Porous Liquids: The Next Frontier

Porous liquids are a new class of molecular- and colloidal-size porous materials that combine permanent porosity of solid sorbents and fluid properties of liquids. Different from transient molecular clathrates, porous liquids have the potential to reinvent materials syntheses and unify homogeneous and heterogeneous separations and catalytic and energy-related processes, previously ascribed to liquids and porous solids, respectively. Surface areas and pore volumes of the first examples of porous liquids based on porous molecular organic cages restricted their potential for technological applications. Recent advances in ionic liquid-based colloidal suspensions or covalently stabilized nanocomposites have improved the adsorption properties and increased our ability to tailor chemical composition and pore architecture. These hybrid porous liquids, however, still present challenges such as high melting temperatures, density, and viscosity. This critical review discusses these challenges and presents opportunities for selected emerging applications based on analogous structure to that of traditional colloidal systems. [Display omitted] Porous liquids (PLs) are a new class of materials with compositions ranging from discrete molecular cages to porous cages and colloidal particles stabilized by bulk molecules and electrostatic charges. A basic unifying principle among all types of PLs is that of size exclusion adsorption, which is governed by the pore openings and prevents self-adsorption. The open pores, having tailorable sizes and selectivity, make these fluids attractive for many applications and redefine homogeneous and heterogeneous separations, catalysis, and even carbon capture and energy storage technologies. These PLs are also new platforms for the design of porous solid materials and composites. Challenges in extracting the full potential of PLs include their high density, viscosity, and melting temperatures. Rationalizing PLs as ideal solutions or colloidal fluids, however, may provide a suitable platform for manipulating these and other physicochemical properties of PLs and for future developments in this field. Porous liquids (PLs) are promising new materials, but their physicochemical properties such as melting temperature, density, and viscosity must be tailored to meet those of most industrial fluids for uses in catalysis, separations, biomedical, and energy storage and conversion. Besides the recent advances in tailoring the surface functional gro