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[Display omitted] • Hollow ZIF-8 in micron accumulated continuously across membrane to construct transport highway. • The real CO 2 transport distance was reduced. • In-situ polymerization intensifies the interface affinity between ZIF-8 and PEO. The hollow filler has been verified to effectively enhance the CO 2 permeability of mixed matrix membrane (MMMs) by constructing low-resistance transport pathway. However, the in-continuity of hollow fillers across the membrane results in insufficient CO 2 permeability. In this work, the micron-sized hollow ZIF-8 (Mic-H-ZIF-8) were designed and proposed to accumulate continuously across the membrane to construct the transport highway for CO 2. Importantly, the in-situ polymerization was utilized to achieve continuous accumulation of the Mic-H-ZIF-8 fillers across the membrane. The Mic-H-ZIF-8 presents cavity size of 4 μm and shell thickness of 100 nm, and three or four Mic-H-ZIF-8 microspheres are aligned sequentially across the membrane, in which the effective gas transport distance is decreased from 13 μm to the range of 0.8–3 μm. Consequently, the CO 2 permeability of 5 wt% Mic-H-ZIF-8/PEO MMM is 224.6 % and 63.5 % higher than those of pure PEO membrane and nanosized hollow ZIF-8/PEO MMM at 0.1 MPa. Meanwhile, the CO 2 /N 2 selectivity is still as high as 70.0. This CO 2 separation performance is far exceeding the Robeson upper bound in 2008, and beyond the McKeown upper bound in 2019 as the feed pressure increasing, confirming the significance of continuous transport highway constructed by micron-sized hollow MOFs on improving CO 2 separation of MMMs. [ABSTRACT FROM AUTHOR]

Facilitated transport membrane with fixed and mobile carriers is essential yet challenging to improve the CO 2 capture. Herein, a facilitated transport membrane with continuous pathway was constructed by the in-situ interlinkage of mobile aniline with the fixed carriers distributing along electrospun polyacrylonitrile (PAN) nanofibers. In this membrane, fixed amine carriers are introduced through the alkalinous hydrolysis of PAN fibers (HPAN), and are distributed along the HPAN fibers to construct a long-range continuous transport pathway for CO 2. The mobile aniline carriers are introduced into the interfibrous voids of the HPAN nanofibers mat (NFM) by in-situ polymerization of Poly (ethylene glycol) diacrylate (PEGDA), which interlink the fixed amine carriers to achieve the facilitated transport pathway continuous completely. And the fixed amine and mobile aniline carriers are demonstrated to co-exist in the An/PEO@HPAN membrane (NFCM) by the FTIR and XPS results. Meanwhile, the XRD and DSC results indicate that the introduction of aniline increases the free volume of PEO matrix, which is beneficial for enhancing CO 2 permeation. Therefore, the 10 wt% An/PEO@HPAN-3h NFCM presents 90.81 % and 13.15 % increases in CO 2 permeability and CO 2 /N 2 selectivity under mixed gas at 0.3 MPa in contrast with the membrane without mobile aniline carriers. Under mixed gas conditions, this NFCM exhibits CO 2 permeability of 202.93 Barrer and CO 2 /N 2 selectivity of 83.89 at 0.1 MPa, reaching the 2019 McKeown upper bound. [Display omitted] • Fixed amine carriers are distributed along the HPAN nanofibers. • Mobile aniline carriers are introduced with in-situ polymerization of PEGDA. • Aniline interlinks the long-range continuous transport pathway in short range. • Continuous facilitated transport pathway improves CO 2 permeability. [ABSTRACT FROM AUTHOR]

• In-situ position of ILs into cages of ZIF-8 was proposed to tune cage size. • CO 2 -philic cages constructed by ILs improve CO 2 adsorption. • Molecular simulation reveals increased CO 2 adsorption by increasing ILs in cages. • CO 2 /N 2 selectivity of MMMs is increased due to pore screening and CO 2 adsorption. The regulation on cage size and CO 2 -philic environment of metal–organic frameworks (MOFs) is essential to improve CO 2 capture. In this work, [Bmim][Tf 2 N] was proposed to position into cages of ZIF-8 to achieve the selective permeation of CO 2 by pore screening and CO 2 adsorption. [Bmim][Tf 2 N] was introduced into cages of ZIF-8 by "adsorption-infiltration" strategy. Due to the strong interaction between [Tf 2 N]− and ZIF-8, the cages present a CO 2 -philic environment, which preferentially attracts CO 2 to enter these cages, ensuring the dissolution selectivity of CO 2. Besides, the proper cage size tuned by [Bmim][Tf 2 N] provides CO 2 with a faster transport channel due to its smaller average kinetic diameter than N 2 , guaranteeing the diffusion selectivity of CO 2. Consequently, the CO 2 separation in [Bmim][Tf 2 N]@ZIF-8/Pebax MMMs is intensified. With increasing the [Bmim][Tf 2 N] content in cages of ZIF-8, the pore volume by BET results decreases and the CO 2 adsorption from molecular simulation increases. In response, the CO 2 /N 2 selectivity of [Bmim][Tf 2 N]@ZIF-8/Pebax MMMs is enhanced constantly. Meanwhile, the CO 2 permeability is declined due to the narrowed cage size. All of these results demonstrate the significance of pore screening and CO 2 adsorption induced by [Bmim][Tf 2 N]. Specifically, [Bmim][Tf 2 N] 8 @ZIF-8/Pebax MMM at filler loading of 15 wt% exhibits the CO 2 permeability of 108.3 Barrer and the CO 2 /N 2 selectivity of 86.7, exceeding the 2008 Robeson upper bound. Especially the CO 2 /N 2 selectivity locates at a higher level than those of most reported works, indicating that appropriate tuning of the physicochemical properties within the nanocages of MOFs is significative to improve CO 2 capture. [ABSTRACT FROM AUTHOR]

Pore size adjustment has been considered to be a successful strategy for enhancing the sieving of MOF-based mixed matrix membranes (MMMs). However, the increase in CO 2 /N 2 selectivity usually comes at the expense of permeability. Herein, the regulating on the pore size of polystyrene-modified hollow NH 2 -MIL-101 (PHNM) is achieved by controlling the confined dissolving of PSA polymer chain. During the etching of PSA template, the dissolved PSA polymer chains diffused outward through the pores and intergranular space of NH 2 -MIL-101 under the concentration difference. As a consequence, the pores of NH 2 -MIL-101 were unavoidably constrained by the partly dissolved PSA segments, achieving the regulation on the pore size. Meanwhile, there are also some PSA segments adhering to the surface of NH 2 -MIL-101 to form a PSA coating layer. In this unique PHNM, the reduced pore size endows it with better CO 2 /N 2 selectivity than NH 2 -MIL-101. Meanwhile, the high interface compatibility provided by surface-modified PSA segments and the enhanced CO 2 affinity of PHNM resulting from amino groups also synergistically improve the CO 2 /N 2 selectivity. Additionally, the hollow core offers gas molecules a low-resistance transfer channel, improving the permeability of CO 2. The hollow size of PHNM was adjusted from 33 to 57 nm by controlling the etching time of PSA, and the pore size of PHNM was regulated from 0.58 to 0.83 nm by controlling the confined dissolving process of PSA. Thus, the PHNM-based MMMs exhibit high CO 2 permeability as well as high CO 2 /N 2 selectivity. Compared with NH 2 -MIL-10/Pebax MMM, the MMM with PHNM-2 loading of 10 wt% shows 30% and 21% enhancements in the CO 2 permeability (226.3 Barrer) and CO 2 /N 2 selectivity (71.3), respectively, far exceeding the Robeson upper bound (2008). These results reveal that the PHNM based MMMs express a great potential in CO 2 separation. [Display omitted] • Confined dissolving of PSA polymer chain is proposed to tune pore size. • Pore size of MIL-101 is regulated from 0.58 to 0.83 nm. • Surface-modified PSA and amino groups intensify interface compatibility. • Hollow structure constructs low-resistance region to improve CO 2 permeability. [ABSTRACT FROM AUTHOR]

[Display omitted] • PSA modified hollow NH 2 -ZIF-8 (PHNZ) with high amino content was designed. • PSA hard template strategy was used to synthesis NH 2 -ZIF-8 rapidly. • The vesicle shape of PHNZ constructs low-resistance region to improve CO 2 permeability. • CO 2 /N 2 selectivity is improved by PSA layer and CO 2 affinity of amino groups. The amino functionalization of MOFs has been verified to be effective in improving the selective permeation of CO 2. However, the introduction of amino groups into ZIF-8 by mixed ligands strategy is hard to achieve due to the high steric hindrance of benzene ring in 2-aminobenzimidazole ligand, resulting in insufficient content of amino groups. Therefore, in this work, polystyrene-acrylate (PSA) template is proposed to provide abundant adsorption and reaction sites for the rapid synthesis of NH 2 -ZIF-8 with high content of 2-aminobenzimidazole. Furthermore, the incomplete etching strategy is used to construct PSA modified hollow NH 2 -ZIF-8 nanospheres (PHNZ). Importantly, the thickness of PSA layer and the hollow size are adjusted by the etching time, as revealed by the SEM and TEM images. In this PHNZ, the modified PSA can provide good interface compatibility between PHNZ and Pebax matrix to enhance the CO 2 selectivity, while the hollow structure can reduce the mass transfer resistance and improve the gas permeability. Moreover, the introduced amino groups can enhance the CO 2 affinity of PHNZ and further improve the CO 2 /N 2 selectivity of the PHNZ-based mixed matrix membranes (MMMs). Benefiting from the synergy of good interface compatibility and enhanced CO 2 affinity from the amino groups, the PHNZ/Pebax MMMs present greatly improved CO 2 /N 2 selectivity in contrast with pure Pebax and NH 2 -ZIF-8 based membranes. Besides, as the etching time increases, the PHNZ-2 and PHNZ-3 based MMMs present a higher CO 2 permeability than that of NH 2 -ZIF-8 based MMM, revealing the significance of the hollow structure. The PHNZ-2/Pebax MMM with filler loading of 10 wt% expresses the best gas separation performance with the CO 2 permeability of 121.9 Barrer and CO 2 /N 2 selectivity of 96.6, respectively, showing an increase of 54.7 % and 98.0 % in contrast with pure Pebax membrane. Meanwhile, this CO 2 separation performance is far beyond the Robeson upper bound in 2008 and close to the McKeown upper bound in 2019, demonstrating that the proposed PHNZ displays a promising and competitive potential in MMM based CO 2 capture. [ABSTRACT FROM AUTHOR]

Layered double hydroxide (LDH) bearing numerous hydroxyl groups shows high affinity with CO 2 and is promising in mixed matrix membranes (MMMs) based CO 2 capture. However, its non-porous structure limits the further improvement of CO 2 permeability. In this work, 3D hollow CoNi-LDH nanocages were developed to construct low-resistance and CO 2 -philic transport channel in MMM by in-situ etching of ZIF-67 template. The resultant material exhibits hollow structure with cavity size of about 500 nm, mesopores and micropores from LDH stacking and ZIF-67 template. The outer layered CoNi-LDH nanosheets can attract more CO 2 molecules by their abundant hydroxyl groups, resulting in an improvement in dissolution selectivity of CO 2 over N 2. Meanwhile, the tortuous gas diffusion paths originated from 2D nanosheet stacking can further enhance the CO 2 selectivity over N 2. Moreover, the hollow nanocages provide CO 2 molecules with fast transport path, resulting in high CO 2 permeability. As a result, compared with pure Pebax membrane and 2D LDH/Pebax MMM, all the 3D hollow CoNi-LDH/Pebax MMMs present enhanced CO 2 permeability. The 3D hollow CoNi-LDH-2h/Pebax MMM performs the highest CO 2 permeability of 135.49 Barrer, which are increased by 141.95% and 71.50% than those of the above two membranes, respectively. The selectivity of 3D hollow CoNi-LDH-2h/Pebax MMM is about 26.30% higher than that of the pure Pebax membrane. The present membrane presents comparable CO 2 capture capacity in contrast with most reported Pebax based MMMs and surpasses the Robeson upper bond. Together with the good long-term stability, the 3D hollow CoNi-LDH nanocages are believed to be a promising candidate for MMMs to improve CO 2 capture. [Display omitted] • MMM with low resistance and CO 2 -philic transport channel was constructed. • 3D Hollow CoNi-LDH nanocages were developed by etching ZIF-67 template. • Hollow and porous structure ensures the high CO 2 permeability. • Abundant hydroxyl groups and tortuous diffusion paths ensure high selectivity. [ABSTRACT FROM AUTHOR]

Metal organic frameworks (MOFs) based mixed matrix membrane (MMM) for CO 2 capture shows insufficient CO 2 permeability due to random disperse of MOFs in form of individual particle. Therefore, in this work, a continuous MOFs transport pathway for CO 2 with low resistance was constructed in the MMM by assistance of electrospun nanofiber. Specifically, PAN electrospun nanofiber mat (NFM) was utilized as skeleton to obtain continuous ZIF-8 nanofibers. Then flexible polyethylene glycol (PEG) molecules were photo-polymerized in situ into the inner-voids within ZIF-8@PAN NFM to form dense membrane. As a result, ZIF-8 particles are distributed in PEO matrix continuously, leading to a low-resistance transport pathway for gas molecules in MMM, which is proved by the cross-sectional SEM images. Furthermore, the higher Tg of ZIF-8@PAN-x/PEO MMM by DSC also indicates the good interfacial compatibility between ZIF-8 and PEO. Compared with pure PEO membrane, all the ZIF-8@PAN-x/PEO MMMs present both enhanced CO 2 permeability and CO 2 /N 2 selectivity. The enhanced CO 2 permeability is attributed to the continuous ZIF-8 transport pathway, and the improved selectivity is ascribed to the size screening from nanofibers overlapping and stacking and the tortuous transport pathway. Importantly, compared with ZIF-8/PEO MMM, in which ZIF-8 particles are randomly dispersed into PEO matrix, the ZIF-8@PAN-4/PEO MMM with the same ZIF-8 loading of about 16.6 wt% presents enhanced CO 2 permeability and CO 2 /N 2 selectivity, which are increased by 52.4% and 44.3%, respectively. This is due to the continuous ZIF-8 transport pathway and good interfacial compatibility, which is also confirmed by the result of gas diffusivity and solubility coefficients. Together with the outstanding mechanical strength and stability, the proposed MMM with continuous ZIF-8 transport pathway paves a new way to improve CO 2 permeability. [Display omitted] • MMM with continuous MOFs pathway was constructed to capture CO 2. • PAN nanofibers were used to induce MOFs continuous in long-range. • MMM was obtained by in-situ polymerization of PEG within MOFs NFM. • Both high permeability and selectivity were achieved by continuous gas pathway. [ABSTRACT FROM AUTHOR]

[Display omitted] • PEI was introduced into ZIF-8 HNTs to obtain versatile filler for MMM. • The –NH 2 groups in PEI can facilitate CO 2 transport in presence of H 2 O. • Residence of PEI into nanocages of ZIF-8 can adjust its effective sieving size. • Hydrogen bond between PEI and Pebax can strengthen interfacial compatibility. • 1D hollow nanotube provides fast transport channel with low resistance. 1D nanotube (HNT) based MMM presents high CO 2 permeation due to its long and hollow structure. However, the improvement of selectivity is still challenging. In this study, small PEI molecules with abundant amino groups were introduced into the nanocages of ZIF-8 HNTs to construct facilitated CO 2 transmission channel with low resistance. In the PEI@ZIF-8 HNTs, the –NH 2 groups can facilitate CO 2 transport in presence of H 2 O, resulting in an improvement in both CO 2 permeability and selectivity. Second, the introduction of PEI into the nanocages of ZIF-8 can adjust the effective sieving size to enhance CO 2 selectivity. Third, the hydrogen bond between PEI and Pebax can strengthen the interfacial compatibility, further improving CO 2 /N 2 selectivity of the MMMs. Finally, the 1D hollow structure of PEI@ZIF-8 HNTs provides CO 2 molecules with low-resistance and fast transport channel, enhancing the CO 2 permeability. Consequently, both the high CO 2 permeability and the high CO 2 /N 2 selectivity are acquired by the versatile filler of PEI@ZIF-8 HNTs. PEI@ZIF-8 HNTs based MMM at filler loading of 7 wt% under dry mixed gas, presents CO 2 permeability of 177 Barrer and CO 2 /N 2 selectivity of 72, which are 40% and 10.8% higher than those of ZIF-8 HNTs based MMM, respectively. Moreover, the permeability of CO 2 and the selectivity of CO 2 /N 2 reach 306 Barrer and 79 respectively under the wet mixed gas, which is far beyond the Robeson upper bound in 2008 and exceeds the McKeown upper bound in 2019. The proposed PEI@ZIF-8 HNTs are believed to be promising filler for MMMs based CO 2 capture. [ABSTRACT FROM AUTHOR]

[Display omitted] • Highly permeable PTMSP fibers provide continuous and fast transport pathway. • EFCM was obtained by in-situ polymerization of PEG within fibers voids. • PTMSP fibers skeleton reinforces the membrane mechanical properties. • Both high CO 2 permeability and selectivity were acquired. • High CO 2 selectivity was mainly due to the high affinity between PEO and CO 2. Electrospun fibers composite membrane shows an insufficient CO 2 permeability due to the impermeable polymer fibers. In this work, highly permeable poly(1-trimethylsilyl-1-propyne) (PTMSP) electrospun fiber were utilized to construct continuous and fast transport pathway with low-resistance for gas molecules in PEO matrix. The PEO/PTMSP electrospun fiber composite membrane (EFCM) was obtained by the in-situ polymerization of polyethylene glycol (PEG) into the voids of PTMSP electrospun fibers, which is demonstrated by FTIR and XPS characterizations. Furthermore, the obtained EFCM is dense and defect-free, which is confirmed by SEM images. Specifically, the PTMSP fibers and PEO matrix present good interfacial compatibility, as revealed by DSC results. In addition, PTMSP electrospun fibers perform as skeleton for EFCM to reinforce the membrane mechanical properties. The PEO/PTMSP EFCM shows CO 2 permeability of 281 Barrer and CO 2 /N 2 selectivity of 32.94. The CO 2 permeability is 280% higher than that of pure PEO membrane, which is resulted from the continuous and fast transport pathway provided by PTMSP electrospun fibers. The CO 2 /N 2 selectivity is enhanced by 4 to 6 times in comparison with pure PTMSP membrane and PTMSP c-EFM, which can be attributed to the affinity between EO groups of PEO matrix and CO 2 molecules and also the screening effect from the tortuous pathway of PTMSP fibers. This superior gas separation performance of PEO/PTMSP EFCM exceeds most reported PTMSP based membranes, especially its selectivity of CO 2 over N 2 is significantly high. Consequently, this proposed EFCM with continuous and fast transport pathway holds a competitive prospect for polymer based CO 2 capture. [ABSTRACT FROM AUTHOR]

The electrospun nanofiber mat (NFM) with 3D networks has advantages of high porosity and large specific surface area, but its porous structure limits the application in gas membrane separation. Therefore, in this work, a novel and defect-free nanofibers interpenetrating composite membrane is proposed for CO 2 /N 2 separation. And it is constructed by in-situ polymerization of low-molecular-weight polyethylene glycol (PEG) into the inner-voids within PAN NFM. In this nanofiber composite membrane (NFCM), PAN nanofibers interpenetrate into PEO matrix to form a "reinforced-concrete" structure with good interfacial compatibility between them, which has been demonstrated by SEM, EDS, ATR-FTIR and C1s XPS characterizations. Particularly, the PAN nanofiber acts as "Rebar" framework, while the void-sealing polymer PEO serves as "Concrete". They are bonded into a whole through adhesive force to bear the external force together, resulting in elevated mechanical properties than the pure PEO membrane. Furthermore, the CO 2 permeability of each PEO/PAN NFCM shows a minor decease in contrast with corresponding pure PEO membrane due to the barriers of PAN nanofibers to CO 2 molecules. However, the CO 2 /N 2 selectivity of each NFCM has been increased by 13–15 in contrast with its corresponding pure PEO membrane. This enhancement can be explained by the size screening from PAN nanofibers overlapping and stacking and the tortuous transport pathway along the impermeable PAN nanofibers. As a result, the 3:7/PAN NFCM exhibits a CO 2 permeability of 343 Barrer and a CO 2 /N 2 selectivity of 65.4, exceeding the Robeson upper bond of 2008. Together with the excellent mechanical properties, the proposed nanofibers interpenetrating composite membrane displays a bright prospect for CO 2 capture. [Display omitted] • Nanofibers interpenetrated composite membrane was proposed to capture CO 2. • The NFCM mimicks "reinforced-concrete" to be mechanically robust. • In-situ polymerization of PEG is proposed to seal the inner-voids within PAN NFM. • Overlap and stack of nanofibers provide size screening and tortuous transport pathway. [ABSTRACT FROM AUTHOR]