Aerogels are a special class of materials composed of a solid nano-scale skeleton filled with a large volume of gas, exhibiting unique properties such as high porosity, high specific surface area, and ultra-low density. These characteristics endow aerogels with broad application prospects across multiple fields: in construction and aerospace, they serve as highly efficient sound- and heat-insulating materials; in energy applications, they can be used in energy storage devices; in environmental contexts, they function as gas adsorbents and water purification agents; and in biomedical fields, they aid in rapid internal homeostasis and wound healing. Currently, aerogels are manufactured on an industrial scale worldwide, primarily serving as high-performance thermal insulation materials. The preparation of aerogels typically involves three main stages: gel formation, drying preparation, and the drying process. First, a wet gel is formed via sol-gel chemistry—a solid, highly porous matrix saturated with solvent. Subsequently, specialized drying techniques must be employed to remove the liquid from the pores while preserving the integrity of the solid framework. Drying is the most critical and challenging step in aerogel fabrication, as capillary pressure within the pores may cause collapse of the network structure. Given that aerogel pore sizes generally range between 2 and 100 nanometers, the capillary pressure inside the pores can reach up to 1000 bar. This immense pressure leads to pore collapse, cracking of the dried sample, and significant shrinkage. Therefore, preventing the formation of phase interfaces during solvent removal has become a central scientific challenge in aerogel synthesis. Commonly used drying methods include ambient drying, freeze-drying, and supercritical drying. Among these, supercritical drying stands out as a reliable method for producing high-performance inorganic and organic aerogels due to its ability to eliminate surface tension.


Silica aerogels are the most extensively studied and widely applied type of aerogel material. Research using silica aerogels as a representative example demonstrates that supercritical carbon dioxide drying yields ideal products with high specific surface area, high porosity, and low density. Compared to conventional freeze-drying, supercritical drying better preserves the original nanoporous structure of gels by avoiding large-pore formation and reduction in specific surface area caused by ice crystal growth.


Organic aerogels, such as resorcinol-formaldehyde, polyurethane, and polyimide aerogels, combine the flexibility of organic materials with the porous architecture of aerogels. Although supercritical drying has become a widely used method for preparing polymer aerogels, studies have shown that it can still lead to significant shrinkage under certain conditions. The mechanisms underlying polymer aerogel shrinkage during supercritical drying remain incompletely understood and require further investigation. Additionally, varying drying procedures often involve long processing times and the need to pre-exchange solvents using liquid carbon dioxide—factors that may result in low reproducibility and high CO₂ consumption, posing challenges for industrialization.


Bio-based aerogels are typically made from hydrophilic biopolymers, which are unstable in water-rich environments, presenting unique challenges during drying. Due to the low solubility of water in supercritical CO₂, the solvent exchange step is particularly critical. Researchers have developed several innovative strategies to address this issue. For example, hydrophobic bio-aerogels can be prepared by forming food-grade oil gels using edible oils, followed by removal via supercritical CO₂. This approach eliminates traditional solvent exchange and drying steps. Using hydrophobic polymers such as ethyl cellulose and low-molecular-weight oils facilitates efficient oil removal, enabling the formation of low-density, stable aerogels. Studies have shown that in some cases, CO₂ not only acts as a drying agent but also contributes to the formation of the aerogel’s nano-fiber structure. For instance, CO₂ treatment can induce physical crosslinking of chitosan chains, endowing the material with excellent optical and thermal insulation properties. The solvent exchange process prior to supercritical CO₂ drying can be cumbersome and time-consuming. To overcome this, researchers have attempted direct formation of polysaccharide aerogels in ethanol, thereby eliminating the need for solvent exchange. Pectin, alginate, xanthan gum, and guar gum are dissolved in water, gelled in ethanol, and then directly dried using supercritical CO₂. The addition of ethanol maximizes hydrophobic interactions while minimizing hydrophilic ones. Based on this principle, a novel biocompatible ethanol-induced pectin–xanthan gum aerogel has been developed for biomedical applications such as orthopedics.


Supercritical drying also demonstrates strong applicability for multi-component composite and hybrid aerogels. The interface stability between different components and compatibility with the drying process are key considerations. By optimizing processing conditions, structurally intact, multifunctional aerogel materials with uniform component distribution can be achieved.


Supercritical drying is a core technology for producing high-performance aerogels, capable of perfectly preserving the nanoporous structure of wet gels by eliminating interfacial surface tension between gas and liquid phases. Low-temperature supercritical CO₂ drying, due to its mild critical conditions and environmental friendliness, has become the most widely used method today. Process parameters such as temperature, pressure, drying agent flow rate, and depressurization rate significantly affect drying outcomes; optimizing these parameters can reduce processing time and cost while maintaining product quality. Supercritical drying has proven highly effective in the fabrication of silica aerogels, organic polymer aerogels, bio-based aerogels, and composite aerogels. However, compared to freeze-drying and ambient-pressure drying, it involves higher equipment investment and operating costs. In the future, advancements in continuous production, process intensification, green solvent development, and intelligent control are expected to overcome current limitations and promote the industrial application of high-performance aerogel materials across broader fields. With the continuous emergence of new aerogel materials and ongoing optimization of drying processes, supercritical drying technology will undoubtedly play an increasingly important role in the field of aerogel science and engineering.