Synthesis,characterization, X-ray structural analysis and study of oxidative properties of propyltriphenylphosphonium bromochromate

The complex of propyltriphenylphosphonium bromochromate(VI), PrPh₃P[CrO₃Br] is easily synthesized in nearly quantitative yield using a direct reaction of chromium(VI) oxide and propyltriphenylphosphonium bromide. This compound is a versatile reagent for the efficient and selective oxidation of organic substrates, in particular for alcohols to their corresponding aldehydes or ketones, under mild conditions. This compound was characterized by IR, UV/Visible, ¹³C-n.m.r. and ¹H-n.m.r. techniques. It crystallized in the monoclinic form and its crystal and molecular structure have been determined by X-ray crystallography.     

Investigation of electrostatic charge distribution within the reactor wall fouling and bulk regions of a gas–solid fluidized bed

The distribution of charge within the wall fouling region and bulk of a fluidized bed reactor was investigated. Experiments were conducted in a 0.1 m in diameter carbon steel fluidization column under atmospheric conditions. Polyethylene particles were fluidized with extra dry air at 1.5 the minimum fluidization velocity (bubbling flow regime) for 1 h. Using an online Faraday cup measurement technique, the net charge-to-mass ratio (q/m), as well as the size distribution of all particles adhered to the column wall and those in the bulk of the bed was determined. The wall particles were found to be predominantly negatively charged while those which did not adhere to the wall were predominantly positively charged. The charge distribution within each region was then investigated by a custom made charged particle separator that separated the particles according to their charge magnitude and polarity. It was determined that although the net charge of the wall layer particles was negative, a significant amount of positively charged particles existed within each sample and therefore the entire wall particle layer. This suggests that the wall layer was formed through layering between positively and negatively charged particles. Particles in the bulk of the bed also consisted of bipolarly charged particles.     

Electron Beam Reduction Method for Preparing the Catalyst Layer in the Growth of Carbon Nanotubes

In this paper, electron beam (e-beam) reduction method is applied for the catalyst layer preparation in the growth of carbon nanotubes (CNTs). A hot cathodic electron beam facility was employed to electron bombarding of catalyst layer before stage of CNTs growth. This new method leads to reducing the diameter of particles via sputtering and evaporating the surface of catalyst. The growth of CNTs was performed on the Fe catalyst layer with SiO₂ substrate in an environment of different mixed gases (H₂, NH₃ and C₂H₂) by thermal chemical vapor deposition (TCVD) system. The morphology of the electron beam reduced catalyst particles were probed by atomic force microscopy (AFM). All samples were analyzed by scanning electron microscopy (SEM) before and after growth of CNTs. SEM analyses clarified that the catalyst grains have been smaller under effect of electron beam bombardment.     

Comparison of the performance of different modified graphene oxide nanosheets for the extraction of Pb(II) and Cd(II) from natural samples

Graphene nanosheets were modified with amino groups and the resulting material was used as a sorbent for the extraction of cadmium and lead ions. The nanosheets were characterized by IR spectroscopy, transmission electron microscopy, thermal gravimetric analysis and elemental analysis. The effects of sample pH, eluent parameters (type, concentration and volume of eluent), flow rates (of both sample and eluent), and of a variety of other ions on the efficiency of the extraction of Cd(II) and Pb(II) were optimized. Following solid phase extraction, the elements were determined by FAAS. The limits of detection are <0.9 μg L^?1 for Pb(II) and <5 ng L^?1 for Cd(II). The relative standard deviations are <2.2 %. The method was validated by analyzing several certified reference materials and was then used for Pb(II) and Cd(II) determination in natural waters and vegetables.

Synthesis and characterization of three new fluorovanadate complexes: N(C2H5)4[VOF4], N(CH3)4[VOF3Cl], N(C4H9)4[VOF3Br] and theoretical calculations of VOF4, VOF3Cl and VOF3Br ions

The reaction of VOF₃ with (C₂H₅)₄NF, (CH₃)₄NCl and (C₄H₉)₄NBr salts in anhydrous CH₃CN produced new complexes with the anion general formula [VOF₃X]⁻ in that (X = F⁻, Cl⁻, Br⁻). These were characterized by elemental analysis, IR, UV/Visible and ¹⁹F NMR spectroscopy. The optimized geometries and frequencies of the stationary point are calculated at the B3LYP/6-311G level of theory. Theoretical results showed that the VX (X = F, Cl, Br) bond length values for the [VOF₃X]⁻ in compounds 1-3 are 1.8247, 2.4031 and 2.5595 Å, respectively. Also, the VF₅ bond length values in [VOF₃X]⁻ are 1.824, 1.812 and 1.802 Å, respectively. These results reveal that the bond order for VX bonds decrease from compounds 1 to 3, while for VF₅ bonds, the bond orders increase. It can be concluded that the decrease of VX bonds lengths and the increase of VF₅ bond lengths in compounds 1-3 result from the increase of the hyperconjugation from compounds 1 to 3. Harmonic vibrational frequencies and infrared intensities for VOF₄⁻, VOF₃Cl⁻ and VOF₃Br⁻ are studied by means of theoretical and experimental methods. The calculated frequencies are in reasonable agreement with the experiment values. These data can be used in models of phosphoryl transfer enzymes because vanadate can often bind to phosphoryl transfer enzymes to form a trigonal-bipyramidal structure at the active site.     

Magnetic ion imprinted polymer nanoparticles for the preconcentration of vanadium(IV) ions

An ion imprinted polymer coated onto magnetite (Fe₃O₄) nanoparticles is shown to be a useful magnetic sorbent for the fairly selective preconcentration of vanadium. The sorbent was prepared by radical copolymerization of 3-(triethoxysilyl)propyl methacrylate (the monomer), ethylene glycol dimethacrylate (the cross-linker), and the vanadium(IV) complex of 1-(2-pyridylazo-2-naphthol) in the presence of magnetite nanoparticles. The material was characterized by IR spectroscopy, scanning electron microscopy, and thermal analysis. The vanadium(IV) ions were removed from the imprint by a solution containing thiourea and HCl, and the eluent was submitted to AAS. The analytical efficiency and relative standard deviation are 99.4 and ±2.3 %, respectively, under optimum conditions, and the limit of detection is 20 ng mL^?1. The method was successfully applied to the preconcentration and determination of vanadium(IV) ions in crude oil. Figure

An ion imprinted polymer is coated on to magnetite nanoparticles as a useful magnetic sorbent for the fairly selective preconcentration of vanadium which can be used for vanadium determination in crude oil.     

Dipyridylamine-modified nanoporous silicas as new sorbents for the separation and pre-concentration of palladium

Nanoporous silicas of the type SBA-15 (Santa Barbara Amorphous) and MCM-48 (Mobile Composition of Material) were modified with dipyridylamine (dipy) and used as solid phases for the extraction of Pd(II) ions. The experimental conditions (pH, sample and eluent flow rates, type and quantity of eluent) were optimized. The recovery values were ~ 99.7 and ~ 93.4% for dipy-MCM-48 and dipy-SBA-15, respectively, the limits of detection were <0.08 and <0.11 ng L^?1, the pre-concentration factors were 725 and 550, and the adsorption capacity was >78 mg g^?1. The procedure was applied to the preconcentration of Pd(II) in real samples.