Chemical synthesis of mesoporous CuO from a single precursor: Structural, optical and electrical properties

We report a simple method for growing photoluminescent mesoporous CuO nanoparticles by a chemical route, using the single precursor technique. The final products were characterized by powder X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), N₂ adsorption-desorption isotherm, UV-vis absorption spectroscopy, photoluminescence (PL) spectroscopy, Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy and Hall measurements. Structural analysis reveals that the average pore diameter of the as-prepared CuO is about 38.8 Å and it comes with an average surface area of 66.63 m²/g. N₂-sorption analysis shows that the resulting isotherm as type IV; which is the characteristic of mesoporous materials. The average crystal diameter, as derived from the XRD data analysis is found to be about 20 nm. FESEM measurement reveals that the material is composed of cubic nanoparticles. The UV-vis spectrum of the material shows significant amount of blue-shift in the band gap energy (E_g), due to the quantum confinement effect exerted by the nanocrystals. The Raman study of the CuO nanostructures also indicates the high crystalline nature of the material. From the positive sign of Hall coefficient, the p-type conduction nature of the deposited film is established. The film was found to show high magnetoresistance, which is in the order of 10⁵ Ω.     

Intramolecular 1,3-dipolar cycloaddition reactions in the synthesis of complex annelated quinolines, α-carbolines and coumarins

In this study, we report the synthesis of several novel dihydroisoxazole-, tetrahydroisoxazole- and dihydropyrazole-fused pyrido[2,3-b]quinolines, α-carbolines, and pyrido[2,3-c]coumarins, respectively, from simple precursors and by exploring intramolecular 1,3-dipolar cycloaddition reactions involving nitrile oxides, nitrones, and nitrile imines as 1,3-dipoles.     

A two component thermoreversible hydrogel of riboflavin and melamine: Enhancement of photoluminescence in the gel form

A new thermoreversible hydrogel of riboflavin and melamine supramolecular complex (> or =0.02%, w/v) shows enhanced photoluminescence properties through H-bonding.     

Electrical bistability in electrostatic assemblies of CdSe nanoparticles

We report electrical bistability in electrostatic assembly of CdSe nanoparticles. We obtained thin films of the nanoparticles via layer-by-layer electrostatic assembly technique, which provided a nanoscale control to tune the thickness. Devices based on such thin films exhibit electrical bistability along with memory phenomenon. The bistability is due to charge confinement in the nanoparticles. Conduction mechanism changes from an injection-dominated to a bulk one during switching from a low- to a high-conducting state. Additionally, results from impedance spectroscopy show that the dielectric constant of the material increases during the transition. Both random-access and read-only memory applications are observed in these systems.     

A novel and facile synthesis of 3,5-Disubstituted isothiozoles under metal free conditions using acetophenones and dithioesters

Abstract

A facile and conveniently simple new protocol is devised for the synthesis of 3,5-disubstituted and annulated isothiozoles under transition metal and catalyst free conditions utilizing easily available acetophenones, dithioesters and NH₄OAc. This strategy involves C=O and C=S functionalization via sequential imine formation followed by intra molecular cyclization and aerial oxidation forming consecutive C?N and S?N bonds respectively in one pot. This protocol offers a low cost, user friendly, straight forward and widely applicable approach to 3,5-disubstituted isothiazoles.     

Stereoselective palladium-catalyzed allylic alkylations of peptide amide enolates

Pd-catalyzed allylations are an excellent tool for stereoselective peptide modifications, being clearly superior to normal alkylations. The reactions proceed not only in high yield, but also high regio- and diastereoselectivities, and trans-products are formed exclusively. Therefore, this is a powerful synthetic tool for natural product and drug synthesis.     

Nucleophilic reactivity of a series of peroxomanganese(III) complexes supported by tetradentate aminopyridyl ligands

Peroxomanganese(iii) adducts have been postulated as important intermediates in manganese-containing enzymes and small molecule oxidation catalysts. Synthetic peroxomanganese(iii) complexes are known to be nucleophilic and facilitate aldehyde deformylation, offering a convenient way to compare relative reactivities of complexes supported by different ligands. In this work, tetradentate dipyridyldiazacycloalkane ligands with systematically perturbed steric and electronic properties were used to generate a series of manganese(ii) and peroxomanganese(iii) complexes. X-Ray crystal structures of five manganese(ii) complexes all show the ligands bound to give trans complexes. Treatment of these Mn(II) precursors with H(2)O(2) and Et(3)N in MeCN at -40 °C results in the formation of peroxomanganese(iii) complexes that differ only in the identity of the pyridine ring substituent and/or the number of carbons in the diazacycloalkane backbone. To determine the effects of small ligand perturbations on the reactivity of the peroxo group, the more thermally stable peroxomanganese(iii) complexes were reacted with cyclohexanecarboxaldehyde. For these complexes, the rate of deformylation does not correlate with the expected nucleophilicity of the peroxomanganese(iii) unit, as the inclusion of methyl substituents on the pyridines affords slower deformylation rates. It is proposed that adding methyl-substituents to the pyridines, or increasing the number of carbons on the diazacycloalkane, sterically hinders nucleophilic attack of the peroxo ligand on the carbonyl carbon of the aldehyde.     

Effective photocatalytic degradation of organic pollutant by ZnS nanocrystals synthesized via thermal decomposition of single-source precursor

2-Aminocyclopentene-1-dithiocarboxylate complex of zinc(II) has been synthesized and found to be an effective single-source precursor for the preparation of ZnS NCs (rod and sphere) by the use of ethylenediamine and hexadecylamine as structure directing solvents. Structural characterizations were carried out using XRD, TEM and BET measurements and the optical properties by UV-Vis and PL spectroscopic techniques. The prepared ZnS NCs show effective photocatalytic activity towards the degradation of Rose Bengal dye (RB) under light irradiation for their probable application in waste water treatment. The degradation mechanism of RB dye under light irradiation is established by terephthalic acid photoluminescence probing technique.     

Thermosolutal Convection in a Rectangular Concentric Annulus: A Comprehensive Study

This investigation presents numerical treatment of governing equations pertaining to thermosolutal flow within an annulus and an application of a model describing the important physical phenomenon as found in muffle furnace. The inner side of the annulus is exposed to high temperature and high solute concentration while the outer side of the annulus is maintained at low temperature and low solute concentration. Darcy-Brinkman-Forchheimer model is used to study the flow, heat and solute transfer in a non-Darcian saturated porous media. The solution is obtained upon application of control volume integration. Modified MAC method is used for the numerical solution of governing equations. Gradient dependent consistent hybrid upwind scheme of second order (GDCHUSSO) is used for discretization of the convective terms. The parameters such as Rayleigh-Darcy number, Darcy number, buoyancy ratio and width ratio, that govern the flow phenomenon have been identified and their effects are critically examined. The fluid flow pattern in the annular space and the associated heat and mass transfer are conceptualized from the obtained isoconcentration, isotherm and flowline contour maps.