Hierarchy in inorganic membranes

Thin films of a few μm thickness for particle filtration and gas separation cannot be applied as self-supporting layers since they are mechanically insufficiently strong. Therefore, these top layers for particle filtration and gas separation are usually deposited on porous mechanically strong supports with a hierarchical pore structure. To reduce the pressure drop of a gas stream over the membrane and to ensure high fluxes in filtration and gas separation, the cross section of the support is usually asymmetric or graded with a small thickness of the layer with the smallest pore size called the top layer. Since the pressure drop over a capillary with radius r is ∼r4, the layer with the smallest pore size should be as thin as possible. The disk-like planar supports are usually prepared by sequential tape casting which is an expensive technology. Tubular supports with a hierarchical cross section can be prepared in one step by hollow fiber spinning, double mantle spinning or centrifugal casting. © 2016 The Royal Society of Chemistry

Highly oriented, neutral and cation-free AlPO4 LTA: From a seed crystal monolayer to a molecular sieve membrane

An oriented, neutral and cation-free AlPO4 LTA molecular sieve membrane with high hydrogen selectivity was prepared on porous α-Al 2O3 supports through secondary growth of a highly oriented AlPO4 LTA monolayer. © 2011 The Royal Society of Chemistry

Facile synthesis of LTA molecular sieve membranes on covalently functionalized supports by using diisocyanates as molecular linkers

Much effort has been paid towards the preparation of hydrophilic zeolite LTA membranes, and these zeolite LTA membranes have showed excellent performance in hydrophilic separations. However, there are only a few reports on successful shape-selective separations of gas mixtures on zeolite LTA membranes, most separation factors reported so far were lower than the corresponding Knudsen constants. It is often found that zeolite LTA membranes contain inter-crystalline defects to degrade their separation selectivity, which result from the problems that the isolated crystals on the support surface grow together to form a continuous supported LTA layer. In the present work, via urethane bonds formed by the reaction of isocyanate groups with surface hydroxyls, a facile synthesis method is developed for the seeding-free preparation of supported dense zeolite LTA layers by using 1,4-diisocyanate as a molecular binder to anchor the zeolite nutrients onto the support surface. The α-Al2O3 supported zeolite LTA membrane with a thickness of about 3.5 μm displays molecular sieving performance in gas permeation tests. © 2011 The Royal Society of Chemistry

Stepwise synthesis of sandwich-structured composite zeolite membranes with enhanced separation selectivity

Sandwich-structured composite zeolite membranes with enhanced hydrogen selectivity were prepared on porous α-Al 2O 3 supports by using 3-aminopropyltriethoxysilane as an interlayer. © 2012 The Royal Society of Chemistry

In situ formation of LDH membranes of different microstructures with molecular sieve gas selectivity

Research on interlayer gallery-based gas and liquid separation has gained widespread attention. A series of layered materials like lamellar ZSM-5, graphene and its derivatives have been fabricated into membranes showing fascinating gas/liquid separation properties. Layered double hydroxides (LDHs) are prominent representatives of layered compounds composed of regularly arranged brucite-like 2D sheets. Here we successfully prepared well-intergrown NiAl-CO3 LDH membranes in one step. Particularly it was found that CO2 dissolved in the precursor solution exerted great influence on the microstructure of prepared membranes. Trace amounts of CO2 in the precursor solution led to the formation of ab-oriented 0.6 mu m thick LDH membranes, while randomly oriented 5 mu m thick LDH membranes formed from CO2-saturated precursor solutions. Both ab-& randomly oriented LDH membranes showed clear size-based selectivity and H-2 was found to preferentially permeate through the interlayer galleries. However, randomly oriented LDH membranes showed a much higher H-2 selectivity possibly due to the decreased density of mesoscopic defects. Furthermore, in addition to the NiAl-CO3 LDH membrane, a compact and randomly oriented ZnAl-NO3 LDH membrane with reasonable gas selectivity was successfully prepared here by proper optimization of the synthesis conditions.EC/FP7/263007Alexander von Humboldt FoundationFP7-NMP-2010-LARGE-4, no. 26300

Highly hydrogen permselective ZIF-8 membranes supported on polydopamine functionalized macroporous stainless-steel-nets

Inspired by the bio-adhesive ability of the marine mussel, highly hydrogen permselective ZIF-8 membranes were prepared on polydopamine functionalized stainless-steel-nets (SSNs). With polydopamine functionalization of SSNs under mild conditions, the nucleation and growth of well-intergrown ZIF-8 membranes were promoted through the formation of strong non-covalent and covalent bonds, which was helpful to enhance the membrane's separation selectivity while maintaining high permeance. For binary mixtures at 100 degrees C and 1 bar, the mixture separation factors of H-2-CO2, H-2-N-2, H-2-CH4 and H-2-C3H8, were found to be 8.1, 15.0, 23.2 and 329.7, which by far exceed the corresponding Knudsen coefficients and those of the as-reported ZIF-8 membranes. The ZIF-8 membranes also displayed high permeances, with the H-2 permeance higher than 2.1 x 10(-5) mol m(-2) s(-1) Pa-1 due to the high void volume of the SSNs.National Natural Science Foundation of China/21276262Chinese Academy of Science Visiting Professorship for Senior International Scientists/2013T1G0047NIMTE/Y20808A0

MXene-based Membranes for Drinking Water Production

The soaring development of industry exacerbates the shortage of fresh water, making drinking water production an urgent demand. Membrane techniques feature the merits of high efficiency, low energy consumption, and easy operation, deemed as the most potential technology to purify water. Recently, a new type of two-dimensional materials, MXenes as the transition metal carbides or nitrides in the shape of nanosheets, have attracted enormous interest in water purification due to their extraordinary properties such as adjustable hydrophilicity, easy processibility, antifouling resistance, mechanical strength, and light-to-heat transformation capability. In pioneering studies, MXene-based membranes have been evaluated in the past decade for drinking water production including the separation of bacteria, dyes, salts, and heavy metals. This review focuses on the recent advancement of MXene-based membranes for drinking water production. A brief introduction of MXenes is given first, followed by descriptions of their unique properties. Then, the preparation methods of MXene membranes are summarized. The various applications of MXene membranes in water treatment and the corresponding separation mechanisms are discussed in detail. Finally, the challenges and prospects of MXene membranes are presented with the hope to provide insightful guidance on the future design and fabrication of high-performance MXene membranes

MOF membrane synthesis in the confined space of a vertically aligned LDH network

MOF membranes have gained widespread attention due to their unprecedented gas separation performance. Relying on physical interactions, we successfully deposited MOF seeds on a substrate modified with a network of vertically aligned LDH walls before secondary growth of the MOF layer. ZIF-8 membranes thus prepared show considerable H-2 permeance with high H-2-CH4 selectivity. This approach is in general suitable for the deposition of nanoparticles on solid surface and their subsequent growth into a dense layer.EC/FP7/263007Alexander von Humboldt FoundationFP7-NMP-2010-LARGE-4, Nr. 26300