1. Field of the Disclosure
This disclosure generally relates to a new class of partially fluorinated porous materials which bind aliphatic and aromatic hydrocarbons, fluorocarbons and freons with high weight adsorption capacities. More particularly, the disclosure relates to separation of materials by exclusion principle, as well as by differential diffusion rates, and selective separation of isomers of xylene by the same principle.
2. Background of the Technology
Traditional Metal-Organic Frameworks (MOFs) and Covalent Organic Frameworks (COFs) are porous materials characterized by thermal stability, high porosities and modular synthesis. Despite these advantages, their applications are hampered by limited solubility, prohibitively high melting and sublimation points, and moisture sensitivity.
Chemistry of such porous materials has been advanced over the past two decades with the development of crystallographically ordered hybrid structures such as MOFs1 and COFs.2,3 These two classes of materials allow facile modification of pore sizes, shapes, surface functionalities and polarities. In three-dimensional MOFs and COFs, pores are generally formed by surrounding them on all sides with covalent bonds: thus, the whole crystal is one molecule, and the well-defined atomic positions translate into well-defined pores.
While “crystal-as-a-molecule” strategy allows superior control over pore properties, MOFs and COFs are difficult to recrystallize, difficult to grow on surfaces4 or deposit from solution,5 and their characterization is overly dependent on the growth of crystalline samples. In addition, many of the metal-ligand bonds in MOFs and reversibly formed organic bonds in COFs (e.g. boroxines, boronate esters, imines) are hydrolytically highly sensitive.
Formation of pores within a crystal structure should not require that the entire crystal be an infinite covalently connected net, and should simply require a crystal of a molecule which organizes into a porous structure. However, such structures are rare and difficult to predict a priori;6 furthermore, even when a small molecule can be organized into a porous structure, such structures are typically fragile after solvent removal and they are unsuitable for many applications.
Recently, molecular crystals characterized by high porosity have been developed.7-18 These can be intrinsically or extrinsically porous. In the intrinsically porous case, the molecule itself contains a large pore, typically within a macrocycle or a molecular capsule. Organization of these within the crystal then results in an extended structure which replicates individual molecules' porosities. In extrinsically porous case, the molecule itself is inherently porous, and all porosity comes as the consequence of its crystal packing. Using an intrinsic strategy, materials with surface areas over 3,500 m2 g−1 have been constructed, as well as extrinsically porous molecular crystals with surface areas in excess of 3,000 m2 g−1. However, these molecular crystals use hydrolytically sensitive imine and boronate ester functionalities and therefore are fragile.
Therefore, there is a need for lightweight, solution processable materials that are easily synthesized, thermally stable, and highly porous, wherein such materials bind aliphatic and aromatic (such as xylenes) hydrocarbons, fluorocarbons, and freons with high weight adsorption capacities while being hydrolytically stable and non-fragile. Such materials would serve an unmet need in petrochemical industry, environmental remediation and analysis, and pre- and post-combustion technologies.