High Surface Area Mesoporous Silicon Nanoparticles Prepared via Two-Step Magnesiothermic Reduction for Stoichiometric CO2 to CH3OH Conversion

Magnesiothermic reduction of silicon oxide can result in the formation of nanostructured, mesoporous elemental silicon (mp-Si), which has been explored in a variety of energy applications such as Li-ion battery anodes, photocatalytic water splitting, CO2 reduction, drug delivery vehicles, and sensors as well as for gas storage. The physical properties of the resultant mp-Si generated via magnesiothermic reduction, and thus the potential utility, are highly dependent on the specific reduction conditions utilized. Herein, we report a modified magnesiothermic reduction method which allows for the synthesis of high surface area mp-Si nanoparticles. The reaction was initiated at 650 °C and then cooled to a lower temperature to minimize heat-induced morphological damage. The nanoparticles were characterized by using powder X-ray diffraction, scanning and transmission electron microscopies, and N2 adsorption isotherm measurements. Particles prepared by using two-step annealing with the initial processing condition of 650 °C for 30 min followed by 300 °C for 4 h resulted in crystalline and completely reduced mp-Si with a high specific surface area of 542 ± 18 m2/g. mp-Si nanoparticles generated by using these specific parameters were further used for stoichiometric CO2 conversion to CH3OH, and the reaction yields were 2.5 times higher than prior reports, demonstrating usefulness in effecting an important chemical transformation.