A High-Performance N2-Selective MXene Membrane with Double Selectivity Mechanism for N2/CH4 Separation.

Membrane-based separation process for unconventional natural gas purification (mainly N2/CH4 separation) has attracted more attention due to its considerable economic benefits. However, the majority of separation membranes at this stage, particularly N2-selective membranes, achieve the desired separation target by mainly relying on the diffusivity-selectivity mechanism. To overcome the limitation of a single mechanism, 2D lamellar MXene membranes with a double selectivity mechanism are prepared to enhance N2 permeance and N2/CH4 selectivity via introducing unsaturated metal sites into MXene, which can form specific interactions with N2 molecules and enhance N2 permeation. The resulting membranes exhibit an inspiring N2/CH4 separation performance with an N2 permeance of 344 GPU and N2/CH4 selectivity of 13.76. The collaboration of the double selectivity mechanism provides a new idea for the development of a novel N2-selective membrane for N2 removal and CH4 purification, which further broadens the application prospects of membrane separation technology in the field of unconventional natural gas purification.

Designing Metal-Organic Framework (MOF) Membranes for Isomer Separation.

Membrane-based separation has the merit of low carbon footprint. In this study, the pore size of metal-organic framework (MOF) membranes is rationally designed for discriminating various pairs of hydrocarbon isomers. Specifically, Zr-MOF UiO-66 (UiO stands for University of Oslo) membranes are developed for separating p/o-xylene due to their proper pore size. For n-hexane/2-methylpentane separation, the functional groups and proportion of the ligands in UiO-66 are gradually adjusted to effectively regulate the pore size, and UiO-66-33Br membranes are constructed. In addition, relying on the utilization of ligands with shorter length, MOF-801 membranes with smaller pore size are fabricated for n/i-butane separation.

Highly Water-Permeable Metal-Organic Framework MOF-303 Membranes for Desalination.

New membrane materials with excellent water permeability and high ion rejection are needed. Metal-organic frameworks (MOFs) are promising candidates by virtue of their diversity in chemistry and topology. In this work, continuous aluminum MOF-303 membranes were prepared on α-Al2O3 substrates via an in situ hydrothermal synthesis method. The membranes exhibit satisfying rejection of divalent ions (e.g., 93.5% for MgCl2 and 96.0% for Na2SO4) on the basis of a size-sieving and electrostatic-repulsion mechanism and unprecedented permeability (3.0 L·m-2·h-1·bar-1·µm). The water permeability outperforms typical zirconium MOF, zeolite, and commercial polymeric reverse osmosis and nanofiltration membranes. Additionally, the membrane material exhibits good stability and low production costs. These merits recommend MOF-303 as a next-generation membrane material for water softening.

Rational Design of Mixed Matrix Membranes Modulated by Trisilver Complex for Efficient Propylene/Propane Separation.

The application of membrane-based separation processes for propylene/propane (C3 H6 /C3 H8 ) is extremely promising and attractive as it is poised to reduce the high operation cost of the established low temperature distillation process, but major challenges remain in achieving high gas selectivity/permeability and long-term membrane stability. Herein, a C3 H6 facilitated transport membrane using trisilver pyrazolate (Ag3 pz3 ) as a carrier filler is reported, which is uniformly dispersed in a polymer of intrinsic microporosity (PIM-1) matrix at the molecular level (≈15 nm), verified by several analytical techniques, including 3D-reconstructed focused ion beam scanning electron microscropy (FIB-SEM) tomography. The π-acidic Ag3 pz3 combines preferentially with π-basic C3 H6 , which is confirmed by density functional theory calculations showing that the silver ions in Ag3 pz3 form a reversible π complex with C3 H6 , endowing the membranes with superior C3 H6 affinity. The resulting membranes exhibit superior stability, C3 H6 /C3 H8 selectivity as high as ≈200 and excellent C3 H6 permeability of 306 Barrer, surpassing the upper bound selectivity/permeability performance line of polymeric membranes. This work provides a conceptually new approach of using coordinatively unsaturated 0D complexes as fillers in mixed matrix membranes, which can accomplish olefin/alkane separation with high performance.

Porous Graphene Oxide/Porous Organic Polymer Hybrid Nanosheets Functionalized Mixed Matrix Membrane for Efficient CO2 Capture.

The computational simulation of porous graphene oxide (PGO) indicated that it has great potential for the preparation of gas separation membranes. However, scaling up the manufacture of multilayer, defect-free porous graphene oxide membrane with consistently sized nanopores is extremely challenging. Here, we prepared layer-by-layer CO2-philic Pebax@1657 membranes that were functionalized by o-hydroxyazo-hierarchical porous organic polymers (o-POPs) and PGO. The d-spacing of pristine PGO could be finely regulated through CO2-philic o-POPs to facilitate the permeability of CO2. In addition, the o-POPs exhibit "N2-phobic, CO2-philic" properties with the phenolic hydroxyl and the azo group. The best of the POP-PGO membrane exhibits that the CO2 permeability and ideal selectivity of CO2/N2 are 232.7 Barrer and 80.7, respectively, and it has surpassed the Robeson's upper bound (2008).