A Smart Polycage Membrane with Responsive Osmotic Energy Conversion Based on Synchronously Switchable Microporosity and Chargeability.

Membranes with specific pore sizes are widely used in molecular separation, ion transport, and energy conversion. However, the molecular understanding of structure-property performance in membrane science has been an urgent and long-standing problem. A promising but challenging solution lies in the fine-tuning of the membrane microstructure and properties to control membrane performance. Here, we designed an exofunctionalized triskelion cage to construct smart polycage membranes with concurrently responsive pore apertures and charge property. The synthetic polyaza cage is decorated with exoextended aldehyde groups for membrane fabrication and multiple amine sites for postmodification. The engineered polycage membranes thereby are endowed with pH-responsive porosity and chargeability, which serve as excellent candidates to explore the influence of the pore size and charge properties on membrane performance. In this regard, we successfully demonstrated the responsive osmotic energy conversion of the polycage membrane with a power density increase of over fourfold. This result indicates that the chargeability here outcompetes microporosity in energy conversion performance, which is further supported by molecular simulations. Therefore, this smart polycage membrane not only offers a feasible strategy to regulate the membrane microstructure and charge property reversibly but also balances pore size and chargeability to control the membrane performance at the molecular level.