No abstract

Zeolitic nanotubes Nanotubes generally have solid walls, but a low-dimensional version of zeolites now introduces porosity into such structures. Korde et al . used a structure-directing agent with a hydrophobic biphenyl group center connecting two long alkyl chains bearing hydrophilic bulky quaternary ammonium head groups to direct hydrothermal synthesis with silicon-rich precursors (see the Perspective by Fan and Dong). The nanotubes have a mesoporous central channel of approximately 3 nanometers and zeolitic walls with micropores less than 0.6 nanometers. Electron microscopy and modeling showed that the outer surface is a projection of a large-pore zeolite and the inner surface is a projection of a medium-pore zeolite. —PDS

High-quality 2D MFI nanosheet coatings were prepared on a-alumina hollowf iber supports by vacuum filtration and then transformed into molecular sieving membranes by two sequential hydrothermal treatments.T his processing method eliminates the need for specially engineered silica-based support materials that have so far been necessary to allow the formation of functional membranes from 2D MFI nanosheets.T he sequential steps enhance adhesion of the membrane on the fiber support, fill in nanoscale gaps between the 2D nanosheets,a nd preserve the desirable (0k0) out-ofplane orientation without the need of any support engineering or modification. The membrane exhibits high performance for separation of n-butane from i-butane,a nd for other technologically important hydrocarbon separations.T he present findings have strong implications on strategies for obtaining thin, highly selective zeolite membranes from 2D zeolites in atechnologically scalable manner.Membrane-based separations have high potential for energy efficiency and cost reduction in chemical processes. Inorganic molecular sieving zeolite membranes [1] can offer anumber of advantages,such high permeability and selectivity as well as excellent thermal and chemical stability,inmany applications.However,the difficulty of low-cost and scalable fabrication of zeolite membranes is ak ey barrier to their widespread application. In the last few years,t he emergence of zeolitic membranes based upon two-dimensional (2D) zeolite nanosheets [2] has created an opportunity to overcome this barrier.Inprinciple,uniform and thin (0.1-1 mm) coatings of high-aspect ratio zeolite nanosheets can be deposited on nearly any kind of porous membrane substrate and then perform af inal zeolite growth step to close the nanoscopic gaps between the nanosheets,thereby creating very high-flux molecular sieving membranes.F or example,n anosheets (3-5nminthickness) of zeolite MFI have been synthesized both by exfoliation of 2D MFI layered stacks [2a, 3] as well as by seedassisted bottom-up methods. [2b] TheM FI nanosheets produced by the latter route offer particularly attractive structural features,s uch as av ery high aspect ratio favorable for thin coatings,v ery short diffusion pathways through the nanosheet, high-yield production without need for an exfoliation process,a nd good dispersibility in water. MFI membranes fabricated from these MFI nanosheets have shown high fluxes and excellent separation of xylene isomers and also of butane isomers. [2b, 4] Despite the excellent separation performance of the above MFI membranes,t heir current fabrication process faces considerable hurdles in practical feasibility and scalability.Atpresent the fabrication process is only possible on porous Stçber silica-derived disk-type supports.I th as been hypothesized that such as upport provides an optimal delivery of silicate reactants to the 2D MFI nanosheet coating and facilitates its growth into adefectfree membrane,a nd its properties are difficult to replicate with other types of silica-cont...

A synthesis method to obtain new zeolite imidazolate framework (ZIF) materials that are otherwise difficult to synthesize by known techniques such as direct crystallization or solvent-assisted linker exchange, is demonstrated. Treatment of an easily synthesized “template” ZIF (such as ZIF-8) with an acid gas (humid SO2) allows controlled demolition of metal-linker coordination bonds, while preserving overall crystal topology. The partially demolished crystals are then reconstructed into highly crystalline mixed-linker ZIFs with unique characteristics by insertion of different linkers that displace the damaged linkers. One illustration shows the synthesis of a series of mixed-linker ZIFs containing benzimidazole linkers that show entirely different gate-opening and diffusion characteristics from ZIFs of the same composition prepared by direct crystallization. Also shown is the synthesis of new mixed-linker SOD-topology ZIFs containing bulky halobenzimidazole and alkylbenzimidazole linkers, which are very difficult to synthesize by other methods. The present method is seen to considerably reduce thermodynamic or kinetic barriers for replacement and insertion of linkers into ZIF topologies.

High-quality 2D MFI nanosheet coatings were prepared on a-alumina hollowf iber supports by vacuum filtration and then transformed into molecular sieving membranes by two sequential hydrothermal treatments.T his processing method eliminates the need for specially engineered silica-based support materials that have so far been necessary to allow the formation of functional membranes from 2D MFI nanosheets.T he sequential steps enhance adhesion of the membrane on the fiber support, fill in nanoscale gaps between the 2D nanosheets,a nd preserve the desirable (0k0) out-ofplane orientation without the need of any support engineering or modification. The membrane exhibits high performance for separation of n-butane from i-butane,a nd for other technologically important hydrocarbon separations.T he present findings have strong implications on strategies for obtaining thin, highly selective zeolite membranes from 2D zeolites in atechnologically scalable manner.Membrane-based separations have high potential for energy efficiency and cost reduction in chemical processes. Inorganic molecular sieving zeolite membranes [1] can offer anumber of advantages,such high permeability and selectivity as well as excellent thermal and chemical stability,inmany applications.However,the difficulty of low-cost and scalable fabrication of zeolite membranes is ak ey barrier to their widespread application. In the last few years,t he emergence of zeolitic membranes based upon two-dimensional (2D) zeolite nanosheets [2] has created an opportunity to overcome this barrier.Inprinciple,uniform and thin (0.1-1 mm) coatings of high-aspect ratio zeolite nanosheets can be deposited on nearly any kind of porous membrane substrate and then perform af inal zeolite growth step to close the nanoscopic gaps between the nanosheets,thereby creating very high-flux molecular sieving membranes.F or example,n anosheets (3-5nminthickness) of zeolite MFI have been synthesized both by exfoliation of 2D MFI layered stacks [2a, 3] as well as by seedassisted bottom-up methods. [2b] TheM FI nanosheets produced by the latter route offer particularly attractive structural features,s uch as av ery high aspect ratio favorable for thin coatings,v ery short diffusion pathways through the nanosheet, high-yield production without need for an exfoliation process,a nd good dispersibility in water. MFI membranes fabricated from these MFI nanosheets have shown high fluxes and excellent separation of xylene isomers and also of butane isomers. [2b, 4] Despite the excellent separation performance of the above MFI membranes,t heir current fabrication process faces considerable hurdles in practical feasibility and scalability.Atpresent the fabrication process is only possible on porous Stçber silica-derived disk-type supports.I th as been hypothesized that such as upport provides an optimal delivery of silicate reactants to the 2D MFI nanosheet coating and facilitates its growth into adefectfree membrane,a nd its properties are difficult to replicate with other types of silica-cont...