Synthesis and characterization of silica xerogels obtained via fast sol–gel process

Abstract

The synthesis and physical properties of high surface area silica xerogels obtained by a two-step sol–gel process in the absence of supercritical conditions are reported. The hydrolysis and condensation reactions were followed by infrared spectroscopy. The increment in the bands corresponding to silanol and hydroxyl groups suggests that the hydrolysis reaction was complete during the first 30 min. The effect on surface area and global reaction time under various reaction conditions, such as type of alkaline catalyst and solvents, water–monomer and solvent–monomer molar ratios, was also studied. The obtained results suggest that surface area was increased using 3-aminopropyltriethoxysilane as catalyst. The use of isopropyl alcohol as solvent promotes the reduction of the capillary stress, giving a well-structured xerogel. As a conclusion, with H2O/i-PrOH/TEOS in a molar ratio of 10:4:1, it was possible to obtain silica xerogels with surface areas about 1,240 m2/g. Such surface areas are comparable with those obtained under supercritical conditions (aerogels), and higher than those xerogels conventionally obtained under normal condition (500–800 m2/g).