Synthesis of multi-functional porous superhydrophobic trioxybenzene cross-linked silica aerogels with improved textural properties

Abstract

The development of organically modified cross-linked silica aerogels with an ordered porous structure and a high surface area is of utmost importance for practical applications. However, practical applications have been limited, as the organic cross-linkers lead to decrease the textural properties due to large phase separation and large size difference between organic and inorganics. Also cross-linkers are not commercially available or are prohibitively expensive. To overcome these, we proposed to use small size organic cross-linker i. e aryl group with three cross-linking sites to minimize phase separation and to obtain ordered silica network. Initially, three cross-linkers are synthesized starting from trihydroxybenzene and tetraethoxysilane using acid catalyst. Further, using these cross-linkers, trioxybenzene cross-linked silica aerogels were prepared by a simple cost-effective sol-gel process. Three different structural isomers of trihydroxybenzene precursors were used to analyze its suitability to obtain cost-effective silica aerogels with high porosity and hydrophobicity. Among these cross-linked silica aerogels, 1,3,5-trihydroxybenzene cross-linked aerogels possess a high surface area (1268 m2/g) and uniform porous morphology with a highly interconnected structure due to symmetry and lower phase separation. It also exhibits low density (0.02431 g/cm3) and low shrinkage, leading to excellent thermal insulation performance with low thermal conductivity (0.061 W/m·K). Also, the cross-linked aerogels are hydrophobic without using silylating reagents. This is helpful for large-scale production of aerogels for thermal applications.