Palladium metal nanoparticle size control through ion paired structures of [PdCl(4)](2-) with protonated PDMAEMA

The mean diameter of palladium metal particles produced by citrate reduction of the (H(+))(n) PDMAEMA/[PdCl(4)](2-) aqueous system increases from 1.4 nm to 5.0 nm as the pH decreases from 6.3 to 3.3 and the (H(+))(n) PDMAEMA/[PdCl(4)](2-) species undergo conversion from a cross linked polymer network to a single chain structure.     

Synthesis of Monodisperse Lanthanum Hydroxide Nanoparticles and Nanorods by Sonochemical Method

In this work, monodisperse nanoparticles and nanorods of lanthanum hydroxide was synthesized from the reaction of lanthanum(III) nitrate and sodium hydroxide by sonochemical method. The effect of some of the parameters such as feeding rate of precursors, different solvents of reaction, time of sonication, and various surfactants on the particle size and morphology of products was studied. The as-prepared products were characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy.     

Multi-objective optimization of a plate and frame heat exchanger via genetic algorithm

In the present paper, a plate and frame heat exchanger is considered. Multi-objective optimization using genetic algorithm is developed in order to obtain a set of geometric design parameters, which lead to minimum pressure drop and the maximum overall heat transfer coefficient. Vividly, considered objective functions are conflicting and no single solution can satisfy both objectives simultaneously. Multi-objective optimization procedure yields a set of optimal solutions, called Pareto front, each of which is a trade-off between objectives and can be selected by the user, regarding the application and the project’s limits. The presented work takes care of numerous geometric parameters in the presence of logical constraints. A sensitivity analysis is also carried out to study the effects of different geometric parameters on the considered objective functions. Modeling the system and implementing the multi-objective optimization via genetic algorithm has been performed by MATLAB.     

Synthesis and Characterization of Conductive Polypyrrole/Montmorillonite Nanocomposites via One-pot Emulsion Polymerization

A series of electrically conductive polypyrrole/clay nanocomposites were synthesized in this work by using one-pot emulsion oxidative polymerization of pyrrole in the presence of unmodified clay and using DBSNa as the surfactant. The effect of surfactant on the morphological and electrical properties of PPy also were investigated and discussed in some extent. Electrical conductivity of the samples was measured by using samples in which the conductive materials was sandwiched between two Ni electrodes at room temperature. PPy/MMT nanocomposites were characterized by using XRD, TEM, TGA and DSC means of investigation. Intercalated structures were determined for the nanocomposites as confirmed by XRD and TEM studies. Electrical conductivity of the nanocomposites was measured to be dependent to the clay content, and the methods of preparation. Measurement also showed that polymerization of pyrrole monomers pre-intercalated between the clay gallery spaces of the clay led to higher conductivity for the nanocomposite in the same level of clay content. Thermal property measurements showed a lower thermal decomposition rate for the PPy/MMT nanocomposites with respect to the PPy.     

The immobilized Ni(II)‐thiourea complex on silica‐layered copper ferrite: A novel and reusable nanocatalyst for one‐pot reductive‐acetylation of nitroarenes

In this study, magnetically nanoparticles of CuFe₂O₄@SiO₂@PTMS@Tu@Ni(II) as novel and reusable catalyst were prepared. Synthesis of the Ni (II)‐nanocatalyst was carried out through the complexation of Ni(OAc)₂·4H₂O with the immobilized thiourea on silica‐layered CuFe₂O₄. The prepared nanocomposite system was then characterized using SEM, EDX, XRD, VSM, ICP‐OES, Raman, UV–Vis and FT‐IR analyses. Catalytic activity of the Ni(II)‐CuFe₂O₄ system was investigated towards rapid reduction of aromatic nitro compounds to arylamines with sodium borohydride as well as one‐pot reductive‐acetylation of nitroarenes to acetanilides with NaBH₄/Ac₂O system without the isolation of intermediate arylamines. All reactions were carried out in H₂O within 3–7 min to afford the products arylamines/acetanilides in high to excellent yields. Reusability of the Ni(II)‐nanocatalyst was examined for seven consecutive cycles without the significant loss of the catalytic activity.     

Simultaneous spectrophotometric determination of nitrite and nitrate by flow injection analysis.

A new catalytic spectrophotometric method is reported for the simultaneous determination of nitrite and nitrate by flow injection analysis, based on the catalytic effect of nitrite on the redox reaction between pyrogallolsulfonephthalein and potassium bromate in acidic media. Nitrate can also be on-line reduced to nitrite with a modified copper-coated cadmium reduction column. The reaction was monitored spectrophotometrically by measuring the decrease in the absorbance of pyrogallolsulfonephthalein at 465 nm. Various analytical parameters such as effects of acidity, reagent concentrations, flow rates, sample sizes, lengths of the reaction coil and temperatures were studied and were optimized. Under the optimized conditions, the calibration graph was linear for 2.4 to 160 ng ml(-1) of nitrite and 4.0 to 100 ng ml(-1) of nitrate. The influences of potential interfering cations and anions for nitrite and nitrate determination were studied. The method is successfully applied for food and water samples. Up to ten samples can be analyzed per hour.     

Hydrogen evolution reaction and formic acid oxidation by decorated nanostructural Pt/Pd on a copper-filled nanoporous stainless steel

In this work, a 304 stainless steel (SS) was anodized to prepare nanoporous SS (NPSS) with an average size of about 75 nm and then filled with copper (Cu/NPSS) using pulsed electrodeposition method. Afterward, a nanostructural Pt and Pd film was deposited by galvanic replacement (GR) on the Cu/NPSS to prepare modified electrode (PtPd/Cu/NPSS) for hydrogen evolution reaction (HER) and formic acid electrooxidation (FAO). The electrocatalytic activity of the modified electrode and its structural characterization have been studied by voltammetric methods, electrochemical impedance spectroscopy (EIS), inductively coupled plasma optical emission spectrometry (ICP-OES), and field emission scanning electron microscopy (FESEM). The results show that the nanostructural Pt₁Pd₁/Cu/NPSS composition, with low Pt loading and suitable stability, has a good electrocatalytic performance toward HER (E_Onset = + 12 mV vs. NHE) and FAO (E_Onset = ?180 mV vs. NHE). For HER observed a high mass activity of noble metals (87.54 mA cm^?2μg _Pd+Pt ^?1 ) in comparison with Pt deposited Cu/NPSS (41.5 mA cm^?2 μg _Pt ^?1 ) at the same applied potential of ? 0.25 V versus NHE. Also, the fabricated electrocatalysts with more electrochemically active surface area in comparison with Pd/Cu/NPSS and Pt/Cu/NPSS revealed more resisting to the poisoning components and good stability for FAO.     

ZrOCl2·8H2O on montmorillonite K10 accelerated conjugate addition of amines to α,β-unsaturated alkenes under solvent-free conditions

At room temperature, ZrOCl₂·8H₂O on montmorillonite K10 efficiently catalyzes conjugate addition of amines to a variety of conjugated alkenes such as α,β-unsaturated carbonyl compounds, carboxylic esters, nitriles and amides under solvent-free conditions. The catalyst can be recycled for subsequent reactions without any appreciable loss of efficiency.     

Rapid Microwave Induced Palladium Catalyzed Amination of Aryl Bromides

Summary.  The palladium-catalyzed coupling reaction of aryl bromides with various amines under microwave irradiation was studied using PdCl₂ [P(o-tolyl)₃]₂ which gave various aryl amines in good yields. The reactions were carried out under normal atmospheric conditions. Received September 3, 2001. Accepted October 10, 2001     

Synthesis of Substituted Pyrazino[5,6-b]pyrimidine and Some Indole Derivatives

Refluxing dimethyl acetylenedicarboxylate (DMAD) or 1,2-dibenzoylacetylene with isatin-3-thiosemicarbazone or isatin-3-thiocarbohydrazone in methanol produced 3-substituted oxindoles in good yields. Reaction of equimolecular amounts of 5,6-diamino-urasil-solfate, trans-(1R,2R)-diaminocyclohexane, and 3,4-diamino-1,2,4-triazol-5-methyl hydrochlorid with isatin in ethanol (85%) afforded tetracyclic ring systems and ring-opened products in mild reaction conditions.