Efficient capture of C₂H₂ from CO₂ and C_nH₄ by a novel fluorinated anion pillared MOF with flexible molecular sieving effect

The efficient separation of acetylene (C₂H₂) from carbon dioxide (CO₂) and C_nH₄ (n = 1 and 2) to manufacture high purity C₂H₂ and recover other light hydrocarbons is technologically important, while posing significant challenges. Herein, we reported a new TiF₆²⁻ anion (TIFSIX) pillared metal-organic framework (MOF) ZNU-5 (ZNU = Zhejiang Normal University) with ultramicropores for highly selective C₂H₂ capture with low adsorption heat through gate opening based molecular sieving effect. ZNU-5 takes up a large amount of C₂H₂ (128.6 cm³/g) at 1.0 bar and 298 K but excludes CO₂, CH₄, and C₂H₄. Such high capacity has never been realized in MOFs with molecular sieving. The breakthrough experiments further confirmed the highly selective C₂H₂ separation performance from multi-component gas mixtures. 3.3, 2.8, and 2.2 mmol/g of C₂H₂ is captured at ZNU-5 from equimolar C₂H₂/CO₂, C₂H₂/CO₂/CH₄, and C₂H₂/CO₂/CH₄/C₂H₄ mixtures, respectively. Furthermore, 2.6, 2.0, and 1.5 mmol/g of > 98% purity C₂H₂ can be recycled from the desorption process. Combining high working capacity, low adsorption heat, as well as good recyclability, ZNU-5 is promising for C₂H₂ purification.