Abstract
The magnesiothermic reduction (MgTR) of silica has been recently shown to produce porous silicon which can be used in applications such as photocatalysis and energy storage. MgTR typically requires ≥650 °C to achieve meaningful conversions. However, high temperatures are detrimental to the highly desired porosity of silicon, while also raising doubts over the sustainability of the process. In this work we show for the first time that the onset temperature of the MgTR is dependent on the particle size of the feedstock silica. Using both in-house synthesised and commercial silica, we have shown that only particles ≤20 nm are able to trigger the reaction at temperatures as low as 380 °C, well below a previously reported cut-off temperature of 500 °C, producing porous, crystalline silicon. The decrease in temperature requirement from ≥650 °C to 380 °C achieved with little modification to the overall process, without any additional downstream processing, presents significant implications for sustainable and economical manufacturing of porous silicon.
Highlights
The magnesiothermic reduction (MgTR) of silica has been recently shown to produce porous silicon which can be used in applications such as photocatalysis and energy storage
It has recently been shown that the magnesiothermic reduction (MgTR) as a bulk method of producing porous silicon has great potential for scaling up, especially when compared to the carbothermal[4] and electrochemical etching methods.[5]
It was shown that higher reduction temperatures ($650 C) favour reaction completion,[6] higher temperatures are detrimental for the desired porosity due to sintering of nanocrystals
Summary
It is likely that side reactions which consume the freshly formed silicon (e.g. the formation of magnesium silicide) are favoured at different temperatures These results show that the temperature needed to activate the MgTR reaction is dependent on the particle size of the feedstock silica. It is well known that nanoparticles exhibit enhanced reactivity compared to their bulk counterparts arising.[12,13] This well-known nanoscale effect is likely to reduce the activation barrier for initiating MgTR reaction, and the energy input required to initiate the reaction is lower.[14] This explains our ndings where only the smaller silica nanoparticles (#20 nm) react at temperatures #450 C. The ndings in this paper paves the way for the development of a sustainable and scalable MgTR reaction strategy to produce porous silicon for photocatalysis, energy storage and other applications
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
