Highly phosphonated polypentafluorostyrene: Characterization and blends with polybenzimidazole

In this study we present results of the conductivity and resistance to thermooxidative and condensation reactions of a highly phosphonated poly(pentafluorostyrene) (PWN2010) and of its blends with poly(benzimidazole)s (PBI). This polymer, which combines both: (i) a high degree of phosphonation (above 90%) and (ii) a relatively high acidity (pK_a (–PO₃H₂ ↔ –PO₃H⁻) ∼ 0.5) due to the fluorine neighbors, is designed for low humidity operating fuel cell. This was confirmed by the conductivity measurements for PWN2010 reaching σ = 5 × 10⁻⁴ S cm⁻¹ at 150 °C in dry N₂ and σ = 1 × 10⁻³ S cm⁻¹ at 150 °C (λ = 0.75). Furthermore, this polymer showed only 48% of anhydride formation when annealing it at T = 250 °C for 5 h and only 2% weight loss during a 96 h Fenton test. These properties combined with the ability of the PWN2010 to form homogeneous blends with polybenzimidazoles resulting in stable and flexible polymer films, makes PWN2010 a very promising candidate as a polymer electrolyte for intermediate- and high-temperature fuel cell applications.     

Pechini synthesis and characterization of molybdenum carbide and nickel molybdenum carbide

Carbides, such as η-Ni₆Mo₆C, are considered as low-cost substitutes for noble metal catalysts for present applications in hydrodesulfurization and for a possible future sulfur-tolerant fuel cell anode catalyst. Most synthesis methods set the carbon content of the carbides by a carbon-based atmosphere or solid carbon in the synthesis. We show here that β-Mo₂C and η-Ni₆Mo₆C can be synthesized using a Pechini process, simply by heating metal acetates mixed with citric acid and ethylene glycol in one step under H₂ with the only source of carbon being the precursor solution. The β-Mo₂C forms when heating a Mo-acetate precursor at 850 °C. When using Ni- and Mo-acetates, β-Mo₂C forms at 700 °C and lower temperatures, while η-Ni₆Mo₆C forms during heating at 800-900 °C. The η-Ni₆Mo₆C has a surface area of 95.5 m² g⁻¹ and less than 10 m² g⁻¹ when prepared at 800 and 900 °C, respectively. Some Ni₃C, Ni, and NiC impurities are also present in the nanostructured η-Ni₆Mo₆C that was prepared at 900 °C. The η-Ni₆Mo₆C materials made by the Pechini process are compared with those made from a traditional synthesis, using metal organic precursors at 1000 °C under CO/CO₂ mixtures with a carbon activity of 0.011. Our results imply that H₂ and the Pechini process can be used to achieve carbon activities similar to those obtained by methods using gaseous or solid carbon sources.     

Thermal diffusivity measurement of low-k dielectric thin film by temperature wave analysis

Thermal diffusivity of thin film with low dielectric constant (k), what is called low-k dielectric thin film, 0.31-1.14 μm, including hydrogen-silsesquioxane (HSQ), methyl-silsesquioxane (MSQ), and poly(arylen ether) was examined by temperature wave analysis. The phase shift of temperature wave was observable up to 100 kHz. Thermal diffusivity of HSQ was 4.7 × 10⁻⁷ m² s⁻¹, on the other hand it was not higher than 1.1 × 10⁻⁷ m² s⁻¹ for MSQ or poly(arylen ether) at room temperature. Temperature dependence of thermal diffusivity/thermal conductivity of MSQ was obtained, thermal diffusivity decreased but thermal conductivity increased in a heating scan at 30-150 °C. It was shown that the thermal diffusivity of low-k thin film was correlated with the chemical and the physical structures, the latter was formed in the spin-coating and the curing process.     

X-ray diffraction study on the thermal expansion behavior of cellulose Iβ and its high-temperature phase

Oriented films of cellulose prepared from algal cellulose were hydrothermally treated to convert them into highly crystalline cellulose Iβ. The lateral thermal expansion behavior of the prepared cellulose Iβ films was investigated using X-ray diffraction at temperatures from 20 to 300 °C. Cellulose Iβ was transformed into the high-temperature phase when the temperature was above 230 °C, allowing the lateral thermal expansion coefficient of cellulose Iβ and its high-temperature phase to be measured. For cellulose Iβ, the thermal expansion coefficients (TECs) of the a- and b-axes were α_a = 9.8 × 10⁻⁵ °C⁻¹ and α_b = 1.2 × 10⁻⁵ °C⁻¹, respectively. This anisotropic thermal expansion behavior in the lateral direction is ascribed to the crystal structure and to the hydrogen-bonding system of cellulose Iβ. For the high-temperature phase, the anisotropy was more conspicuous, and the TECs of the a- and b-axes were α_a = 19.8 × 10⁻⁵ °C⁻¹ and α_b = −1.6 × 10⁻⁵ °C⁻¹, respectively. Synchrotron X-ray fiber diffraction diagrams of the high-temperature phase were also recorded at 250 °C. The cellulose high-temperature phase is composed of a two-chain monoclinic unit cell, a = 0.819 nm, b = 0.818 nm, c (fiber repeat) = 1.037 nm, and γ = 96.4°, with space group = P2₁. The volume of this cell is 4.6% larger than that of cellulose Iβ at 30 °C.     

Bio-oil production from Onopordum acanthium L. by slow pyrolysis

In this study, the usability of the plant thistle, Onopordum acanthium L., belonging to the family Asteraceae (Compositae), in liquid fuel production has been investigated. The experiments were performed in a fixed-bed Heinze pyrolysis reactor to investigate the effects of heating rate, pyrolysis temperature and sepiolite percentage on the pyrolysis product yields and chemical compositions. Experiments were carried out in a static atmosphere with a heating rate of 7 °C/min and 40 °C/min, pyrolysis temperature of 350, 400, 500, 550 and 700 °C and particle size of 0.6 < D_p < 0.85 mm. Catalyst experiments were conducted in a static atmosphere with a heating rate of 40 °C/min, pyrolysis temperature of 550 °C and particle size of 0.6 < D_p < 0.85 mm. Bio-oil yield increased from 18.5% to 27.3% with the presence of 10% of sepiolite catalyst at pyrolysis temperature of 550 °C, with a heating rate of 40 °C/min, and particle size of 0.6 < D_p < 0.85 mm. It means that the yield of bio-oil was increased at around 48.0% after the catalyst added. Chromatographic and spectroscopic studies on the bio-oil showed that the oil obtained from O. acanthium L. could be used as a renewable fuels and chemical feedstock.     

A new electrochemiluminescent detection system equipped with an electrically controlled heating cylindrical microelectrode

A new electrochemiluminescent (ECL) detection system equipped with an electrically controlled heating cylindrical microelectrode (HME) was developed in this paper. The cylindrical microelectrode made of platinum wire (25 μm in diameter, 6 mm in long) was used as the working electrode of the ECL detection system, the temperature of the electrode could be controlled electrically. The Ru(bpy)₃²⁺-ECL and Ru(bpy)₃²⁺-C₂O₄²⁻-ECL systems were used to evaluate this ECL detection system. The detection limit for oxalate was found to be 3.0 × 10⁻⁴ mol/L when T_e (temperature of the HME) was 22 °C, and found to be 3.0 × 10⁻⁶ mol/L at 80 °C, which indicates that the detection limit can be improved greatly at higher T_e, based on which, it is possible to establish a more sensitive method for measurement of ECL by using a heated microelectrode.     

New separation methodologies for the distinction of the growth phases of Saccharomyces cerevisiae cell cycle

In the present work two separation techniques, namely the gravitational field-flow fractionation (GrFFF) and the reversed-flow gas chromatography (RFGC), are proposed for the distinction of the growth phases of Saccharomyces cerevisiae (AXAZ-1) yeast cycle at different temperatures (30 °C, 25 °C, 20 °C, and 15 °C) and pH (2.0, 3.0, 4.0 and 5.0) values. During the fermentation processes, differences observed in the peak profiles, obtained by GrFFF, can be related with the unlike cell growth. The distinction of the phases of AXAZ-1 cell cycle with the GrFFF, was also confirmed with the RFGC technique, which presented similar fermentation time periods for the alcoholic fermentation phases. Simultaneously, the reaction rate constant for each phase of the fermentation process and the activation energies were determined with the aid of the RFGC technique. Finally, the application of both the GrFFF and the RFGC techniques, in combination with high-performance liquid chromatography, allowed us to find the ideal experimental conditions (temperature and pH) for the alcoholic fermentation by AXAZ-1. The results indicate that S. cerevisiae cells performed better at 30 °C, whereas at lower temperatures decreases in the fermentation rate and in the number of viable cells were observed. Moreover, the pH of the medium (pH 5.0) resulted in higher fermentation rates and ethanol productivities.     

The direct decomposition of NO over the La2CuO4 nanofiber catalyst

The NO catalytic direct decomposition was studied over La₂CuO₄ nanofibers, which were synthesized by using single walled carbon nanotubes (CNTs) as templates under hydrothermal condition. The composition and BET specific surface area of the La₂CuO₄ nanofiber were La₂Cu_0.88²⁺Cu_0.12⁺O_3.94 and 105.0 m²/g, respectively. 100% NO conversion (turnover frequency-(TOF): 0.17 g_NO/g_catalyst s) was obtained over such nanofiber catalyst at temperatures above 300 °C with the products being only N₂ and O₂. In 60 h on stream testing, either at 300 °C or at 800 °C, the nanofiber catalyst still showed high NO conversion efficiency (at 300 °C, 98%, TOF: 0.17 g_NO/g_catalyst s; at 800 °C, 96%, TOF: 0.16 g_NO/g_catalyst s). The O₂ and NO temperature programmed desorption (TPD) results indicated that the desorption of oxygen over the nanofibers occurred at 80-190 and 720-900 °C; while NO desorption happened at temperatures of 210-330 °C. NO and O₂ did not competitively adsorb on the nanofiber catalyst. For outstanding the advantage of the nanostate catalyst, the usual La₂CuO₄ bulk powder was also prepared and studied for comparison.     

Solid-state cis-trans isomerization reaction of (η-MeC5H4)W(CO)2P(OPr)3I

cis-(η⁵-MeC₅H₄)W(CO)₂P(OⁱPr)₃I (1) was converted to the trans isomer 2 in the solid state (90-110 °C). The reaction was monitored by heating 1 in NMR tubes for periods of time (2-60 min), cooling the tubes to room temperature and determining the conversion by solution ³¹P and ¹H NMR spectroscopy. The data were consistent with a first-order reaction and yielded an activation energy of 59 ± 3 kJ mol⁻¹. Comparative kinetic data were obtained from an in situ analysis of a powder-XRD study of 1. The powder-XRD study was conducted at 80-100 °C (10-60 min), yielding an activation energy of 52 ± 2 kJ mol⁻¹ (first-order reaction). The reaction could not be monitored by single crystal X-ray diffraction as the crystal disintegrated over time on heating. This disintegration process was monitored by optical microscopy and revealed that while the bulk crystal morphology was retained the crystal surface roughened with time. The compounds 1 and 2 were also structurally characterised by X-ray crystallographic techniques.     

A sequential injection system for indirect spectrophotometric determination of lactic acid in yogurt and fermented mash samples

A suitable non-enzymatic method is presented as an alternative to the lactic acid determination in yogurt and fermented mash samples. The oxidative conversion of lactic acid by Ce⁴⁺ to CO₂ was performed in a sequential injection system with a heating coil set at 45 °C. A gas diffusion unit was coupled to the flow system for promoting the permeation of CO₂, which was collected into a bromothymol blue solution (pH 8.4), used as indicator solution for the spectrophotometric determination (619 nm). Simplicity in operation, low reagent consumption, low cost and ruggedness are some remarkable characteristics of the proposed system. Base line drift was < 0.005 h^− 1. A linear range from 20.0 to 100.0 mg L^− 1 lactic acid was obtained (r² = 0.998), and the detection and quantification limits were estimated as 0.158 mg L^− 1 and 1.6 mg L^− 1, respectively. The sampling rate was 22 h^− 1, with a consumption of 0.04 g Ce⁴⁺ per determination. Interferences of matrix components were not detected. Samples of yogurt and sugar cane fermented mash products were analyzed, and no significant difference at 95% confidence level was observed when comparing the proposed method with HPLC analysis.     

Synthesis and characterization of some novel aromatic polyimides

Three new diamines 1,2-di(p-aminophenyloxy)ethylene, 2-(4-aminophenoxy)methyl-5-aminobenzimidazole and 4,4-(aminopheyloxy) phenyl-4-aminobenzamide were synthesized and polymerized with 3,3′,4,4′-benzophenone tetracarboxylic acid dianhydride (BP), 4,4′-(hexafluoroisopropyledene)diphthalic anhydride (HF) and 3,4,9,10-perylene tetracarboxylic acid dianhydride (PD) either by one step solution polymerization reaction or by two step procedure. The later includes ring opening poly-addition to give poly(amic acid), followed by cyclodehydration to polyimides with the inherent viscosities 0.62-0.97 dl/g. Majority of polymers are found to be soluble in most of the organic solvents such as DMSO, DMF, DMAc, m-cresol even at room temperature and few becomes soluble on heating. The degradation temperature of the resultant polymers falls in the ranges from 240 °C to 550 °C in nitrogen (with only 10% weight loss). Specific heat capacity at 300 °C ranges from 1.1899 to 5.2541 J g⁻¹ k⁻¹. The maximum degradation temperature ranges from 250 to 620 °C. T_g values of the polyimides ranged from 168 to 254 °C.     

Evaporation of ionic liquids at atmospheric pressure: study by ion mobility spectrometry

A conventional ion mobility spectrometry (IMS) was used to study atmospheric pressure evaporation of seven pure imidazolium and pyrrolidinium ionic liquids (ILs) with [Tf₂N], [PF₆], [BF₄] and [fap] anions. The positive drift time spectra of the as-received samples measured at 220 °C exhibited close similarity; the peak at reduced mobility K₀ = 1.99 cm² V⁻¹ s⁻¹ was a dominant spectral pattern of imidazolium-based ILs. With an assumption that ILs vapor consists mainly of neutral ion pairs, which generate the parent cations in the reactant section of the detector, and using the reference data on the electrical mobility of ILs cations and clusters, this peak was attributed to the parent cation [emim]. Despite visible change in color of the majority of ILs after the heating at 220 °C for 5 h, essential distinctions between spectra of the as-received and heated samples were not observed. In negative mode, pronounced peaks were registered only for ILs with [fap] anion.     

A thermostat chip of indium tin oxide glass substrate for static polymerase chain reaction and in situ real time fluorescence monitoring

A thermostat chip of indium-tin oxide glass substrate for static chip polymerase chain reaction (PCR) is, for the first time, introduced in this paper. The transparent conductive layer was used as an electro-heating element. Pulse width modulation and fuzzy proportional integration-differentiation algorithm were adopted in the temperature programming of the chip. The temperature distribution was investigated, and a dynamic control precision within ±2 °C was achieved. The highest ramping rates were 37 °C s⁻¹ for heating and 8 °C s⁻¹ for cooling with an electric fan. The PCR reaction vials were constructed with polyethylene tubes or poly(dimethylsiloxane) directly on the thermostat chip; the chip had a typical size of 25 mm × 25 mm and a thickness of 1.1 mm. Static chip PCR was successfully demonstrated either in a single vial or in an up to 8-parallel array vials. In situ real time fluorescence monitoring during PCR of a λ DNA fragments (236 bp) with SYBR Green I was demonstrated using a blue light emission diode as a light source and a photomultiplier as a detector. The method proposed here is characterized by open access, easy fabrication and low cost. This work could be the basis for developing a portable real time PCR system with disposable chips for point of care tests.     

Rietveld refinement and photoluminescent properties of a new blue-emitting material: Eu activated SrZnP2O7

A new efficient blue phosphor, Eu²⁺ activated SrZnP₂O₇, has been synthesized at 1000 °C under reduced atmosphere and the crystal structure and photoluminescence properties have been investigated. The crystal structure of SrZnP₂O₇ was obtained via Rietveld refinement of powder X-ray diffraction (XRD) pattern. It was found that SrZnP₂O₇ crystallizes in space group of P2₁/n (no. 14), Z=4, and the unit cell dimensions are: a=5.30906(2) Å, b=8.21392(3) Å, c=12.73595(5) Å, β=90.1573(3)°, and V=555.390(3) Å³. Under ultraviolet excitation (200-400 nm), efficient Eu²⁺ emission peaked at 420 nm was observed, of which the luminescent efficiency at the optimal concentration of Eu²⁺ (4 mol%) was estimated to be 96% as that of BaMgAl₁₀O₁₇:Eu²⁺. Hence, the SrZnP₂O₇:Eu²⁺ exhibit great potential as a phosphor in different applications, such as ultraviolet light emitting diode and photo-therapy lamps.     

Determination of cadmium and lead in cetacean Dolphinidae tissue from the coast of Bahia state in Brazil by GFAAS

In the present study, cadmium and lead in the muscle, lung, liver and kidney of dolphins (Sotalia guianensis and Stenella clymene) of the Bahia coast in the northwest of Brazil were determined by graphite furnace atomic absorption spectrometry. Samples were digested using a diluted oxidant mixture (HNO₃ + H₂O₂) with a microwave heating program performed in five steps. The optimized temperatures and chemical modifier for the pyrolysis and atomization were 700 °C, 1400 °C and Pd plus Mg for Cd, and 900 °C, 1800 °C and NH₄H₂PO₄ for Pb, respectively. Characteristic masses and limits of detections (n = 20, 3σ) for Cd and Pb were 1.6 and 9.0 pg and 0.82 ng g^− 1 and 0.50 ng g^− 1, respectively. Repeatability ranged from 0.87 to 8.22% for Cd and 4.31 to 8.09% for Pb. The found concentrations presented no statistical differences at the 95% confidence level when compared with the ICP OES methods. Addition and recovery tests were also performed and the results ranged between 87 and 112% for both elements. Samples of cetacean Dolphinidae (S.guianensis and S.clymene) were analyzed, and the higher concentrations ranged from 0.09 to 46.2 µg g^− 1 for Cd and 0.04 to 0.47 µg g^− 1 for Pb in liver, and from 0.133 to 277 µg g^− 1 for Cd in the kidney.     

LiB3O5 crystal structure at 20, 227 and 377 °C

Crystal structure of LiB₃O₅ (a framework of [B₃O₅]⁻ rings and Li atoms located in interspaces) was refined at high temperatures using single-crystal X-ray diffraction, MoKα-radiation, anharmonic approximation, orthorhombic; Pna2₁; Z=4; 20 °C (a=8.444, b=7.378, c=5.146 Å, 1411 F(hkl), R=0.022); 227 °C (a=8.616, b=7.433, c=5.063 Å, 1336 F(hkl), R=0.026), 377 °C (a=8.746, b=7.480, c=5.013 Å, 1193 F(hkl), R=0.035). A high mobility of Li atoms and their highly asymmetric vibrations are revealed. Ellipsoid of Li thermal vibrations is oviform. Li is shifted on heating to 0.26 Å mainly along a-axis causing high thermal expansion in this direction; Li temperature factors are multiplied by 4 on heating. Rigid boron-oxygen groups in LiB₃O₅ remain practically stable on heating similar to α-Na₂B₈O₁₃ and α-CsB₅O₈. At the same time these groups rotate relative to each other like hinges leading to extremely anisotropic thermal expansion (α_a=101, α_b=31, α_c=−71, α_v=60×10⁻⁶ °C⁻¹, 20-530 °C, HTXRPD data).     

Stereoselective Heck arylation of a functionalized cyclopentenyl ether using (S)-N-methyl-pyrrolidine as the stereochemical controller

The study of a series of palladium(0)-catalyzed C2-arylations of a 1-cyclopentenyl ether equipped with a chiral (S)-N-methyl-pyrrolidine auxiliary is reported. Stereoselective Heck monoarylations were performed using aryl iodides under classical heating conditions for 1.7-3.0 h at 80 °C and in one case using 30 min of microwave irradiation at 110 °C. To further explore the scope and nature of this stereoselective methodology, aryl bromides were also utilized as arylating agents, using 20 min of microwave processing at 120-130 °C. High to excellent diastereopurities (90-98% de) were obtained according to ¹H NMR and GC-MS analyses. The prolinol fragment apparently controlled the diastereoselectivity of the Heck reaction by presenting the arylpalladium species from the preferred side of the double bond. By X-ray structure diffraction analysis of an N-quaternized Heck product, the absolute configuration of the new stereocenter was established as (R), supporting a Si-face migratory insertion.     

Thermo-Raman spectroscopy in situ monitoring study of solid-state synthesis of NiO-Al2O3 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-Al₂O₃ 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 NiAl₂O₄ 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-Al₂O₃. 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.     

Thermal aggregation of bovine serum albumin studied by asymmetrical flow field-flow fractionation

The use of asymmetrical flow field-flow fractionation (AsFlFFF) in the study of heat-induced aggregation of proteins is demonstrated with bovine serum albumin (BSA) as a model analyte. The hydrodynamic diameter (d_h), the molar mass of heat-induced aggregates, and the radius of gyration (R_g) were calculated in order to get more detailed understanding of the conformational changes of BSA upon heating. The hydrodynamic diameter of native BSA at ambient temperature was ∼7 nm. The particle size was relatively stable up to 60 °C; above 63 °C, however, BSA underwent aggregation (growth of hydrodynamic diameter). The hydrodynamic diameters of the aggregated particles, heated to 80 °C, ranged from 15 to 149 nm depending on the BSA concentration, duration of incubation, and the ionic strength of the solvent. Heating of BSA in the presence of sodium dodecyl sulfate (1.7 or 17 mM) did not lead to aggregation. The heat-induced aggregates were characterized in terms of their molar mass and particle size together with their respective distributions with a hyphenated technique consisting of an asymmetrical field-flow fractionation device and a multi-angle light scattering detector and a UV-detector. The carrier solution comprised 8.5 mM phosphate and 150 mM sodium chloride at pH 7.4. The weight-average molar mass (M_w) of native BSA at ambient temperature is 6.6 × 10⁴ g mol⁻¹. Incubation of solutions with BSA concentrations of 1.0 and 2.5 mg mL⁻¹ at 80 °C for 1 h resulted in aggregates with M_w 1.2 × 10⁶ and 1.9 × 10⁶ g mol⁻¹, respectively. The average radius of gyration and the average hydrodynamic radius of the heat-induced aggregate samples were calculated and compared to the values obtained from the size distributions measured by AsFlFFF. For comparison static light scattering measurements were carried out and the corresponding average molar mass distributions of solutions with BSA concentrations of 1.0 and 2.5 mg mL⁻¹ at 80 °C for 1 h gave aggregates with M_w 1.7 × 10⁶ and 3.5 × 10⁶ g mol⁻¹, respectively.