Conventional gas separation membranes made of glassy polymers often exhibit increased segmental motion and reduced selectivity when exposed to highpressure condensable gases. Decarboxylation cross-linking can effectively improve the plasticization resistance and gas permeability of polymer membranes, but this usually comes at the expense of the gas selectivity. In this work, enhanced π−π interactions and decarboxylation cross-linking are synergistically designed among polymer chains by introducing benzimidazole units and carboxyl side groups into the 6FDA-PABZ:DABA polyimide (PI-Im-COOH). After the thermal treatment, a cross-linked structure was formed through the decarboxylation reaction as confirmed by FTIR spectroscopy and thermal analysis. The π−π interactions between benzimidazole moieties were simultaneously enhanced as proven by WAXD, UV−vis, and fluorescence spectroscopy. The gas separation performance and plasticization resistance of the decarboxylated PI-Im-COOH membranes were enhanced significantly. In particular, the decarboxylated PI-Im-COOH membranes exhibit higher gas selectivities for CO 2 /CH 4 and CO 2 /N 2 gas pairs than the previously reported decarboxylated membranes. The PI-Im-COOH membrane that was thermally treated at 450 °C for 2 h showed outstanding CO 2 /CH 4 separation performance with a CO 2 permeability of 685.1 barrer and a CO 2 /CH 4 selectivity of 38.1, surpassing the 2008 Robeson upper bound. The synergistic design of enhanced π−π interactions and decarboxylation cross-linking proves to be a facile strategy to regulate interchain interactions and distances to achieve a high performance for natural gas separation.

Trade-off between permeability and nanometer-level selectivity is an inherent shortcoming of membrane-based separation of molecules, while most highly porous materials with high adsorption capacity lack solution processability and stability for achieving adsorption-based molecule separation. We hereby report a hydrophilic amidoxime modified polymer of intrinsic microporosity (AOPIM-1) as a membrane adsorption material to selectively adsorb and separate small organic molecules from water with ultrahigh processing capacity. The membrane adsorption capacity for Rhodamine B reaches 26.114 g m−2, 10–1000 times higher than previously reported adsorptive membranes. Meanwhile, the membrane achieves >99.9% removal of various nano-sized organic molecules with water flux 2 orders of magnitude higher than typical pressure-driven membranes of similar rejections. This work confirms the feasibility of microporous polymers for membrane adsorption with high capacity, and provides the possibility of adsorptive membranes for molecular separation.

Chemical crosslinking is the most commonly used solution to address the issue of poor structure stability and low plasticization resistance of polymer membranes for gas separation. However, the general crosslinking route requires the introduction of reactive groups into the polymer chain and is very likely to weaken the separation performance of membranes. Here, we report a new and nondestructive benzyl-induced crosslinking strategy. Owing to the high reactivity and wide existence in most polymers, the benzyl-induced crosslinking could universally happen in unmodified polymer membranes. Our crosslinked polyimide membrane exhibits unprecedented performance with a CO 2 /CH 4 selectivity > 70, three times that of non-crosslinked membranes, and with CO 2 plasticization pressures above 42 bar, the highest value among the polyimide membranes reported so far. The comprehensive performance surpasses the state-of-the-art 2018 upper bound for mixed gas. Our work provides a facile and reliable route for constructing polymer membranes with highly improved stability and performance.

As one of the gas separation membranes, the thin-film nanocomposite (TFN) membrane can effectively reduce gas transport resistance and improve gas permeance. However, due to the high mobility of the chain in the thin film, it is still a great challenge to realize the TFN membrane with stable separation performance. In this work, we report a less destructive and efficient cross-linking strategy based on metal-ion coordination to improve the stability of the TFN membrane for CO2/CH4 separation. The selective layer is made of carboxylated polyimide as a matrix and UiO-66 nanoparticles (diameters of ∼50 nm) as fillers. By simply immersing TFN membranes in Cu­(NO3)2 solution, coordination bonds are successfully constructed between Cu2+ and carboxyl groups (−COOH). The cross-linked TFN membranes exhibit high CO2/CH4 selectivity of up to 29–35 with CO2 permeance of 110–350 GPU, outperforming most previously reported membranes. Moreover, the plasticization pressure of the cross-linked membranes improves from 0.3–0.9 to 0.9–1.5 MPa, higher than most reported asymmetric and hollow fiber membranes. In the CO2/CH4 (50:50 v/v) mixed-gas permeation tests, the cross-linked membranes retain constant CO2/CH4 selectivity at 23.9–25.2 with increasing mixed-gas feed pressure. The cross-linked membranes also demonstrate stable CO2/CH4 selectivity in the range of 27.2–31.2 within 100 h of testing time under a 1.0 MPa CO2 partial pressure.

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