Inorganic Node-Tuned Reticular Diversification of Metal–Organic Frameworks: Dual-Site Functionalization for Enhanced Methane Separation

Reticular chemistry offers a targeted and streamlined approach to synthesizing metal-organic frameworks (MOFs) through the assembly of predesigned molecular units. In this study, we investigated inorganic node-directed reticular diversification of MOFs by employing a nitrogen-containing aromatic polycarboxylate ligand as a fixed 4-connected organic node. By systematically tuning inorganic secondary building units (SBUs), various topological structures were obtained: the previously reported flu topology (derived from 8-connected nodes), dmc topology (from mixed 3,4-connected nodes), and a new pts-topology MOF (ZJNU-409) built from Zn-based paddlewheel 4-connected nodes. ZJNU-409 possesses a three-dimensional framework containing one-dimensional channels and dual-site functionalization and shows excellent selective performance for C₂H₆, C₃H₈, C₂H₂, and CO₂ over CH₄. Ideal adsorbed solution theory (IAST) calculations yielded selectivities of 135 for C₃H₈/CH₄, 26 for C₂H₆/CH₄, 100 for C₂H₂/CH₄, and 29 for CO₂/CH₄. Fixed-bed breakthrough experiments confirmed that C₂H₆, C₃H₈, C₂H₂, and CO₂ had retention times longer than those of CH₄, and grand canonical Monte Carlo (GCMC) calculations confirmed stronger interactions between the framework and these gases compared to CH₄. These results collectively underscore the potential of ZJNU-409 for efficient methane purification applications.