Solvent-assisted linker exchange functionalization of zeolitic imidazolate framework nanosheets for enhanced carbon dioxide capture in mixed matrix membranes

This study introduces an innovative approach to enhancing CO₂ separation performance by synthesizing amino-functionalized zeolitic imidazolate framework-8 nanosheets via solvent-assisted ligand exchange, focusing on optimizing reaction times to improve adsorption capacity. The resulting 2D ZIF-8-NH₂ (24 h) nanosheets exhibited a significant CO₂ adsorption capacity of 22.1 cm³/g, along with a linker exchange ratio of 34.5 %. Incorporating these nanosheets into mixed matrix membranes of PEBAX-1657 with a 15 wt% loading yielded exceptional results, achieving CO₂ permeability of 460 Barrer and a CO₂/N₂ ideal selectivity of 95, surpassing the 2019 Robeson upper boundary. This performance was attributed to the unique horizontally aligned nanosheet architecture, which facilitated CO₂ diffusion while creating a more tortuous path for N₂, thus enhancing separation efficiency. Furthermore, a thin film nanocomposite (TFN) membrane was developed, demonstrating a remarkable CO₂ permeance of 1,250 GPU and a CO₂/N₂ separation factor of 75 under mixed gas conditions. The TFN membrane maintained its performance during a rigorous 100-hour long-term test, showcasing its commercial viability.