Vacuum-Dried Synthesis of Low-Density Hydrophobic Monolithic Bridged Silsesquioxane Aerogels for Oil/Water Separation: Effects of Acid Catalyst and Its Excellent Flexibility

Low-density hydrophobic monolithic bridged silsesquioxane aerogels were prepared by vacuum drying using terephthalaldehyde (TPAL) and 3-aminopropyl-triethoxysilane (APTES) as precursors and acetic acid as catalyst. The effects of acid on the vacuum-dried synthesis of bridged silsesquioxane aerogels were investigated. The results indicate that the growth mechanism changes from cluster–cluster to monomer–cluster when acid is added, which induces the formation of the low-density monolithic aerogels with increased pore size. The methyltrimethoxysilane (MTMS) co-precursor could endow the aerogels with good hydrophobicity. The densities, pore structure, hydrophobicity, and mechanical properties of the obtained bridged silsesquioxane aerogels were investigated in detail. The results show that the monolithic aerogels possess low density (0.071 g/cm3), high hydrophobicity (contact angle, >140°), and excellent flexibility (Young's modulus, 0.029 MPa). All of these characteristics make the hydrophobic aerogels competitive candidates for oil/water separation.