The separation of He/H₂ using membrane technology has gained significant interest in the field of He extraction from natural gas. One of the greatest challenges associated with this process is the extremely close kinetic diameters of the two gas molecules, resulting in low membrane selectivity. In this study, we investigated the structure-performance relationship of metal-organic framework (MOF) membranes for He/H₂ separation through molecular simulations and machine learning approaches. By conducting molecular simulations, we identified the potential MOF membranes with high separation performance from the Computation-Ready Experimental (CoRE) MOF database, and the diffusion-dominated mechanism was further elucidated. Moreover, random forest (RF)-based machine learning models were established to identify the crucial factors influencing the He/H₂ separation performance of MOF membranes. The pore limiting diameter (PLD) and void fraction (φ), are revealed as the most important physical features for determining the membrane selectivity and He permeability, respectively. Additionally, density functional theory (DFT) calculations were carried out to validate the molecular simulation results and suggested that the electronegative atoms on the pore surfaces can enhance the diffusion-based separation of He/H₂, which is critical for improving the membrane selectivities of He/H₂. This study offers useful insights for designing and developing novel MOF membranes for the separation of He/H₂ at the molecular level.

The separation of CO₂/C₂H₂ mixture by CO₂-selective sorbents is an energy-efficient C₂H₂ purification technique, but is strategically challenging due to their similar molecular size and physicochemical properties. Meanwhile, water is inevitable in CO₂/C₂H₂ mixture and it is usually a significant barrier because of its competitive adsorption with CO₂. To address this challenge, herein, we report the first example of metal–organic framework (MOF) that exhibits water-boosted CO₂ adsorption and CO₂/C₂H₂ separation by anchoring L-arginine (ARG) on the Zr₆ cluster of MOF-808. The CO₂ affinity and capacity in the resulting MOF-808-ARG are markedly facilitated by the presence of water, while the C₂H₂ adsorption is significantly suppressed. Specifically, CO₂ adsorption capacities in adsorption isotherm and breakthrough measurement are increased to 143% and 184%, respectively. In addition, the wet MOF-808-ARG exhibits the record CO₂/C₂H₂ selectivity of 1,180 under zero coverage. Breakthrough experiments reveal that CO₂/C₂H₂ mixture can be completely separated and the result of mass spectrometry indicates that the C₂H₂ purity in the outlet is up to 99.9%. In situ infrared (IR) results and density functional theory (DFT) calculations reveal the water-promoted CO₂ adsorption mechanism that the formation of bicarbonate products in the presence of water is thermodynamically and kinetically more favorable than that without water. Moreover, MOF-808-ARG also possesses excellent water stability and excellent regeneration of CO₂ adsorption. This work provides a new paradigm by transforming the negative effects of water into positive ones for CO₂/C₂H₂ separation.

CO₂ separation performance of polymer membranes can be significantly enhanced by selecting porous fillers with high CO₂ affinity. Ionic liquids incorporation has been recognized as an effective strategy for improving the separation ability of pristine porous fillers. However, the influence of the specific functional groups of ILs in IL@MOF composites on separation performance of MMMs still remains unclear. Herein, we designed three microenvironment-tuned IL@ZIF-8 composites in which the three ILs contain different functional groups (-CH_3, –SO₃H, and –NH₂). Molecular simulation results showed that the NH₂-IL@ZIF-8 has a commendable CO₂ adsorption capacity and CO₂/CH₄ adsorptive selectivity, and the results were well confirmed by the following experimental data. More importantly, the prepared NH₂-IL@ZIF-8 based MMMs also exhibit superior CO₂ separation performance among the three IL@ZIF-8 based MMMs owning to its high CO₂ affinity. Thus, this work can provide guidance for designing IL@MOF composites for MMMs fabrication towards gas separation, and the research mode combining molecular simulation prediction and experimental verification can afford valuable reference for material development in membrane separation field.