Investigation of Azo-cop-2 as a Photo-responsive Low-energy Co2 Adsorbent and Porous Filler in Mixed Matrix Membranes for Co2/N2 Separation

Abstract
As a nanoporous polymer, Azo-COP-2 has been reported for having exceptional CO2/N2 separation performance. In this study, we further investigate the application of Azo-COP-2 as a potential for low-energy CO2 adsorbent and porous filler in mixed matrix membranes for CO2/N2 separation. As an adsorbent, thanks to the presence of azobenzene in its framework, Azo-COP-2 showed lower CO2 uptake when irradiated with UV light than its normal condition. Azo-COP-2 also exhibited a highly efficient CO2 photoswitching between its irradiated and non-irradiated state that has not been observed previously in any nanoporous polymer. Combined with high CO2/N2 selectivity, this property renders Azo-COP-2 to be an excellent candidate for low-energy CO2 capture. A beneficial property was also exhibited by Azo-COP-2 once they were used as porous filler in mixed-matrix membranes (MMMs) using three different polymer matrices: Matrimid, polysulfone and PIM-1. Both permeability and selectivity of the MMMs could be simultaneously improved once ideal interaction between Azo-COP-2 and the polymer could be established. It was found that Azo-COP-2 – polysulfone composites had the best performance. In this case, it was observed that the CO2 permeability and CO2/N2 selectivity could be increased up to 160% and 66.7%, respectively. The strategy then shows the great potential of Azo-COP-2 not only for an advanced low-energy CO2 adsorbent but also to improve the performance of conventional polymeric membrane for CO2 post-combustion capture.