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The effect of humidity on the electrical conductivity of single-walled carbon nanotube (SWCNT) films depends on both the conductivity of individual nanotubes and the electrical contacts between them. Here, we study these factors by comparing the sensor response of nanotubes with fluorine- and nitrogen-containing groups attached to the sidewalls. Experiments carried out in a wide range of relative humidity (RH) at room and elevated temperatures showed that the conductivity of non-functionalized SWCNTs and contacts between them decreases upon the adsorption of water molecules. Covalent fluorination reduces the conductivity of SWCNTs and significantly increases the sensitivity of the film to low concentrations of water vapor. The response at high RH decreases due to the large number of water molecules adsorbed on the conductive regions of the nanotubes. As a result of substitutional reactions of fluorinated SWCNTs with dimethylformamide and ethylenediamine, nitrogen-containing groups are added, the amount of which, however, is much less than the amount of fluorine. This modification of the SWCNTs improves intertube contacts in the film and increases the surface area for water adsorption. Our results show that an increase in the number of functional groups on the SWCNT surface enhances the sensitivity of the sensor to low water concentrations and worsens the response at high RH. SWCNTs modified with ethylenediamine have the highest sensitivity over the entire range of RH. [ABSTRACT FROM AUTHOR]

The huge molecular cluster {Fe30Mo72} has been used as a source of catalyst nanoparticles in catalytic chemical vapour deposition (CCVD) process of carbon nanotubes (CNTs) synthesis. Thermal decomposition of {Fe30Mo72} in air is shown by X‐ray diffraction analysis to produce iron molybdate, which is converted to alloyed Fe‐Mo and Fe nanoparticles at elevated temperature and reduction environment. These nanoparticles supported on MgO, catalyse the growth of single‐walled, double‐walled and/or multi‐walled CNTs depending on the active metal loading and ratio of methane and hydrogen in the feedstock. The structural parameters of the products are studied by transmission electron microscopy and Raman spectroscopy. The best CNT samples are tested as field electron emitters. [ABSTRACT FROM AUTHOR]

Graphene derivatives are promising sensor materials due to their high surface area available for molecule adsorption and conductivity changes under the adsorbate impact. The selectivity of such materials can be tuned through the attaching of certain functional groups preferably interacting with the defined gases. In the present work, we compare the reactivity of graphene oxide, oxyfluorinated graphene, and fluorinated graphene toward gaseous NOx molecules. The interaction of the molecules with the graphene‐based films was monitored by in situ X‐ray photoelectron and near‐edge X‐ray absorption fine structure spectroscopy measurements. The spectra before and after exposure of the films to a gaseous NOx mixture detected equal concentrations of adsorbed NO2 and NO species on graphene oxide, the preferable interaction of oxyfluorinated graphene with NO2 and the absence of the adsorbed molecules on the fluorinated graphene surface. These results are useful for the development of selective graphene‐based gas sensors. [ABSTRACT FROM AUTHOR]

Formic acid is a promising liquid organic hydrogen carrier (LOHC) since it has relatively high hydrogen content (4.4 wt%), low inflammability, low toxicity and can be obtained from biomass or from CO2. The aim of the present research was the creation of efficient 1 wt% Pd catalysts supported on mesoporous graphitic carbon (Sibunit) for the hydrogen production from gas-phase formic acid. For this purpose, the carbon support was modified by pyrolysis of deposited precursors containing pyridinic nitrogen such as melamine (Mel), 2,2′-bipyridine (Bpy) or 1,10-phenanthroline (Phen) at 673 K. The following activity trend of the catalysts Pd/Mel/C > Pd/C ~ Pd/Bpy/C > Pd/Phen/C was obtained. The activity of the Pd/Mel/C catalyst was by a factor of 4 higher than the activity of the Pd/C catalyst at about 373 K and the apparent activation energy was significantly lower than those for the other catalysts (32 vs. 42–46 kJ/mol). The high activity of the melamine-based samples was explained by a high dispersion of Pd nanoparticles (~2 nm, HRTEM) and their strong electron-deficient character (XPS) provided by interaction of Pd with pyridinic nitrogen species of the support. The presented results can be used for the development of supported Pd catalysts for hydrogen production from different liquid organic hydrogen carriers. [ABSTRACT FROM AUTHOR]