Metallothermic Reduction of Silica Nanoparticles to Porous Silicon for Drug Delivery Using New and Existing Reductants

Abstract

Abstract:In this study, the influence of metals (Mg, Al, and Ca) and reaction conditions (time, temperature, and metal grain size) on the metallothermic reduction of Stöber silica nanoparticles (NPs) to form porous Si was explored. Mg metal was found to be an effective reducing agent even at temperatures below its melting point; however, it also induced a high degree of structural damage and morphology change. Al was effective at reducing silica NPs only at its melting point and higher temperatures, but the resulting particles retained a higher degree of structural morphology as compared to those reduced using Mg. Ca was found to be ineffective in reducing silica. A new reductant, a mixture of 70% Mg and 30% Al, was found to induce the least amount of morphology change, and the reactions proceeded at temperatures (450 °C) lower than those required by Mg or Al individually. Furthermore, porous Si-NPs obtained using Mg, Al, and the mixture of 70% Mg and 30% Al as reductants were investigated as carriers for ibuprofen loading and release. Porous Si obtained from Mg and Mg/Al mixture reductions showed higher drug loading and a sustained drug release profile whereas porous Si obtained from Al reduction had lower loading and showed a conventional release profile over 24 hours.

A review of magnesiothermic reduction of silica to porous silicon for lithium-ion battery applications and beyond

“…This effect is determined to be from a higher degree of structural damage of the template at higher temperatures. 52 2.2.3 Reaction time. The reaction time for reduction varies between studies with durations reported from 30 minutes 45 up to 12 hours.…”

“…Increasing the magnesium grain size from ne powder (À325 mesh), chips (4-30 mesh) and foil have shown to decrease the reduction rate, caused by the improper mixing of the reactants. 52 The mixing of the reactants by a ball milling process can provide enough kinetic energy to reach the reaction ignition point, and has been used to perform the magnesium reduction. This method has also been scaled up to a 5 litre scale in an attrition mill.…”

“…Interestingly these mesoporous properties also appear in samples which initially were nonporous such as sand 59 and silica spheres. 51,52 In these cases the nature of the silicon-magnesia interwoven aggregate introduces porosity to the structure through the removal of the magnesia phase. The same effect is seen on non-porous starting silica/silicon used in the 'deep reduction partial oxidation' method.…”

In Situ Formation of Nanoporous Silicon on a Silicon Wafer via the Magnesiothermic Reduction Reaction (MRR) of Diatomaceous Earth

“…Metallothermic reduction reaction (MRR) of silica to silicon has been studied over the past decade [24][25][26][27][28]. This technique has gained a lot of attention because of the low cost involved, lower temperature, and the ready availability of metals such as magnesium and aluminum.…”

Crystallisation Behaviour of Pharmaceutical Compounds Confined within Mesoporous Silicon

“…The magnesiothermic reduction of silica nanoparticles has been reported to increase the surface area from 8.2 m 2 g −1 to 386 m 2 g −1 after a 12-h reaction time at 500 • C. Pore volume also increased from 0.07 cm 3 g −1 to 1.7 cm 3 g −1 . The surface area of silicon particles produced by aluminothermic reduction was a magnitude smaller than the magnesium-reduced product, with the greatest surface area reported as 37 m 2 g −1 after 24 h at 650 • C. Pore volume was determined to be 0.51 cm 3 g −1 after 12 h at 650 • C. Transmission electron microscopy (TEM) images of the porous substrate showed that a aluminothermic reduction produces a less porous substrate than magnesiothermic reduction, with the porous silicon composed of layers [105].…”