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...

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

Separation of radioisotope Kr fromXe is of importance in used nuclear fuel reprocessing. Membrane separation based on zeolite molecular sieves such as chabazite SAPO-34 is an attractive alternative to energy-intensive cryogenic distillation. We report the synthesis of SAPO-34 membranes with considerably enhanced performance via thickness reduction based upon control of a steam-assisted vapor-solid conversion technique followed by ion exchange with alkali metal cations. The reduction of membrane thickness leads to a large increase in Kr permeance from 7.5 to 26.3 gas permeation units (GPU) with ideal Kr/Xe selectivities >20 at 298 K. Cation-exchanged membranes show large (>50%) increases in selectivity at ambient or slight subambient conditions. The adsorption, diffusion, and permeation characteristics of ion-exchanged SAPO-34 materials and membranes are investigated in detail, with potassium-exchanged SAPO-34 membranes showing particularly attractive performance. We then demonstrate the fabrication of selective SAPO-34 membranes on α-alumina hollow fibers.

Zeolitic membranes synthesized using organic structure-directing agents (SDAs) require an activation step to remove the SDA and open their porosity. Activation is typically achieved by high-temperature (> 673 K) calcination. This process has multiple disadvantages, including coke formation due to incomplete removal of the SDA as well as the formation of cracks and other defects due to differential thermal expansion of the membrane layer and the underlying support material. Here we report that high-performance hollow fiber membranes of the small-pore (0.38 nm) zeolite SSZ-13 can be produced via UV irradiation to decompose and remove the SDA. Remarkably, UV irradiation allowed com-plete removal of the bulky SDA (trimethyladamantylammonium hydroxide) from the pores at near-ambient conditions, whereas membranes activated by calcination exhibited severe cracking. The UV-activated SSZ-13 membranes showed excellent H 2 /C 3 H 8 and CO 2 /CH 4 mixture selectivities (up to 810 and 110 whereas the conventionally activated membranes showed poor selectivity (< 5). The combined demonstration of hollow fiber membrane synthesis and low-temperature membrane activation of small-pore zeolite membranes is a significant step in the effort to create reliable, scalable, and low-cost fabrication processes for zeolite membranes for gas separations.[a] Dr.

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...