36 research outputs found
Predicting experimentally stable allotropes: Instability of penta-graphene
International audienceIn recent years, a plethora of theoretical carbon allotropes have been proposed, none of which has been experimentally isolated. We discuss here criteria that should be met for a new phase to be potentially experimentally viable. We take as examples Haeckelites, 2D networks of sp2-carbon–containing pentagons and heptagons, and “penta-graphene,” consisting of a layer of pentagons constructed from a mixture of sp2- and sp3-coordinated carbon atoms. In 2D projection appearing as the “Cairo pattern,” penta-graphene is elegant and aesthetically pleasing. However, we dispute the author’s claims of its potential stability and experimental relevanc
Polyurea-Functionalized Multiwalled Carbon Nanotubes
An in situ polycondensation approach was applied to functionalize multiwalled carbon nanotubes (MWNTs), resulting in various linear or hyperbranched polycondensed polymers [e.g., polyureas, polyurethanes, and poly(urea-urethane)-bonded carbon nanotubes]. The quantity of the grafted polymer can be easily controlled by the feed ratio of monomers. As a typical example, the polyurea-functionalized MWNTs were measured and characterized in detail. The oxidized MWNTs (MWNT-COOH) were converted into acyl chloride-functionalized MWNTs (MWNT-COCl) by reaction with neat thionyl chloride (SOCl2). MWNT-COCl was reacted with excess 1,6-diaminohexane, affording amino-functionalized MWNTs (MWNT-NH2). In the presence of MWNT-NH2, the polyurea was covalently coated onto the surfaces of the nanotube by in situ polycondensation of diisocyanate [e.g., 4,4‘-methylenebis(phenylisocyanate)] and 1,6-diaminohexane, followed by the removal of free polymer via repeated filtering and solvent washing. The coated polyurea content can be controlled to some extent by adjusting the feed ratio of the isocyanato and amino groups. The structure and morphology of the resulting nanocomposites were characterized by FTIR, NMR, Raman, confocal Raman, TEM, EDS, and SEM measurements. The polyurea-coated MWNTs showed interesting self-assembled flat- or flowerlike morphologies in the solid state. The signals corresponding to that of the D and G bands of the carbon nanotubes were strongly attenuated after polyurea was chemically tethered to the MWNT surfaces. Comparative experiments showed that the grafted polymer species and structures have a strong effect on the Raman signals of polymer-functionalized MWNTs
Pseudocarbynes: Charge-Stabilized Carbon Chains
Carbyne is the long-sought
linear allotrope of carbon. Despite
many reports of solid carbyne, the evidence is unconvincing. A recent
report of supposed carbyne shows gold clusters in transmission electron
microscopy (TEM) images. In order to determine the effects of such
clusters, we performed ab initio calculations of uncapped and capped
linear carbon chains and their complexes with gold clusters. The results
indicate that gold dramatically alters the electron densities of the
CC bonds. The resulting charge-stabilization of the carbon
chains leads to pseudocarbynes. These findings are corroborated in
calculations of the structures of crystals containing isolated carbon
chains and those intercalated with gold clusters. Calculated Raman
spectra of these pseudocarbynes with gold clusters are in better agreement
with experiment than calculated spectra of isolated carbon chains.
The current work opens the way toward the design and development of
a new class of metal-intercalated carbon compounds
Stable [60]fullerene carbocations
[60]Fullerene derivatives, C60Ar5Cl (Ar = Ph or 4-FC6H4), react with AlCl3 in solution at room temperature to form Cs symmetrical pentaaryl[60]fullerene carbocations, C60(Ar)5+