Transport properties of nitrile and carbonate solutions of [P66614][NTf2] ionic liquid, its thermal degradation and non-isothermal kinetics of decomposition.

The electrical conductivity, density and diffusion coefficients of trihexyl(tetradecyl)phosphonium bis(trifluoromethylsulfonyl)amide ([P66614][NTf2]) ionic liquid and its binary solutions in acetonitrile, propionitrile, dimethyl and diethyl carbonates were measured in the temperature range of 293-348 K. The electrical conductivity - ionic liquid mole fraction dependencies for the binary solutions were fitted with the empirical Casteel-Amis equation. The temperature dependencies of electrical conductivity were analyzed using the Arrhenius, Litovitz and Vogel-Fulcher-Tammann approaches. The dependences of the Arrhenius activation energy and pre-exponential factor on the mole fraction of ionic liquid in the solutions were fitted with the empirical equations proposed in the literature. The thermo-gravimetric analysis combined with mass spectrometry demonstrated the high thermal stability of [P66614][NTf2] up to 600 K. At higher temperatures the decomposition of [P66614][NTf2] proceeded via the elimination of alkyl radicals as a result of the nucleophilic attack of reactive intermediates to the [P66614]+ cation with the formation of trialkylphosphines. The activation energies of the thermal destruction of [P66614][NTf2] were calculated using the Kissinger equation and non-linear integral isoconversional model.

Adsorption of water and n-hexane on pristine and oxidized carbon nanotube supports of cobalt-based Fischer-Tropsch catalysts.

Adsorption of model polar (water) and non-polar (n-hexane) compounds on the surface of oxidized and non-oxidized carbon nanotube (CNT) supports at different stages of Co/CNT catalyst preparation has been studied to reveal the influence of the surface functionalization of the CNT support on the catalyst selectivity in Fischer-Tropsch synthesis (FTS). Dynamic vapor sorption experiments showed that defunctionalization of the surface of the CNT support during catalyst annealing and reduction led to its hydrophobization and, as a result, no noticeable difference was observed between the adsorption properties of the oxidized and non-oxidized supports towards water and hydrocarbons. Therefore, oxidation of the CNT support does not significantly affect the adsorption properties of the supported catalyst and it is not a crucial factor for the catalyst selectivity in FTS.

Kinetics of the defunctionalization of oxidized few-layer graphene nanoflakes.

Thermal defunctionalization of oxidized jellyfish-like few-layer graphene nanoflakes was studied under non-isothermal conditions by simultaneous thermal analysis. Activation energies for thermal decomposition of different oxygen functional groups were calculated by the Kissinger method and compared with those for oxidized carbon nanotubes. Oxygen content in graphene nanoflakes was found to significantly affect the decomposition activation energies of carboxylic and keto/hydroxy acids because of their acceptor properties and strong distortion of the graphene layers at the edges of the nanoflakes. The structure of the carbon material and the oxygen chemical state significantly influence the decomposition kinetics of thermally stable oxygen-containing groups. The activation energy for thermal decomposition of phenol groups (110-150 kJ mol-1) is close to that for graphene oxide reduction.

3D Frameworks with Variable Magnetic and Electrical Features from Sintered Cobalt-Modified Carbon Nanotubes.

3D frameworks of carbon nanotubes (CNTs) uniformly decorated by cobalt oxide or carbon-encapsulated cobalt nanoparticles were obtained by spark plasma sintering for the first time. The influence of the sintering temperature ( TS) and Co content on the morphology, structure, and electrical and magnetic properties of the obtained materials was investigated by Raman spectroscopy, electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and in situ magnetometry. It was shown that application of the SPS technique allowed simultaneous compaction of the material, formation of CNT framework, and Co oxide reduction. The appearance of the carbon shell around 4-10 nm Co particles was observed at TS > 600 °C. At higher TS, the Co particle size increased (up to 300 nm at 1400 °C), whereas the carbon shell ordered and thickened. The formation of large-size few-layers graphene sheets was observed at TS = 1400 °C. Electrical conductivity of the composites was found to be higher than that of sintered pristine CNTs and varied in the range of 500-12 500 Sm/m. Magnetic experiments demonstrated soft magnetization of the samples and the coercivity of 200-300 Oe. Thus, the obtained CNT-based material is simultaneously compact, formable, electroconductive, and ferromagnetic. Its properties can be tuned by variation of the sintering parameters. Synthesized cobalt-modified carbon 3D structures are promising for the application in magnetic separation, catalysis, fuel cells, and electromagnetic shielding.

Oxidation, defunctionalization and catalyst life cycle of carbon nanotubes: a Raman spectroscopy view.

Pristine, oxidized and defunctionalized carbon nanotubes (CNTs) were studied by Raman spectroscopy, X-ray diffraction, transmission electron microscopy and low temperature nitrogen adsorption. The Raman spectra of the studied samples in the range of 900-1800 cm-1 were deconvoluted into five components to reveal the CNT oxidation mechanism. It was found that the oxidation resulted in the reduction of graphite components and ordering of both the structured and defect part of CNTs. Acid treatment also led to different types of disorders in the surface layers of CNTs. Polyene-type, polyphenylene-type and turbostratic fragments were detected as a result of partial exfoliation. Investigation of defunctionalized CNTs showed the ordering of edge carbon atoms as well as the invariability of the total amount of defects. The study of CNTs as supports for Co-based catalysts revealed a simultaneous decrease in the number of defect fragments and increase in the number of edge carbon atoms during catalyst preparation and reduction.