Radiative heat transfer in a cylindrical mixture of non-gray particulates and molecular gases

The interaction between particulate clouds and molecular gases with respect to radiative heat transfer in a one-dimensional cylindrical medium with black walls is investigated. The particulates are assumed to have a non-gray absorption coefficient with a power-law dependence on wavenumber. The absorption coefficient of the molecular gases is described by the exponential wide-band model. Heat transfer rates are found through the evaluation of internal and external total hemispherical emissivities of the particulate cloud and through evaluation of total band absorptances for the molecular gases, modified to account for the interaction with the particles. Simple, closed-form expressions for the total hemispherical emissivities and total band absorptance are also presented, resulting in good accuracy.     

Supramolecular-based solvent microextraction of carbaryl in water samples followed by high performance liquid chromatography determination

In this study, a simple, rapid, low cost, sensitive and environmentally friendly technique, supramolecular solvent microextraction (SM-SME) followed by high performance liquid chromatography-ultraviolet has been proposed to extract carbaryl from water samples. Parameters, affecting the SM-SME performance such as the weight of decanoic acid (DeA), volume of tetrahydrofuran (THF), pH and salt concentration, were studied and optimised. The effect of the pH on the extraction efficiency was evaluated by one–factor-at-a-time methodology, but the other variables were optimised by a face-centred cube central composite design methodology. Optimum extraction conditions were obtained: DeA: 70 mg; THF: 650 µL; salt concentration: 10% (w/v) NaCl and pH = 2–4), and the performance of the proposed method was evaluated. Under the optimum conditions, good linearity (1.0–500 µg L^?1, r² = 0.9994) was obtained. Limit of detection and limit of quantification were 0.3–1.0 µg L^?1, respectively. Also, the recoveries of the carbaryl were obtained in the ranged from 96% to 105%. Finally, proposed method was successfully applied for the determination of the carbaryl in the water samples of farms run-off and rivers and satisfactory results were obtained.     

New aluminum‐based ionic liquids: Synthesis,characterization, and theoretical study

Synthesis, characterization, spectral and molecular parameters of some new room‐temperature ionic liquids (tetraalkylammonium bromotrichloro aluminum [R₄N]⁺[AlCl₃Br]⁻) have been studied in the present study. All synthesized ionic liquids were characterized by IR, ¹H, ¹³C, and ⁸¹Br‐NMR. In addition, synthesized structures were optimized at the B3LYP/LANL2DZ level of theory and then the structures, molecular specifications, and infrared spectra of these were extracted using Gaussian 03 program. Theoretical data show good agreement with the experimental results. © 2010 Wiley Periodicals, Inc. Heteroatom Chem 20:398–404, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20564     

Quantification of Sub‐Nanomolar Levels of Aluminum by Adsorptive Stripping Voltammetry Using Rubeanic Acid as a Selective Chelating Agent

A novel, sensitive and selective adsorptive stripping procedure for determination of aluminum is presented. The method is based on the adsorptive accumulation of dithiooxamide (Rubeanic acid) complex of aluminum onto a hanging mercury drop electrode, followed by reduction of adsorbed species by voltammetric scan using differential pulse modulation. The influences of control variables on the sensitivity of the proposed method for the determination of aluminum were studied. The optimum analytical conditions were found to be Rubeanic acid (RA) concentration of 8.0×10^?5 M, ammonia buffer (NH₃? NH₄Cl) pH of 6.5, and accumulation potential at ?50 mV vs. Ag/AgCl with an accumulation time of 60 s. The peak currents are proportional to the concentration of aluminum over the 0.3–70 ng mL^?1 ranges with detection limit of 0.012 ng mL^?1. The procedure was applied to the determination of aluminum in the Lab. Water, HCl of Merck and potato samples with satisfactory results.     

Synthesis of multiresponsive β‐cyclodextrin nanocomposite through surface RAFT polymerization for controlled drug delivery

In this study, a unique magnetic, pH, and thermo‐responsive hydrogel nanocomposite was synthesized via surface reversible addition fragmentation chain transfer (RAFT) copolymerization of acrylic acid (AA) and N‐isopropyl acrylamide (NIPAM) in the presence of magnetic β‐cyclodextrin (β‐CD). The nanocomposite demonstrated a pH‐responsiveness behavior at pHs 3 and 9. Moreover, swelling behaviors of nanocomposite were measured in solutions with various temperatures. Furthermore, the nanocomposites exhibited high swelling capacity by applying an external magnetic field because of the presence of Fe₃O₄ nanoparticles in the polymer structure. Besides, the doxorubicin (DOX) loading and releasing behaviors of the hydrogel nanocomposites were studied because of the stimuli‐responsive properties of the synthesized carriers. The adsorption of DOX obeyed a pseudo‐second‐order model and fitted well to the Langmuir isotherm model with the maximum adsorption capacity uptake of 291 mg g^?1. In conclusion, the hydrogel nanocomposites were found to be as potential nanocarriers for use in controlled release applications.     

Novel Bio-Coacervation Extraction of Selenium Based on Microassemblies Biosurfactants with Ionic Liquid and Quantitative Analysis by HPLC/UV

In this work, we introduce a new sample preparation method for the extraction and preconcentration of selenium in dietary supplement tablets and mineral water. The bio-coacervation extraction technique is based on the use of a three-part system consisting of an ionic liquid, a biosurfactant and water. The advantage of this method is that the three components are non-toxic, green and eco-friendly. Parameters affecting the extraction efficiency, such as the amount of biosurfactant, the volumes of water and ionic liquid, pH, ionic strength, time extraction, temperature and the extraction method, were optimized. The calibration graph was linear, in the range of 0.55–40 µg L⁻¹. The detection limit for selenium after quantitative analysis was 0.183 µg L⁻¹ and the enrichment factor 190. The relative standard deviation for six replicate measurements was 4.6 %.

     

Synthesis and Computational Study of Phosphorus Ionic Liquids

The synthesis of six tetraalkylammonium bromopentachlorophosphoride ionic liquids (ILs) is reported here. Their structures were determined by IR, ¹H NMR, and ¹³C NMR spectroscopy. Moreover, thermogravimetric (TG) and differential thermal analysis (DTA) were used to investigate the thermal behavior of these compounds. The results show that these ILs have excellent thermal stability below 145°C, and by decreasing the size of the alkyl groups, the thermal stabilities will increase. Along with the experimental study, these compounds have been studied computationally at the B3LYP/LANL2DZ level of theory using the PC GAMESS/Firefly program package. From these calculations, optimized geometries, molecular parameters, and vibrational spectra of ILs have been calculated. In addition, calculated frequencies are compared with the experimental frequencies after correction by the appropriate scaling factor. This comparison shows that our theoretical data are in good agreement with the experimental results.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.     

Thermal Degradation Kinetics of Polyurethane/Organically Modified Montmorillonite Clay Nanocomposites by TGA

Polyurethane (PU) has been prepared by using polyether polyol (jagropol oil) and 1,6- hexamethylene diisocyanate (HMDI) as a cross-linker. The organically modified montmorillonite clay (MMT) is well-dispersed into urethane matrix by an in situ polymerization method. A series of PU/MMT nanocomposites have been prepared by incorporating varying amounts of nanoclay viz., 1, 3, 5 and 6 wt %. Thermogravimetric analysis (TGA) of the PU/MMT nanocomposites has been performed in order to establish the thermal stability and their mode of thermal degradation. The TGA thermograms exhibited the fact that nanocomposites have a higher decomposition temperature in comparison with the pristine PU. It was found that the thermal degradation of all PU nanocomposites takes place in three steps. All the nanocomposites were stable up to 205°C. Degradation kinetic parameters of the composites have been calculated for each step of the thermal degradation processes using three mathematical models namely, Horowitz–Metzger, Coats–Redfern and Broido's methods.