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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 CO 2 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 CO 2 diffusion channels that significantly improved CO 2 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 CO 2 /N 2 selectivity. The MMMs with 0.5 wt% MCNs showed the best separation performance. In the mixed-gas test, the CO 2 permeability reached 160.69 Barrer, and the CO 2 /N 2 selectivity reached 61.2. In the pure-gas test, the CO 2 permeability and CO 2 /N 2 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 CO 2 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 CO 2 separation. Image 1 • Low-resistance and high-selectivity multi-channels were constructed by introducing MCNs in MMMs. • The structural and transport properties of MCNs/Pebax MMMs were simulated. • CO 2 /N 2 separation performance has exceeded Robeson's upper bound. [ABSTRACT FROM AUTHOR]

Cage-type MOFs based Mixed-matrix membranes (MMMs) hardly exhibit screening effect of gas molecules due to the flexible aperture. Regulation of nanocages of MOFs by Ionic Liquid (IL) has been proved to be effective. Therefore, in this work, an IL adsorption/infiltration two-step strategy is proposed to confine IL into the nanocages of MOFs, achieving fine tuning of effective cage size for screening gas pair with similar size. [Bmim][PF 6 are first adsorbed on the outer-surface of ZIF-8, then through heat treatment, the aperture of ZIF-8 is dilated, and the bigger [Bmim][PF 6 molecules infiltrate through the dilated aperture into the nanocage driven by thermodynamics and differential concentration. When the temperature is down to room temperature, the aperture is narrowed to 3.4 Å, thus [Bmim][PF6] are confined into nanocages, which are confirmed by PXRD, TGA and FT-IR characteristics. By controlling IL content in the cage, the effective cage size of ZIF-8 is tuned to specific slope among dynamic diameters of CO 2 over N 2 , which is perfectly reflected in the CO 2 /N 2 separation. Compared with ZIF-8/Pebax MMMs, the IL@ZIF-8/Pebax MMMs exhibit improved CO 2 /N 2 selectivity but decreased CO 2 permeability, demonstrating effectiveness of cage size adjustment. Furthermore, with the IL molecules inside ZIF-8 cage increasing, the CO 2 /N 2 selectivity of the MMMs continues to rise, indicating cage size screening effect of ZIF-8 by IL infiltration. Especially, the IL 8 @ZIF-8/Pebax MMMs exhibit the best gas separation performances with CO 2 permeability of 117 Barrer and CO 2 /N 2 selectivity of 84.5, beyond the 2008 Robinson upper bound. The proposed strategy provides an effective but facile way to confine IL into the cages of MOFs to precisely screen gas pairs with similar size and can be easily expanded to other IL and MOFs system. Image 1 • Cage Size of MOFs was finely tuned by Ionic Liquid adsorption/infiltration. • IL@MOFs based MMMs present precise gas screening effect over CO 2 and N 2. • Highly selective and permeable CO 2 transport membranes. [ABSTRACT FROM AUTHOR]

Graphene oxide (GO) materials have been widely attempted as functional fillers in mixed matrix membranes (MMMs). In virtue of their high-aspect-ratio sheet structure, they are very effective to tune gas diffusion pathway and enhance selectivity. However, the frequently-used GO sheets are often stacking and folding like barriers in MMMs, and accordingly impair gas permeation ability seriously. In order to make GO fillers stretched and dispersed to decrease mass transfer barriers in MMMs, the modification strategy with continuous ZIF-8 cover layer forming on the surface of GO sheets was proposed. In this composite structure, the rigid ZIF-8 layer, acting like an armor suit, would unfold the GO sheets nicely. Afterwards, the MMMs with ZIF-8@GO flake-like fillers in PEBAx are fabricated by solution casting. SEM images revealed that the specified ZIF-8@GO fillers have been synthesized in accordance with the concept; moreover, the stretched and orderly dispersed structure could be retained well in the MMMs. Gas permeation tests demonstrated that both permeability P CO2 and ideal selectivity α CO2/N2 are enhanced obviously by dredging the pathways for mass transfer. The MMMs containing 20 wt% stretched ZIF-8@GO achieve the best performance, with P CO2 up to 136.2 Barrer and α CO2/N2 up to 77.9 increased 66.0% and 60.0% respectively in comparison with pristine PEBAx membrane. Compare with the MMMs containing equivalent pure GO, this permeability is 74.8% higher, while the ideal selectivity is almost the same. On the whole, the composite flake-like fillers, in which GO sheets were stretched and dispersed perfectly by the ZIF-8 armor, could greatly reduce mass transfer barriers in MMMs and consequently enhance CO 2 separation performance. Image 1 • Pre-Zn(II)-doping method was succeeded in fabricating ZIF-8@GO flake-like fillers. • GO sheets were stretched and unfolded nicely by the armor-like ZIF-8 cover layer. • ZIF-8 armor is the shortcut to bypass GO barriers and reduce permeation resistance. • GO and ZIF-8 are synergistic in ZIF-8@GO composites to enhance CO 2 /N 2 separation. • ZIF-8@GO/PEBAx membranes are excellent with α CO2/N2 = 77.9 and P CO2 = 136.2 Barrer. [ABSTRACT FROM AUTHOR]