Integration of multi-affinity sites into confined channels allows a bismuth-based metal-organic framework to sequestrate multi-component impurities from methane

One-step adsorptive purification of methane (CH4) from the multi-component mixtures containing CO2, acetylene (C2H2) and ethane (C2H6) is of great significance but challenging as distinct mechanisms are involved in the uptake of various gas molecules. Herein, a bismuth-based metal-organic framework (SU-100) bearing multiaffinity sites is applied for simultaneously sequestrating these impurities from CH4. The intrinsic unsaturated Bi (III) sites endow SU-100 with specific recognition of CO2 and C2H2 via complexation with the open metal sites, while the dense distribution of carboxylate and biphenyl moieties in the nano-channels provides strong affinity for C2H6 as well as additional affinity sites for C2H2. Profiting from the exposed functional sites and suitable pore size, SU-100 exhibits decent ideal adsorbed solution theory (IAST) selectivity (CO2/CH4, C2H2/CH4 and C2H6/ CH4) under ambient conditions. Moreover, the adsorption capacity remains unchanged for 10 consecutive cycles. The practical CH4 purification performance is fully demonstrated by dynamic breakthroughs of various binary, ternary (CO2/C2H2/CH4), and quaternary (CO2/C2H2/C2H6/CH4) mixtures, in which more than 2.44 mol kg-1 of pure CH4 can be produced from typical quaternary mixtures. Based on theoretical calculation and in-situ infrared analysis, synergistic effect of multiple interactions (pi complexation, hydrogen bonding and CH- pi interactions) accounts for simultaneous adsorption of multiple gases from CH4. These results underpin highly selective capture of a range of gas mixtures that are relevant to one-step purification of natural gas.