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Nanocarbon synthesis by high-temperature oxidation of nanoparticles.

Nomura K, Kalia RK, Li Y, Nakano A, Rajak P, Sheng C, Shimamura K, Shimojo F, Vashishta P - Sci Rep (2016)

Bottom Line: Initial oxidation produces a molten silica shell that acts as an autocatalytic 'nanoreactor' by actively transporting oxygen reactants while protecting the nanocarbon product from harsh oxidizing environment.Percolation transition produces porous nanocarbon with fractal geometry, which consists of mostly sp(2) carbons with pentagonal and heptagonal defects.This work suggests a simple synthetic pathway to high surface-area, low-density nanocarbon with numerous energy, biomedical and mechanical-metamaterial applications, including the reinforcement of self-healing composites.

View Article: PubMed Central - PubMed

Affiliation: Collaboratory for Advanced Computing and Simulations, Department of Physics &Astronomy, Department of Computer Science, Department of Chemical Engineering &Materials Science, and Department of Biological Sciences, University of Southern California, Los Angeles, CA 90089-0242, USA.

ABSTRACT
High-temperature oxidation of silicon-carbide nanoparticles (nSiC) underlies a wide range of technologies from high-power electronic switches for efficient electrical grid and thermal protection of space vehicles to self-healing ceramic nanocomposites. Here, multimillion-atom reactive molecular dynamics simulations validated by ab initio quantum molecular dynamics simulations predict unexpected condensation of large graphene flakes during high-temperature oxidation of nSiC. Initial oxidation produces a molten silica shell that acts as an autocatalytic 'nanoreactor' by actively transporting oxygen reactants while protecting the nanocarbon product from harsh oxidizing environment. Percolation transition produces porous nanocarbon with fractal geometry, which consists of mostly sp(2) carbons with pentagonal and heptagonal defects. This work suggests a simple synthetic pathway to high surface-area, low-density nanocarbon with numerous energy, biomedical and mechanical-metamaterial applications, including the reinforcement of self-healing composites.

No MeSH data available.


Related in: MedlinePlus

Topology of nanocarbon product.(a) Time evolution of 5-, 6-, and 7-membered carbon rings. Inset shows the populations of 5- and 7-membered rings normalized by the number of 6-membered rings for D = 10 nm. (b) Spatial distributions of 5-membered (red) and the 7-membered (blue) rings superimposed on 6-membered rings (white) at 1.37 ns. (c) Close-up view of the area enclosed with the yellow-dotted line in (b). The magenta arrow points to alternating 5-membered and 7-membered rings forming a grain boundary, and the green arrow indicates a Stone-Wales defect.
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f3: Topology of nanocarbon product.(a) Time evolution of 5-, 6-, and 7-membered carbon rings. Inset shows the populations of 5- and 7-membered rings normalized by the number of 6-membered rings for D = 10 nm. (b) Spatial distributions of 5-membered (red) and the 7-membered (blue) rings superimposed on 6-membered rings (white) at 1.37 ns. (c) Close-up view of the area enclosed with the yellow-dotted line in (b). The magenta arrow points to alternating 5-membered and 7-membered rings forming a grain boundary, and the green arrow indicates a Stone-Wales defect.

Mentions: To further characterize the geometry of the nanocarbon product, we calculate the distribution of 5-, 6-, and 7-membered rings formed by C-C bonds. A defect-free graphene sheet would consist of 6-membered hexagons, and 5-membered pentagons and 7-membered heptagons constitute topological defects called disclinations23. The positive Gaussian curvature associated with pentagonal defects produces curved surfaces commonly observed in fullerenes24, whereas the hyperbolic geometry due to negative-curvature heptagonal defects produces wrinkled surfaces23. Figure 3a shows the number of 5-, 6-, and 7-membered rings as a function of time in a 2,800 K RMD simulation for D = 10 nm. Most of the C rings are hexagons with approximately equal numbers of pentagonal and heptagonal defects. The inset in Fig. 3a shows the ratios of the numbers of pentagonal and heptagonal defects to the number of hexagons as a function of time. Initially, a large number of pentagons are produced, followed by the production of heptagonal defects, but at the end of the simulation the system has almost the same number of pentagons and heptagons (~17–19%). These topological defects are thought to play a crucial role in tailoring the mechanical25 and electronic26 properties of graphene. Results in Fig. 3a suggest that it may be possible to control the reaction time and defect densities and thus tune the electronic and mechanical properties of graphene synthesized in nSiC oxidation reaction.


Nanocarbon synthesis by high-temperature oxidation of nanoparticles.

Nomura K, Kalia RK, Li Y, Nakano A, Rajak P, Sheng C, Shimamura K, Shimojo F, Vashishta P - Sci Rep (2016)

Topology of nanocarbon product.(a) Time evolution of 5-, 6-, and 7-membered carbon rings. Inset shows the populations of 5- and 7-membered rings normalized by the number of 6-membered rings for D = 10 nm. (b) Spatial distributions of 5-membered (red) and the 7-membered (blue) rings superimposed on 6-membered rings (white) at 1.37 ns. (c) Close-up view of the area enclosed with the yellow-dotted line in (b). The magenta arrow points to alternating 5-membered and 7-membered rings forming a grain boundary, and the green arrow indicates a Stone-Wales defect.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4837334&req=5

f3: Topology of nanocarbon product.(a) Time evolution of 5-, 6-, and 7-membered carbon rings. Inset shows the populations of 5- and 7-membered rings normalized by the number of 6-membered rings for D = 10 nm. (b) Spatial distributions of 5-membered (red) and the 7-membered (blue) rings superimposed on 6-membered rings (white) at 1.37 ns. (c) Close-up view of the area enclosed with the yellow-dotted line in (b). The magenta arrow points to alternating 5-membered and 7-membered rings forming a grain boundary, and the green arrow indicates a Stone-Wales defect.
Mentions: To further characterize the geometry of the nanocarbon product, we calculate the distribution of 5-, 6-, and 7-membered rings formed by C-C bonds. A defect-free graphene sheet would consist of 6-membered hexagons, and 5-membered pentagons and 7-membered heptagons constitute topological defects called disclinations23. The positive Gaussian curvature associated with pentagonal defects produces curved surfaces commonly observed in fullerenes24, whereas the hyperbolic geometry due to negative-curvature heptagonal defects produces wrinkled surfaces23. Figure 3a shows the number of 5-, 6-, and 7-membered rings as a function of time in a 2,800 K RMD simulation for D = 10 nm. Most of the C rings are hexagons with approximately equal numbers of pentagonal and heptagonal defects. The inset in Fig. 3a shows the ratios of the numbers of pentagonal and heptagonal defects to the number of hexagons as a function of time. Initially, a large number of pentagons are produced, followed by the production of heptagonal defects, but at the end of the simulation the system has almost the same number of pentagons and heptagons (~17–19%). These topological defects are thought to play a crucial role in tailoring the mechanical25 and electronic26 properties of graphene. Results in Fig. 3a suggest that it may be possible to control the reaction time and defect densities and thus tune the electronic and mechanical properties of graphene synthesized in nSiC oxidation reaction.

Bottom Line: Initial oxidation produces a molten silica shell that acts as an autocatalytic 'nanoreactor' by actively transporting oxygen reactants while protecting the nanocarbon product from harsh oxidizing environment.Percolation transition produces porous nanocarbon with fractal geometry, which consists of mostly sp(2) carbons with pentagonal and heptagonal defects.This work suggests a simple synthetic pathway to high surface-area, low-density nanocarbon with numerous energy, biomedical and mechanical-metamaterial applications, including the reinforcement of self-healing composites.

View Article: PubMed Central - PubMed

Affiliation: Collaboratory for Advanced Computing and Simulations, Department of Physics &Astronomy, Department of Computer Science, Department of Chemical Engineering &Materials Science, and Department of Biological Sciences, University of Southern California, Los Angeles, CA 90089-0242, USA.

ABSTRACT
High-temperature oxidation of silicon-carbide nanoparticles (nSiC) underlies a wide range of technologies from high-power electronic switches for efficient electrical grid and thermal protection of space vehicles to self-healing ceramic nanocomposites. Here, multimillion-atom reactive molecular dynamics simulations validated by ab initio quantum molecular dynamics simulations predict unexpected condensation of large graphene flakes during high-temperature oxidation of nSiC. Initial oxidation produces a molten silica shell that acts as an autocatalytic 'nanoreactor' by actively transporting oxygen reactants while protecting the nanocarbon product from harsh oxidizing environment. Percolation transition produces porous nanocarbon with fractal geometry, which consists of mostly sp(2) carbons with pentagonal and heptagonal defects. This work suggests a simple synthetic pathway to high surface-area, low-density nanocarbon with numerous energy, biomedical and mechanical-metamaterial applications, including the reinforcement of self-healing composites.

No MeSH data available.


Related in: MedlinePlus