Robust porous hydrogen-bonded organic frameworks: Synthesis and applications in gas adsorption and separation

Being an emerging family of crystalline porous materials, hydrogen-bonded organic frameworks (HOFs) are types of ordered supramolecular structures that constructed from organic linkers (including those with organometallic units) via mainly hydrogen bonds. HOFs have now attracted increasing attention in various fields, owing to their valued features such as mild synthetic condition, convenient purification/recovery processes, high processibility and diverse functionality. Great potentials have emerged for HOFs in the field of adsorption and separation, especially for the purification of light hydrocarbons that are crucial to the petrochemical industry. Their practical applications, however, is limited as it is rather difficult to maintain their porous architectures only through hydrogen bonds after removing the lattice solvent molecules. Several types of strategies have hence been developed to solve the issue of HOF structure fragility, including introduction of stronger/different forms of intermolecular interactions, adoption of monomers with rigid backbones, integration of appropriate structural interpenetrations, formation of the cross-linked structures, etc. In this review, the common strategies for constructing HOFs and the important role of each method in enhancing the structural stability of HOFs are briefly introduced. Then, the application of robust porous HOFs in various gases adsorptions and separations is carefully summarized, as well as its mechanism is analyzed in detail from the perspective of supramolecular interactions among the frameworks and gas molecules. The current challenges and the future perspectives for HOFs are discussed with respect to the urgent demands in enhancing their performance, which propose a broader vision of HOFs in developing novel functional porous materials.