Azo-COP-2 is a nanoporous polymer with exceptional CO2/N2 separation performance. In this study, we further investigate the application of Azo-COP-2 as a low-energy CO2 adsorbent and porous filler in mixed matrix membranes (MMMs) for CO2/N2 separation. As an adsorbent, the UV-irradiated Azo-COP-2 showed lower CO2 uptake than in the nonirradiated state, and Azo-COP-2 also exhibited highly efficient CO2 photoswitching between the two states. Combined with high CO2/N2 selectivity, this makes Azo-COP-2 an excellent candidate for low-energy CO2 capture and release. Azo-COP-2 is also shown to be a beneficial filler in MMMs. For polysulfone-based MMMs, the CO2 permeability and CO2/N2 selectivity could be increased up to 160% and 66.7%, respectively. The strategy shows the great potential of Azo-COP-2 not only for a low-energy CO2 adsorbent but also to improve the performance of conventional polymeric membranes for CO2 postcombustion capture. © 2019 American Chemical Society.