Design of multifunctional magnetic hybrid silica aerogels with improved properties

A streamlined synthesis approach is proposed to develop a multifunctional magnetite doped hybrid silica aerogel by taking advantage of the versatility of the sol-gel process and flexibility of the crosslinking reaction. To this avail, magnetite NPs, at concentrations from 0.05 to 0.2 mg/mL, were mixed at the nanoscale with the initial solution containing the silica precursors and the crosslinker. For an effective and sustainable linkage of magnetite to the silica network, the surface of the magnetite was chemically coated with an active silylation agent to compatibilize the surface chemistry of these nanoparticles with the chemistry of silica. It has been shown that at a certain dopant concentration, the magnetite doped aerogels gained several interesting improvements in the final properties over their undoped counterparts, particularly an increase in the compressive strength (up to 2.6 MPa, with ca. 3× increase) with only a marginal increase in the density (up to ∼ 0.29 g cm−3, with 20% increment) and decrease in the active surface area (down to ∼ 49 m2 g−1 and 7% reduction). Importantly, a good deal of improvement regarding the thermal insulation performance for doped aerogels has been obtained due to the opacification behavior of the magnetite dopants at temperatures above 300 K. The significant improvements concerning the physical and mechanical properties combined with the magnetic properties (up to 11 emu g−1 at room temperature) make these multifunctional hybrid aerogels suitable for some applications, ranging from selective magnetic separation for environmental cleaning and magnetic drug delivery to catalysis, etc.