Two Solvent-Induced In(III)-Based Metal–Organic Frameworks with Controllable Topology Performing High-Efficiency Separation of C<sub>2</sub>H<sub>2</sub>/CH<sub>4</sub> and CO<sub>2</sub>/CH<sub>4</sub>
Meng Feng, PeiPei Zhou, Jingyu Wang, Xirong Wang, Dongmei Wang, Chunxia Li
Abstract
For pure acetylene manufacturing and natural gas purification, the development of porous materials displaying highly selective C2H2/CH4 and CO2/CH4 separation is greatly important but remains a major challenge. In this work, a plausible strategy involving solvent-induced effects and using the flexibility of the ligand conformation to make two In(III) metal–organic frameworks (MOFs) is developed, showing topological diversity and different stability. The X-shaped tetracarboxylic ligand H4TPTA ([1,1′:3′,1″-terphenyl]-4,4′,4″,6′-tetracarboxylic acid) was selected to construct two new heteroid In MOFs, namely, {[CH3NH3][In(TPTA)]·2(NMF)} (MOF 1) and {[In2(TPTA)(OH)2]·2(H2O)·(DMF)} (MOF 2). MOF 1 is a (4, 4)-connected net showing a pts topology with a large channel that is not conducive to fine gas separation. By contrast, with the reduction of SBU from uninucleated In to an {In-OH-In}n chain, MOF 2 has a (4, 6)-connected net with the fsc topology with an ∼5 Å suitable micropore to confine matching small gas. The permanent porosity of MOF 2 leads to the preferential adsorption of C2H2 over CO2 with superior C2H2/CH4 (332.3) and CO2/CH4 (31.2) separation selectivities. Meanwhile, the cycling dynamic breakthrough experiments showed that the high-purity C2H2 (>99.8%) capture capacities of MOF 2 were >1.92 mmol g–1 from a binary C2H2/CH4 mixture, and its separation factor reached 10.