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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]

We report the fabrication of high-performance NO2 gas sensors based on oxyfluorinated graphene (OFG) layers. At room temperature, the times of adsorption/desorption of NO2 on/from the surface of thin OFG films are less than 1200 s and can be reduced by increasing the operation temperature. The sensors are capable of detecting NO2 molecules at sub-ppm level with a sensitivity of 0.15 ppm−1 at 348 K. The temperature dependence of the rate constants shows that the simultaneous presence of a large number of fluorine- and oxygen-containing groups on the graphene surface provides the formation of low-energy sites (ΔHa < 0.1 eV) for NO2 adsorption. The combination of the high sensitivity of the sensor and a reasonable adsorption/desorption time of the analyte is promising for on-line monitoring. [ABSTRACT FROM AUTHOR]

Herein, ZIF-8 pre-grown on carbon cloth (CC) leads to preferential and homogenizing Zn deposition to accelerate Zn-ion diffusion. CC with uniform Zn deposits induced from ZIF-8 promotes rapid Zn plating, resulting in balanced kinetics between electrodes. The as-assembled ZICs show a high specific capacitance of 302 F g−1 at 0.5 A g−1, an outstanding rate performance of 188 F g−1 at 20 A g−1 and 100% capacitance retention after 10000 cycles. [ABSTRACT FROM AUTHOR]

This is the first report on carbon–hydrogen (C–H) bond activation in benzene over a palladium catalyst supported on graphene oxide (GO) leading to the sole formation of biphenyl with a yield of 78%. The reaction was performed for 12 h in the presence of acetic acid and oxygen at 80 °C. XPS studies indicated that in the initial catalyst, Pd is mainly present as Pd(II) species on the GO surface. The interaction of these species with acetic acid during the reaction generates Pd acetate species. Density functional theory (DFT) studies revealed that the adsorption of the first benzene molecule on the Pd acetate is weak (0.15 eV) and the energy barrier of the following C–H bond scission is high, equal to 1.67 eV. The adsorption of the second benzene molecule is relatively strong (0.40 eV); acetic acid molecules are then released, leaving the biphenyl Pd intermediate, which enables biphenyl molecule formation. The presence of oxygen and acetic acid is needed for closing the catalytic cycle via the regeneration of the reactive Pd acetate. [ABSTRACT FROM AUTHOR]

The applicability of Cu/C catalysts is limited by sintering of Cu leading to deactivation in catalytic reactions. We show that the problem of sintering could be resolved by N-doping of the carbon support. Cu nanocatalysts with 1 at% of metal were synthesized by Cu acetate decomposition on N-free and N-doped (5.7 at% N) mesoporous carbon supports as well as on thermally expanded graphite oxide. Catalytic properties of these samples were compared in hydrogen production from formic acid decomposition. The N-doping leads to a strong interaction of the Cu species with the support providing stabilization of Cu in the form of clusters of less than 5 nm in size and single Cu atoms, which were observed in a significant ratio by atomic resolution HAADF/STEM even after testing the catalyst under harsh conditions of the reaction at 600 K. The mean size of the obtained Cu clusters was by a factor of 7 smaller than that of the particles in the N-free catalyst. The N-doped Cu catalyst possessed good stability in the formic acid decomposition at 478 K for at least 7 h on-stream and a significantly higher catalytic activity than the N-free Cu catalysts. The nature of the strongly interacting Cu species was studied by XPS, XRD and other methods as well as by DFT calculations. The presence of single Cu atoms in the N-doped catalysts should be attributed to their strong coordination by pyridinic nitrogen atoms at the edge of the graphene sheets of the support. We believe that the N-doping of the carbon support will allow expanding the use of Cu/C materials for different applications avoiding sintering and deactivation. [ABSTRACT FROM AUTHOR]

We report the fabrication of high-performance NO 2 gas sensors based on oxyfluorinated graphene (OFG) layers. At room temperature, the times of adsorption/desorption of NO 2 on/from the surface of thin OFG films are less than 1200 s and can be reduced by increasing the operation temperature. The sensors are capable of detecting NO 2 molecules at sub-ppm level with a sensitivity of 0.15 ppm -1 at 348 K. The temperature dependence of the rate constants shows that the simultaneous presence of a large number of fluorine- and oxygen-containing groups on the graphene surface provides the formation of low-energy sites (Δ H a < 0.1 eV) for NO 2 adsorption. The combination of the high sensitivity of the sensor and a reasonable adsorption/desorption time of the analyte is promising for on-line monitoring.