A Smart Polycage Membrane\nwith Responsive Osmotic\nEnergy Conversion Based on Synchronously Switchable Microporosity\nand Chargeability

Membranes\nwith specific pore sizes are widely used in\nmolecular\nseparation, ion transport, and energy conversion. However, the molecular\nunderstanding of structure–property performance in membrane\nscience has been an urgent and long-standing problem. A promising\nbut challenging solution lies in the fine-tuning of the membrane microstructure\nand properties to control membrane performance. Here, we designed\nan exofunctionalized triskelion cage to construct smart polycage membranes\nwith concurrently responsive pore apertures and charge property. The\nsynthetic polyaza cage is decorated with exoextended aldehyde groups\nfor membrane fabrication and multiple amine sites for postmodification.\nThe engineered polycage membranes thereby are endowed with pH-responsive\nporosity and chargeability, which serve as excellent candidates to\nexplore the influence of the pore size and charge properties on membrane\nperformance. In this regard, we successfully demonstrated the responsive\nosmotic energy conversion of the polycage membrane with a power density\nincrease of over fourfold. This result indicates that the chargeability\nhere outcompetes microporosity in energy conversion performance, which\nis further supported by molecular simulations. Therefore, this smart\npolycage membrane not only offers a feasible strategy to regulate\nthe membrane microstructure and charge property reversibly but also\nbalances pore size and chargeability to control the membrane performance\nat the molecular level.