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Efficient fabrication of nanoporous si and Si/Ge enabled by a heat scavenger in magnesiothermic reactions.

Luo W, Wang X, Meyers C, Wannenmacher N, Sirisaksoontorn W, Lerner MM, Ji X - Sci Rep (2013)

Bottom Line: Magnesiothermic reduction can directly convert SiO2 into Si nanostructures.Despite intense efforts, efficient fabrication of highly nanoporous silicon by Mg still remains a significant challenge due to the exothermic reaction nature.By employing table salt (NaCl) as a heat scavenger for the magnesiothermic reduction, we demonstrate an effective route to convert diatom (SiO2) and SiO2/GeO2 into nanoporous Si and Si/Ge composite, respectively.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, Oregon State University, Corvallis, Oregon 97331, USA.

ABSTRACT
Magnesiothermic reduction can directly convert SiO2 into Si nanostructures. Despite intense efforts, efficient fabrication of highly nanoporous silicon by Mg still remains a significant challenge due to the exothermic reaction nature. By employing table salt (NaCl) as a heat scavenger for the magnesiothermic reduction, we demonstrate an effective route to convert diatom (SiO2) and SiO2/GeO2 into nanoporous Si and Si/Ge composite, respectively. Fusion of NaCl during the reaction consumes a large amount of heat that otherwise collapses the nano-porosity of products and agglomerates silicon domains into large crystals. Our methodology is potentially competitive for a practical production of nanoporous Si-based materials.

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Related in: MedlinePlus

Microscopy studies, and adsorption/desorption isotherms and pore size distribution analyses of Nano-Si, revealing small domain sizes and high porosity.(a) A TEM image and the corresponding SAED pattern (inset); (b) An HRTEM image that corresponds to the red-square marked area in (a); (c) Nitrogen adsorption-desorption isotherms and (d) pore size distribution of Nano-Si.
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f2: Microscopy studies, and adsorption/desorption isotherms and pore size distribution analyses of Nano-Si, revealing small domain sizes and high porosity.(a) A TEM image and the corresponding SAED pattern (inset); (b) An HRTEM image that corresponds to the red-square marked area in (a); (c) Nitrogen adsorption-desorption isotherms and (d) pore size distribution of Nano-Si.

Mentions: The Transmission Electron Microscopy (TEM) and High-Resolution TEM (HRTEM) images provide more detailed structural information for Nano-Si. As a representative TEM image shows (Fig. 2a), Nano-Si exhibits a nanoporous structure formed by Si nanocrystals about 10 nm in size, consistent with the XRD results. The corresponding selected-area electron diffraction (SAED) pattern reveals diffraction rings of Nano-Si (inset of Fig. 2a), which is consistent with the XRD and Raman results. A representative HRTEM image shows lattice fringes with a d-spacing of 0.32 nm (Fig. 2b) that is assigned to the (111) planes of cubic Si phase. In order to examine the porosity of Nano-Si, nitrogen adsorption and desorption isotherms were measured (Fig. 2c). Calculations based on the isotherms give a Brunauer-Emmett-Teller (BET) surface area of ~ 295.5 m2/g and a pore volume of ~ 1.2 cm3/g. According to the BET surface area and assuming a density of 2.33 g/cm3 of Si, a particle size of ~ 9 nm can be estimated for the Nano-Si, which is consistent with the FESEM results (detailed calculation in Supplementary Methods). The pore size distribution shown in Figure 2d suggests that the Nano-Si has pores of about 22 nm in diameter. In contrast, Bulk-Si exhibits a much lower BET surface area of ~ 5.2 m2/g and a tiny pore volume of 0.01 cm3/g (Supplementary Fig. S4), indicative of a very dense material.


Efficient fabrication of nanoporous si and Si/Ge enabled by a heat scavenger in magnesiothermic reactions.

Luo W, Wang X, Meyers C, Wannenmacher N, Sirisaksoontorn W, Lerner MM, Ji X - Sci Rep (2013)

Microscopy studies, and adsorption/desorption isotherms and pore size distribution analyses of Nano-Si, revealing small domain sizes and high porosity.(a) A TEM image and the corresponding SAED pattern (inset); (b) An HRTEM image that corresponds to the red-square marked area in (a); (c) Nitrogen adsorption-desorption isotherms and (d) pore size distribution of Nano-Si.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3713525&req=5

f2: Microscopy studies, and adsorption/desorption isotherms and pore size distribution analyses of Nano-Si, revealing small domain sizes and high porosity.(a) A TEM image and the corresponding SAED pattern (inset); (b) An HRTEM image that corresponds to the red-square marked area in (a); (c) Nitrogen adsorption-desorption isotherms and (d) pore size distribution of Nano-Si.
Mentions: The Transmission Electron Microscopy (TEM) and High-Resolution TEM (HRTEM) images provide more detailed structural information for Nano-Si. As a representative TEM image shows (Fig. 2a), Nano-Si exhibits a nanoporous structure formed by Si nanocrystals about 10 nm in size, consistent with the XRD results. The corresponding selected-area electron diffraction (SAED) pattern reveals diffraction rings of Nano-Si (inset of Fig. 2a), which is consistent with the XRD and Raman results. A representative HRTEM image shows lattice fringes with a d-spacing of 0.32 nm (Fig. 2b) that is assigned to the (111) planes of cubic Si phase. In order to examine the porosity of Nano-Si, nitrogen adsorption and desorption isotherms were measured (Fig. 2c). Calculations based on the isotherms give a Brunauer-Emmett-Teller (BET) surface area of ~ 295.5 m2/g and a pore volume of ~ 1.2 cm3/g. According to the BET surface area and assuming a density of 2.33 g/cm3 of Si, a particle size of ~ 9 nm can be estimated for the Nano-Si, which is consistent with the FESEM results (detailed calculation in Supplementary Methods). The pore size distribution shown in Figure 2d suggests that the Nano-Si has pores of about 22 nm in diameter. In contrast, Bulk-Si exhibits a much lower BET surface area of ~ 5.2 m2/g and a tiny pore volume of 0.01 cm3/g (Supplementary Fig. S4), indicative of a very dense material.

Bottom Line: Magnesiothermic reduction can directly convert SiO2 into Si nanostructures.Despite intense efforts, efficient fabrication of highly nanoporous silicon by Mg still remains a significant challenge due to the exothermic reaction nature.By employing table salt (NaCl) as a heat scavenger for the magnesiothermic reduction, we demonstrate an effective route to convert diatom (SiO2) and SiO2/GeO2 into nanoporous Si and Si/Ge composite, respectively.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, Oregon State University, Corvallis, Oregon 97331, USA.

ABSTRACT
Magnesiothermic reduction can directly convert SiO2 into Si nanostructures. Despite intense efforts, efficient fabrication of highly nanoporous silicon by Mg still remains a significant challenge due to the exothermic reaction nature. By employing table salt (NaCl) as a heat scavenger for the magnesiothermic reduction, we demonstrate an effective route to convert diatom (SiO2) and SiO2/GeO2 into nanoporous Si and Si/Ge composite, respectively. Fusion of NaCl during the reaction consumes a large amount of heat that otherwise collapses the nano-porosity of products and agglomerates silicon domains into large crystals. Our methodology is potentially competitive for a practical production of nanoporous Si-based materials.

Show MeSH
Related in: MedlinePlus