Exploring the potential of porous organic cage membranes: Recent advances and applications

Porous organic cages (POCs) emerge as a new category of crystalline extended solids —assembled by discrete organic molecules— featuring cage-shaped architectures and inherent cavities. The unique synthesis and assembly of cage molecules endow POCs with intriguing strengths of high porosity, amendable open-pore structures, and favored solution processability. This yields multiple options for designs and fabrications of POC-based membranes with huge potential in advanced gas/liquid separations. This review highlights crucial characteristics of POCs such as window-cavity structure and tunable porosity, processability, hydrophilicity, and surface charge for membrane design and performance. A further discussion on the fabrication of POC membranes based on molecular designs is directed towards structure–property correlation analyses of POC membranes. Applications of reported POC membranes in gas separation, liquid separation, and other related separations are explored. Current challenges and future outlook on POC membranes are given to provide a guidance for design and fabrication of functional POC membranes with a broader range of customized separations.