Low-Cost Preparation of Hydrophobic Silica Aerogels from Water Glass Using Water as the Sole Solvent

To address the dependence on organic solvents, costly silicon precursors, and complex processing in conventional silica aerogel preparation, this study developed a green and low-cost aqueous route using water glass as the silicon source. The sol–gel process was optimized through an orthogonal experimental design by regulating precursor concentration, pH, temperature, and catalyst dosage, enabling the formation of a stable three-dimensional silica network. Under the optimized conditions, the unmodified silica aerogel exhibited low density, high porosity, and a typical mesoporous structure, with a specific surface area of 707.87 m2/g, an average pore size of 5.75 nm, and a thermal conductivity of 0.0408 W/(m·K). After HMDS vapor-phase modification, hydrophobic methyl groups were introduced onto the aerogel surface, increasing the water contact angle to 132.3°. Among the modified samples, S3 showed the lowest thermal conductivity of 0.0360 W/(m·K), indicating good thermal insulation performance. This work provides a feasible strategy for preparing hydrophobic silica aerogels through a cost-effective aqueous process, showing potential for greener and large-scale production of silica aerogel materials.