Synthesis of a novel Al₂O₃–SiO₂ composite aerogel with high specific surface area at elevated temperatures using inexpensive inorganic salt of aluminum

We have developed a new sol–gel route to synthesize Al₂O₃–SiO₂ composite aerogel using inexpensive inorganic salt of aluminum. The approach, which is straightforward, inexpensive, and safe, can be employed to produce a monolithic mesoporous material with a high specific surface area, which is heat-treated at high temperatures. The results show that SiO₂ is essentially amorphous, whereas Al₂O₃ predominately exists as polycrystalline boehmite which consists of fibrous particles and web-like microstructures. As the heat treatment temperature increases to 600 °C, the structural transition from boehmite to γ-Al₂O₃ occurs within the composite. When the composite is heat-treated at 1100 °C, SiO₂ crystallization occurs and the mullite phase begins to appear. The specific surface area decreases with an increase in heat treatment temperatures; however, it remains 120 m²/g until 1200 °C. The heat treatment process improves the quality of the three-dimensional aerogel network, and the pore distribution becomes uniform after heat treatment.