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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

Multifunctional porous silica shell as a nanocapsule and nanoreactor.(a) Snapshot of the silica nanocapsule in a 10 nm nSiC at 2,800 K after 2 ns. Here yellow and red spheres are silicon and oxygen atoms, respectively. (b) Mean square displacement of oxygen atoms covalently bonded to silicon atoms. At 2,800 K, oxygen atoms diffuse rapidly through the silica shell, facilitating oxidation reactions at the interface of the SiC core. (c–e) Morphologies of the silica shell show that silica layer forms a highly porous spherical shell structure. Isosurface plots at mass densities 2.1 g/cm3 and 2.2 g/cm3 are used to represent the outer surface (gray) and interface (blue) of the silica shell, respectively. Images c to e show xz cut surfaces at three different y positions.
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f4: Multifunctional porous silica shell as a nanocapsule and nanoreactor.(a) Snapshot of the silica nanocapsule in a 10 nm nSiC at 2,800 K after 2 ns. Here yellow and red spheres are silicon and oxygen atoms, respectively. (b) Mean square displacement of oxygen atoms covalently bonded to silicon atoms. At 2,800 K, oxygen atoms diffuse rapidly through the silica shell, facilitating oxidation reactions at the interface of the SiC core. (c–e) Morphologies of the silica shell show that silica layer forms a highly porous spherical shell structure. Isosurface plots at mass densities 2.1 g/cm3 and 2.2 g/cm3 are used to represent the outer surface (gray) and interface (blue) of the silica shell, respectively. Images c to e show xz cut surfaces at three different y positions.

Mentions: We observe that graphene flakes nucleate and are ‘woven’ at the nSiC surface, and the silica shell (Fig. 4a) plays a surprisingly active role in the synthesis of graphene flakes. The molten silica shell absorbs environmental oxygen, which becomes part of the Si-O bond network. The O atoms move toward the silica/nSiC interface through a sequence of bond-switching events30 and bond preferentially to Si rather than C, as shown in Fig. 1e,f. To quantify oxygen transport in the molten silica shell at 2,400 K and 2,800 K, we calculate the mean square displacement (MSD) averaged over all O atoms bonded to Si (Fig. 4b). Comparison with Fig. 2a shows a positive correlation between the MSD and the amount of carbon product. These results demonstrate that rapid oxygen transport in the molten silica shell plays an essential role in the production of nanocarbon. This autocatalytic role of the silica ‘nanoreactor’31 is akin to autocatalytic behavior of reaction products during detonation of pentaerythritol tetranitrate, where H2O products are directly involved in the breakage of N-O and formation of C-O bonds32. We have also observed such a mechanism in hydrogen production from water by LiAl particles. In that system, QMD simulations reveal that bridging oxygen atoms between Al and Li play an active role in the breaking of O-H and formation of Al-O bonds33.


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)

Multifunctional porous silica shell as a nanocapsule and nanoreactor.(a) Snapshot of the silica nanocapsule in a 10 nm nSiC at 2,800 K after 2 ns. Here yellow and red spheres are silicon and oxygen atoms, respectively. (b) Mean square displacement of oxygen atoms covalently bonded to silicon atoms. At 2,800 K, oxygen atoms diffuse rapidly through the silica shell, facilitating oxidation reactions at the interface of the SiC core. (c–e) Morphologies of the silica shell show that silica layer forms a highly porous spherical shell structure. Isosurface plots at mass densities 2.1 g/cm3 and 2.2 g/cm3 are used to represent the outer surface (gray) and interface (blue) of the silica shell, respectively. Images c to e show xz cut surfaces at three different y positions.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f4: Multifunctional porous silica shell as a nanocapsule and nanoreactor.(a) Snapshot of the silica nanocapsule in a 10 nm nSiC at 2,800 K after 2 ns. Here yellow and red spheres are silicon and oxygen atoms, respectively. (b) Mean square displacement of oxygen atoms covalently bonded to silicon atoms. At 2,800 K, oxygen atoms diffuse rapidly through the silica shell, facilitating oxidation reactions at the interface of the SiC core. (c–e) Morphologies of the silica shell show that silica layer forms a highly porous spherical shell structure. Isosurface plots at mass densities 2.1 g/cm3 and 2.2 g/cm3 are used to represent the outer surface (gray) and interface (blue) of the silica shell, respectively. Images c to e show xz cut surfaces at three different y positions.
Mentions: We observe that graphene flakes nucleate and are ‘woven’ at the nSiC surface, and the silica shell (Fig. 4a) plays a surprisingly active role in the synthesis of graphene flakes. The molten silica shell absorbs environmental oxygen, which becomes part of the Si-O bond network. The O atoms move toward the silica/nSiC interface through a sequence of bond-switching events30 and bond preferentially to Si rather than C, as shown in Fig. 1e,f. To quantify oxygen transport in the molten silica shell at 2,400 K and 2,800 K, we calculate the mean square displacement (MSD) averaged over all O atoms bonded to Si (Fig. 4b). Comparison with Fig. 2a shows a positive correlation between the MSD and the amount of carbon product. These results demonstrate that rapid oxygen transport in the molten silica shell plays an essential role in the production of nanocarbon. This autocatalytic role of the silica ‘nanoreactor’31 is akin to autocatalytic behavior of reaction products during detonation of pentaerythritol tetranitrate, where H2O products are directly involved in the breakage of N-O and formation of C-O bonds32. We have also observed such a mechanism in hydrogen production from water by LiAl particles. In that system, QMD simulations reveal that bridging oxygen atoms between Al and Li play an active role in the breaking of O-H and formation of Al-O bonds33.

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