Achieving a water–oil interface imbalance has been identified as a critical factor in the demulsification of water-in-oil emulsions. However, conventional demulsifying membranes generally break the interface balance by depending on a relatively high transmembrane pressure. Here, we present a "contact demulsification" concept to naturally and quickly achieve disruption of the water–oil interface balance. For this purpose, a novel demulsifying membrane with a high flux of the organic component has been developed via the simple vacuum assembly of zeolitic imidazolate framework-8 (ZIF-8)@reduced graphene oxide (rGO) microspheres (ZGS) on a polytetrafluoroethylene (PTFE) support, followed by immobilization processing in a polydimethylsiloxane (PDMS) crosslinking solution. Due to the micro-nano hierarchies of the ZGS, the prepared ZIF-8@rGO@PDMS/PTFE (ZGPP) membranes feature a unique superhydrophobic surface, which results in a water–oil interface imbalance when a surfactant-stabilized water-in-oil emulsion comes into contact with the membrane surface. Under a low transmembrane pressure of 0.15 bar (15 kPa), such membranes show an excellent separation efficiency (~99.57%) and a high flux of 2254 L·m^–2·h^–1, even for surfactant-stabilized nanoscale water-in-toluene emulsions (with an average droplet size of 57 nm). This "contact demulsification" concept paves the way for developing next-generation demulsifying membranes for water-in-oil emulsion separation.

The adsorptive separation of CH₄ from CO₂ is a promising process for upgrading natural gas. However, thermodynamically selective adsorbents exhibit a strong affinity for CO₂ and thus require a high energy compensation for regeneration. Instead, kinetic separation is preferred for a pressure swing adsorption process, although precise control of the aperture size to achieve a tremendous discrepancy in diffusion rates remains challenging. Here, we report a guest solvent-directed strategy for fine-tuning the pore size at a sub-angstrom precision to realize highly efficient kinetic separation. A series of metal–organic frameworks (MOFs) with isomeric pore surface chemistry were constructed from 4,4′-(hexafluoroisopropylidene)-bis(benzoic acid) and dicopper paddlewheel notes. The resultant CuFMOF·CH₃OH (CuFMOF-c) exhibits an excellent kinetic separation performance thanks to a periodically expanding and contracting aperture with the ideal bottleneck size, which enables the effective trapping of CO₂ and impedes the diffusion of CH₄, offering an ultrahigh kinetic selectivity (273.5) and equilibrium-kinetic combined selectivity (64.2). Molecular dynamics calculations elucidate the separation mechanism, and breakthrough experiments validate the separation performance.

Mixed-matrix membranes (MMMs), which combine porous materials with a polymeric matrix, have gained considerable research interest in the field of gas separation due to their complementary characteristics and cooperative activation. The tailorability and diversity of porous materials grant MMMs extendable functionalities and outstanding separation performance. To achieve the full potential of MMMs, researchers have focused on the rational matching of porous fillers with polymeric matrixes to achieve enhanced compatibility at the interfaces of these materials. In this review, we highlight state-of-the-art advances in combining metal–organic frameworks (MOFs) and metal–organic cages (MOCs) with polymeric matrixes to fabricate MMMs using different strategies. We further discuss the opportunities and challenges presented by the future development of MMMs, with the aim of boosting MMM fabrication with judicious material design and selection.

Developing efficient adsorbents with high uptake and selectivity for separation and recovery of C₂H₆ and C₃H₈ from natural gas is an important but challenging task. In this work, we demonstrate that high surface polarity and suitable pore diameter are two key factors that can synergistically enhance the separation performance, exemplified by metal–organic framework (MOF)-303 and Matériaux de l'Institut Lavoisier (MIL)-160, both possessing one-dimensional (1D) open channels with high density of heteroatoms and desired pore size (5–7 Å). Significantly, the uptake of MOF-303 for C₃H₈ is up to 3.38 mmol∙g⁻¹ at 298 K and 5 kPa with a record-high C₃H₈/CH₄ (5:85, v/v) ideal adsorbed solution theory (IAST) selectivity of 5114 among all reported MOFs. In addition, MOF-303 also displays high C₂H₆ uptake capacity (at 10 kPa) and C₂H₆/CH4 (10:85, v/v) selectivity, reaching 1.59 mmol∙g⁻¹ and 26, respectively. Owing to the larger pore diameter and lower density of heteroatoms within its 1D channels, MIL-160 shows apparently lower uptake and selectivity compared to those of MOF-303, though the values exceed those of majority of reported MOFs. Density functional theory (DFT) calculations verify that the high surface polarity and the suitable pore diameter synergistically enhance the affinity of the frameworks toward C₃H₈ and C₂H₆, giving rise to the high loading capacity and selectivity for C₃H₈ and C₂H₆. Both MOFs feature remarkable moisture stability without structural change upon exposure to 95% relative humidity (RH) for a month. In addition, synthesis of both compounds can be readily scaled up through one-pot reactions to afford about 5 g samples with high crystallinity. Finally, the substantial potential of MOF-303 and MIL-160 as advanced adsorbents for efficient separation of C₃H₈/C₂H₆/CH₄ has been demonstrated by ternary breakthrough experiments, regeneration tests, and cyclic evaluation. The excellent separation performance, high stability, low cost, and good scalability endow both MOFs promising adsorbents for natural gas purification and recovery of C₂H₆ and C₃H₈.