Volume 232, Issue 3

This work suggests a connection between Landau-Zener transition probabilities between two crossing potentials in the classically accessible WKB regime and Landau-Lifshitz transition probabilities in the classically inaccessible WKB regime. It is based on the uniform Airy (UAi) approximation which represents a generalization of quantum transition probabilities for linear crossing potentials with constant coupling. The performance of the UAi approximation is tested by comparison with distorted-wave probabilities for an exponential potential model and illustrated for potentials that determine the intersection of two ab initio vibronic potential surfaces of the NO-Ar system.

Microwave enhanced gold nanoparticles (Au NPs) were synthesized using gum Arabic as both reducing and stabilizing agents. Response surface methodology was applied to study effects of the Au NPs synthesized parameters, namely, microwave exposure time (90–180 s) and the amount of AgNO 3 solution (1–10 mL) on the mean particle size, mixture solution color and concentration of the synthesized Au NPs. The colloidal solution containing well-dispersed and spherical fabricated Au NPs with mean particle size (22 nm) and maximum concentration (159 ppm) and color (1.12 absorbance unit, a.u.), were obtained at the optimal synthesis conditions, using 8.17 mL of HAuCl 4 (1 mM) and 2 mL of gum Arabic solution (4% w/v) during microwave exposure time of 180 s. The physico-chemical properties of the synthesized Au NPs at obtained optimum synthesis conditions were characterized by Fourier transform-infrared spectroscopy, UV-Vis spectroscopy, dynamic light scattering, X-ray diffraction, transmission electron microscopy and field emission scanning electron microscopy.

The electrochemical behavior of paracetamol (PC) was investigated at carbamazepine (CBZ) film coated carbon paste electrode in 0.2 M PBS of pH 7.4 by cyclic voltammetric technique. The modified electrode was exhibited a good electrochemical activity towards the oxidation of paracetamol, which results in a noticeable improvement of the peak currents and feasible oxidation as compared to the bare carbon paste electrode. Under optimal experimental conditions the electrochemical response to PC was linear in the concentration range from 1.0×10 −4 M to 3.94×10 −4 M with a detection limit of 0.24 μM by cyclic voltammetric technique. The sensitivity, long-term stability, reproducibility was shown by the modified electrode. Finally, the proposed method was successfully applied to determine PC in pharmaceutical samples.

The catalytic wet oxidation is one the methods used for elimination of dyes from aqueous medium in which various metal based materials can be used as heterogeneous catalysts. Bimetallic oxides as heterogeneous catalysts have gained much attention as bimetallization improve the catalytic properties of the resulting particles. The biosynthetic green method is the most viable and simple method for synthesis of bimetallic oxides nanoparticles. Here, we report the green synthesis of CoFe 2 O 4 particles using Azadirachata indica leaves extract as reducing and stabilizing agent. The synthesized particles were characterized using X-ray diffraction, thermogravimetric analysis, Fourier-transform infrared spectroscopy and scanning electron microscopy. The synthesized CoFe 2 O 4 particles were tested as a catalyst for mineralization of rhodamine B and methylene blue dyes in the presence of hydrogen peroxide in aqueous media. More than 95% dyes degraded in 120 min. The reaction kinetics was described in terms of Langmuir–Hinshelwood mechanism which suggests that molecules of dye and hydrogen peroxide adsorbed surface of CoFe 2 O 4 and then react together.

In addition to enthalpy–entropy compensation (EEC), anti-enthalpy–entropy compensation (AEEC) phenomenon is also found in literature. The reports on the latter are limited, and analyses and justifications are so far unclear. Herein we present demonstration on the nature and possibility of the AEEC phenomenon. Although literature reports so far have mostly shown linear AEEC, we have found both linear and non-linear dependences. The non-linearity we consider arises from large “free energy window” (FEW) like EEC, recently presented and discussed. Attempts have been made to rationalize the observations in terms of solvation–desolvation phenomenon of the involved processes anticipated in previous studies. We have found that enthalpy and entropy of formation of gaseous and solid materials may also exhibit AEEC, it can be thus classified as a global phenomenon. In addition to AEEC, the phenomenon of no-enthalpy–entropy compensation (NEEC) is also reported. Thus, the phenomena EEC, AEEC and NEEC are thermodynamic puzzles that require close attention and analysis. With the help of wide range of physical chemical processes, an elaborate general understanding of the linear and non-linear AEEC phenomena has been attempted. The experimental data herein used are collected from literature reports, new measurements were not done. A variety of examples have supported possible generality of AEEC.

Densities, ρ and ultrasonic speeds, u of L-histidine (0.02–0.12 mol·kg −1 ) in water and 0.1 mol·kg −1 aqueous citric acid solutions were measured over the temperature range (298.15–313.15) K with interval of 5 K at atmospheric pressure. From these experimental data apparent molar volume Φ V , limiting apparent molar volume Φ V O and the slope S V , partial molar expansibilities Φ E O , Hepler’s constant, adiabatic compressibility β , transfer volume Φ V, tr O , intermolecular free length ( L f ), specific acoustic impedance ( Z ) and molar compressibility ( W ) were calculated. The results are interpreted in terms of solute–solute and solute–solvent interactions in these systems. It has also been observed that L-histidine act as structure maker in water and aqueous citric acid.

Mineral dust aerosol participates in heterogeneous chemistry in the atmosphere. In particular, the hydroxyl groups on the surface of aluminosilicate clay minerals are important for heterogeneous atmospheric processes. These functional groups may be altered by acidic processing during atmospheric transport. In this study, we exposed kaolinite (KGa-1b) and montmorillonite (STx-1b) to aqueous sulfuric acid and then rinsed the soluble reactants and products off in order to explore changes to functional groups on the mineral surface. To quantify the changes due to acid treatment of edge hydroxyl groups, we use 19 F magic angle spinning nuclear magnetic resonance spectroscopy and a probe molecule, 3,3,3-trifluoropropyldimethylchlorosilane. We find that the edge hydroxyl groups (OH) increase in both number and density with acid treatment. Chemical reactions in the atmosphere may be impacted by the increase in OH at the mineral edge.

CoMo nanoparticles (NPs) supported on reduced graphene oxide (RGO) were synthesized by a one-step in situ co-reduction of an aqueous solution of cobalt(II) chloride, sodium molybdate dihydrate and graphene oxide (GO) using NaBH 4 as the sole reductant under ambient conditions. The powder XRD, FTIR, EDS and TEM were employed to characterize the structure, size and composition of the CoMo/RGO catalysts. The as-synthesized Co 0.9 Mo 0.1 /RGO catalysts exhibited high catalytic activity for the hydrolytic dehydrogenation of ammonia borane (AB) at room temperature. The as-synthesized Co 0.9 Mo 0.1 /RGO nanocatalysts exhibited much higher catalytic activity than Co/RGO, Mo/RGO and the RGO-free Co 0.9 Mo 0.1 counterpart. Moreover, kinetic studies indicate that the catalytic hydrolysis of AB by Co 0.9 Mo 0.1 /RGO has first order kinetics with respect to the the catalyst concentration, but zero order kinetics with respect to the substrate concentration. The Co 0.9 Mo 0.1 /RGO catalyst has a turnover frequency (TOF) of 15.8 mol H 2 ·(mol·Co 0.9 Mo 0.1 /RGO) −1 ·min −1 at 25°C. Furthermore, the Co 0.9 Mo 0.1 /RGO show good recyclability for hydrogen generation from an aqueous solution of AB, which enables the practical reuse of the catalysts. Hence, this general method can be easily extended to the facile preparation of other RGO-based metallic systems.