Polymer bidirectional induction for ultrathin ZIF-8 membrane with chemisorption site towards in-situ enhanced H2/CO2 separation

Metal-organic framework (MOF) membranes have demonstrated significant potential in replacing traditional polymer membranes for gas separation. However, synergistically enhancing gas permeance and selectivity remains challenging in MOF membrane design, particularly when framework pore apertures surpass gas kinetic diameters. Here, an innovative strategy is reported for engineering ultrathin ZIF-8 membranes with chemical adsorption sites via polymer bidirectional induction. The polyethyleneimine (PEI)-Zn 2+ interface layer facilitated the formation of ultrathin ZIF-8 membranes (~78.4 nm) by guiding small-sized crystal growth. Meanwhile, the competitive coordination of PEI with 2-methylimidazole induced the pendant of partially coordinated ligands in the ZIF-8 cavity to form chemisorption sites. This structural alteration enabled the in-situ chemical adsorption of CO 2 in the cavity of ZIF-8, thus contracting the window apertures and enhancing the molecular sieving efficiency. As a result, the ultrathin ZIF-8 membrane exhibited an excellent H 2 /CO 2 ideal selectivity of 34.2 with a remarkable H 2 permeance of 7143.6 GPU in single-gas tests, outperforming other reported ZIF-8 membranes. During mixed-gas H 2 /CO 2 testing, the in situ structural changes demonstrated robust pressure-performance stability and long-term gas separation capability. This work advances the development of ZIF-8 membranes for efficient separation of H 2 /CO 2 , and offers a feasible design principle and theoretical guidance for MOF-based gas separation membranes.