Highly permselective and durable membrane materials have been sought for energy-efficient C 3 H 6 /C 3 H 8 separation. Mixed-matrix membranes (MMMs) comprising ap olymer matrix and metal-organic frameworks (MOFs) are promising candidates for this application;h owever,r ational matching of filler-matrix is challenging and their separation performances need to be further improved. Here,w ep ropose an ovel strategy of "defect engineering" in MOFs as an additional degree of freedom to design advanced MMMs. MMMs incorporated with defect-engineered MOFs exhibit exceptionally high C 3 H 6 permeability and maintained C 3 H 6 / C 3 H 8 selectivity,e specially with enhanced stability under industrial mixed-gas conditions.T he gas transport, sorption, and material characterizations reveal that the defect sites in MOFs provide the resulting MMMs with not only ultrafast diffusion pathwaysb ut also favorable C 3 H 6 sorption by forming complexation with unsaturated open metal sites, confirmed by in situ FT-IR studies.M ost importantly,t he concept is also valid for different polymer matrices and gas pairs,d emonstrating its versatile potential in other fields.

Among the existing separation technologies, membrane-based gas separation is a promising candidate to replace or supplement conventional distillation processes due to its low energy consumption and ease of scale-up. [2] However, conventional polymeric membranes are inherently prone to (1) the strong trade-off relationship between permeability and selectivity, (2) physical aging over time, and (3) plasticization by condensable gases. Thus, they rarely meet the desired gas separation performances for practical use. [3,4] Molecular sieves with well-defined microporosity have been widely studied as a promising membrane material beyond polymeric membranes. [5,6] In particular, carbon molecular sieve (CMS) membranes prepared by controlled pyrolysis of polymer precursors exhibit both excellent thermal and chemical stability and strong size sieving ability. This material is amorphous and has a microporous structure including ultramicropores (<7 Å) for selective molecular sieving. These pores are formed by the slits between sp 2 -hybridized graphene sheets and micropores (7-20 Å) for transport pathways consisting of voids between the stacked sheets (Scheme 1a). The hierarchical microporosity in CMS membranes is known to be responsible for their superior gas separation performances relative to polymeric membranes. The stability conferred by the rigid carbonaceous structures also enables CMS membranes to be potentially useful under harsh operating conditions (i.e., high temperature and pressure). [6][7][8] Nevertheless, the ultrafine separation between the gas pairs with extremely similar sizes (Δd < 0.5 Å) including natural gas separation (e.g., CO 2 /CH 4 ) and olefin/ paraffin separation (e.g., C 3 H 6 /C 3 H 8 ) is highly challenging for commercial applications, even for CMS membranes. [9][10][11][12] The difficulty in the preparation of CMS thin-membranes (<1 µm) to reduce mass transport resistance is another critical concern related to the scale-up production of CMS membranes. [9,13] Thus, to address previously mentioned challenges, further studies on developing new materials are required.In general, free volume elements and intrinsic micro porosity in a polymer precursor govern the formation of micropores Fine control of ultramicroporosity (<7 Å) in carbon molecular sieve (CMS) membranes is highly desirable for challenging gas separation processes. Here, a versatile approach is proposed to fabricate hybrid CMS (HCMS) membranes with unique textural properties as well as tunable ultramicroporosity. The HCMS membranes are formed by pyrolysis of a polymer nanocomposite precursor containing metal-organic frameworks (MOFs) as a carbonizable nanoporous filler. The MOF-derived carbonaceous phase displays good compatibility with the polymer-derived carbon matrix due to the homogeneity of the two carbon phases, substantially enhancing the mechanical robustness of the resultant HCMS membranes. Detailed structural analyses reveal that the in situ pyrolysis of embedded MOFs induces more densified and interconnected carbon struct...

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Highly permselective and durable membrane materials have been sought for energy-efficient C 3 H 6 /C 3 H 8 separation. Mixed-matrix membranes (MMMs) comprising ap olymer matrix and metal-organic frameworks (MOFs) are promising candidates for this application;h owever,r ational matching of filler-matrix is challenging and their separation performances need to be further improved. Here,w ep ropose an ovel strategy of "defect engineering" in MOFs as an additional degree of freedom to design advanced MMMs. MMMs incorporated with defect-engineered MOFs exhibit exceptionally high C 3 H 6 permeability and maintained C 3 H 6 / C 3 H 8 selectivity,e specially with enhanced stability under industrial mixed-gas conditions.T he gas transport, sorption, and material characterizations reveal that the defect sites in MOFs provide the resulting MMMs with not only ultrafast diffusion pathwaysb ut also favorable C 3 H 6 sorption by forming complexation with unsaturated open metal sites, confirmed by in situ FT-IR studies.M ost importantly,t he concept is also valid for different polymer matrices and gas pairs,d emonstrating its versatile potential in other fields.

No abstract