Controlled magnesiothermic reduction of nickel phyllosilicate-coated silica nanoparticles

Magnesiothermic reduction (MgTR) is a convenient route capable of reducing oxides such as SiO₂ to produce porous Si. The Mg/SiO₂ system is optimized, understood, and has enabled researchers to tailor synthesis conditions that afford materials suitable for targeted applications. The extension of MgTR to hierarchical, multi-component oxide precursors containing transition metals remains underexplored. In this study, we investigate nickel phyllosilicate-coated Stöber silica nanoparticles as a prototypical hierarchical MgTR precursor. Through methodical variation of the Mg content, processing temperature, and heating profile, we elucidate the influence of these experimental parameters on reaction pathways, phase purity, morphological control, and porosity. This approach reveals competing byproduct pathways responsible for intractable impurities, loss of phase control, and morphological degradation, while demonstrating that NiSi₂ is the preferentially formed silicide phase under small scale optimized conditions. Porous Si@NiSi₂ nanoparticles were successfully synthesized, with surface areas increasing from 40 m² g^-1 in the nickel phyllosilicate-coated precursor to 148 m² g^-1 following MgTR and purification. X-ray diffraction of crude and purified products confirmed NiSi₂/Si phase formation; X-ray photoelectron spectroscopy verified the reduction of both Ni and Si. Electron microscopy confirmed particle shape retention and surface topology characteristic of MgTR, as well as preservation of the hierarchical architecture of the precursor nanoparticles. Nitrogen adsorption measurements confirmed mesopore generation consistent with the observed surface area enhancement. This work presents an example of how MgTR can be used to convert hierarchical, multi-component oxide precursors, providing insight into reaction pathway control and enabling the targeted synthesis of complex nanostructures.