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

Abstract

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, CO 2 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 N 2 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 m 2 /g. mp-Si nanoparticles generated by using these specific parameters were further used for stoichiometric CO 2 conversion to CH 3 OH, and the reaction yields were 2.5 times higher than prior reports, demonstrating usefulness in effecting an important chemical transformation.

Photocatalytic hydrogen generation using mesoporous silicon nanoparticles: influence of magnesiothermic reduction conditions and nanoparticle aging on the catalytic activity

“…We have previously determined the specific surface area of mp-Si650, mp-Si100, mp-Si200, and mp-Si300 samples using N 2 adsorption measurements to be 174 ± 22, 364 ± 18, 412 ± 15, and 527 ± 21 m 2 g −1 , respectively. 30,34 Optical absorption measurements were performed on mp-Si NPs dispersed in ethanol (Fig. S4 †) and all the samples exhibited a typical absorption profile observed for nanostructured Si Fig.…”

“…To address the issue of heat induced structural damage, our group recently introduced a two-temperature heating method where the reaction is initiated at 650°C, but the bulk of the reaction is carried out at a second lower temperature. 30 The heat released from the exothermic magnesiothermic reduction provides the additional energy required to sustain the reaction at lower temperatures. Three sets of mp-Si NPs were prepared using the two-temperature heating method, where the reaction was initially heated to 650°C for 0.5 h followed by a second step of heating at 100 (mp-Si100), 200 (mp-Si200), or 300°C (mp-Si300) for 6 h. The powder XRD patterns of all three samples showed characteristic reflections corresponding to elemental Si (Fig.…”

“…The mp-Si NPs were prepared using either the conventional single temperature heating method or recently reported two-temperature heating method. 30 The particle morphology was analyzed using scanning electron microscopy and transmission electron microscopy (SEM and TEM). The amount of oxygen in mp-Si NPs was determined using energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS).…”

The π‐hole tetrel bond betweenX2TOandCO2: Substituent effects and its potential adsorptivity forCO2

“…The separation, absorption, capture, and conversion of CO 2 have been extensively studied with silicon‐containing materials. [ 58–61 ] However, these studies seldom explained the relevant mechanism through the existence of the tetrel bond.…”

Exploiting nanoscale effects enables ultra-low temperature to produce porous silicon

“…Alternatively, a two-step reduction method has been demonstrated whereby the MgTR can progress at 300 C, however this method requires the reactants to be heated initially to 650 C to trigger the reaction. 8 In addition to the need for carrying out MgTR at lower temperatures to maintain porosity, from scalability and sustainability perspectives, being able to lower the temperature requirement without sacricing the porosity and most importantly, yield, would have positive implications to this process. Herein, for the rst time, we demonstrate a method of achieving the MgTR reaction at low temperatures (<450 C) without the use of eutectics or prior need of heating to 650 C, to produce porous silicon with yields comparable to silicon made at temperatures above 650 C. Through a systematic study, we demonstrate the importance and the effects of particle size of the silica feedstock on MgTR temperature.…”