroxybenzyl alcohol, 2-benzylphenol, and 4-benzylphenol) were analyzed to facilitate the interpretation of the spectra of the resins. The consumptions of free phenol and free formaldehyde, as well as the progress of the methylolation and condensation reactions were easily monitored by following the changes in intensity of the characteristic Raman bands. The results for the cured resins obtained by Raman spectroscopy were in good agreement with the structures and residual reactivities studied by CP/MAS ¹³C NMR spectroscopy and differential scanning calorimetry (DSC), respectively. The results of the study show Raman spectroscopy to be a promising tool for the online monitoring and control of phenol-formaldehyde resol resin synthesis and curing; in addition, Raman spectroscopy offers an effective and fast method for structural study of the solid state resins.     

Infra-red and Raman spectroscopic study on the thermal stability and high temperature transformation of hydroazafullerene C59HN

Hydroazafullerene C₅₉HN was studied by vibrational infra-red and Raman spectroscopy and its thermal stability was examined. Fingerprints modes were identified and unambiguously differentiate it from bisazafullerene. At 700 K full transformation to bisazafullerene occurred, while an intermediate metastable phase was identified at 540 K showing different spectra where the splitting of most of the lines is strongly reduced.     

Hydrogen storage on chemically activated carbons and carbon nanomaterials at high pressures

Hydrogen adsorption measurements have been carried out at different temperatures (298 K and 77 K) and high pressure on a series of chemically activated carbons with a wide range of porosities and also on other types of carbon materials, such as activated carbon fibers, carbon nanotubes and carbon nanofibers. This paper provides a useful interpretation of hydrogen adsorption data according to the porosity of the materials and to the adsorption conditions, using the fundamentals of adsorption. At 298 K, the hydrogen adsorption capacity depends on both the micropore volume and the micropore size distribution. Values of hydrogen adsorption capacities at 298 K of 1.2 wt.% and 2.7 wt.% have been obtained at 20 MPa and 50 MPa, respectively, for a chemically activated carbon. At 77 K, hydrogen adsorption depends on the surface area and the total micropore volume of the activated carbon. Hydrogen adsorption capacity of 5.6 wt.% at 4 MPa and 77 K have been reached by a chemically activated carbon. The total hydrogen storage on the best activated carbon at 298 K is 16.7 g H₂/l and 37.2 g H₂/l at 20 MPa and 50 MPa, respectively (which correspond to 3.2 wt.% and 6.8 wt.%, excluding the tank weight) and 38.8 g H₂/l at 77 K and 4 MPa (8 wt.% excluding the tank weight).     

Spectroscopic investigation of proton-conducting, cross-linked linear poly(ethylenimine) hydrochloride membranes

The degree of cross-linking for linear poly(ethylenimine) hydrochloride, cross-linked using malonaldehyde generated in situ, was determined from the ratio of the cross-link to backbone hydrogens obtained using ¹H NMR spectroscopy. The a.c. conductivity is highest at intermediate degrees of cross-linking (ca. 0.45), approximately 1 × 10⁻³ S/cm at room temperature and 75% relative humidity. IR and Raman spectroscopy were used to characterize the cross-linked network. The presence of the β-aminoethenyliminium cross-linker units can be identified through a series of bands between 1570 and 1640 cm⁻¹. Other changes in the spectra identified as a function of degree of cross-linking are discussed.     

High-Temperature Raman Spectra and Thermal Expansion of Wollastonite

Unpolarized single-crystal Raman spectra in the temperature interval of 298–1235 K and powder X-ray diffractometry data from room temperature up to 1295 K have been obtained from a natural triclinic wollastonite of almost-ideal composition. Room-temperature spectra, along with the temperature dependencies of nine major Raman modes, are presented. The temperature shifts of the Raman modes indicate a discontinuity in the temperature range of 950–980 K. No corresponding changes are observed in the temperature dependencies of the lattice parameters. Thermal expansion coefficients for the lattice parameters in the temperature range of 298–1295 K are given.     

Electrodeposition of Pt-Ru nanoparticles on fibrous carbon substrates in the presence of nonionic surfactant: Application for methanol oxidation

Liquid crystalline and micellar aqueous solutions of the nonionic surfactant Triton X-100 were used to direct the electrodeposition of Pt-Ru nanoparticles onto graphite felts, which were investigated as novel anodes for the direct methanol fuel cell. The effects of surfactant concentration, current density and deposition time in the preparation of these three-dimensional electrodes were studied in a factorial experiment and the electrodes were characterized by SEM and ICP-AES. Cyclic voltammetry, chronoamperometry and chronopotentiometry were carried out to assess the activity of the catalyzed felts for methanol oxidation. The presence of Triton X-100 (40-60 wt.%) coupled with an acidic plating solution were essential for the efficient co-electrodeposition of Ru in the presence of Pt to yield approximately a 1:1 Pt:Ru atomic ratio in the deposit. The highest mass specific activity, 24 A g⁻¹ at 298 K (determined by chronoamperometry after 180 s at 0 V versus Hg/Hg₂SO₄, K₂SO_4std), was obtained for the Pt-Ru electrodeposited in the presence of 40 wt.% Triton X-100 at 60 A m⁻², 298 K for 90 min. Surfactant mediated electrodeposition is a promising method for meso-scale (ca. 10-60 nm diameter) catalyst particle preparation on three-dimensional electrodes.     

Osmotic coefficients of polyelectrolyte solutions, measurements and correlation

Osmotic coefficient data for aqueous sodium polyanetholesulfonic acid, sodium polyacrylate and polydiallyl dimethylammonium chloride solutions were determined at 298 K by employing the isopiestic method. The measured osmotic coefficients increase with increasing concentration in the experimental concentration range (0.1-1.5 m). A molecular thermodynamic model developed previously for polyelectrolyte solutions has been used to fit the experimental data. The concentration dependence of the osmotic coefficients can be described satisfactorily.     

Thermal decomposition of hydrazine in sub- and supercritical water at 25 MPa

Supercritical water flow-through test facility (SCW-TF) for the study of hydrothermal fluids is described. The hydrodynamic behavior of the flow-through reactor is examined from ambient to supercritical water conditions by performing residence time distribution measurements. The results indicate that at 25 MPa, the employed reactor configuration exhibits plug flow behavior with a small extent of dispersion over the temperature range from 298 to 773 K. The experimentally determined effective volume of the reactor was used for the calculation of mean residence times of the fluid in the “hot zone” of the flow-through system. The thermal stability of hydrazine in aqueous solution was examined along the 25 MPa isobar from 473 to 725 K. The obtained first-order rate constant for the thermal decomposition of hydrazine increases from 3.73 × 10⁻⁴ s⁻¹ at 473 K to about 0.31 s⁻¹ at 725 K.     

Comparative study of first- and second-order Raman spectra of MWCNT at visible and infrared laser excitation

Comparative studies of first- and second-order Raman spectra of multi-walled carbon nanotubes (MWCNT) and three other graphitic materials - carbon fiber, powdered graphite and highly ordered pyrolytic graphite - are reported. Three laser excitation wavelengths were used: 514.5, 785 and 1064 nm. In first-order Raman spectra, the positions of the bands D, G and D′ (1100-1700 cm⁻¹) presented very similar behavior, however the intensity (I) ratio I_D/I_G ratio showed differed behaviors for each material which may be correlated to differences in their structural ordering. In the second-order spectra, the G′ band varied strongly according to structure with the infrared laser excitation.     

Decomposition and carbonisation of wood biopolymers—a microstructural study of softwood pyrolysis

Pyrolysis of softwood (spruce and pine) is investigated in the temperature range between 298 K and 1673 K within narrow intervals. A heating rate of 2 K/min and the use of thin wood sections allow one to fully preserve the original cellular wood structure without the formation of cracks. Thermal degradation of the wood biopolymers and evolution of the atomic/molecular and mesoscopic structure of the carbonaceous material is studied by wide-angle X-ray scattering, small-angle X-ray scattering and Raman spectroscopy. An isotropic and almost structureless material marks a clear transition region between 580 K and 620 K, where the crystal structure of the cellulose microfibrils is completely degraded and the scattering contrast based on the density difference between cellulose microfibrils and polyoses/lignin has fully disappeared. After the complete decomposition of the wood nanocomposite structure, the charring process commences with the formation of aromatic structures, and a strongly increasing scattering signal at small angles indicates the formation and growth of nanopores. The developing graphene sheets show a slight preferred orientation with respect to the oriented cellular structure of the material. It is concluded that the unique microfibril orientation of cellulose in the native wood cell wall might affect the carbonaceous material, in agreement with recent predictions in the literature.     

Effect of functionalized carbon nanotubes on the thermal conductivity of epoxy composites

Direct functionalized carbon nanotubes (CNTs) were utilized to form the heat flow network for epoxy composites through covalent integration. A method of preparing a fully heat flow network between benzenetricarboxylic acid grafted multi-walled carbon nanotubes (BTC-MWCNTs) and epoxy matrix is described. A Friedel-Crafts modification was used to functionalize MWCNTs effectively and without damaging the MWCNT surface. Raman spectra, X-ray photoelectron spectra and thermogravimetric analysis reveal the characteristics of functionalized MWCNTs. The scanning electron microscope images of the fracture surfaces of the epoxy matrix showed BTC-MWCNTs exhibited higher solubility and compatibility than pristine-MWCNTs. The MWCNTs/epoxy composites were prepared by mixing BTC-MWCNTs and epoxy resin in tetrahydrofuran, followed by a cross-linking reaction with a curing agent. The BTC was grafted onto the MWCNTs, creating a rigid covalent bond between MWCNTs and epoxy resin and forming an effective network for heat flow. The effect of functionalized MWCNTs on the formation of the heat flow network and thermal conductivity was also investigated. The thermal conductivity of composites exhibits a significant improvement from 0.13 to 0.96 W/m K (an increase of 684%) with the addition of a small quantity (1-5 vol%) of BTC-MWCNTs.     

Effects of annealing temperature on the photocatalytic activity of N-doped TiO2 thin films

The effects of annealing temperature on the photocatalytic activity of nitrogen-doped (N-doped) titanium oxide (TiO₂) thin films deposited on soda-lime-silica slide glass by radio frequency (RF) magnetron sputtering have been studied. Glancing incident X-ray diffraction (GIAXRD), Raman spectrum, scanning electron microscopy (SEM), atomic force microscopy (AFM) and UV-vis spectra were utilized to characterize the N-doped TiO₂ thin films with and without annealing treatment. GIAXRD and Raman results show as-deposited N-doped TiO₂ thin films to be nearly amorphous and that the rutile and anatase phases coexisted when the N-doped TiO₂ thin films were annealed at 623 and 823 K for 1 h, respectively. SEM microstructure shows uniformly close packed and nearly round particles with a size of about 10 nm which are on the slide glass surface for TiO₂ thin films annealed at 623 K for 1 h. AFM image shows the lowest surface roughness for the N-doped TiO₂ thin films annealed at 623 K for 1 h. The N-doped TiO₂ thin films annealed at 623 K for 1 h exhibit the best photocatalytic activity, with a rate constant (k_a) of about 0.0034 h⁻¹.     

The optimum average nanopore size for hydrogen storage in carbon nanoporous materials

A thermodynamical model of hydrogen storage in slitpores is presented and applied to carbon and BN nanoporous materials. The model accounts for the quantum effects of the molecules in the confining potential of the slitpores. A feature of the model is a new equation of state (EOS) of hydrogen, valid over a range of pressures wider than any other known EOS, obtained using experimental data in the range 77-300 K and 0-1000 MPa, including data in the region of solid hydrogen. The model reproduces the experimental hydrogen storage properties of different samples of activated carbons and carbide-derived carbons at 77 and 298 K and at pressures between 0 and 20 MPa, for an average nanopore width of about 5 Å. The model predicts that in order to reach the US Department of Energy hydrogen storage targets for 2010, the nanopore widths should be equal to or larger than 5.6 Å for applications at low temperatures, 77 K, and any pressure, and about 6 Å for applications at 300 K and at least 10 MPa.     

Structure, composition, and chemical reactivity of carbon nanotubes by selective nitrogen doping

Carbon nanotubes (CNTs) doped with a range of nitrogen contents (0-10 at.%) were prepared via a floating catalyst CVD method using ferrocene, NH₃, and xylene or pyridine. XPS and Raman microscopy were used to assess quantitatively the compositional and structural properties of the nitrogen-doped carbon nanotubes (N-CNTs). XPS analysis indicates a shift in and broadening of the C 1s spectra track with increasing disorder induced by selective nitrogen doping. N 1s XPS spectra show three principle types of nitrogen coordination (pyridinic, pyrolic, and quaternary), with the pyridinic-like fraction selectively increased from 0.0 to 4.5 at.%. First-order Raman spectra were fit with five peaks that vary in intensity and width with nitrogen content. The ratio of the D and G bands’ integrated intensities scaled linearly with nitrogen content. Iodimetric titrations were used to gauge the number of reducing sites on as-prepared N-CNTs, representing the first report of nitrogen doping as a means to deterministically effect the chemical reactivities of carbon nanotubes. The reported methodology for the regulated growth and selective nitrogen doping of CNTs presents new ways to study systematically the influence of nanocarbon composition and structure on chemical and electrochemical reactivity for a host of applications.     

Effects of concentration and temperature on the formation process of decanethiol self-assembled monolayer on Au(1 1 1) followed by electrochemical reductive desorption

The formation process of self-assembled monolayer (SAM) of decanethiol (C10SH) on Au(1 1 1) single crystal electrode has been investigated for wide range of C10SH concentration (0.1-500 μM) and temperature (253-298 K). The amount and quality of C10SH SAM were determined from area and position, respectively, of reductive desorption peak of the SAM modified Au(1 1 1) electrode measured in 0.5 M KOH aqueous solution. The kinetic analysis indicates that SAM formation proceeded by two steps, diffusion-limited physisorption followed by chemisorption.