Multi-functional polydopamine coating: simultaneous enhancement of interfacial adhesion and CO2 separation performance of mixed matrix membranes

Inspired by marine mussel's adhesive system and facilitated transport membranes, we proposed a novel strategy to simultaneously improve the MOF- polymer interface and CO2 separation performance by coating polydopamine (PDA) on the surface of ZIF-8. PDA@ ZIF-8 played multiple roles in enhancing the membrane performance. First, the inherent high permeability of ZIF-8 with ultra- microporosity was anticipated to optimize the fractional free volume and enhance the gas permeability of MMMs. Second, the PDA coating can mitigate the interfacial defects and improve the adhesion between ZIF-8 and the polymer matrix. Finally, the abundant - OH and amino groups in PDA have strong interaction with CO2 molecules, which can effectively facilitate CO2 transport. The membrane separation performance for pure gases (CO2 and N-2) of the PDA@ ZIF-8 incorporated Pebax membrane was investigated and compared with that of the ZIF-8-incorporated membrane without the PDA coating. An anti-tradeoff effect was obtained by addition of PDA@ ZIF-8. In particular, the Pebax/PDA@ ZIF-8-15 MMM showed the best gas separation performance with a CO2 permeability of 267.74 Barrer and a CO2/N-2 selectivity of 62.65, surpassing Robeson's upper bound from 2008.