Mechanism of yttrium atom formation in electrothermal atomization from metallic and metal-carbide surfaces of a heated graphite atomizer in atomic absorption spectrometry

Mechanism of Y atom formation from pyrocoated graphite, tantalum and tungsten metal surfaces of a graphite tube atomizer has been studied and a mechanism for the formation for Y atoms is proposed for the first time. The following is the mechanism of yttrium atom formation regardless of whether the atomizing surface is pyrolytic graphite, tantalum or tungsten metal.

     

Role of energy irradiation in aiding pretreatment of lignocellulosic biomass for improving reducing sugar recovery

With the depletion of crude oil reserves, the ever-increasing global energy consumption encourages the efforts to find alternative renewable sources for production of biofuels and value-added chemicals. The conversions of lignocellulosic biomass into biofuels and commodity chemicals via the biotechnological pathway have been the recent trend. Specifically, these products can be obtained through fermentation of reducing sugars, which are the main but basic derivatives from the biomass. In order to overcome the recalcitrant structure of the biomass for effective reducing sugar recovery, a pretreatment stage is normally required. Currently, one of the most novel forms of biomass pretreatment is using energy irradiation methods such as electron beam, gamma ray, pulsed electrical field, microwave and ultrasound. In general, these technologies are often used together with other more conventional chemical and/or biological pretreatment techniques for enhancing sugar recovery. Nevertheless, energy irradiation offers significant improvement in terms of possible cost reduction opportunities and reduced toxicity. Hence, this review highlights the recent studies of using energy irradiation for pretreating biomass as well as the industrial applications of reducing sugars in biotechnological, chemical and fuel sectors. In short, more research needs to be done at the scientific, engineering and economic levels to make energy irradiation one of the front runners in the field of biomass pretreatment.     

Ultrasonic velocities, densities, viscosities, electrical conductivities, Raman spectra, and molecular dynamics simulations of aqueous solutions of Mg(OAc)2 and Mg(NO3)2: Hofmeister effects and ion pair formation

The ultrasonic velocities, densities, viscosities, and electrical conductivities of aqueous solutions of magnesium nitrate and magnesium acetate have been measured from dilute to saturation concentrations at 0 < or = t/degrees C < or = 50. The temperature derivative of the isentropic compressibility, kappa(s), became zero at 2.28 and 2.90 mol kg(-1) for Mg(OAc)2 and Mg(NO3)2 solutions, respectively, at 25 degrees C. The total hydration numbers of the dissolved ions were estimated to be, respectively, 24.3 and 19.2 at these concentrations. Differences in kappa(s) for various M2+ salts, using the present and literature data, correlated with reported M2+-OH2 bond lengths and to a lesser extent with cationic charge densities (ionic radii). The influence of anions on kappa(s) appears to follow the Hofmeister series and also correlates approximately with the anionic charge density. Substantial differences between Mg(OAc)2(aq) and Mg(NO3)2(aq) occur with respect to their structural relaxation times (derived from compressibility and viscosity data) and their electrical conductivities. These differences were attributed to a much greater ion association in Mg(OAc)2 solutions. Raman spectra recorded at 28 degrees C confirmed the presence of various types of contact ion pairs including mono- and bidentate complexes in Mg(OAc)2(aq). In Mg(NO3)2(aq), only noncontact ion pairs appear to be formed even at high concentrations. The experimental results are supported by molecular dynamics simulations, which also reveal the much stronger tendency of OAc- compared to NO3- to associate with Mg2+ in aqueous solutions. The simulations also allow an evaluation of the ion-ion and ion-water radial distribution functions and cumulative sums and provide a molecular picture of ion hydration in Mg(OAc)2(aq) and Mg(NO3)2(aq) at varying concentrations.     

Monte Carlo study of surfactant adsorption on heterogeneous solid surfaces

The equilibrium between free surfactant molecules in aqueous solution and adsorbed layers on structured solid surfaces is investigated by lattice Monte Carlo simulation. The solid surfaces are composed of hydrophilic and hydrophobic surface regions. The structures of the surfactant adsorbate above isolated surface domains and domains arranged in a checkerboard-like pattern are characterized. At the domain boundary, the adsorption layers display a different behavior for hydrophilic and hydrophobic surface domains. For the checkerboard-like surfaces, additional adsorption takes place at the boundaries between surface domains.     

Isentropic Compressibility,Shear Relaxation Time,and Raman Spectra of Aqueous Calcium Nitrate and Cadmium Nitrate Solutions

Speed of sound, viscosity and Raman spectra of aqueous calcium nitrate and cadmium nitrate solutions were measured as functions of molality and temperature. The isentropic compressibility isotherms for both systems cross over in a narrow molality region. In comparison with Ca(NO₃)₂(aq) solutions, Cd(NO₃)₂(aq) solutions have lower isentropic compressibilities due to a lower charge to radius ratio. The observed Raman spectral changes in the ₃ (1400 cm^–1) and ₄ (700 cm^–1) modes with an increase in molality suggest that the symmetry of NO₃^– changes from D_3h to C_2v, and solvent-separated and/or solvent-shared ion pairs are formed in both systems. The results from plotting electrical conductivity versus shear relaxation time also imply that the influence of the solvent-separated and/or solvent-shared ion pairs begins 2.0 mol-kg^–1 for these systems. The larger values for the ₃ mode for Cd(NO₃)₂(aq) solutions indicate stronger solvent-separated and/or solvent-shared ion pairs formation in comparison to Ca(NO₃)₂(aq) solutions.     

Molecular adsorption-mediated control over the electrical characteristics of polycrystalline CdTe/CdS solar cells.

The effect of surface treatments on p-CdTe/n-CdS solar cell performance was examined. Adsorption of organic molecules with various magnitudes and directions of the dipole moment on p-CdTe resulted in controlled changes in electron affinity and surface bond bending. Similar adsorption on CdTe in state-of-the-art p-CdTe/n-CdS solar cells changes the cell performance, and we explain this by a combination of increased series resistance and changes in light absorption and in cell photovoltage. While at this stage no improvement in performance has been found with these cell structures, which are the result of years of empirical optimization, the molecular effect on the photovoltage shows that it is possible in this way to control the photovoltaic effect at this junction. Separate optimization may well lead to improvement by inserting a dipole layer near the photovoltaic interface. Our results also show that this is even possible when dipole adsorption is performed on the complete polycrystalline thin-film cell.     

Thermoanalysis of quasi-ternary As2(S,Se, Te)3 semiconductor glasses

In comparison with other chalcogenide glassy systems, less attention has been paid to the quasi-ternary (quaternary) system As₂(S, Se, Te)₃. In this paper, thermal methods were used to characterize ten different quaternary homogenous semiconductor glasses that were prepared by mixing the stoichiometric binary systems As₂S₃, As₂Se₃ and As₂Te₃. The ratios of the constituent binaries in the quasi-ternary glasses exerted a great influence on their thermal spectrum. The samples poor in As₂Te₃ showed neither the exothermic nor the endothermic peak due to crystallízation (T _c) and melting (T _m), respectively, but only the glass transition (T _g). Three transition temperatures,T _g, T_c andT _m, were detected for other compositions. On the other hand, a phase separation was observed in the samples rich in As₂Te₃. A cyclic scanning technique was used to investigate the thermally-induced phases during two consecutive heat ing-cooling cycles covering the temperature rangeT _g?T_m. The energy of decompositionE _d decreased on increase of the ratio As₂S₃/As₂Se₃ (at constant As₂Te₃), whereas it increased on increase of the ratio As₂Te₃/As₂Se₃ (at constant As₂Se₃ or As₂S₃).     

Antimycobacterial activity of flavonoids from Lantana camara Linn

Linaroside (1) and lantanoside (2), two flavonoids isolated from Lantana camara and their common acetyl derivative (3) were examined for antimycobacterial activity against Mycobacterium tuberculosis, strain H(37)Rv. These compounds exhibited 30, 37 and 98% inhibition, respectively at 6.25 microg mL(-1) concentration. Among these flavonoids acetylated compound was found to be the most active.     

The effect of UV radiation on the thermal degradation of cellulose triacetate

The effect of UV radiation on the thermal degradation of cellulose triacetate (CTA) has been investigated. Simultaneous thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) have been performed on CTA samples of 0.25 mm thickness. These samples were exposed to different energy fluences of UV in the range 2.3–113 kJ/cm². The specific heat capacity, C_p, has been evaluated for unexposed and exposed CTA samples using DSC method. The results indicate that the transition temperatures, onset temperatures of evaporation, specific heat capacity and the thermal activation energy of decomposition, E_a are affected by the UV energy fluence owing to the simultaneous processes of degradation and crosslinking.