Superhydrophobic silica aerogel microspheres from methyltrimethoxysilane: rapid synthesis via ambient pressure drying and excellent absorption properties

Abstract

Silica aerogels are nanostructured porous solids with an open pore structure, high surface area, high porosity, low bulk density, and low thermal/electrical conductivity, which have drawn great interest in both science and technology. Generally, silica aerogels are prepared via a sol–gel process with a subsequent drying step, in which a supercritical condition is usually employed to dry wet silica gels. However, the supercritical drying is a limiting factor for synthesis efficiency and cost. Ambient pressure drying (APD) is considered an alternative and more practical approach. However, the tedious surface modification and solvent exchange steps involved in conventional APD for the synthesis of silica aerogels (bead- or bulk-type) are still challenges. In this study, a novel APD method was successfully developed for the drying of precursor silica microspheres that were obtained via a water-in-oil (W/O) emulsion method using methyltrimethoxysilane (MTMS). The resultant silica aerogel microspheres were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and the Brunauer–Emmett–Teller (BET) method. The results indicate that silica aerogel microspheres possess similar characteristics to those aerogels prepared by supercritical drying. The silica aerogel microspheres have a mean diameter of approximately 300 μm, a bulk density as low as 0.08 g cm−3, a specific surface area as high as 853 m2 g−1, a pore size distribution between 2 and 45 nm, and an average pore size of 16 nm. In addition, the aerogels are superhydrophobic with a contact angle as high as 172°, and they exhibit excellent absorption capability and recyclability for organic liquids and oils. A new production route for silica aerogel microspheres will greatly expand the commercial utilization of these materials.