Cover picture: transition-metal-catalyzed unzipping of single-walled carbon nanotubes into narrow graphene nanoribbons at low temperature (angew. Chem. Int. Ed. 35/2011)

Narrow, smooth-edged graphene nanoribbons are needed for graphene electronics to replace the current silicon technology. In their Communication on page?8041?ff., J. Wang, F. Ding, et?al. report a smart strategy for cutting single-walled carbon nanotubes (gray) into narrow graphene nanoribbons in H(2) gas (green) with a single transition-metal atom (Cu, red) as the chemical scissors.     

Stability of narrow zigzag carbon nanotubes

First principles calculations of the electronic structure and total energy of narrow zigzag carbon nanotubes and their corresponding flat graphene strips have been carried out to assess the relative stability of the tube form. The results indicate that the smallest energetically stable carbon nanotube has a radius of about 0.2 nm. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2003     

Ab initio study of ice catalyzation of HOCl + HCl reaction

Experiments proved that the reaction of HOCl + HCl was very slow in the gas phase, but on ice surface it was rapid. In this work the ice catalysis of HOCl + HCl reaction was investigated by using ab initio molecular orbital theory. We applied the Hartree–Fock self‐consistent field and the second‐order Møller–Plesset perturbation theory with the basis sets of 6‐31G* to the model system. The complexes and transition state were obtained along the reaction with and without the presence of ice surface. By comparing the results, a possible catalyzation mechanism of ice on the reaction is proposed. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 78: 281–284, 2000     

Electrochemical unzipping of multi-walled carbon nanotubes for facile synthesis of high-quality graphene nanoribbons

Here we report a remarkable transformation of carbon nanotubes (CNTs) to nanoribbons composed of a few layers of graphene by a two-step electrochemical approach. This consists of the oxidation of CNTs at controlled potential, followed by reduction to form graphene nanoribbons (GNRs) having smooth edges and fewer defects, as evidenced by multiple characterization techniques, including Raman spectroscopy, atomic force microscopy, and transmission electron microscopy. This type of "unzipping" of CNTs (single-walled, multi-walled) in the presence of an interfacial electric field provides unique advantages with respect to the orientation of CNTs, which might make possible the production of GNRs with controlled widths and fewer defects.     

Boron nanotubes.

A survey of novel classes of nanotubular materials based on boron is presented. Pure boron nanotubes are a consequence of a general Aufbau principle for boron clusters and solid boron phases, which postulates various novel boron materials besides the well-known bulk phases of boron based on boron icosahedra. Furthermore, several numerical studies suggest the existence of a large family of compound nanotubular materials derived from crystalline AlB2. We compare these novel boron-based nanotubular materials to standard nanotubular systems built from carbon, and point out a number of remarkable structural and electronic properties that make boron-based nanotubular materials an ideal component for composite nanodevices and extended nanotubular networks.     

Theoretical investigation of an acid catalyst for viable release of H2 from BN nanotubes: A local pair natural orbital coupled cluster approach

Catalytic removal of H₂ from boron-nitride (BN)-based nanomaterials at ambient conditions is of paramount importance in order to develop lightweight hydrogen storage media. Here, the DLPNO-CCSD(T) technique is used to calculate accurate relative energies and activation barriers of Brønsted acid-initiated removal of H₂ from hydrogenated BN nanotubes (HBNNTs) with six different acids. Three crucial steps are identified in the mechanism: first H₂ release, catalyst regeneration via proton transfer, and second H₂ release to ensure feasibility of the dehydrogenation proposal. Our computational studies reveal that sulfonic acids with appropriate electrophilicity can facilitate dehydrogenation of HBNNT at a low free energetic cost (∆G^‡ = 17 kcal/mol). Importantly, these findings illustrate the possibility of H₂ release from BN nanomaterials at ambient conditions and provides hope for a sustainable chemical hydrogen storage strategy.     

Initial Subsurface Incorporation of Oxygen into Ru(0001): A Density Functional Theory Study

The adsorption and diffusion of oxygen on Ru(0001) surfaces as a function of coverage are systematically investigated by using density functional theory. A high incorporation barrier of low‐coverage adsorbed oxygen into the subsurface is discovered. Calculations show that the adsorption of additional on‐surface oxygen can lower the penetration barrier dramatically. The minimum penetration barrier obtained is 1.81 eV for a path starting with oxygen in mixed on‐surface hcp and fcc sites at an oxygen coverage of 0.75 ML, which should be regarded as close to 1 ML. Energy diagrams show that oxygen‐diffusion barriers on the surface and in the subsurface are much lower than the penetration barrier. Oxygen diffusion on the surface is an indispensable step for its initial incorporation into the subsurface.     

Fluorination of single walled carbon nanotubes at low temperature: Towards the reversible fluorine storage into carbon nanotubes

Fluorination of single walled carbon nanotubes was carried out at low temperature in the −191/25 °C range under 1 atm pure fluorine gas. In such conditions, the resulting C–F bonding is significantly weaker than for samples fluorinated at 280 °C. If the fluorination is performed at low temperature, fluorine atoms can be then removed from the host structure by moderated heating until 300 °C or by vacuum without strong damage on the tubes. After thermal defluorination, the resulting sample can be refluorinated similarly than the pristine tubes.     

Addition of carbenes to the sidewalls of single-walled carbon nanotubes

The addition of carbenes CX(2) (X=H, Cl) to single-walled carbon nanotubes (SWNTs) was investigated by density functional theory and finite, hydrogen-terminated nanotube clusters or periodic boundary conditions in conjunction with basis sets of up to polarized triple-zeta quality. For armchair [(3,3) to (12,12)] and zigzag tubes [(3,0) to (18,0)], reaction of CH(2) with the C--C bond oriented along the tube axis (A) is less exothermic than with those C--C bonds having circumferential (C) orientation. This preference decreases monotonically with increasing tube diameter for armchair, but not for zigzag tubes; here, tubes with small band gaps have a very low preference for circumferential addition. Axial addition results in cyclopropane products, while circumferential addition produces "open" structures for both armchair and zigzag tubes. The barriers for addition of dichlorocarbene to a (5,5) SWNT, studied for a finite C(90)H(20) cluster, are higher than that for addition to C(60), in spite of similar diameters of the carbon materials. Whereas addition of CCl(2) to [60]fullerene proceeds in a concerted fashion, addition to a (5,5) armchair SWNT is predicted to occur stepwise and involve a diradicaloid intermediate according to B3LYP, PBE, and GVB-PP computations. Addition to C bonds of (5,5) armchair tubes resulting in the thermodynamically more stable insertion products is kinetically less favorable than that to A bonds yielding cyclopropane derivatives.     

CO combustion on supported gold clusters.

Recent progress in the understanding of the fascinating catalysis of CO combustion by supported gold particles is summarized. Focusing on size-selected gold clusters consisting of only a few atoms, that is, the size regime with properties nonscalable from the bulk properties, we discuss the current knowledge of the different factors controlling the reactivity at the molecular level. These factors include the role of the oxide support, its defects, cluster charging as well as the structural fluxionality of clusters, the cluster size dependency, and the promotional effect of water. By combining experimental results with quantum mechanical ab initio calculations, a detailed picture of the reaction mechanism emerges. While similar mechanisms might be active for gold nanoparticles in the scalable size regime, it is shown that for different systems (defined by the cluster size, the support, experimental conditions, etc.) the reaction mechanism differs and, hence, no generalized explanation for the catalytic driving force of small gold particles can be given.     

Complex Reaction Environments and Competing Reaction Mechanisms in Zeolite Catalysis: Insights from Advanced Molecular Dynamics

The methanol‐to‐olefin process is a showcase example of complex zeolite‐catalyzed chemistry. At real operating conditions, many factors affect the reactivity, such as framework flexibility, adsorption of various guest molecules, and competitive reaction pathways. In this study, the strength of first principle molecular dynamics techniques to capture this complexity is shown by means of two case studies. Firstly, the adsorption behavior of methanol and water in H‐SAPO‐34 at 350 °C is investigated. Hereby an important degree of framework flexibility and proton mobility was observed. Secondly, the methylation of benzene by methanol through a competitive direct and stepwise pathway in the AFI topology was studied. Both case studies clearly show that a first‐principle molecular dynamics approach enables unprecedented insights into zeolite‐catalyzed reactions at the nanometer scale to be obtained.     

Deformation of single‐walled carbon nanotubes by interaction with graphene: A first‐principles study

The interaction between single‐walled carbon nanotubes (SWNTs) and graphene were studied with first‐principles calculations. Both SWNTs and single‐layer graphene (SLG) or double‐layer graphene (DLG) display more remarkable deformations with the increase of SWNT diameter, which implies a stronger interaction between SWNTs and graphene. Besides, in DLG, deformation of the upper‐layer graphene is less than in SLG. Zigzag SWNTs show stronger interactions with SLG than armchair SWNTs, whereas the order is reversed for DLG, which can be interpreted by the mechanical properties of SWNTs and graphene. Density of states and band structures were also studied, and it was found that the interaction between a SWNT and graphene is not strong enough to bring about obvious influence on the electronic structures of SWNTs. © 2015 Wiley Periodicals, Inc.     

Physical properties of silicone foams filled with carbon nanotubes and functionalized graphene sheets

Free-rising silicone foams were made with loading fractions of up to 0.25 wt.-% functionalized graphene sheets (FGS) and up to 1.0 wt.-% carbon nanotubes (CNTs) using hydrogen as blowing agent. Scanning electron microscopy of the samples revealed an open cellular structure and a homogeneous dispersion of both types of nanofillers. The incorporation of nanofiller affected the foaming process and thus the final foam density and cellular structure. Transmission electron microscopy revealed the formation of a CNT network throughout the sample, while FGS presented an exfoliated and intercalated dispersion. The thermal stability of the samples was drastically affected by the presence of both nanofillers. Both nanofillers showed a positive effect on the compressive response of the foams. However, the nanocomposite foams were found to decrease the acoustic absorption with nanofiller content probably due to the variable foam structure and improved stiffness.