Supercritical drying of gels is considered as the most important step of aerogel production since it enables preservation of the three-dimensional pore structure which lead to unique material properties such as high porosity, low density, and large surface area. An understanding of the kinetics of supercritical drying is necessary to provide insight into material development, scale-up, and optimization of the aerogel manufacturing process. Thus, investigation of supercritical drying is gaining increased attention in recent years. This review paper covers the experimental considerations and techniques to study the kinetics of supercritical drying, fundamental mass transfer mechanisms during the drying process and modeling efforts to predict the drying kinetics for varying operating conditions and gel properties. Transport phenomena involving diffusion, convection, spillage by volume expansion, and axial dispersion are discussed by providing the fundamental equations and empirical correlations to predict transfer coefficients. A detailed review of literature covering experimental and theoretical studies on kinetics of supercritical drying is presented.

Metal–organic frameworks (MOFs) are crystalline nanoporous coordination polymers made of metal ions and organic linkers. Aerogels are highly nanoporous amorphous polymers that can be organic, inorganic, or hybrid. Both of these unique materials have been extensively investigated in many laboratories around the world for a wide range of applications ranging from separations to catalysis, resulting in thousands of published articles in a wide variety of journals. MOF/aerogel composites (MOFACs) are a new class of nanostructured materials that are attracting increasing attention because of their favorable properties. The combination of the micro- and mesoporosities of MOFs with the meso- and macroporosities of aerogels makes MOFACs hierarchically multimodal porous materials. With their high surface areas and combined morphological, mechanical, physicochemical, and functional properties of both MOFs and aerogels, MOFACs have demonstrated outstanding performances in various applications. Herein we provide an overview of the techniques used to synthesize MOFACs in various shapes such as monoliths or particles based on incorporation of MOFs into the porous networks of aerogels along with literature examples. The synthesis of aerogel-supported metals and metal oxides using MOFACs as precursors is also described. Several applications of these composites are reviewed, including adsorption, separation, catalysis, energy conversion, and storage devices such as batteries and supercapacitors. Future prospects in synthesis techniques and applications are provided to address opportunities and challenges in the field of MOFACs.