Kinetic analysis of the complex process of poly(vinyl alcohol) pyrolysis using a new coupled peak deconvolution method

A peak deconvolution procedure used for the analysis of data corresponding to simultaneous overlapping processes begins with separation of individual processes using functions such as Gaussian, Lorentzian, Weibull, and Fraser–Suzuki (FS) followed by application of kinetic analysis methods to the separated peaks. We propose a coupled peak deconvolution procedure to link the parameters of the FS functions of similar peaks in two DTG curves obtained at different linear heating rates, so that the coordinates of each peak can be obtained in a constrained manner. The proposed technique is a kinetic deconvolution method rather than a pure mathematical deconvolution technique. To analyze individual peaks in our study, the non-parametric kinetic and Freidman’s isoconversional methods have been applied to determine kinetic triplet of each process. This technique has been tested with both simulated and experimental data. Using this technique, the effects of molecular weight and degree of hydrolysis of polyvinyl alcohol (PVA) samples on reaction mechanism and activation energy of thermal degradation were studied. The presence of acetate group in the PVA samples causes thermal stability, decreases the rate of main reactions, and increases the activation energy. The results of this study may help tailor heat-resistant materials with proper choice of polymer characteristics.     

Mixed‐Metal MIL‐100(Sc,M) (M=Al,Cr, Fe) for Lewis Acid Catalysis and Tandem CC Bond Formation and Alcohol Oxidation

The trivalent metal cations Al³⁺, Cr³⁺, and Fe³⁺ were each introduced, together with Sc³⁺, into MIL‐100(Sc,M) solid solutions (M=Al, Cr, Fe) by direct synthesis. The substitution has been confirmed by powder X‐ray diffraction (PXRD) and solid‐state NMR, UV/Vis, and X‐ray absorption (XAS) spectroscopy. Mixed Sc/Fe MIL‐100 samples were prepared in which part of the Fe is present as α‐Fe₂O₃ nanoparticles within the mesoporous cages of the MOF, as shown by XAS, TGA, and PXRD. The catalytic activity of the mixed‐metal catalysts in Lewis acid catalysed Friedel–Crafts additions increases with the amount of Sc present, with the attenuating effect of the second metal decreasing in the order Al>Fe>Cr. Mixed‐metal Sc,Fe materials give acceptable activity: 40 % Fe incorporation only results in a 20 % decrease in activity over the same reaction time and pure product can still be obtained and filtered off after extended reaction times. Supported α‐Fe₂O₃ nanoparticles were also active Lewis acid species, although less active than Sc³⁺ in trimer sites. The incorporation of Fe³⁺ into MIL‐100(Sc) imparts activity for oxidation catalysis and tandem catalytic processes (Lewis acid+oxidation) that make use of both catalytically active framework Sc³⁺ and Fe³⁺. A procedure for using these mixed‐metal heterogeneous catalysts has been developed for making ketones from (hetero)aromatics and a hemiacetal.     

Magnetic Coupling Constants of Self‐Assembled CuII [3×3] Grids: Alternative Spin Model from Theoretical Calculations

This paper reports a theoretical analysis of the electronic structure and magnetic properties of a ferromagnetic Cu^II [3×3] grid. A two‐step strategy, combining calculations on the whole grid and on binuclear fragments, has been employed to evaluate all the magnetic interactions in the grid. The calculations confirm an S=7/2 ground state, which is in accordance with the magnetisation versus field curve and the thermal dependence of the magnetic moment data. Only the first‐neighbour coupling terms present non‐negligible amplitudes, all of them in agreement with the structure and arrangement of the Cu 3d magnetic orbitals. The results indicate that the dominant interaction in the system is the antiferromagnetic coupling between the ring and the central Cu sites (J₃=J₄≈?31 cm^?1). In the ring two different interactions can be distinguished, J₁=4.6 cm^?1 and J₂=?0.1 cm^?1, in contrast to the single J model employed in the magnetic data fit. The calculated J values have been used to determine the energy level distribution of the Heisenberg magnetic states. The effective magnetic moment versus temperature plot resulting from this ab initio energy profile is in good agreement with the experimental curve and the fitting obtained with the simplified spin model, despite the differences between these two spin models. This study underlines the role that the theoretical evaluations of the coupling constants can play on the rationalisation of the magnetic properties of these complex polynuclear systems.     

Propane-1,2,3-triyl tris(hydrogen sulfate): A mild and effcient recyclable catalyst for the synthesis of biscoumarin derivatives in water and solvent-free conditions简

A simple, efficient, and ecofriendly procedure has been developed using propane-l,2,3-triyl tris（hydrogen sulfate） as a catalyst for the synthesis of biscoumarin derivatives in water and solvent-free conditions. The significant features of the present protocol are simplicity, environmentally benign, high yields, no chromatographic separation, and recyclability of the catalyst.     

CH4 reforming with CO2 for syngas production over La2O3 promoted Ni catalysts supported on mesoporous nanostructured γ-A12O3

Nanostructured -y-A12O3 with high surface area and mesoporous structure was synthesized by sol-gel method and employed as catalyst support for nickel catalysts in methane reforming with carbon dioxide. The prepared samples were characterized by XRD, N2 adsorption-desorption, TPR, TPO, TPH, NH3-TPD and SEM techniques. The BET analysis showed a high surface area of 204 m2.g-1 and a narrow pore-size distribution centered at a diameter of 5.5 nm for catalyst support. The BET results revealed that addition of lanthanum oxide to aluminum oxide decreased the specific surface area. In addition, TPR results showed that addition of lanthanum oxide increased the reducibility of nickel catalyst. The catalytic evaluation results showed an increase in methane conversion with increasing lanthanum oxide to 3 mol% and further increase in lanthanum content decreased the catalytic activity. TPO analysis revealed that the coke deposition decreased with increasing lanthanum oxide to 3 mol%. SEM and TPH analyses confirmed the formation of whisker type carbon over the spent catalysts. Addition of steam and Oxide to drv reformin feed increased the methane conversion and led to carbon free ooeration in combined orocesses.     

Morphology of polyaniline nanofibers synthesized under different conditions

Polyaniline nanofibers are readily synthesized by bulk polymerization; ammonium per sulphate (APS) is used as oxidizing agent and hydrochloric acid as dopant without any hard or soft templates. A detailed study was conducted on the effect of a variety of synthetic conditions on the size and morphology of the polyaniline nanostructure. These conditions include the concentration of dopant, and the APS-to-aniline and acid-to-aniline molar ratios. The morphology of the nanofibers was confirmed by SEM and TEM. XRD and FT-IR and UV–visible spectroscopy were used for structural characterization of nanofibers. The results showed that not only the microstructure of the polyaniline product, but also other characteristics, for example conductivity, crystallinity, and, more importantly, the efficiency of the process are strongly affected by the synthetic conditions.     

Ab-initio molecular dynamics and hybrid explicit-implicit solvation model for aqueous and nonaqueous solvents: GFP chromophore in water and methanol solution as case study

Solute–solvent interactions are proxies for understanding how the electronic density of a chromophore interacts with the environment in a more exhaustive way. The subtle balance between polarization, electrostatic, and non-bonded interactions need to be accurately described to obtain good agreement between simulations and experiments. First principles approaches providing accurate configurational sampling through molecular dynamics may be a suitable choice to describe solvent effects on solute chemical–physical properties and spectroscopic features, such as optical absorption of dyes. In this context, accurate energy potentials, obtained by hybrid implicit/explicit solvation methods along with employing nonperiodic boundary conditions, are required to represent bulk solvent around a large solute–solvent cluster. In this work, a novel strategy to simulate methanol solutions is proposed combining ab initio molecular dynamics, a hybrid implicit/explicit flexible solvent model, nonperiodic boundary conditions, and time dependent density functional theory. As case study, the robustness of the proposed protocol has been gauged by investigating the microsolvation and electronic absorption of the anionic green fluorescent protein chromophore in methanol and aqueous solution. Satisfactory results are obtained, reproducing the microsolvation layout of the chromophore and, as a consequence, the experimental trends shown by the optical absorption in different solvents.     

Selective cytotoxicity of organotin(IV) compounds with 2,3-dihydroxybenzyldithiocarbazate Schiff bases

Research on Chemical Intermediates - A series of tridentate ONS Schiff bases were synthesised via condensation by reacting 2,3-dihydroxybenzaldehyde with S-2-methylbenzyldithiocarbazate (S2MBDTC)...     

Intelligence Way from Eco-friendly Synthesis Strategy of New Heterocyclic Pyrazolic Carboxylic α-Amino Esters

The α-amino acid derivatives constitute a class of compounds of particular medicinal and synthetic attention and considerable interest has been devoted to their synthesis in recent years. In the present work, we develop the computational study of the synthesis reaction of new pyrazolyl α-amino esters derivatives using the Gaussian 09 based on the DFT/B3LYP density functional theory method, with the base 6-31G(d, p) to ensure the possibility of carrying out these reactions within the laboratory of synthesis. Indeed, this research has encouraged us to establish an economical synthesis strategy of these products in overall yields of 73.5% to 87% to have access to new active biomolecule through the O-alkylation reaction between methyl α-azidoglycinate N-benzoylated and primary pyrazole alcohols[(3,5-dimethyl-1H-pyrazol-1-yl)methanol, (1H-pyrazol-1-yl)methanol and (3-ethoxy-5-methyl-1H-pyrazol-1-yl)methanol] under different operating conditions. The structure of the prepared heterocyclic systems was characterized by conventional spectroscopic techniques, like ¹H NMR, ¹³C NMR, and MS. The results revealed that the experimental study is in good correlation with the computational one.     

Fabrication of Electrochemical Sensor Based on CeO2−SnO2 Nanocomposite Loaded on Pd Support for Determination of Nitrite at Trace Levels

Here, an electrochemical sensor based on CeO₂‐SnO₂/Pd was prepared and used for highly selective and sensitive determination of nitrite in some real samples. This nanocomposite was characterized by various methods like X‐ray photoelectron spectroscopy, X‐ray diffraction, energy dispersive spectroscopy, Fourier‐transform infrared spectroscopy, field emission scanning electron microscopy, and transmission electron microscopy. The electrochemical behavior of the sensor was evaluated by cyclic voltammetry. The results showed excellent catalytic property of the nanocomposite as a an electrocatalyst for nitrite oxidation. In the following, the experimental parameters affecting the analytical signal for nitrite were optimized. Under the optimal conditions, the limit of detection and sensitivity of the sensor were calculated as 0.10 μM and 652.95 μA.mM^?1.cm^?2, respectively. Also, the response of the sensor was linear in the range of 0.36 to 2200 μM of nitrite. Finally, some of the inherent features of the sensor such as repeatability, reproducibility and stability were examined after evaluation of the sensor selectivity in the presence of several interfering species.