In situ crystallization of ZnAl2O4/ZnO nanocomposite on alumina granule for photocatalytic purification of wastewater

Research on Chemical Intermediates - ZnAl2O4/ZnO nanocomposites with different ZnO (20, 30, and 40 mol%) concentrations and coated samples on supports were successfully prepared through...     

One-Pot Synthesis of 3,4-Dihydropyrimidin-2(1H)-ones and Their Sulfur Derivatives with H2SO4 Supported on Silica Gel or Alumina

The one-pot condensation of aromatic aldehydes, β-dicarbonyl compounds, and urea or thiourea in the presence of H₂SO₄ supported on silica gel or alumina (80% m/m) in refluxing n-hexane produces 3,4-dihydropyrimidin-2(1H)-ones and their sulfur derivatives in high to excellent yields.     

An investigation of Forex market efficiency based on detrended fluctuation analysis: A case study for Iran

The efficient market hypothesis (EMH) states that asset prices fully reflect all available information. As a result, speculators cannot predict the future behavior of asset prices and earn excess profits at least after adjusting for risk. Although initial tests of the EMH were performed on stock market data, the EMH was soon applied to other markets including foreign exchange (FX). This study uses the detrended fluctuation analysis (DFA) technique to test 01:12:2005–18:04:2010 Iranian Rial/US Dollar exchange rate time series data to see if it can be explained by the weak form of the EMH. Moreover, to determine changes in the degree of inefficiency over time, the whole period has been divided into four subperiods. The study shows that the Iranian Forex market (the Rial/Dollar case) is weak-form inefficient over the whole period and in each of the subperiods. However, the degree of inefficiency is not constant over time. The findings suggest that profitable risk-adjusted trades could be made using past data.     

Polyelectrolyte Nanocomposite Membranes Using Imidazole-Functionalized Nanosilica for Fuel Cell Applications

The preparation and characterization of a new type of nanocomposite polyelectrolyte membrane, based on DuPont Nafion/imidazole-modified nanosilica (Im-Si), for direct methanol fuel cell applications is described. Related to the interactions between the protonated imidazole groups, grafted on the surface of nanosilica, and negatively charged sulfonic acid groups of Nafion, new electrostatic interactions can be formed in the interface of Nafion and Im-Si which result in both lower methanol permeability and also higher proton conductivity. Physical characteristics of these manufactured nanocomposite membranes were investigated by scanning electron microscopy, thermogravimetry analysis, differential scanning calorimetry, Fourier transform infrared spectroscopy, water uptake, methanol permeability, and ion-exchange capacity, as well as proton conductivity. The Nafion/Im-Si membranes showed higher proton conductivity, lower methanol permeability and, as a consequence, higher selectivity parameter in comparison to the neat Nafion or Nafion/silica membranes. The obtained results indicated that the Nafion/Im-Si membranes could be utilized as promising polyelectrolyte membranes for direct methanol fuel cell applications.     

Kinetic Study of Radical Polymerization VIII. A Comprehensive Study of Solution Copolymerization of Vinyl Acetate and Methyl Acrylate by 1H‐NMR Spectroscopy

Radical copolymerization reaction of vinyl acetate (VA) and methyl acrylate (MA) was performed in a solution of benzene‐d₆ using benzoyl peroxide (BPO) as the initiator at 60°C. Kinetic studies of this copolymerization reaction were investigated by on‐line ¹H‐NMR spectroscopy. Individual monomer conversions vs. reaction time, which was followed by this technique, were used to calculate the overall monomer conversion, as well as the monomer mixture and the copolymer compositions as a function of time. Monomer reactivity ratios were calculated by various linear and nonlinear terminal models and also by simplified penultimate model with r _2(VA)=0 at low and medium/high conversions. Overall rate coefficient of copolymerization was calculated from the overall monomer conversion vs. time data and k _p  . k _t ^?0.5 was then estimated. It was observed that k _p  . k _t ^?0.5 increases with increasing the mole fraction of MA in the initial feed, indicating the increase in the polymerization rate with increasing MA concentration in the initial monomer mixture. The effect of mole fraction of MA in the initial monomer mixture on the drifts in the monomer mixture and copolymer compositions with reaction progress was also evaluated experimentally and theoretically.     

Organically modified montmorillonite and chitosan–phosphotungstic acid complex nanocomposites as high performance membranes for fuel cell applications

Nanocomposite membranes based on polyelectrolyte complex (PEC) of chitosan/phosphotungstic acid (PWA) and different types of montmorillonite (MMT) were prepared as alternative membranes to Nafion for direct methanol fuel cell (DMFC) applications. Fourier transform infrared spectroscopy (FTIR) revealed an electrostatically fixed PWA within the PEC membranes, which avoids a decrease in proton conductivity at practical condition. Various amounts of pristine as well as organically modified MMT (OMMT) (MMT: Cloisite Na, OMMT: Cloisite 15A, and Cloisite 30B) were introduced to the PEC membranes to decrease in methanol permeability and, thus, enhance efficiency and power density of the cells. X-ray diffraction patterns of the nanocomposite membranes proved that MMT (or OMMT) layers were exfoliated in the membranes at loading weights of lower than 3 wt.%. Moreover, the proton conductivity and the methanol permeability as well as the water uptake behavior of the manufactured nanocomposite membranes were studied. According to the selectivity parameter, ratio of proton conductivity to methanol permeability, the PEC/2 wt.% MMT 30B was identified as the optimum composition. The DMFC performance tests were carried out at 70 °C and 5 M methanol feed and the optimum membrane showed higher maximum power density as well as acceptable durability compared to Nafion 117. The obtained results indicated that owing to the relatively high selectivity and power density, the optimum nanocomposite membrane could be considered as a promising polyelectrolyte membrane (PEM) for DMFC applications.