A review on recent advances in hierarchically porous metal and metal oxide nanostructures as electrode materials for supercapacitors and non-enzymatic glucose sensors

The remarkable significance of electrode materials in industrial processes, energy, sustainability and diabetes monitoring has captivated scientists to develop advance nanomaterials for the benefit of life across the globe. Here in, the recent developments in nanostructured porous metal and metal oxide composite materials for supercapacitor applications and non-enzymatic glucose sensors (NEGS) has been extensively discussed. The essential and active electrode materials from the research and application perspective has been emphasized in detail. We have also evaluated the worthiness, taxonomical classification, efficiency, specific capacitance and sensitivity of these materials for the aforementioned potential applications. Eventually, we concluded the review by providing the aspect ratio, surface morphology, particle size and specific surface area of these materials that plays an indispensable role for their promising potential applications.     

Effect of substitution of K ions on the structural and electrical properties of nanocrystalline MgAl2O4 spinel oxide

Potassium substituted nanosized magnesium aluminates having a nominal composition Mg_1−xK_xAl₂O₄ where x=0.0, 0.25, 0.5, 0.75, 1.0 have been synthesized by the chemical co-precipitation method. The samples have been characterized by means of X-ray diffraction (XRD), scanning electron microscope (SEM), and dc electrical resistivity measurements. The XRD results reveal that the samples are spinel single phase cubic close packed crystalline materials. The calculated crystallite size ranges between 6 and 8 nm. The behaviour of the lattice constant seems to deviate from the Vegard's law. While X-ray density clearly increases, the bulk density and consequently, the percentage porosity do not exhibit a significant change on increasing the K⁺ content. The SEM micrographs suggest homogeneous distribution of the nanocrystallites in the samples. The dc electrical resistivity exhibits a typical semiconducting behaviour. Substitution of a Mg²⁺ ion by a K⁺ ion provides an extra hole to the system, which forms small polaron. Thermally activated hopping of these small polarons is believed to be the conduction mechanism in the Mg_1−xK_xAl₂O₄. The activation energy of hopping of small polarons has been calculated and found K⁺ ions content dependent.     

Solubility of hydrocarbons in water: Experimental measurements and modeling using a group contribution with association equation of state (GCA-EoS)

In this communication, new experimental data on the solubility of n-hexane, cyclo-hexane and iso-octane in pure water are reported. The data have been measured using a static-analytic technique that takes advantage of a Rolsi™ sampling device in the temperature range of 298–353 K and at pressures up to 0.5 MPa. The experimental data measured in this work at 298 K have been compared with some selected data from the literature and good agreement is found. A group contribution plus association equation of state, namely the GCA-EoS, is used to model the phase equilibrium of water + hydrocarbon (C₂ to n-C₆, cy-C₆, i-C₄ and i-C₈) system. The predictions of the model are found in good agreement with the experimental data measured in this work and some selected data from the literature.     

Kinetics of the thermal isomerization of cis-methylcyclopropane carboxylic acid

The gas-phase thermal decomposition of cis-2-methylcyclopropane carboxylic acid was investigated in the temperature range 692–753 K and pressure between 10 and 70 Torr. Arrhenius parameters were determined for homogeneous, unimolecular formation of the isomeric products and for the overall loss-rate of the reactant. The determined values are in accordance with the Arrhenius parameters that were reported previously for the thermal unimolecular reactions of cyclopropane and other substituted cyclopropanes. The formation of isomeric products and the observed Arrhenius parameters are consistent with a biradical mechanism. The effect of surface on the reaction was studied at 732 K using the packed reaction vessel. It was observed that the rate of production of all isomeric products and the total loss of cis-2-methylcyclopropane carboxylic acid were not affected by increasing surface to volume ratio.     

Fingerprint analysis of thermolytic decarboxylation of tryptophan to tryptamine catalyzed by natural oils

A number of N,N-dialkylated tryptamines show psychoactive properties in man which resulted in a renewed interest in psychopharmacological research. Attempts to manufacture these derivatives are increasing within a clandestine environment, where literature procedures are adapted and information is exchanged on the Internet. One such example is based on the thermolytic decarboxylation of tryptophan to tryptamine as the precursor to psychoactive derivatives. This procedure was proposed to make use of household solvents such as turpentine substitute and white spirit to facilitate decarboxylation. Discussions on websites also suggested the catalytic use of natural oils in order to accelerate these reactions. In this research, the analytical characterization of this preparation procedure was carried out using gas chromatography-ion trap single and tandem stage mass spectrometry in electron and chemical ionization mode that led to the identification of previously unreported 1-mono and 1,1-disubstituted tetrahydro-beta-carboline (THBCs) by-products. The tryptamine product and several THBC by-products were determined quantitatively and a "fingerprint" analysis of the crude products allowed for the differentiation between the essential oil catalysts involved as indicated by the presence of tetrahydro-beta-carbolines and their imine intermediates.     

Analytical and semi-analytical solutions to flows of two immiscible Maxwell fluids between moving plates

Unsteady flows of two immiscible Maxwell fluids in a rectangular channel bounded by two moving parallel plates are studied. The fluid motion is generated by a time-dependent pressure gradient and by the translational motions of the channel walls in their planes. Analytical solutions for velocity and shear stress fields have been obtained by using the Laplace transform coupled with the finite sine-Fourier transform. These analytical solutions are new in the literature and the method developed in this paper can be generalized to unsteady flows of n-layers of immiscible fluids. By using the Laplace transform and classical method for ordinary differential equations, the second form of the Laplace transforms of velocity and shear stress are determined. For the numerical Laplace inversion, two accuracy numerical algorithms, namely the Talbot algorithm and the improved Talbot algorithm are used.     

Pressure dependence and branching ratios in the decomposition of 1-pentyl radicals: shock tube experiments and master equation modeling

The decomposition and intramolecular H-transfer isomerization reactions of the 1-pentyl radical have been studied at temperatures of 880 to 1055 K and pressures of 80 to 680 kPa using the single pulse shock tube technique and additionally investigated with quantum chemical methods. The 1-pentyl radical was generated by shock heating dilute mixtures of 1-iodopentane and the stable products of its decomposition have been observed by postshock gas chromatographic analysis. Ethene and propene are the main olefin products and account for >97% of the carbon balance from 1-pentyl. Also produced are very small amounts of (E)-2-pentene, (Z)-2-pentene, and 1-butene. The ethene/propene product ratio is pressure dependent and varies from about 3 to 5 over the range of temperatures and pressures studied. Formation of ethene and propene can be related to the concentrations of 1-pentyl and 2-pentyl radicals in the system and the relative rates of five-center intramolecular H-transfer reactions and β C-C bond scissions. The 3-pentyl radical, formed via a four-center intramolecular H transfer, leads to 1-butene and plays only a very minor role in the system. The observed (E/Z)-2-pentenes can arise from a small amount of beta C-H bond scission in the 2-pentyl radical. The current experimental and computational results are considered in conjunction with relevant literature data from lower temperatures to develop a consistent kinetics model that reproduces the observed branching ratios and pressure effects. The present experimental results provide the first available data on the pressure dependence of the olefin product branching ratio for alkyl radical decomposition at high temperatures and require a value of <ΔE(down)(1000 K)> = (675 ± 100) cm(-1) for the average energy transferred in deactivating collisions in an argon bath gas when an exponential-down model is employed. High pressure rate expressions for the relevant H-transfer reactions and β bond scissions are derived and a Rice Ramsberger Kassel Marcus/Master Equation (RRKM/ME) analysis has been performed and used to extrapolate the data to temperatures between 700 and 1900 K and pressures of 10 to 1 × 10(5) kPa.