Abstract: The possibility of confinement effects inside a carbon nanotube provides new application opportunities, e.g., growth of novel carbon nanostructures. However, the understanding the precise role of catalystfeedstock in the nanostructure synthesis is still elusive. In our simulation-based study, we investigate the Ni-catalyzed growth mechanism of encapsulated carbon nanostructures, viz. double-wall carbon nanotube and graphene nanoribbon, from carbon and hydrocarbon growth precursors, respectively. Specifically, we find that the tube and ribbon growth is determined by a catalyst-vs-feedstock competition effect. We compare our results, i.e., growth mechanism and structure morphology with all available theoretical and experimental data. Our calculations show that all encapsulated nanostructures contain metal (catalyst) atoms and such structures are less stable than their pure counterparts. Therefore, we study the purification mechanism of these structures. In general, this study opens a possible route to the controllable synthesis of tubular and planar carbon nanostructures for today’s nanotechnology.

Abstract: Using self-consistent KohnSham density-functional theory molecular dynamics simulations, we demonstrate the theoretical possibility to synthesize NiC60, the incarfullerene Ni@C60 and the heterofullerene C59Ni in an ion implantation setup. The corresponding formation mechanisms of all three complexes are elucidated as a function of the ion implantation energy and impact location, suggesting possible routes for selectively synthesizing these complexes.

Abstract: Ion irradiation of carbon nanotubes very often leads to defect formation. However, we have recently shown that Ar ion irradiation in a limited energy window of 1025 eV may enhance the initial cap nucleation process, when the carbon network is in contact with the metal nanocatalyst. Here, we employ reactive molecular dynamics simulations to demonstrate that ion irradiation in a higher energy window of 1035 eV may also heal network defects after the nucleation stage through a non-metal-mediated mechanism, when the carbon network is no longer in contact with the metal nanocatalyst. The results demonstrate the possibility of beneficially utilizing ions in e.g. plasma-enhanced chemical vapour deposition of carbon nanotubes.

Abstract: Utilizing ammonia as a storage medium for hydrogen is currently receiving increased attention. A possible method to retrieve the hydrogen is by plasma-catalytic decomposition. In this work, we combined an experimental study, using a dielectric barrier discharge plasma reactor, with a plasma kinetic model, to get insights into the decomposition mechanism. The experimental results revealed a similar effect on the ammonia conversion when changing the flow rate and power, where increasing the specific energy input (higher power or lower flow rate) gave an increased conversion. A conversion as high as 82 % was achieved at a specific energy input of 18 kJ/Nl. Furthermore, when changing the discharge volume from 31 to 10 cm3, a change in the plasma distribution factor from 0.2 to 0.1 was needed in the model to best describe the conversions of the experiments. This means that a smaller plasma volume caused a higher transfer of energy through micro-discharges (non-uniform plasma), which was found to promote the decomposition of ammonia. These results indicate that it is the collisions between NH3 and the high-energy electrons that initiate the decomposition. Moreover, the rate of ammonia destruction was found by the model to be in the order of 1022 molecules/(cm3 s) during the micro-discharges, which is 5 to 6 orders of magnitude higher than in the afterglows. A considerable re-formation of ammonia was found to take place in the afterglows, limiting the overall conversion. In addition, the model revealed that implementation of packing material in the plasma introduced high concentrations of surface-bound hydrogen atoms, which introduced an additional ammonia re-formation pathway through an Eley-Rideal reaction with gas phase NH2. Furthermore, a more uniform plasma is predicted in the presence of MgAl2O4, which leads to a lower average electron energy during micro-discharges and a lower conversion (37 %) at a comparable residence time for the plasma alone (51 %).

Abstract: Sensitive multi-element analysis techniques together with major-element and isotopic analyses were applied to spring, mine and surface waters in the vicinity of an important known zinclead deposit in a carbonate environment, in the Les Malines area (Gard, France). Both the dissolved and suspended phases were investigated, and concretions and sediments were also considered in some cases. This methodological test shows that the ore body leaves various clear fingerprints, such as the Zn, As, Sb, Pb and U levels in the dissolved phase, the sulfate increment and the δ 34S. Some of the elements in solution are controlled by slightly soluble compounds, e.g. Zn by smithsonite and hydrozincite, Ba by barite, and Pb by hydrocerussite. Mapping the saturation indices for these elements appears useful for displaying the hydrogeochemical anomaly.

Abstract: The equilibrium bond length, harmonic frequency, first and second order anharmonicity constants, rotational and centrifugal distortion constants, as well as the rotation-vibrational and centrifugal coupling constants for the ground X(2) Sigma(+) and first excited A(2) Pi states of the SiN radical have been calculated at the complete active space SCF (CASSCF), multireference CI (MRCI) and coupled cluster (CCSD(T)) levels using Dunning's correlation-consistent basis sets. The excitation energy of the A(2) Pi State has also been computed at these theoretical levels. Dipole moments of SiN in the X(2) Sigma(+) and A(2) Pi states are given. Our study shows that core correlation must be considered in order to obtain satisfactory accuracy for the spectroscopic constants.

Abstract: A molecular dynamics (MD) study of MgxAlyOz thin films grown by magnetron sputtering is presented using an ionic model and comparing two potential sets with formal and partial charges. The applicability of the model and the reliability of the potential sets for the simulation of thin film growth are discussed. The formal charge potential set was found to reproduce the thin film structure in close agreement with the structure of the experimentally grown thin films. Graphical abstract A molecular dynamics study of growth of MgxAlyOz thin films is presented using an ionic model and comparing two potential sets with formal and partial charges. The simulation results with the formal charge potential set showed a transition in the film from a crystalline to an amorphous structure, when the Mg metal content decreases below 50% in very close agreement with the structure of the experimentally deposited films.

Abstract: Thermal-catalytic gas processing is integral to many current industrial processes. Ever-increasing demands on conversion and energy efficiencies are a strong driving force for the development of alternative approaches. Similarly, synthesis of several functional materials (such as nanowires and nanotubes) demands special processing conditions. Plasma catalysis provides such an alternative, where the catalytic process is complemented by the use of plasmas that activate the source gas. This combination is often observed to result in a synergy between plasma and catalyst. This Review introduces the current state-of-the-art in plasma catalysis, including numerous examples where plasma catalysis has demonstrated its benefits or shows future potential, including CO2 conversion, hydrocarbon reforming, synthesis of nanomaterials, ammonia production, and abatement of toxic waste gases. The underlying mechanisms governing these applications, as resulting from the interaction between the plasma and the catalyst, render the process highly complex, and little is known about the factors leading to the often-observed synergy. This Review critically examines the catalytic mechanisms relevant to each specific application.

Abstract: Reactive oxygen and nitrogen species (RONS) are involved in many biochemical processes, including nitrooxidative stress that causes cancer cell death, observed in cancer therapies such as photodynamic therapy and cold atmospheric plasma. However, their mechanisms of action and selectivity still remain elusive due to the complexity of biological cells. For example, it is not well known how RONS generated by cancer therapies permeate the cell membrane to cause nitro-oxidative damage. There are many studies dedicated to the perme­ation of RONS across native and oxidized membranes, but not across nitrated membranes, another lipid product also generated during nitro-oxidative stress. Herein, we performed molecular dynamics (MD) simulations to calculate the free energy barrier of RONS permeation across nitrated membranes. Our results show that hy­drophilic RONS, such as hydroperoxyl radical (HO2) and peroxynitrous acid (ONOOH), have relatively low barriers compared to hydrogen peroxide (H2O2) and hydroxyl radical (HO), and are more prone to permeate the membrane than for the native or peroxidized membranes, and similar to aldehyde-oxidized membranes. Hy­drophobic RONS like molecular oxygen (O2), nitrogen dioxide (NO2) and nitric oxide (NO) even have insignif­icant barriers for permeation. Compared to native and peroxidized membranes, nitrated membranes are more permeable, suggesting that we must not only consider oxidized membranes during nitro-oxidative stress, but also nitrated membranes, and their role in cancer therapies.

Abstract: The destruction of ethylene in a dielectric barrier discharge plasma is investigated by the combination of kinetic modeling and experiments, as a case study for plasma-based gas purification. The influence of the specific energy deposition on the removal efficiency and the selectivity toward CO and CO2 is studied for different concentrations of ethylene. The model allows the identication of the destruction pathway in dry and humid air. The latter is found to be mainly initiated by metastable N2 molecules, but the further destruction steps are dominated by O atoms and OH radicals. Upon increasing air humidity, the removal efficiency drops by ±15% (from 85% to 70%), but the selectivity toward CO and CO2 stays more or less constant at 60% and 22%, respectively. Beside CO and CO2, we also identified acetylene, formaldehyde, and water as byproducts of the destruction process, with concentrations of 1606 ppm, 15033 ppm, and 185 ppm in humid air (with 20% RH), respectively. Finally, we investigated the byproducts generated by the humid air discharge itself, which are the greenhouse gases O3, N2O, and the toxic gas NO2.