Metal–organic frameworks (MOFs) are a rapidly growing class of crystalline porous materials known for their high surface area and tunable porosity, making them ideal for various applications, including gas separation. While the utility of MOFs primarily stems from their intrinsic micropores, fabricating MOF-based membranes further enhances their applicability, particularly in CO₂ separation from flue gas (CO₂/N₂) and natural gas (CO₂/CH₄). In this work, we developed an in situ synthesis method to fabricate MIL-160 membranes on ceramic tubular substrates for gas separation. MIL-160, with its three-dimensional interconnected channels and a pore-limiting diameter of 4.3 Å, is well-suited for separating small gas molecules. Through multiple synthesis trials, we produced MIL-160 membranes with distinct crystal morphologies─ball, flake, and cuboid─and characterized them using X-ray diffraction, scanning electron microscopy, nitrogen physisorption, gas adsorption, thermogravimetric analysis, and confocal microscopy. The crystal morphology was found to significantly influence membrane quality, particularly in reducing grain boundaries and pinholes. Confocal microscopy revealed substantial defects in the ball- and flake-shaped membranes, while the cuboid-shaped membrane showed minimal dye infiltration, indicating fewer defects and a more uniform structure. Single-gas permeation tests confirmed the superior performance of the cuboid-shaped MIL-160 membrane, achieving ideal CO₂/N₂ and CO₂/CH₄ selectivities of 56.8 and 130, respectively, with a CO₂ permeance of 75.5 GPU. In mixed-gas tests, the membrane reached a CO₂/N₂ selectivity of 259 at X_CO2 = 0.5, and a CO₂/CH₄ selectivity of 224 at X_CO2 = 0.2. Additionally, molecular simulations of binary gas adsorption supported these findings, demonstrating competitive CO₂ adsorption in the presence of N₂ and CH₄. This study highlights the potential of in situ synthesis of MIL-160 membranes on tubular substrates as a scalable and effective solution for CO₂ removal from flue gas and natural gas.

中文翻译：

---

原位合成具有高选择性的 MIL-160 管式膜，用于气体分离


金属有机框架 （MOF） 是一类快速增长的结晶多孔材料，以其高表面积和可调孔隙率而闻名，使其成为包括气体分离在内的各种应用的理想选择。虽然 MOF 的用途主要源于其固有的微孔，但制造基于 MOF 的膜进一步增强了它们的适用性，特别是在从烟气 （CO₂/N₂） 和天然气 （CO₂/CH₄） 中分离 CO₂ 时。在这项工作中，我们开发了一种原位合成方法，可以在陶瓷管状衬底上制造 MIL-160 膜以进行气体分离。MIL-160 具有三维互连通道和 4.3 Å 的孔隙限制直径，非常适合分离小分子气体。通过多次合成试验，我们生产了具有不同晶体形态（球形、片状和长方体）的 MIL-160 膜，并使用 X 射线衍射、扫描电子显微镜、氮气物理吸附、气体吸附、热重分析和共聚焦显微镜对其进行表征。发现晶体形态对膜质量有显著影响，特别是在减少晶界和针孔方面。共聚焦显微镜显示球形和片状膜中存在大量缺陷，而长方体膜显示出最小的染料渗透，表明缺陷较少且结构更均匀。单一气体渗透测试证实了长方体形状 MIL-160 膜的卓越性能，在 CO₂ 渗透率为 75.5 GPU 的情况下，分别实现了 56.8 和 130 的理想 CO₂/N₂ 和 CO₂/CH₄ 选择性。 在混合气体测试中，在 X_CO2 = 0.5 时，膜的 CO₂/N₂ 选择性达到 259，在 X_CO2 = 0.2 时，CO₂/CH₄ 选择性为 224。此外，二元气体吸附的分子模拟支持了这些发现，证明了在 N₂ 和 CH₄ 存在下 CO₂ 吸附的竞争性。本研究强调了在管状基材上原位合成 MIL-160 膜作为从烟气和天然气中去除 CO₂ 的可扩展且有效的解决方案的潜力。