Fine-Tuning and Selective-Binding within an Anion-Functionalized Ultramicroporous Metal-Organic Framework for...

Olefin/paraffin separation is one of the intrinsically challenging tasks, mainly realized through the energy-intensive cryogenic distillation techniques. Here, we report the efficient separation of both propylene/propane (C₃H₆/C₃H₈) and ethylene/ethane (C₂H₄/C₂H₆) mixtures for the first time by a cheap and customized anion-functionalized metal-organic framework, ZU-36 (also termed as GeFSIX-3-M, M = Ni²⁺, Co²⁺), through molecular recognition and cross-section matching mechanism. Specifically, the pore window size of the fine-tuned ZU-36-Ni (4.42 × 4.42 Ų) decorated with high density of electronegative anions matches well with the cross section of C₃H₆ (4.16 × 4.65 Ų) and C₂H₄ (3.28 × 4.18 Ų), leading to efficient separation of C₃H₆/C₃H₈ and C₂H₄/C₂H₆. The high uptake capacity and separation selectivity of ZU-36-Ni were confirmed by adsorption isotherms and breakthrough tests. Binary dynamic breakthrough results showed that ZU-36-Ni can trap 1.35 mmol g^-1 C₃H₆ and 1.08 mmol g^-1 C₂H₄ from C₃H₆/C₃H₈ and C₂H₄/C₂H₆ mixtures, respectively. The separation selectivity for C₃H₆/C₃H₈ on ZU-36-Ni calculated from the breakthrough tests is 19, which sets a new benchmark for C₃H₆/C₃H₈ separation. The proposed cross-section matching mechanism together with proper selective binding affinity may serve as a guide for the design of effective porous materials for other important gas separation.