Polyimide based mixed matrix membranes incorporating Cu-BDC nanosheets for impressive helium separation

Incompatibility between particles and polymers has the adverse consequence on the performance of mixed matrix membranes (MMMs). To overcome this problem, MMMs containing Cu-BDC nanosheets with two various polyimides (6FDA-DAM and Matrimid) were fabricated and tested for He separation. High aspect ratio of nanosheets (more than 100) was confirmed by TEM and AFM Analyses. FESEM images of MMMs showed that the nanosheets were uniformly distributed all over the matrices and there was no symptom of micro scale polymer-filler phase void up to 15 wt%. Also due to the interface interaction established between two phases, rigidification of chains happened and resulted in increasing T-g and decreasing FFV of polymers. Addition of particles to matrices led to the permeability of He increased slightly until 9 wt% loading, but it was reduced at 12 and 15 wt %. Actually, the oriented stacking of nanosheets caused the permeability of CH4 and N-2 reduced significantly and gave rise to developed ideal selectivities. The best MMMs for both polymers was observed at loading of 15 wt%, so that for 6FDA-DAM based MMM, He/CH4 and He/N-2 ideal selectivities enhanced by 2570 and 2320% compared to pure 6FDA-DAM and surpassed the 2008 Robeson upper bound.