SILICA AEROGEL SYNTHESIS: FROM SOL–GEL TO DRYING

The production of silica aerogels (SA) has gained significant interest recently because of their ultra-high porosity, very low density, and multifunctional uses. This review highlights recent methods of synthesis, focusing on scalable and reproducible techniques suitable for practical applications. Special attention is given to how catalysts and pH influence hydrolysis, condensation, and gelation, as these factors determine the structure of the gel network. Post-gel treatments like aging and solvent exchange are identified as critical steps to reinforce the skeleton and remove residuals before drying. Surface modification through silylation is emphasized for enabling ambient-pressure drying (APD), making the aerogels hydrophobic, and helping to partially restore the porous structure. A comparison of drying techniques is provided: supercritical drying (SCD) preserves excellent pore structure but requires high energy and safety precautions, while freeze-drying (FD) offers a cost-effective alternative when ice crystallization is carefully controlled. Finally, the link between synthesis parameters and key properties, such as density, pore size distribution, surface area, and wettability, is summarized to facilitate reproducibility.