A selective colorimetric and fluorescence chemosensing sensor for Cr<Superscript>3+</Superscript> based on a rhodamine base derivative

A rhodamine-conjugated coumarin (L) was used in designing a selective fluorescence chemosensor for the determination of trace amounts of Cr³⁺ ions in acetonitrile–water (MeCN/H₂O (90:10, %v/v) solutions. The intensity of the fluoresce emission of the chemosensor is intensified upon addition of Cr³⁺ ions in MeCN/H₂O (90:10, %v/v) solutions, due to the formation of a selective 1:1 complex between L and Cr³⁺ ions. The fluorescence enhancement versus Cr³⁺ concentration has been found to be linear from 1.0?×?10^?7 to 1.8?×?10^?5 M and a detection limit of 7.5?×?10^?8 M. The proposed fluorescent probe proved to be highly selective towards Cr³⁺ ions as compared to other common metal ions and could be successfully applied to the determination of Cr³⁺ concentrations in some water and wastewater samples.     

Micellar-catalyzed reactions for flow-injection systems : Determination of pyridoxal

The advantages of applying the solubilization and catalytic properties of aqueous micelle solutions to reactions taking place in flow-injection systems are demonstrated. The reaction of pyridoxal (a B₆ vitamin) with cyanide was investigated in both aqueous and micellar cetyltrimethylammonium bromide (CTAB) solution. Higher sensitivities and lower limits of detection were obtained for the micellar carrier, with the pseudo-first-order reaction rate increasing by a factor of two in 0.05 M CTAB relative to water carrier. Because the micellar aggregates also increase fluorescence quantum yields, use of fluorescence detection gave further signal enhancement, with the limit of detection lowered by a factor of three. Measurement of dispersion in the two systems was also investigated and compared. A new method of characterizing dispersion in flow-injection systems, based on moment analysis of exponentially modified Gaussian peak shapes, is described.     

Preparation and Characterization of DGEBA/EPN Epoxy Blends with Improved Fracture Toughness

The physical and mechanical properties of blends composed of two kinds of epoxy resins of different numbers of functional groups and chemical structure were studied.One of the resins was a bifunctional epoxy resin based on diglycidyl ether ofbisphenol A and the other resin was a multifunctional epoxy novolac resin.Attempt was made to establish a correlation between the structure and the final properties of cured epoxy samples.The blend samples containing high fraction of multifunctional epoxy resin showed higher solvent resistance and lower flexural modulus compared with the blends containing high fraction of bifunctional epoxy resin.The epoxy blends showed significantly higher ductility under bending test than the neat epoxy samples.The compressive modulus and strength increased with increasing of multifunctional epoxy in the samples,probably due to enhanced cross-link density and molecular weight.Morphological analysis revealed the presence of inhomogeneous sub-micrometer structures in all samples.The epoxy blends exhibited significantly higher fracture toughness (by 23％ at most) compared with the neat samples.The improvement of the fracture toughness was attributed to the stick-slip mechanism for crack growth and activation of shear yielding and plastic deformation around the crack growth trajectories for samples with higher content of bifunctional epoxy resin as evidenced by fractography study.     

The Importance of Polarity/Polarizability Interaction on the Acidity Behavior of 9,10-Anthraquinone and 9-Anthrone Derivatives in Methanol-Water Mixed Solvents Using Target Factor Analysis and QSPR Approaches

The influence of solvent properties on acidity constants of some newly synthesized 9,10-anthraquinone and 9-anthrone derivatives was studied in methanol-water mixtures in a composition range of 0.57 to 1.0 methanol mole fraction. The model was established by using both multiple linear regression and target factor analysis. Both methods revealed that the solvent polarity/polarizability parameter ^* is a major factor in controlling the acidity behavior of the anthraquinones and anthrones studied in binary methanol-water mixed solvents. A QSPR study was conducted to drive the relationships between the ^* coefficient s and the polarity/polarizability of molecules. Both dipole moment and polarizability were found to have a linear relationship with s. The results confirm that, in the dipolar protic solvents used, the dipole-dipole interaction (for neutral molecules) and the ion-dipole interaction (for ionized molecules) are the major factors controlling the acidity behavior of these compounds.     

Optimization of synthesis procedure and structure characterization of manganese tungstate nanoplates

A simple and fast chemical method was used for synthesis of manganese tungstate nanoplates in flower-like clusters; while Taguchi robust design was employed as statistical method for optimization of the experimental parameters for the procedure. Ultrafine manganese tungstate plates in flower-like clusters were synthesized via a direct precipitation method involving addition of manganese ion solution to the aqueous tungstate reagent. Effects of various reaction conditions such as manganese and tungstate concentrations, flow rate of reagent addition and reactor temperature on the thickness of the synthesized manganese tungstate plates were investigated experimentally. Analysis of variance (ANOVA) showed that manganese tungstate nanoplates could be effectively synthesized by tuning significant parameters of precipitation procedure. Meanwhile, optimum conditions for synthesis of MnWO4 nanoplates via this simple, fast, and cost effective method were proposed. The structure and composition of the prepared nanoplates under optimum conditions were characterized by EDX, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), FT-IR spectroscopy, and photoluminescence techniques.      

Synthesis and activity measurement of some water-gas shift reaction catalysts

The effect of calcination temperature on the activity and some properties of low temperature water gas shift reaction catalysts has been investigated. The activities of catalysts have been determined using a fixed bed catalytic reactor. The following results may be deduced from the present study. 1. The catalysts' total surface area decreased with increasing calcination temperature, presumably due to the partial sintering of the catalysts particles. 2. The presence of an amorphous CuO phase within the structure of some catalysts may be related to the desirable conditions prevailing during synthesis of the latter. 3. Observation of a similar trend between the increase in copper crystallite particle size and enhancement of catalyst activities with increasing calcination temperature demonstrates the important contribution made by the copper crystallite phase to the overall activities of water gas shift reaction catalysts. This revised version was published online in June 2006 with corrections to the Cover Date.     

Optimization of profenofos organophosphorus pesticide degradation by zero-valent bimetallic nanoparticles using response surface methodology

This study synthesized bimetallic Fe/Ni nanoparticles and used them for catalytic degradation of profenofos, an organophosphorus pesticide. This novel bimetallic catalyst (Fe/Ni) was characterized by scanning electron microscopy (SEM), energy-dispersive X-ray analysis spectroscopy (EDAX) and X-ray diffraction (XRD). The bimetallic nano-catalyst was prepared at diameters of 20–50 nm and was shown to effectively degrade profenofos. A three-factor central composite design combined with response surface methodology was used to maximize profenofos removal using the bimetallic system. A quadratic model was built to predict degradation efficiency. ANOVA was used to determine the significance of the variables and interactions between them. Good correlation between the experimental and predicted values was confirmed by the high F-value (16.38), very low P-value (<0.0001), non-significant lack of fit, an appropriate coefficient of determination (R² = 0.936) and adequate precision (14.75). The highest removal rate attained was 94.51%.     

Strong red emissions induced by Pt–Pt interactions in binuclear cycloplatinated(II) complexes containing bridging diphosphines

A series of dinuclear cycloplatinated(II) complexes with general closed formula of [Pt₂Me₂(C^N)₂(μ‐P^P)] (C^N = 2‐vinylpyridine (Vpy), 2,2′‐bipyridine N‐oxide (O‐bpy), 2‐(2,4‐difluorophenyl)pyridine (dfppy); P^P = 1,1‐bis(diphenylphosphino)methane (dppm), N,N‐bis(diphenylphosphino)amine (dppa)) are reported. The complexes were characterized by means of NMR spectroscopy. Due to the presence of dppm and dppa with short backbones as bridging ligands, two platinum centres are located in front of each other in these complexes so a Pt…Pt interaction is established. Because of this Pt…Pt interaction, the complexes have bright orange colour under ambient light and are able to strongly emit red light under UV light exposure. These strong red emissions originate from a ³MMLCT (metal–metal‐to‐ligand charge transfer) electronic transition. In most of these complexes, the emissions have unstructured bell‐shaped bands, confirming the presence of large amount of ³MMLCT character in the emissive state. Only the complexes bearing dfppy and dppa ligands reveal dual luminescence: a high‐energy structured emission originating from ³ILCT/³MLCT (intra‐ligand charge transfer/metal‐to‐ligand charge transfer) and an unstructured low‐energy band associated with ³MMLCT. In order to describe the nature of the electronic transitions, density functional theory calculations were performed for all the complexes.