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.