Smart light-responsive hierarchical metal organic frameworks constructed mixed matrix membranes for efficient gas separation

One type of new light-responsive hierarchical metal organic framework (MOF) has been successfully prepared using Co(NO 3 ) 3 ·6H 2 O as the metal salt and 4,4′-azobenzenedicarboxylic acid as the ligand by microwave method for the first time. It is found that MOF [Co(AzDC)] exhibits a light-responsive characteristic to SO 2 adsorption due to the presence of azo group from the ligand. The light-responsive hierarchical MOFs are incorporated into Matrimid® 5218 (PI) matrix to prepare mixed matrix membranes (MMMs) for gas separation application. The morphology, crystallinity, chain mobility and thermal stability of MMMs are explored. Results show that Co(AzDC) may elevate both the CO 2 (SO 2 ) permeability and CO 2 (SO 2 )/N 2 selectivity of the MMMs. In particular, the Co(AzDC) doped MMMs exhibit the significantly improved CO 2 (SO 2 )/N 2 selectivity from 33 (123) for PI control membrane to 78 (420) for MMMs, overcoming the 2008 Robeson upper bound for CO 2 /N 2 system. Size-sieving effect of Co(AzDC) with pore size 0.35 ​nm enhances the selectivity, while the –N=N– group from Co(AzDC) shows affinity to CO 2 molecular rather than N 2 , also elevating selectivity of MMMs. In brief, enhanced selectivity of high-performance membrane is attributed to incorporation of Co(AzDC) particles, which displays synergistic effects both in size-sieving and CO 2 -philic interaction for CO 2 /N 2 separation. Smart highly selective interface is constructed in MMMs by switching the configuration of MOFs from cis to trans . The SO 2 permeability and SO 2 /N 2 selectivity of MMMs are investigated under both visible light and ultraviolet light states, and the SO 2 /N 2 separation performance under visible light is notably improved in comparison with that under ultraviolet light state.