Electrostatically Driven Size-Sieving of Carbon Dioxide From Acetylene Enabled by a Cation-Gated Molecular Sieve.

Developing molecular sieves is vital, energy-saving, but very challenging for gas separations in the petrochemical industry. Current molecular sieves reported for inverse CO2/C2H2 separation are very scarce and suffer from low CO2 capacity and poor diffusion within the restricted nanopores. Herein, we report an electrostatically driven size-sieving of CO2 from C2H2 in a porous cation-gated molecular sieve (Na-RHO) with high CO2 capacity and fast diffusion. Na-RHO features large pore cavities (10.7 Å) interconnected by small Na+-gated pore windows (3.4 Å), in which the Na+-gated pore windows enable a complete size-exclusion of C2H2 due to the electrostatically driven sieving effect, and large pore cavities provide enough pore spaces to take up large amount of CO2 with fast diffusion. Such an electrostatically driven molecular-sieving mechanism for Na-RHO was studied by gas sorption isotherms and theoretical calculations, leading to both the record-high CO2/C2H2 selectivity (3.35 × 106) and CO2 uptake capacity (188.0 cm3 cm-3) at ambient conditions. Breakthrough experiments show that Na-RHO can directly separate CO2 impurity from CO2/C2H2 mixtures, with the highest dynamic selectivity (70.4) and C2H2 productivity (150.6 L kg-1) by far. This work provides a new strategy for designing more efficient molecular sieves with high gas capacity and diffusion for gas separations.