Constructing low-resistance and high-selectivity transport multi-channels in mixed matrix membranes for efficient CO2 separation

Conventional two-dimensional (2D) fillers in membranes have undesirable gas transport resistance owing to their interfacial barriers. In this work, 2D microporous carbon nanoplates (MCNs) were proposed to construct low-resistance and high-selectivity gas transport channels in mixed-matrix membranes (MMMs) to enhance the CO2 separation performance. MCNs were synthesized using a phase-transition material as a removable template and incorporated with Pebax-1657 to prepare MMMs. Micropores measuring 0.58 nm in the MCNs provided low-resistance CO2 diffusion channels that significantly improved CO2 permeability, as confirmed by the diffusion coefficient calculated through molecular simulation. Meanwhile, the random and effective stacking of the MCNs in the MMMs created highly selective gas transport channels that dramatically enhanced CO2/N2 selectivity. The MMMs with 0.5 wt% MCNs showed the best separation performance. In the mixed-gas test, the CO2 permeability reached 160.69 Barrer, and the CO2/N2 selectivity reached 61.2. In the pure-gas test, the CO2 permeability and CO2/N2 selectivity were 123 Barrer and 76, exhibiting distinct increases of 53.0% and 28.8% compared to those of the pristine Pebax membrane. Notably, the best CO2 separation performance of the prepared MMMs exceeded Robeson's upper bound. The proposed template-removal 2D MCNs with low-resistance and high-selectivity transport multi-channels facilitate a new process for molecularly selective and energy-efficient CO2 separation.