Transformation of Al-CDC from 3D crystals to 2D nanosheets in macroporous polyacrylates with enhanced CH4/N2 separation efficiency and stability

[Display omitted] •High surface energy of PA induced low-energy-barrier orientation crystallization.•The morphology of Al-CDC was transformed from 3D crystals to 2D nanosheets.•Ultrathin films provided high adsorption efficiency and low diffusion barrier.•The composite yields optimum selectivity of CH4/N2 among available adsorbents.•Hydrophobic shell enhanced the water and recycling stability of composite. Development of materials with high efficiency and long-life cycles for CH4/N2 separation is of importance for coal-bed methane purification. Herein, a composite was prepared by in-situ growing the specific aluminum-based metal–organic framework (MOF) with trans-1,4-cyclohexanedicarboxylicacid as ligand (Al-CDC) on the internal macroporous surface of polyacrylates (PA). Due to the surface-induced low-energy-barrier orientation crystallization, the morphology of Al-CDC was transformed from three-dimensional (3D) crystals to two-dimensional (2D) nanosheets, forming ultrathin films with higher adsorption efficiency and lower diffusion barrier. As a result, the adsorption efficiency can be increased by 1.73 times compared with bulk Al-CDC and the selectivity of CH4/N2 (50/50, v/v) mixed gas is 13.75, which is the highest value reported so far. Furthermore, the hydrophobic feature of PA enhanced the water and recycling stability of composite, providing promising adsorbent for coal-bed methane purification using pressure swing adsorption process.