Fe3O4-Graphene oxide nanocomposite: Synthesis of 5-sulfanyl tetrazole derivatives of alkyls,indoles, and pyrroles

In this work, the use of Fe₃O₄/geraphene oxide nanocomposite as an efficient catalyst for the synthesis of 5-sulfanyltetrazole derivatives of indoles, pyrroles, and 5-alkyl sulfanyltetrazoles is described. These compounds are readily obtained by the reaction of the starting heterocycles indoles, N-aryl pyrroles, alkyl thiocyanates, and trimethylsilyl azide in good to excellent yields. Moreover, Fe₃O₄/GO nanocomposite could be easily separated from the reaction mixtures by an external permanent magnet and reused at least six times continuously without significant reduction in the product yield and its catalytic activity.     

Preparation of different graphene nanostructures for hydrogen adsorption

In this study, different types of graphene were synthesized to investigate hydrogen adsorption capacity at different pressures (0–34 bar) at room temperature (298 K). Graphene and nanoporous graphene were prepared by Chemical Vapor Deposition (CVD) method, using methane as a carbon source at a temperature of 900 °C over copper plates and nickel oxide nanocatalyst. The nickel oxide nanocatalyst was prepared by sol–gel method, whereas graphene oxide was prepared through modified Hummer's method. The products were characterized by X‐ray diffraction, field emission‐scanning electron microscopy, energy dispersive spectroscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, Brunauer–Emmett–Teller and Raman spectroscopy. The adsorption of hydrogen was done by volumetric method. High adsorption capacity was achieved in nanoporous graphene because of its high pore volume (2.11 cm³/g) and large specific surface area (850 m²/g). Hydrogen adsorption values for nanoporous graphene, graphene and graphene oxide were determined as 2.56, 1.70 and 0.74 wt%, respectively. In addition, the hydrogen adsorption of graphene nanostructures fitted nicely to the selected two‐parameter and three‐parameter adsorption isotherm models. The adsorption isotherm model coefficients have been found for a 0–34 bar pressure range. The parameter values for all adsorbents showed proper conformity to the model and experimental data. Copyright © 2016 John Wiley & Sons, Ltd.     

A novel sacrificial interlayer-based method for the preparation of silicon carbide membranes

A novel method is presented based on the use of sacrificial interlayers for the preparation of nanoporous silicon carbide membranes. It involves periodic and alternate coatings of polystyrene sacrificial interlayers and silicon carbide pre-ceramic layers on the top of slip-casted tubular silicon carbide supports. Membranes prepared by this technique exhibit single gas ideal separation factors of helium and hydrogen over argon in the ranges 176–465 and 101–258, respectively, with permeances that are typically two to three times higher than those of silicon carbide membranes prepared previously by the more conventional techniques. Mixed-gas experiments with the same membranes indicate separation factors as high as 117 for an equimolar H₂/CH₄ mixture. We speculate that the improved membrane characteristics are due to the sacrificial interlayers filling the pores in the underlying structure and preventing their blockage by the pre-ceramic polymer. The new method has good promise for application to the preparation of a variety of other inorganic microporous membranes.     

Synthesis and antibacterial evaluation of new sulfanyltetrazole derivatives bearing piperidine dithiocarbamate moiety

A series of new alkyl or aryl sulfanyltetrazole derivatives containing dithiocarbamate moiety (5a–6e) were synthesized. The structures of the compounds were characterized by IR, ¹H NMR, ¹³C NMR spectra, and elemental analysis data. The present study examines the antibacterial potential of novel synthetic sulfanyltetrazole compounds against clinically important gram-positive and -negative strains. The results of screening showed that attachment of dithiocarbamate to sulfanyltetrazole derivatives results in enhancement of antibacterial activity. The compound 6d showed the best activity among the tested compounds. Also, the less polar 2,5-disubstituted sulfanyltetrazole regioisomers showed an increased antibacterial activity compared with the corresponding more polar regioisomers.     

A new hydrogen cyanide chemiresistor gas sensor based on graphene quantum dots

Graphene quantum dots (GQDs), synthesised via controlled carbonisation of citric acid, were reduced by hydrazine hydrate and then used as hydrogen cyanide (HCN) gas sensors. Checking of the reduction step by Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) techniques revealed that most of the oxygen-containing functional groups were removed from the GQDs. It was observed the reduction process is necessary for sensitising of GQDs for HCN gas. The electrical resistance of the reduced GQDs was increased as a result of their exposure to HCN gas. Accepting a p-type semiconducting characteristic for GQD material, the above-mentioned behaviour suggested electron donation from HCN to GQD. The sensor response to HCN gas was reversible, suggesting a reversible adsorption/desorption phenomenon of HCN to the GQDs. The response as well as the recovery time of the sensor was different depending on the HCN concentration tested. The developed sensor showed linear HCN response from 1 to 100 ppm. The detection limit of the sensor was estimated to be 0.6 ppm (S/N). Relative standard deviation f HCN determination by the developed sensor was calculated to be 5.7% (n = 4, [HCN] = 50 ppm). The sensor response was did not vary significantly within 6 months.     

Bulky organosilicon compounds based on sulfanyltetrazoles: their synthesis and in vitro antibacterial evaluation

The study introduces different organosilicon derivatives incorporating sulfanyltetrazole ring for biological applications. Initially, the sulfanyltetrazole derivatives and halo-analogues (Br, I) were synthesized. Later, selective reaction of tris(trimethylsilyl)methyllithium (TsiLi) in the presence (?46 and 0 °C) and absence (room temperature) of CS₂ with halo-sulfanyltetrazole derivatives yielded new multifunctional sulfanyltetrazole regioisomers with SH, C = S, ethynylthio and SiMe₃ groups, respectively. All the synthesized compounds were characterized by IR, ¹H-NMR, ¹³C-NMR spectra and elemental analysis data. The compounds were screened for their antibacterial activities against clinically important gram-positive and gram-negative bacteria using the spectrophotometric microdilution method. The preliminary screening indicated that the organosilicon derivatives incorporating SH and C = S (mercapto-silyl-thiones) and silyl-thioalkynes have antibacterial activities, whereas no antibacterial activity was observed on compounds containing (Me₃Si)₃C groups. Of the synthesized compounds, compound 5d showed the best activity against all the tested organisms (3.91–31.25 µg/mL).