Boosting C3H8/C2H6/CH4 Separation Performance by an Aluminum-Based Nanoporous Metal–Organic Framework with Densely Hydroxyl-Functionalized Surface

The development of nanoporous metal–organic frameworks (MOFs) capable of effectively separating and purifying CH4 is of significant importance. High surface polarity and suitable pore diameter are two key factors that can synergistically enhance separation performance. Herein, we report two hydroxyl-functionalized Al-MOFs (CAU-1-OH and CAU-1-(OH)2) for the separation and purification of natural gas. They both possess two different types of nanocages as well as a densely hydroxyl-functionalized surface. Significantly, CAU-1-(OH)2 demonstrated exceptional selectivity in separating C3H8/CH4 (50:50, v/v) and C2H6/CH4 (50:50, v/v), with selectivity values of 990 and 36, respectively, surpassing those of most reported porous materials. The dynamic breakthrough experiment of the ternary mixture can generate pure CH4 exceeding 3.46 mmol g–1, which adequately demonstrates the actual CH4 purification performance of CAU-1-(OH)2. Finally, molecular simulations and in situ infrared experiments verified that the high surface polarity and 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. These results support the significant potential of the double hydroxyl-modified nanomaterial CAU-1-(OH)2 for purifying methane from natural gas.