Carbon Nanodiscs Research Articles

Tribological properties of fluorinated nanocarbons with different shape factors

The structural parameters of fluorinated nanocarbons presenting different shapes, i.e. spherical, tubular and discotic are investigated and correlated to their tribological properties. Different fluorination rates of graphitized carbon blacks (0D), carbon nanofibres (1D) and a mixture of carbon nanodiscs and nanocones (2D) were achieved under pure molecular fluorine gas flow (direct fluorination). Raman spectrometry, X-ray diffraction and 19F solid state nuclear magnetic resonance underline similar structure and nature of the CF bonds (covalent) for equivalent fluorine contents. In spite of the similarities of physical–chemical properties at equivalent fluorine contents, the tribological properties of the fluorinated nanocarbons differ. Those properties are discussed taking into account the role of the fluorine content and location of the fluorine atoms in the decrease of the interparticle interactions and in the cleavage of the external fluorocarbon layers to form the tribofilm. Finally, the effect of the shape is discussed.

Electrochemical properties of carbon nanodiscs

Carbon nanodiscs are new bottom-up prepared nanomaterials with well-defined diameter and thickness (of 1–2 μm and 20–50 nm, respectively). We investigate their electrochemical performance towards oxidation and reduction of small inorganic molecules as well as biomarkers. We have found that carbon nanodiscs exhibit faster observable heterogeneous electron transfer rates than graphite. However, this can be due to nanographitic impurities within the nanodiscs sample.

Nanocarbonaceous Filters for the Achievement of Highly Sensitive and Selective NO2 Monitoring by Means of Phthalocyanine-Based Resistive Sensors

The most recent results obtained on the development of selective gas sensing devices for nitrogen dioxide (NO2) monitoring associating phthalocyanine-based gas sensor and nanocarbonaceous chemical filter will be described. Since its electrical conductivity is very weakly modulated by reducing gases, copper phthalocyanine (CuPc) is a relevant semiconductor for the development of resistive sensors dedicated to oxidizing pollutants and confers to sensing devices a first level of selectivity. Ozone (O3) being the main interfering pollutant for NO2 monitoring in the context of air quality control, our approach consists in the implementation of a relevant chemical filter highly impervious to O3 and weakly reactive with NO2 placed upstream a CuPc-based sensing device. Because O3 is very reactive with carbon-carbon double bonds, different nanocarbons have been investigated as filter: activated carbons, single and multi-wall carbon nanotubes, nanofibres, nanodiscs. The filtering yields towards the target gases have been for the first time experimentally quantified. We have established the strong influence of the specific surface area of the materials which must be moderate to ensure a selective filtering. By means of graphitization and fluorination treatments, the dangling bonds, the carbonaceous matrix defects and the surface oxygenated groups (SOGs) have been identified as the most active sites of reaction. Amongst all the nanocarbons studied, a mixture of nanocones (30%) and nanodiscs (70%) has exhibited the highest filtering selectivity towards O3 and the best durability. Mechanisms of reaction are proposed and confirmed by complementary characterization techniques (Raman spectroscopy, SEM, EPR, NEXAFS). An original sensing device including carbon nanodiscs as filter and CuPc-based resistive sensor has been developed and exhibits high metrological performances in agreement with the required specifications of air quality control context: high sensitivity in the 0-200 ppb concentration range, high level of repeatability, threshold and resolution close to 10 ppb, total selectivity towards NO2, low sampling time. Strategies to enhance the durability of the filter as well as the sensing device will be finally discussed and the improvements assessed.

Friction Properties of Fluorinated Carbon Nanodiscs and Nanocones

The tribologic properties of carbon nanodiscs and nanocones and their fluorinated derivatives are investigated and correlated to their structure and chemical composition (atomic fluorine/carbon ratio). Two families of products are studied obtained by fluorination of ill ordered and highly graphitized carbon nanodiscs and nanocones. The studies clearly point out that friction properties of the nanoparticles are strongly dependent on the structure of the initial carbonaceous compounds. Better tribologic behaviour is obtained when the initial nanoparticles structure is highly ordered (graphitized particles). In that case, an optimum of fluorination rate is put in evidence.

Fluorinated nanocarbons using fluorinating agent: Strategies of fluorination and applications

The fluorination method strongly influences the physical properties of the resulting fluorinated carbon materials. Two fluorination ways, direct fluorination under pure fluorine gas and controlled fluorination by the decomposition of TbF4, have been used for the fluorination of particular nanocarbons: carbon nanofibers and a mixture of carbon nanodiscs and nanocones. Then, fluorocarbon matrix structures have been determined owing to solid state 19F NMR for MAS conditions at a spinning speed of 30 kHz. It reveals that the fluorination mechanism depends on the fluorination conditions but not on the starting nanocarbons morphology, i.e. tubular or planar. Finally, the electrochemical properties of carbon nanofibers fluorinated by the two ways are detailed. Controlled fluorination allows an increase of the power densities of fluorinated carbon nanofibers used as electrode in primary lithium batteries.

Direct Fluorination of Carbon Nanocones and Nanodiscs

This work focuses on the reactivity of carbon nanodiscs and nanocones with respect to pure fluorine gas. The starting materials, as-synthesized without post-treatment, consist of a mixture of nanodiscs (approximately 70% w/w), nanocones (approximately 20% w/w) and amorphous carbons (approximately 10% w/w). In order to investigate their reactivity in pure F2 gas, two experiment sets have been performed: (i) in situ Thermo Gravimetric Analysis under diluted F2 and relative F2 pressure measurements, which highlight the temperature domain for an efficient fluorination, and then, allow the fluorination conditions to be optimized; (ii) the fluorination under pure F2 gas was performed at temperatures ranged between room temperature and 450 degrees C. Ex situ characterization was carried out using 13C and 19F solid state Nuclear Magnetic Resonance and Scanning Electron Microscopy. For the low reaction temperature (up to 300 degrees C), the chemical stability of these kinds of nanocarbons prevents from intensive fluorination. On the other hand, at temperature higher than 300 degrees C, the fluorination is important but competes with the material decomposition. The fluorination mechanism has been established taking into account NMR and SEM data.

Effect of graphitization on fluorination of carbon nanocones and nanodiscs

The reactivity with pure fluorine gas of a mixture of carbon nanodiscs and nanocones was investigated. The starting materials were the as-prepared mixture, which results from cracking of heavy oils, and the sample post-treated at 2700 °C in argon atmosphere in order to increase the graphitization degree. The effect of this graphitization on the resulting fluorinated carbons was highlighted in terms of structural and morphological features using 13C and 19F solid-state nuclear magnetic resonance, electron paramagnetic resonance, Raman spectroscopy, atomic force microscopy and scanning electron microscopy. These characterizations were used to explain the electrochemical properties of these materials when used as an electrode in a primary lithium battery.

A transmission electron microscope and electron diffraction study of carbon nanodisks

The pyrolytic Kvaerner carbon-black and hydrogen process yields industrial amounts of carbon nanodisks and nanocones. We here report on the first detailed transmission electron microscope and electron diffraction study of such carbon nanodisks. The carbon nanodisk rim thickness ranges from 5–6 nm to 60–70 nm, but most disks are 10–30 nm thick. In agreement with earlier reported results, we find that the disk diameters fall within the range from 500 to 4000 nm. Most nanodisks display six identical pairs of facets. The two associated interfacial angles are θ 1 = (22 ± 1)° and θ 2 = 60.0°− θ 1. The nanodisk fracture surfaces reveal that the nanodisks are multi-layered structures. When the incident electron beam is perpendicular to the plane of the nanodisk we find that the diffraction patterns consist of concentric and continuous rings, on top of which there are discrete sets of diffraction spots. These spots display six-fold rotational symmetry and are consistent with the diffraction patterns of graphite layers.

A density functional theory study on the effect of shape and size on the ionization potential and electron affinity of different carbon nanostructures

Theoretical investigations were performed to study the structures and properties of different carbon nanoclusters. The computed properties were compared with those of the fullerene. The studied systems included carbon nano capsule, carbon nano bowl (one side closed tube), carbon nano disk and fullerene. The geometries of all species were optimized at the B3LYP level of theory using the 6-31G(d) basis set. Geometry of the silicon analog of fullerene (Si 60) was also optimized at the same level of the theory. The HOMO–LUMO energy gap, ionization potential and electron affinity of studied clusters are reported and compared with those of the fullerene. It was found that the computed electronic properties are significantly influenced by the shape and size of different carbon nanoclusters.