Rational rigidity control in heterobimetallic MOF nanosheets for precise molecular sieving

Metal-organic framework (MOF) nanosheet membranes are promising for H 2 purification because their highly tunable pore networks permit precise control of the sieving aperture. However, unavoidable linker rotation in MOFs impedes precise molecular sieving, with the impact further amplified in low-dimensional 2D nanosheets due to increased conformational freedom. Herein, we establish a rational rigidity-control strategy in heterobimetallic Zn (100-x) Co x (Bim)(OAc) nanosheets achieved by in-situ dual-metal integration. Moderate Co 2+ incorporation reinforces the framework rigidity while preserving structural integrity, which sharpens molecular sieving. At an optimal Co 2+ content of ∼30 %, the Zn (100-x) Co x (Bim)(OAc) nanosheet membrane exhibits an exceptional H 2 /CO 2 selectivity of 243, a 180 % improvement over the more flexible Zn(Bim)(OAc) membrane. However, excessive Co 2+ incorporation induces structural disorder, demonstrating that an optimal balance between rigidity enhancement and structural integrity is crucial for maximizing separation performance, providing an opening avenue for rational design in 2D MOF nanosheet membranes.