Dual-Ligand-Engineered Ultramicroporous Porphyrinic MOF for Efficient C₂H₆/C₂H₄ and C₂H₂/CO₂ Separations

Ultramicroporous MOFs capable of simultaneously separating C₂H₆/C₂H₄ and C₂H₂/CO₂ mixtures remain rare due to the stringent requirements on pore confinement and adsorption-site distribution. Here, we report a dual-ligand engineered porphyrin-based framework, Zn-TCPP-mtz, constructed from Zn²⁺ nodes, tetrakis(4-carboxyphenyl)porphyrin (TCPP), and 5-methyl-1H-tetrazole (mtz). The incorporated mtz ligands bridge adjacent porphyrin layers and, together with interlayer hydrogen-bonding interactions, result in a compact stacking arrangement featuring 1D ultramicropores (7.2 × 4.8 Å²) decorated with N/O functional sites and hydrophobic methyl groups. This tailored pore environment enables Zn-TCPP-mtz to adsorb 2.63 and 2.56 mmol g^-1 of C₂H₆ and C₂H₄, respectively, as well as 3.14 and 1.89 mmol g^-1 of C₂H₂ and CO₂ at 298 K and 1 bar, achieving selectivities of 1.5 for C₂H₆/C₂H₄ and 3.1 for C₂H₂/CO₂. Dynamic breakthrough experiments confirm one-step production of high-purity C₂H₄ (>99.9%) and C₂H₂ (>99.5%) with productivities of 3.0 and 16.3 L kg^-1, respectively. DFT calculations reveal that the ultramicroporous channels provide well-defined interaction sites that stabilize C₂H₆ over C₂H₄ and C₂H₂ over CO₂ through multiple dispersion-dominated contacts. This study demonstrates that the dual-ligand strategy can be extended to construct porphyrin-based frameworks with controlled pore architectures and stable adsorption environments, enabling the integration of multiple C₂ gas separations within a single material platform.