Ensemble Effects in the Temperature-Dependent Photoluminescence of Silicon Nanocrystals

In this work the temperature-dependent photoluminescence of alkyl-capped silicon nanocrystals with mean diameters of between 3 and 9 nm has been investigated. The nanocrystals were characterized extensively by FTIR, TEM, powder XRD, and X-ray photoelectron spectroscopy prior to low-temperature and time-resolved photoluminescence spectroscopy experiments. The photoluminescence (PL) properties were evaluated in the temperature range of 41–300 K. We found that the well-known temperature-dependent blueshift of the PL maximum decreases with increasing nanocrystal diameter and eventually becomes a redshift for nanocrystal diameters larger than 6 nm. This implies that the observed shifts cannot be explained solely by band-gap widening, as is commonly assumed. We propose that the luminescence of drop-cast silicon nanocrystals is affected by particle ensemble effects, which can explain the otherwise surprising temperature dependence of the luminescence peak.     

Improving catalytic converter performance by controlling the structural and redox properties of Zr-doped CeO2 nanorods supported Pd catalysts

Research on Chemical Intermediates - The work herein introduces a facile and novel synthesis procedure for producing Zr-doped CeO2 nanorod catalysts applicable for upgrading the car catalytic...     

A brief radiological survey and associated occupational exposure to radiation in an open pit slate mine in Kashan,Iran

Journal of Radioanalytical and Nuclear Chemistry - A comprehensive radiological survey was carried out in an open-cut slate stone quarry. The activity of 226Ra, 228Ra and 40 K in the ore...     

A new strategy for the synthesis of 2-mercaptobenzazole derivatives by green chemistry metrics

Abstract

A green and efficient method has been developed for the synthesis of 2-mercaptobenzazole derivatives via the reaction of commercially available aniline derivatives with low-cost and nontoxic potassium thiocyanate in water. The reactions proceeded smoothly under catalyst- and ligand-free conditions to give the corresponding products in good to excellent yields. The versatility, low cost, and environmental friendliness, in combination with high yields and easy work-up makes the procedure noteworthy.     

On Complementable Semihypergroups

In this article, we first introduce the notion of complementable semihypergroup, proving that the classes of simplifiable semigroups, groups, simplifiable semihypergroups, and complete hypergroups are examples of complementable semihypergroups. Then we define when two semihypergroups are disjoint and find examples of such semihypergroups. Finally, we discuss on the complementable property of K_H-hypergroups.     

Atmospheric reaction pathways of methanimine and nitroxyl: a theoretical study

Structural Chemistry - The kinetics and mechanisms of atmospheric reaction of methanimine (H2CNH) with nitroxyl on the singlet surface were studied by employing DFT, MP2, and CCSD(T) methods along...     

Iodide-selective carbon paste electrodes based on recently synthesized Schiff base complexes of Fe(III)

A new modified carbon paste electrode (CPE) based on a recently synthesized Schiff base complex of Fe(III) as a suitable carrier for I⁻ ion is described. The electrode exhibits a super Nernstian slope of 71.0±0.3 mV per decade for I⁻ ion over a wide concentration range from 1.0×10⁻⁶ to 5.0×10⁻¹ M, with a low detection limit of 6.5×10⁻⁷ M. It has a relatively fast response time, a satisfactory reproducibility and relatively long life time. The proposed sensor shows a fairly good selectivity toward I⁻ ion in comparison to other common anions. The potentiometric response is independent of the pH of the test solution in the pH range 3.5–10.0. Spectrophotometric studies confirmed the redox-type response mechanism of the electrode toward iodide ion. The proposed electrode was used as an indicator electrode in potentiometric titration of iodide ion.     

Classification of methamphetamine seized in different regions of Iran using GC–MS and chemometrics

According to the intensive physical and mental risk of methamphetamine (crystal) on human, it is important to focus on the prevention of distribution and decrease of the usage of methamphetamine. In the current study, attempts was on the application of GC–MS analysis combined with chemometrics to present a classification model for methamphetamine samples seized in different regions of Iran. In this work, principal component analysis was not able to discriminate samples from different geographic regions. For the discrimination goal, partial least squares discriminant analysis (PLS-DA) and extended canonical variate analysis (ECVA) were utilized and a classification model was constructed to differentiate methamphetamine samples seized in three regions of Iran, i.e., south, west and central. PLS-DA showed good performance in calibration step; however, ECVA indicated better prediction ability. The difference of the classified samples can be because of difference in the synthetic root used in each of three investigated regions. Class sensitivity and selectivity for all three regions were excellent in ECVA model with nonsignificant misclassifications. Cross-validation and external validation using a test set confirmed the obtained classification model. Statistical results indicated a regional production/distribution pattern in the country.     

The catalytic performance of different promoted iron catalysts on combined supports Al<Subscript>2</Subscript>O<Subscript>3</Subscript> for carbon dioxide hydrogenation

Global warming, fossil fuel depletion and fuel price increases have motivated scientists to search for methods for the storage and reduction of the amount of greenhouse gases, especially CO₂. The hydrogenation process has been introduced as an emerging method of CO₂ capture and convertion into value-added products. In this study, new types of catalysts are introduced for CO₂ hydrogenation and are compared based on catalytic activity and product selectivity. The physical properties of the samples are specified using BET. Iron catalysts supported on γ-Al₂O₃ with different metal promoters (X = Ni, K, Mn, Cu) are prepared through the impregnation method. Moreover, Fe–Ni catalysts supported on HZSM5-Al₂O₃ and Ce–Al₂O₃ are synthesized. Samples are reduced by pure H₂ and involved in hydrogenation reaction in a fixed bed reactor (H₂/CO₂ = 3, total pressure = 10 MPa, temperature = 523 K, GHSV = 2000, 1250 nml/min). All catalysts provide high conversion in hydrogenation reactions and the results illustrate that the selectivity of light hydrocarbons is higher than that of methane and CO. It is found that Ni has a promoting effect on the conversion fluctuations throughout the reaction with 66.13% conversion. Using combined supported catalysts leads to enhancing catalytic performance. When Fe–Ni/γ–Al₂O₃—HZSM5 is utilized, CO₂ conversion is 81.66% and the stability of the Fe–Ni catalyst supported on Al₂O₃ and Ce–Al₂O₃ furthey improves.     

Ring-Open Analogues of Adenine Nucleoside. Aminoacyl Derivatives of Cyclo- and Acyclo-Nucleosides

The synthesis of acyclic analogues of ribo- and deoxyribonucleosides is described. These compounds (Table 3) are both poor substrates and poor inhibitors of adenosine deaminase. The synthesis of dinucleotides from these analogues is also described, and the activity along with the inhibitory properties of some of them are studied against deaminase enzyme. These nucleotides are resistant to degradation by phosphodiesterases. HCl impregnated on silica gel is an excellent reagent for the preparation of the chloromethyl ether precursors of acyclo-nucleosides. A general and rapid procedure is developed for the preparation and isolation of the 5′-aminoacyl derivatives of robo- and arabinonucleosides. Quinoline has a marked effect on aminoacylations without racemization. Compounds 35a , b possess remarkable antiviral effects in vitro. A procedure is also developed for the conversion of acyclo-ribonucliosides 13e , f to acyclo-deoxyribonucleosides 11e , f .