Thermodynamic studies on Sn–Te–O system

The standard Gibbs energy of formation of tin tellurate, SnTe₃O₈(s) was determined from its vapour pressure measurements over the temperature range 973–1,158 K by employing thermogravimetry-based transpiration method. The temperature dependence of vapour pressure of TeO₂ over the mixture SnTe₃O₈(s) + SnO₂(s) generated by the incongruent vapourisation reaction, SnTe₃O₈(s) → SnO₂(s) + 3 TeO₂(g) could be represented as: log (p (TeO₂, g)/Pa ± 0.03) = 13.943–14,181 (K/T) (973–1,158 K). The standard Gibbs energy of formation of SnTe₃O₈(s) was also determined by measuring the oxygen potential of SnO₂(s)–Te(s)–SnTe₃O₈(s) phase mixture by the electromotive force method. Enthalpy increments of SnTe₃O₈(s) were determined by inverse drop calorimetric method in the temperature range 523–973 K. The thermodynamic functions, viz., heat capacity, entropy and free energy functions were derived from the measured values of enthalpy increments. A mean value of ?1,642 ± 2.0 kJ mol^?1 was obtained for $ \Updelta_{\text{f}} H_{298}^{\circ } $ (SnTe₃O₈, s) by combining the value of Δ_f $ G^{\circ } $ (SnTe₃O₈, s) derived from vapour pressure data and the free energy functions derived from the drop calorimetric data.     

Sorption–desorption studies of six pyrethroids and mirex on soils using GC/MS-NICI

Sorption–desorption equilibria of six pyrethroids (permethrin, cyfluthrin, cypermethrin, λ-cyhalothrin, deltamethrin and fenvalerate) and mirex were determined in soils possessing a range of organic content (1.15–2.46%). Solutions (in deionized water, pH 6.5–7.4) of the samples were shaken using a mechanical shaker for 24?h. The suspensions were centrifuged and aliquots of clear supernatant were passed through a C-18 column (SPE extraction). The eluates were concentrated to dryness before a volumetric standard was added. The analytes were determined by gas chromatography with negative ion chemical ionization mass spectrometry (GC/MS-NICI) either in SIR or SCN mode. Sorption isotherm parameters (n and k) were calculated according to the Freundlich equation. The values of n are around unity. Permethrin and cyfluthrin were the least sorbed pyrethroids, k<2, mirex and fenvalerate the most. The effect of the pH on sorption was examined also (at pH values 2, 4, 6 and 9). Sorption behaviour on different soils and silica was also examined. Desorption studies were conducted on the same pyrethroid solutions. After sorption, the supernatant was replaced with a similar volume of deionized water. Desorption was achieved by removing all the supernatant from the centrifuged samples and then replacing it with deionized water. This equilibration process was repeated five times. Each time the suspension was centrifuged, concentrated and analyzed using GC/MS analysis. The residual amount of pyrethroid on the soil was calculated as the difference between the initial amount and the desorbed amount (mass balance).     

Effect of structural and thermodynamic factors on the sorption of hydrogen by metal–organic framework compounds

The characteristics of the sorption of hydrogen by metal–organic framework compounds (MOF) were examined, and the structural and thermodynamic factors that favor the sorption of H₂ by such substances were determined. The effect of the structure of the MOF and the size and geometry of the pores on the sorption characteristics was analyzed. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 45, No. 2, pp. 67-87, March-April, 2009.     

Sorption—desorption studies of anionic dyes on alumina pretreated with acids

Sorption—desorption behaviour of the anionic dyes naphthol blue-black (NB) and lissamine green ‘BN’ (LG) on chromatographic alumina, pretreated with mineral acids, is described. Alumina samples of surface-phase pH 1.0–8.0 were prepared and studied for their sorption behaviour. The sorption was found to vary with surface pH of the substrate and acid used for pretreatment. Quantitative sorption was shown at pH ⩽ 4.0 (NB) and pH ⩽ 3.5 (LG) on Al₂O₃ treated with HNO₃ [Al₂O₃(n)], and maximum sorption occurred at pH 5.0 (NB) and pH 5.5 (LG) on Al₂O₃ treated with H₂SO₄ [Al₂O₃(s)] and pH 2.5 (NB) and pH 3.0 (LG) on Al₂O₃ treated with H₃PO₄ [Al₂O₃(p)]. Variation in sorption with time (10 min-72, h), temperature (30–60°C) and regeneration of the substrates with aqueous electrolytes is also reported. Desorption efficacy of anions was in the order: PO³⁻₄ > SO²⁻₄ > NO⁻₃. The acid-treatment, and hence the specifically adsorbed anions (NO⁻₃, SO²⁻₄, PO³⁻₄), appears to modify the sorption properties of alumina significantly. It appears that the controlling force for adsorption is predominantly ion exchange. A few synthetic mixtures of the dyes were separated by column chromatography, using inorganic electrolytes as eluents.     

Thermophysical studies on uranyl nitrate hexahydrate–Iron (III) nitrate nonahydrate system

Individual nitrates, UO₂(NO₃)₂·6H₂O and Fe(NO₃)₃·9H₂O as well as their binary mixtures in various mol ratios have been studied using simultaneous thermal techniques and X-ray powder diffraction measurements. Nature and stoichiometry of hydroxynitrates of iron and uranium were altered by changing the heating rates for the equal mass of binary nitrate mixtures under identical gas flow conditions. Evolved gas analysis and thermogravimetric measurements indicated the absence of direct interaction between two nitrates in the binary nitrate mixtures. Both the nitrates decomposed independently in the mixtures to their respective oxides. These results have been supported by X-ray powder diffraction measurements. Phase diagram of UO₂(NO₃)₂·6H₂O–Fe(NO₃)₃·9H₂O system containing 0–100 mol% of UO₂(NO₃)₂·6H₂O was constructed using differential thermal analysis technique. The formation of the eutectic at 33 °C for 50 mol% uranyl nitrate hexahydrate–50 mol% iron (III) nitrate nonahydrate mixture has been observed for the first time.     

Thermodynamics and kinetics of hydrogen absorption–desorption of vanadium synthesized by aluminothermy

This paper studies the addition (0–40% w/w) of natural zeolite (NZ, 84% clinoptilolite) in blended cements made with Portland cement (PC) with low and medium C₃A content. The isothermal calorimetry was used to understand the effect of NZ on the early cement hydration. For low C₃A cement, the addition of NZ produces mainly a dilution effect and then the heat released curve is similar to plain cement with lower intensity. For medium C₃A cement, the curve shows the C₃S peak in advance and a high intensity of third peak attributed to C₃A hydration. The high cation fixed of NZ reduces the ions concentration (especially alkalis) in the mixing water stimulating the PC hydration. The flowability decreases when the NZ replacement level increases. Results of Fratini’s test show that NZ with both PCs used presents slow pozzolanic activity. At early age, XRD and FTIR analyses confirm that hydration products are the same as that of the corresponding PC and the CH is progressively reduced after 28 days and some AFm phases (hemi- and monocarboaluminate) appear depending on the NZ percentage and the PC used. For low replacement levels, the compressive strength is higher than the corresponding PC from 2 to 28 days. For high replacement levels, the early compressive strength is lower than that of corresponding plain PC and the pozzolanic reaction improves the later compressive strength of blended cements.     

Hydrogen chemisorption on carbon structure with mixed sp2–sp3 hybridization: empirical potential studies

Hydrogen storage is a key technology for the advancement of hydrogen and fuel cell power technologies in transportation, stationary, and portable applications. The currents state of art shows that there is no existing material which could be used as efficient storage medium. In this paper we present a new concept of a non-conventional engineering storage solution. It is based on the recent theoretical and experimental discoveries which show existence of a new meta-stable phase of graphite with mixed sp²–sp³ hybridization called diaphite. By means of the molecular dynamics calculations with adaptive intermolecular reactive empirical bond order potential empirical potential we show that the increase of the hydrogen-carbon binding energy on diaphite is related to the transformation of local bonds geometry from sp² hybridization to sp³. We propose and discuss a scenario of fully reversible photo-stimulated process of adsorption/desorption of hydrogen on/of diaphite.     

Intermolecular charge—transfer studies on p-tolylthiourea—iodine system

Intermolecular charge—transfer spectra of p-tolylthiourea (as a donor) and iodine (as an acceptor) in very dilute solutions in carbontetrachloride and dichloromethane were studied spectrophotometrically in the u.v.-visible region. The changes in spectra are attributed to the formation of a 1:1 charge—transfer complex, whose equilibrium constant (K _c), heat of formation (ΔH⁰) and entropy change (ΔS⁰) were computed for the visible band of the molecular complex. The results are: ΔH⁰ = −13.3±0.4 kcal/mol; ΔS⁰ = −30.7±0.8 e.u. and K _c, s = 1023 and 675 (units, 1./mol) in carbontetrachloride and dichloromethane respectively. Ionization potentials of the donor were calculated from the energies of the charge—transfer transitions and the effect of solvent on the ionization has been investigated. The formation of a 1:2 charge—transfer complex, DA₂, is very likely in case of using more diluted solutions than used in the visible region. This shows the dual property of iodine for both acceptance and donation in the near u.v. region, this in turn confirms the presence of iodine dimer.     

A resonance light-scattering off–on system for studies of the selective interaction between adriamycin and DNA

On the basis of the resonance light scattering (RLS) of Ag nanoparticles (AgNPs), an RLS off–on system was developed for studies of the selective interaction between adriamycin (ADM) and DNA. In this strategy, addition of ADM could induce a proportional decrease in the RLS intensity of AgNPs; this could be used to detect trace amounts of ADM with a detection limit of 12.75 ng mL⁻¹ in the range 0.021–10.0 μg mL⁻¹. Subsequently, by investigating the ability of different DNA sequences to restore the RLS intensity of the analytical systems, we found that ADM was selective to dsDNA and had an obvious preference for sequences that were rich in guanine and cytosine bases. In order to validate the results of the RLS assay, fluorescence quenching was used, and binding constants and binding numbers of each system were calculated. Compared with other methods, this RLS off–on strategy was more sensitive, fast, and reliable. It has also supplied a novel method for studying the sequence selectivity of DNA-targeted anticancer drugs and is a novel application of the RLS technique in analytical chemistry.     

Gas–solid interactions in the hydrogen/single-walled carbon nanotube system

Gas–solid interactions between hydrogen and single-walled carbon nanotubes (SWNTs) were investigated using highly purified SWNTs. The activation energy of hydrogen desorption, measured to be 0.21 eV, indicates that hydrogen is physisorbed in the pores and that inter-tube pores have an adsorption potential of about −0.21 eV, which induces hydrogen physisorption at ambient temperature. The total amount of adsorbed hydrogen, about 0.3 wt% at 9 MPa, shows that 38% of the inter-tube sites are occupied. These findings are interpreted in terms of the chemical potential of hydrogen and the adsorption potential of the inter-tube pores.     

Peculiarities of sorption isotherm and sorption chemisms of caesium by mixed nickel–potassium ferrocyanide based on hydrated titanium dioxide

The effect of ⁶⁰Co source γ-radiation on β-carotene and chlorophyll-b solutions and on methyl blue dye fixed on cotton fabric has been investigated by colorimetric measurements. For the three reactive pigments, the result obtained shows that the power-law function can be used to predict the value of color difference according to γ-radiation dose. This same behaviour was observed during examination of many other published data. Based on these observations, the power-law function has been proposed as an empirical distribution for modeling the color variation of biologic molecules as a function of irradiation dose.     

Thermal studies of furosemide–caffeine binary system that forms a cocrystal

Thermal techniques, differential scanning calorimetry (DSC), and hot stage microscopy (HSM) have been used to study the interactions between furosemide and caffeine that are known to form a 1:1 cocrystal. This system has been used as an example to study the probable mechanism of cocrystal formation when the individual components, which are polymorphic, are heated. The study indicates that the phase transition of the low temperature stable polymorph of furosemide initiates cocrystal formation. This result suggests increased mass transfer rate can trigger cocrystal formation. The binary phase diagram (composition–temperature plots) of furosemide–cocrystal–caffeine system was determined from the DSC curves. The results imply that the cocrystal forms eutectic with caffeine but not with furosemide. This study has thus exemplified the use of DSC in understanding binary phase system where the two components form a cocrystal.     

Phase diagram and dissolution studies of the fenofibrate–acetylsalicylic acid system

Enhancement of the dissolution rate of poorly soluble compounds through the formation of drug–drug eutectics was investigated using fenofibrate and acetylsalicylic acid. Solid–liquid equilibria in the system under study were investigated by differential scanning calorimetry (DSC). The phase diagram for the whole range of compositions was constructed. In addition, existence of a metastable polymorph of fenofibrate has been confirmed. The investigation has revealed that acetylsalicylic acid and fenofibrate form a simple eutectic mixture containing 0.958 mol fraction of fenofibrate at the eutectic point. Dissolution rate improvement of fenofibrate correlated with the phase diagram. The amount of fenofibrate released from the solid dispersions that contained fenofibrate as the eutectic mixture with acetylsalicylic acid was at least threefold higher compared to untreated fenofibrate.     

Transport Coefficients of Hydrogen and Argon–Hydrogen Plasmas

Calculated values of the viscosity, thermal conductivity, and electrical conductivity of hydrogen and mixtures of argon and hydrogen at high temperatures are presented. Combined ordinary, pressure, temperature, and electric field diffusion coefficients are also given for the mixtures. The calculations, which assume local thermodynamic equilibrium, are performed for atmospheric pressure plasmas in the temperature range from 300 to 30,000 K. The results are compared with those of previously published studies. Generally, the agreement is reasonable; those discrepancies that exist are attributed to the improved values of some of the collision integrals used here in calculating the transport coefficients.     

Experimental study on combustion characteristics of diesel–hydrogen dual-fuel engine

As a clean and sustainable energy source, hydrogen is widely considered as an engine fuel by top researchers. In view of the fact that the uneven fuel mixture of diesel fuel deteriorated the combustion and emissions process, it is expected to adopt diesel and hydrogen dual-fuel combustion technology to optimize combustion and heat release of diesel engine. In this study, experiments are carried out on a diesel engine and the combustion characteristics of the engine with different hydrogen ratios (RH) are compared. It has been found that hydrogen addition is conducive to accelerate the heat release rate and improve the thermal efficiency. Specifically, compared with pure diesel conditions, the peak pressure increased by 7.7% and the cumulative heat release rate increased by 3.7% under the condition of RH of 20%. Moreover, although the effect on the ignition delay period is not clear, the higher RH brings about earlier heat release center and more cumulative heat release while enhancing the heat release of premixed combustion reducing the diffusion combustion and post-combustion.

     

Importance of aliphatic C–H hydrogen bonding on anion recognition

We have designed and synthesised new anion receptors 1 and 2, both of their C–H groups were at the α positions to carbonyl groups and further polarised by the attached polarising substituents. This enabled us to study hydrogen bonding donor ability of C–H bonds. The polarising substituents are electron withdrawing cyano group for host 1, while charged pyridinium group for host 2. As expected from charge effects, host 2 shows roughly an order of magnitude higher binding constants against various anion guests than those of receptor 1. Since the magnitude of polarisation change should be greatest for C–H group among various hydrogen bonding groups, this indicates the importance of C–H hydrogen bonding. In contrast, the relative order of binding constants was the same for both host 1 and 2. The order of association constants was found to be (CH₃)₂POO^? > CH₃COO^? > C₆H₅COO^? > Cl^? > Br^?. DFT calculation results were in good agreement with experimental binding constants and confirmed the importance of charged group substitution. In addition, receptor 1 showed the highest association constant for dimethyl phosphinate, which is implicated in many metabolic diseases.     

Helium–hydrogen microplasma device (MPD) on postage-stamp-size plastic–quartz chips

A new design of a miniaturized, atmospheric-pressure, low-power (e.g., battery-operated), self-igniting, planar-geometry microplasma device (MPD) for use with liquid microsamples is described. The inexpensive MPD was a hybrid, three-substrate quartz–plastic–plastic structure and it was formed on chips with area the size of a small postage stamp. The substrates were chosen for rapid prototyping and for speedy device-geometry testing and evaluation. The ~700-µm (diameter) and 7-mm (long) He–H₂ (3% H₂) microplasma was formed by applying high-voltage ac between two needle electrodes. Operating conditions were found to be critical in sustaining stable microplasma on plastic substrates. Spectral interference from the electrode materials was not observed. A small-size, electrothermal vaporization system was used for introduction of microliter volumes of liquids into the MPD. The microplasma was operated from an inexpensive power supply. And, operation from a 14.4-V battery has been demonstrated. Microplasma background emission in the spectral range between 200 and 850 nm obtained using a portable, fiber-optic spectrometer is reported. Analyte emission from microliter volumes of dilute single-element standard solutions of Cd, Cu, K, Li, Mg, Mn, Na, Pb, and Zn is documented. Element-dependent precision was between 10–25% (the average was 15%) and detection limits ranged between 1.5 and 350 ng. The system was used for the determination of Na in diluted bottled-water samples.