A Rigid–Flexible Zn-DMOF with Dynamic Pore Recognition for Enhanced C2H2/CO2 Separation

A rigid–flexible Zn-DMOF was developed for selective C 2 H 2 /CO 2 separation. • Activation-induced pore contraction enabled dynamic recognition of C 2 H 2 . • Zn-chdc-DABCO retained high C 2 H 2 uptake but greatly improved C 2 H 2 /CO 2 selectivity. • Efficient breakthrough separation was maintained under varying flow rates and humidity. Separating C 2 H 2 from CO 2 is challenging because of their similar sizes and physicochemical properties. Adsorption-based separation using metal–organic frameworks (MOFs) offer a promising alternative. Here, a rigid–flexible framework strategy is used to introduce guest-discriminating dynamic recognition into a 1,4-diazabicyclo[2.2.2]octane (DABCO)-based MOF (DMOF) platform by replacing rigid 1,4-benzenedicarboxylate with flexible trans-1,4-cyclohexanedicarboxylate, affording Zn-trans-1,4-cyclohexanedicarboxylic acid (chdc)-DABCO. Activation induces pore contraction and generates a confined environment that selectively strengthens C 2 H 2 binding while leaving CO 2 largely unaffected. As a result, Zn-chdc-DABCO preserves a C 2 H 2 uptake comparable to that of Zn-DMOF at 298 K and 100 kPa, yet displays markedly enhanced affinity toward C 2 H 2 , a distinct gate-opening response to C 2 H 2 , and little framework response toward CO 2 . The zero-coverage isosteric heat of adsorption reaches 43.9 kJ·mol –1 for C 2 H 2 , substantially higher than that for CO 2 (29.3 kJ·mol –1 ), and the equimolar C 2 H 2 /CO 2 ideal adsorbed solution theory selectivity reaches 8.2, more than four times that of Zn-DMOF. Dynamic breakthrough experiments further confirm efficient separation under mixed-gas, variable-flow, and humid conditions. This work shows that rigid–flexible cooperative design offers an effective route to overcoming the capacity/selectivity trade-off in difficult gas separations. A rigid–flexible Zn-DMOF was engineered to enable activation-induced pore contraction and guest-discriminating dynamic recognition, thereby achieving enhanced selective C 2 H 2 /CO 2 separation with efficient C 2 H 2 recovery. Download: Download high-res image (204KB) Download: Download full-size image