The new, mesoporous silica channel based strategy for magnesiothermic
reduction of silica to produce silicon is illustrated in
Figure 1. In this process, vertically aligned mesoporous silica channels
are generated on a two dimensional GO substrate. While GO
was used in this study, depending on target applications different
types of substrates can be employed for this purpose. The mesoporous
silica layer was then formed by simply mixing a solution of the
GO substrate with a solution of cetyltrimethylammonium chloride
(CTACl) in 1 M NaOH, followed by addition of tetraethyl orthosilicate
(TEOS) (Figure 1a)13. By using this approach to control the pH
precisely at 11.7, the mesoporous silica structure are produced via
soft-templating of the block copolymer CTACl followed by hydrolytic
condensation with TEOS (Figure 1b). The mesoporous silica
formed in this manner was blended with the magnesium granules,
placed within an alumina crucible, and heated in a tube furnace at
650uC under an atmosphere of argon (500 sccm) and hydrogen
(50 sccm). In this process, magnesium infiltrates into the pores
and covers the surface of the mesoporous silica template
(Figure 1b), where it promotes the magnesiothermic reaction (equation
1) to produce silicon and magnesium oxide (Figure 1c). Loss of
oxygen from silica enables the silicon atoms to arrange into a crystalline
phase1. Finally, magnesium oxide generated in the reduction
reaction is removed by using 1 M hydrochloric acid (Figure 1d).
Vacuum filtration then leads to isolation of a dark brown silicon
nanoparticle powder that does not contain any unreacted silica
(Figure 1e).