From natural clay minerals to porous silicon nanoparticles

Nanostructured silicon has gained increasing interests due to its unique properties and wide applications. A facile, low-cost, and scalable strategy for producing nanostructured silicon remains a challenge. In this work, three natural clay minerals with different nanostructures, i.e., tabular halloysite, layered montmorillonite, and chain-layered palygorskite, were directly employed as precursors to synthesize porous nanostructured silicon via a combination of molten salt and magnesiothermic reduction. Results indicated that molten salt could efficiently absorb the massive heat generated from the exothermic reaction, which consequently inhibited the formation of high temperature phases (i.e., spinel and mullite) and the fusion of the generated silicon nanoparticles. Apart from acting as a reductant, metal Mg also consumed a part of the released heat through its vaporization to further lower the local reaction temperature. As a result, the as-synthesized nanostructured silicon showed large specific surface areas and enhanced porous architectures, e.g., 115.5 m(2)/g of specific surface area and 0.547 cm(3)/g of porosity for the sample obtained from palygorskite. Moreover, the microstructure and morphology of the resulting nanostructured silicon could be readily adjusted by properly choosing the clay mineral precursors and the added amounts of NaCl and Mg. Our strategy does not need to specially eliminate Al in day minerals before reduction reaction, and greatly broadened the selection of clay minerals that can be directly used as silicon precursors, which would be beneficial to the practical production and wide applications of nanostructured silicon.