Synthesis of Core-Shell (Pd-Au) Bimetallic Nanoparticles in Microemulsions

Palladium-gold core-shell nanoparticles were synthesized in the aqueous domains of water in oil microemulsions by the sequential reduction of H₂PdCl₄ and HAuCl₄. The nanoparticles were characterized by ultraviolet-visible (UV-vis) spectroscopy and transmission electron microscopy (TEM). The UV-vis spectra confirm the presence of palladium nanoparticles after reducing H₂PdCl₄. These particles have been used as seeds for the core-shell particles. UV-vis spectra show that, after reducing HAuCl₄, the surface plasmon absorption of the nanoparticles is dominated by gold, revealing the encapsulation of the palladium seeds. These results agree with crystallographic analysis performed with high-resolution TEM pictures, as well as with selected area electron diffraction. The TEM pictures show the core-shell nanoparticles with an average diameter of 9.1 nm, as compared with 5 nm for the palladium seeds, in good agreement with the used Pd:Au molar ratio.     

Synthesis,solid‐state,and charge‐transport properties of conjugated polythiophene‐S,S‐dioxides

An alkylated semiconducting polymer comprising alternating bithiophene‐[all]‐S,S‐dioxide and aromatic monothiophene units in the polymer backbone was synthesized with the intent of modifying the energy gap and lowest unoccupied molecular orbital for use as a stable n‐type semiconductor. Films spun from this semiconducting polymer were characterized utilizing X‐ray scattering, near edge X‐ray absorption fine structure spectroscopy, ultraviolet photoelectron spectroscopy, and thin‐film field effect transistors to determine how oxidation of the thiophene ring systems impacts the structural and electronic properties of the polymer. The thiophene‐S,S‐dioxide polymers have lower optical and electrical band gaps than corresponding thiophene polymers. X‐ray scattering results indicate that the polymers are well ordered with the π–π stacking distances increased by 0.4 Å relative to analogous thiophene polymers. The electrical stability of these polymers is poor in transistors with a drop in the field effect mobility by approximately one order of magnitude upon addition of just 5% of the thiophene‐S,S‐dioxide unit in a copolymer with thiophene. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Adsorptive Removal of Thorium(IV) from Aqueous Solutions Using Synthesized Polyamidoxime Chelating Resin: Equilibrium,Kinetic, and Thermodynamic Studies

In this study, an amidoximated chelating ion exchange resin was prepared by poly-acrylonitrile (PAN) grafted potato starch. The adsorbent characterizations such as specific surface area, pore volume, average pore radius, and Fourier transform infrared (FTIR) spectrum of the resin were measured. The effects of pH, adsorbent dosage, contact time, initial concentration of thorium ion, and temperature on adsorption of thorium ion from aqueous solutions were investigated. Four isotherm models including Langmuir, Freundlich, Dubinin-Radushkevich, and Temkin were applied to analyze the equilibrium isotherm data. The results showed that Langmuir and Temkin models had a good agreement with experimental data. The maximum capacity of the adsorbent using the Langmuir isotherm model was 227.27 mg · g^?1. The kinetic models like pseudo-first-order, pseudo-second-order, Elovich, and intraparticle were examined to describe the adsorption process. The kinetics of the adsorption process was found to follow the pseudo-second-order kinetic model. The thermodynamic parameters (ΔG°, ΔH°, ΔS°) were also calculated using equilibrium constant values at various temperatures (25, 35, 45, 55°C) and the positive value for ΔH° showed an endothermic adsorption process. The study suggests that the prepared adsorbent has promising potential for the removal of thorium from wastewaters.      

A Membrane Sensor for Selective Determination of Bisacodyl in Tablets

A novel PVC membrane sensor for bisacodyl based on bisacodyl‐phosphotungstate ion pair complex was prepared. The influence of membrane composition (i.e. percent of PVC, plasticizer, and ion‐pair complex), pH of test solution and foreign cations on the electrode performance were investigated. The optimized membrane demonstrates Nernstian response (60.3 ± 2.1 mV per decade) for bisacodyl cations over a wide linear range from 8.0 × 10^?5 to 5.0 × 10^?3 M at 25 °C. The potentiometric response is independent from the pH of the solution in the pH range of 1.5–3.5. The proposed sensor has the advantages of easy preparation, good selectivity, fast response time, and small interferences from hydrogen ions. It was successfully used for determination of bisacodyl in tablets, and the results obtained with the electrode were in good agreement with the official chromatographic method.     

Mild pre-heating of organic cation-exchanged clays enhances their interactions with nitrobenzene in aqueous environment

Aqueous sorption kinetics and equilibrium isotherms of nitrobenzene were studied on two series of sorbents that were prepared by (i) replacing inorganic exchangeable cations in Wyoming bentonite with tetraethylammonium (TEA) and benzyltrimethylammonium (BTMA) and (ii) heating synthesized complexes in air at different temperatures (between 150 and 420°C). The aim of this work was to examine recently observed enhancement of aqueous sorption of a probe organic sorbate on organoclays after mild thermal pre-treatment of sorbents. Thermal pre-treatment of TEA- and BTMA-clays at 150°C results in the maximal enhancement of nitrobenzene–sorbent interactions as compared with treatment of original bentonite and its exchange complexes formed with long-chain quaternary ammonium (n-hexadecyltrimethylammonium, HDTMA). Based on C, N content data and FTIR spectra of TEA- and BTMA-clay complexes, no indications of decomposition of organic matter were found in organoclays heated at 250°C (and below this temperature). Suppressed hydration of pre-heated sorbents resulting in a lessening of water–organic sorbate competition for sorption sites is considered to be responsible for thermally induced enhancement of nitrobenzene–sorbent interactions. In the HDTMA-based organoclays, the long-chain aliphatic groups of the quaternary ammonium can additionally interact with clay surface thus competing with organic sorbate–sorbent surface interactions and, in this way, mitigating the enhancement of nitrobenzene sorption on thermally treated sorbents.     

Three‐Component Reaction of an Isocyanide and a Dialkyl Acetylenedicarboxylate with a Phenacyl Halide in the Presence of Water: An Efficient Method for the One‐Pot Synthesis of γ‐Iminolactone Derivatives

The zwitterion, formed from the reaction of an alkyl isocyanide and a dialkyl acetylenedicarboxylate, reacts with phenacyl halides in H₂O to produce γ‐iminolactone derivatives in high yields. H₂O helps to avoid the use of highly toxic and environmentally unfavorable solvents for this conversion.     

Three‐Component Reaction of Isocyanides and 2‐Formylbenzoic Acid with Dibenzylamine Catalyzed by Silica Nanoparticles under Solvent‐Free Conditions

Reaction of an isocyanide with an iminium ion intermediate, formed by reaction between 2‐formylbenzoic acid and dibenzylamine in the presence of silica nanoparticles (silica NP, ca. 42 nm) proceeds smoothly at room temperature to afford isocoumarin (=1H‐2‐benzopyran‐1‐one) derivatives in high yields (Scheme 1 and Table 1).     

Experimental study on convective heat transfer and entropy generation of carbon black nanofluid turbulent flow in a helical coiled heat exchanger

Journal of Thermal Analysis and Calorimetry - The convective heat transfer coefficient (CHTC) of a fluid is one of the most effective factors on the performance of a fluid in heat transfer...