Synthesis of nano‐sized magnetite mesoporous carbon for removal of Reactive Yellow dye from aqueous solutions

In this study, core‐shell structures of magnetite nanoparticles coated with CMK‐8 ordered mesoporous carbon (Fe₃O₄@SiO₂‐CMK‐8 NPs) have been successfully synthesized for the first time by carbonizing sucrose inside the pores of the Kit‐6 mesoporous silica. The nano‐sized mesoporous particles were characterized by X‐ray diffraction, Fourier transform‐infrared spectroscopy, scanning electron microscope, dynamic light scattering, vibrating‐sample magnetometer, Brunauer–Emmett–Teller (BET) and transmission electron microscopy instruments. The obtained nanocomposite was used for removal of Reactive Yellow 160 (RY 160) dye from aqueous samples. The N₂ adsorption–desorption method (at 77 K) confirmed the mesoporous structure of synthesized Fe₃O₄@SiO₂‐CMK‐8 NPs. Also, the surface area was calculated by the BET method and Langmuir plot as 276.84 m²/g and 352.32 m²/g, respectively. The surface area, volume and pore diameter of synthesized nanoparticles (NPs) were calculated from the pore size distribution curves using the Barrett–Joyner–Halenda formula (BJH). To obtain the optimum experimental variables, the effect of various experimental parameters on the dye removal efficiency was studied using Taguchi orthogonal array experimental design method. According to the experimental results, about 90.0% of RY 160 was removed from aqueous solutions at the adsorbent amount of 0.06 g, pH 3 and ionic strength = 0.05 m during 10 min. The pseudo‐second order kinetic model provided a very good fit for the RY 160 dye removal (R² = 0.999). The Langmuir, Freundlich, Temkin and Dubinin–Radushkevich models were applied to describe the equilibrium isotherms, and the Langmuir isotherm showed the best fit to data with the maximum adsorption capacity of 62.893 mg/g. Furthermore, the Fe₃O₄@SiO₂‐CMK‐8 NPs could be simply recovered by external magnet, and exhibited recyclability and reusability for a subsequent six runs.     

A high‐order compact finite‐difference lattice Boltzmann method for simulation of steady and unsteady incompressible flows

A high‐order compact finite‐difference lattice Boltzmann method (CFDLBM) is proposed and applied to accurately compute steady and unsteady incompressible flows. Herein, the spatial derivatives in the lattice Boltzmann equation are discretized by using the fourth‐order compact FD scheme, and the temporal term is discretized with the fourth‐order Runge–Kutta scheme to provide an accurate and efficient incompressible flow solver. A high‐order spectral‐type low‐pass compact filter is used to stabilize the numerical solution. An iterative initialization procedure is presented and applied to generate consistent initial conditions for the simulation of unsteady flows. A sensitivity study is also conducted to evaluate the effects of grid size, filtering, and procedure of boundary conditions implementation on accuracy and convergence rate of the solution. The accuracy and efficiency of the proposed solution procedure based on the CFDLBM method are also examined by comparison with the classical LBM for different flow conditions. Two test cases considered herein for validating the results of the incompressible steady flows are a two‐dimensional (2‐D) backward‐facing step and a 2‐D cavity at different Reynolds numbers. Results of these steady solutions computed by the CFDLBM are thoroughly compared with those of a compact FD Navier–Stokes flow solver. Three other test cases, namely, a 2‐D Couette flow, the Taylor's vortex problem, and the doubly periodic shear layers, are simulated to investigate the accuracy of the proposed scheme in solving unsteady incompressible flows. Results obtained for these test cases are in good agreement with the analytical solutions and also with the available numerical and experimental results. The study shows that the present solution methodology is robust, efficient, and accurate for solving steady and unsteady incompressible flow problems even at high Reynolds numbers. Copyright © 2014 John Wiley & Sons, Ltd.     

Electronic and transport properties of monolayer graphene defected by one and two carbon ad-dimers

Using density functional theory combined with non-equilibrium Green’s function method, we have investigated the electronic and transport properties of graphenes defected by one and two carbon ad-dimers (CADs), placed parallel to the graphene lattice. Addition of these CADs to graphenes creates 3D paired pentagon–heptagon defects (3D-PPHDs). The band structure, density of states (DOS), quantum conductance, projected DOS, as well as the current–voltage characteristic per graphene super-cells containing each type of 3D-PPHD are calculated. The local strain introduced to graphene by 3D-PPHDs forces the C-bonds in the dimers to hybridize in sp ³-like rather than sp ²-like orbitals, creating localized states at the center of the corresponding defect below the Fermi energy. Simulations show that the zero-bias conductances per super-cells containing defects created by one and two CADs exhibit dip about ~0.579 and ~0.253 eV below their corresponding Fermi levels, respectively. These can be attributed to the localized states around the same energy levels. Simulations also show that the enhanced carriers scatterings within the graphenes defected by the 3D-PPHDs have increased their overall resistances, as compared with the pristine graphene. Moreover, the current–voltage characteristic calculated per super-cell for each case shows that the current for those containing one and two CADs, at an applied voltage of 0.5 V, is ~5 and 13 % less than the current calculated for the pristine super-cell of the same size.     

Cobalt(II)-selective membrane electrode based on N,N′-di(thiazol-2-yl)formimidamide

A new PVC-membrane electrode for Co²⁺ ions based on N,N′-di(thiazol-2-yl)formimidamide (TF) as membrane carrier has been developed. The electrode resulted in Nernstian response (29.5?±?0.4?mV decade^?1) for Co²⁺ ion over a wide concentration range (2.5?×?10^?7 ?1.0?×?10^?1?M) with a detection limit of 6.1?×?10^?8?M. The sensor has a response time of about 10?s, and can be used for at least 2 months without observing any deviation from the Nernstain response. The electrode revealed good selectivity towards cobalt(II) ion over a wide variety of alkali, alkaline earth, transition, and heavy metal ions and could be used in the pH range 2.0–7.0. The electrode was used for determination of Co²⁺ in real samples.     

An efficient palladium catalytic system for microwave assisted cyanation of aryl halides

Application of a new catalytic system for cyanation reaction of various aryl halides using K₄[Fe(CN)₆] as cyanating source was examined. The reactions were performed under microwave irradiation and results showed that application of this catalytic system and DMF at 130 °C minimized the reaction times from hours to minutes in good to excellent yields.     

One‐Pot Synthesis of New 1,5‐Disubstituted Tetrazoles Bearing 2,2‐Bis(trimethylsilyl)ethenyl Groups via The Ugi Four‐Component Condensation Reaction Catalyzed by MgBr2·2Et2O

A simple one‐pot Ugi four‐component condensation reaction has been developed for the synthesis of tetrazoles bearing 2,2‐bis(trimethylsilyl)ethenyl groups from the synthesized 4‐[2,2‐bis(trimethylsilyl) ethenyl]benzaldehyde ( 1 ), various amines, isocyanides, and trimethylsilylazide at room temperature, without solvent, and in the presence of catalytic amounts of MgBr₂·2Et₂O as catalyst.     

Reductive amination of aldehydes and ketones to their corresponding amines with N-methylpyrrolidine zinc borohydride

A simple and convenient procedure for reductive amination of aldehydes and ketones using N-methylpyrrolidine zinc borohydride (ZBHNMP) as a reducing agent is described. The reactions are carried out with 1 equiv of amine and 1 equiv of aldehyde or ketone using 1 equiv of ZBHNMP in methanol under neutral conditions at room temperature.