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.

Gas separation performance of mixed matrix membrane heavily depends on the pore structure of the nanofillers. Metal-organic frameworks (MOFs) are promising platform materials for constructing molecular-selective pores for specific applications. In this work, deliberately-selected polymers with CO₂ affinity (PVAm, Pebax and PEI) are employed as pore regulators to manipulate the pore chemistry and size of MOF UiO-66 nanoparticles and consequently control gas transport rate of CO₂ and N₂ molecules. The branched polymer (polyethyleneimine (PEI)) grafted UiO-66, denoted as UKI, is beneficial to enhancing the membrane selectivity. The UKI doped Pebax/mPSf membranes exhibit CO₂/N₂ selectivity up to 278, 6.5 times of the bare Pebax/mPSf membranes. Meanwhile, the CO₂ permeance is boosted from around 690 to 1120 GPU (1 GPU = 10⁻⁶ cm³ (STP)·cm⁻²·s⁻¹·cmHg⁻¹ = 3.35 × 10⁻¹⁰ mol m⁻² s⁻¹·Pa⁻¹). The block copolymer (poly(ether block amide) (Pebax)) grafted UiO-66, denoted as UKX, is conducive to increasing the membrane permeance. The UKX doped Pebax/mPSf membranes exhibited CO₂ permeance up to 1683 GPU, 2.45 times of the bare Pebax/mPSf membranes. Meanwhile, CO₂/N₂ selectivity increased from around 42 to 146. Additionally, excellent pressure-resistant property and outstanding stability are observed under simulated flue gas.

Membrane-based separation processes can improve separation efficiency and reduce the environmental hazards and energy costs of traditional separation processes. Mixed matrix membranes (MMMs) with broad development prospects are frequently restricted by interfacial incompatibility and the blockage of gas transport channels in the filler matrix. Here, we report a new type of high-valence metal-induced microporous polymer (HMMP-1) filler, with a high density of free amine groups, and having excellent alkaline stability. The HMMP-1 nanoparticles were incorporated into polyvinylamine (PVAm) to prepare facilitated transport mixed matrix membranes (MMMs). The resulting HMMP-1 based MMMs maintain their pore aperture structure, which is mainly due to the excellent compatibility between the polymer component in the HMMP-1 and PVAm. Amine-rich nanochannels with appropriate pore size allow rapid CO₂ transport through the filler pores by preferential adsorption monomolecular surface diffusion, leading to high CO₂ permeance and excellent separation performance for CO₂/CH₄, CO₂/N₂ and CO₂/H₂ compared with many other reported membranes. A techno-economic evaluation suggests that the MMM is feasible for carbon capture from post-combustion flue gas.