Results: 1 - 20of3827

Syntheses of 2-aryl and 2,3-substituted indoles were realized by modified double elimination protocol. Under basic conditions, vinyl sulfones derived from the reaction of 2-aminobenzyl sulfone with benzaldehydes underwent cyclization and alkylation followed by elimination of sulfinic acid to afford 2,3-substituted indoles.

Li–S batteries are heavily researched as they are capable of meeting the demands of electrification of transport systems, provided their inherent polysulfide shuttling can be prevented to enhance the cycle life. Although several approaches have been made to mitigate the shuttling effect, success is limited due to the poor adsorption capability of polysulfides on the cathode surface. Herein, we propose an efficient approach of using two-dimensional materials with permanent dipoles in the separator to inhibit mass transport of polysulfides from cathode and subsequent parasitic reactions on the metallic lithium anode. Two-compartment H-cell experiments coupled with spectroscopic studies, such as ultraviolet–visible absorption, nuclear magnetic resonance spectroscopy, and Fourier transform infrared spectroscopy, are used to demonstrate the interactions between the two-dimensional materials-modified separator and polysulfide species. Furthermore, electrochemical properties reveal the excellent specific capacity of 1210 mAh g–1 and self-discharge studies suggest the feasibility of modified separator for commercial applications.

Lithium–sulfur (Li–S) chemistry is projected to be one of the most promising for next-generation battery technology, and controlling the inherent “polysulfide shuttle” process has become a key research topic in the field. Regulating intermediary polysulfide dissolution by understanding the metamorphosis is essential for realizing stable and high-energy-density Li–S batteries. As of yet, a clear consensus on the basic surface/interfacial properties of the sulfur electrode has not been achieved, although the catalytic phenomenon has been shown to result in enhanced cell stability. Herein, we present evidence that the polysulfide shuttle in a Li–S battery can be stabilized by using electrocatalytic transition metal dichalcogenides (TMDs). Physicochemical transformations at the electrode/electrolyte interface of atomically thin monolayer/few-layer TMDs were elucidated using a combination of spectroscopic and microscopic analysis techniques. Preferential adsorption of higher order liquid polysulfides and subsequent conversion to lower order solid species in the form of dendrite-like structures on the edge sites of TMDs have been demonstrated. Further, detailed electrochemical properties such as activation energy, exchange current density, rate capabilities, cycle life, etc. have been investigated by synthesizing catalytically active nanostructured TMDs in bulk quantity using a liquid-based shear-exfoliation method. Unveiling a specific capacity of 590 mAh g–1 at 0.5 C rate and stability over 350 cycles clearly indicates yet another promising application of two-dimensional TMDs.

A second-harmonic generation (SHG) crystal 2-amino-5-nitropyridinium-toluenesulfonate (2A5NPT) has been synthesized. Good quality single crystal of 2A5NPT was successfully grown by the slow evaporation method with dimensions 16 × 15 × 8 mm3. The unit cell dimensions were determined from single crystal X-ray diffraction studies. GAUSSIAN 98W has been used to calculate the first-order hyperpolarizability of 2A5NPT. The calculated first-order hyperpolarizability of 2A5NPT is 142 × 10−30 esu. The structural perfection of the grown crystals has been analyzed by high-resolution X-ray diffraction (HRXRD) rocking curve measurements. Fourier transform infrared (FTIR) spectral studies have been performed to identify the functional groups. The optical transmittance window and the lower cutoff wavelength of the 2A5NPT have been identified by UV−vis−NIR studies. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) were used to study its thermal properties. Powder test with Nd:YAG laser radiation shows a high second harmonic generation.

Batch distillation is known to be less energy efficient than its continuous counterpart. However, it has received renewed interest last years owing to the flexibility it offers. In an effort to reduce energy consumption, a batch distillation with a side withdrawal (BDS) was proposed recently. In this contribution, we first construct the fundamental model for an unsteady state BDS process and simulate the column to derive an operational policy. Although the representative process was proved as an energy efficient scheme, in order to improve further the thermodynamic efficiency of the BDS structure, we propose an adaptive vapor recompression mechanism that considers the top vapor recompression with a variable speed. Apart from the compression ratio (CR), the other two manipulated variables involved are the external heat input to the reboiler through steam and the flow rate of overhead vapor entering the compressor. It is investigated that the two manipulated variables are required to adapt simultaneously throughout the batch operation; one is the CR and another one is either the heat input to the still or the overhead vapor rate. Finally, the influence of the adaptive vapor recompression scheme on the energetic and economic aspects is evaluated through intensive comparison against the conventional stand alone column. The proposed adaptive vapor recompression strategy appears overwhelmingly superior to its conventional counterpart in terms of thermal efficiency and economic performance.

The synthesized (Bi1.88Fe0.12)(Fe1.42Te0.58)O6.87 is characterized with so far the highest Fe content among pyrochlores. Consequently, it exhibits a strong spin-glass magnetic transition at around 20 K. The dielectric relaxation in the same temperature range originates from multiwall hopping of the displaced ions on A and O′ sites. The displacement was confirmed with the structural analysis of the pyrochlore using Rietveld refinement on joint neutron and X-ray diffraction data. At room temperature, the pyrochlore exhibits a cubic Fd3̅m symmetry (a = 10.38804 (13) Å) with Fe3+ ions sharing A and B structural sites. The refined results indicate on a displacive disorder with A-site positioned at 96g and O′ positioned at 32e. The lattice vibrational analysis using Raman spectra is in agreement with the displacive disorder of the pyrochlore.

We investigated the structure and magnetic properties of Ce-doped NiO and Co3O4 samples. The multiemission centers created in the nanostructures observed from PL spectra were obviously due to the formation of interstitials (Nii and Coi) and oxygen vacancies (VO) by the incorporation of Ce3+ ions into the lattice site which affects the band gap structure of the material. Room-temperature magnetic study was demonstrated for Ce-doped NiO and Co3O4 nanostructures using a vibrating sample magnetometer. The origin of magnetism in these samples was related to the finite size and importantly oxygen vacancies created by the Ce ion dopant, which was confirmed from the decrease of magnetization value at room temperature compared to undoped NiO and Co3O4 samples.

A number of silica supported nickel carbonate systems were studied by positron annihilation lifetime spectroscopy (PAS) and nitrogen gas adsorption method (BET) to evaluate the pore size distribution in the samples. Results show that the long-lived o-Ps component gives a pore size much smaller than the average pore radius obtained from BET analysis. This indicates that o-Ps represents the pores of smaller size in a sample with wide pore size distribution.