Abstract
Methylsilsesquioxane (MSQ) aerogels with uniform mesopores were facilely prepared via a sol–gel process followed by microwave drying with methyltrimethoxysilane (MTMS) as a precursor, hydrochloric acid (HCl) as a catalyst, water and methanol as solvents, hexadecyltrimethylammonium chloride (CTAC) as a surfactant and template, and propylene oxide (PO) as a gelation agent. The microstructure, chemical composition, and pore structures of the resultant MSQ aerogels were investigated in detail to achieve controllable preparation of MSQ aerogels, and the thermal stability of MSQ aerogels was also analyzed. The gelation agent, catalyst, solvent, and microwave power have important roles related to the pore structures of MSQ aerogels. Meanwhile, the microwave drying method was found to not only have a remarkable effect on improving production efficiency, but also to be conducive to avoiding the collapse of pore structure (especially micropores) during drying. The resulting MSQ aerogel microwave-dried at 500 W possessed a specific surface area up to 821 m2/g and a mesopore size of 20 nm, and displayed good thermal stability.
Highlights
Silica aerogel is a low-density porous solid material with three-dimensional reticulate skeletons formed by interconnected SiO2 nanoparticles [1]
We found that microwave drying has a remarkable effect on improving production efficiency, and is conducive to avoiding collapse of the pore structure, resulting from thermal gradients during drying
With the increase in propylene oxide (PO) volume, the gelation time of aerogels decreased until the volume of PO was 1.0 mL, which indicates that 1.0 mL of PO is enough to participate in the ring-opening reaction with hydrochloric acid (HCl) for slowly elevating the pH of sol [31]
Summary
Silica aerogel is a low-density porous solid material with three-dimensional reticulate skeletons formed by interconnected SiO2 nanoparticles [1]. Benefiting from its special structure, silica aerogel possesses various unique properties [2,3,4,5] such as high specific surface area and porosity, low thermal conductivity, high visible-light transmittance, and low dielectric constant. Owing to these properties, silica aerogel was applied in various fields such as catalyst carriers [6,7,8], heat insulation [9,10,11], acoustic insulation [12,13,14], Cherenkov radiation detectors [15], adsorbents [16,17,18,19], and thermal energy storage [20]. Supercritical drying, which needs special conditions such as high pressure and high temperature, prevents aerogels from industrial manufacturing and extended applications
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