A thermostable anion-pillared metal-organic framework for C2H2/C2H4 and C2H2/CO2 separations

Abstract

A thermostable anion-pillared metal-organic framework TIFSIX-2-Ni-i (also referred to as ZU-12-Ni, TIFSIX = hexafluorotitanate, 2 = 4,4′-bipyridylacetylene, i = interpenetrated) has been synthesized for the first time. Structural characterizations show that TIFSIX-2-Ni-i exhibits a 2-fold interpenetrated network with narrow aperture of 5.1 Å (H-H distance) and abundant inorganic anion sites in the channel. The subtle change in metal and inorganic linkers results in the enhancement of the thermal stability of TIFSIX-2-Ni-i. Importantly, TIFSIX-2-Ni-i shows high-performing separation properties, especially for the important separations of C2H2/C2H4 and C2H2/CO2 mixtures. Adsorption data demonstrate that TIFSIX-2-Ni-i enables effective C2H2 capture (4.21 mmol/g, at 298 K and 1 bar), and achieves highly selective separation of C2H2 over C2H4 or CO2 with the IAST selectivity of 22.7 (C2H2/C2H4: 1/99) and 10.0 (C2H2/CO2: 2/1) at 298 K and 1 bar. Dispersion-corrected density functional theory (DFT-D) calculations confirm the preferential adsorption of C2H2 over C2H4 and CO2. Furthermore, the potential of industrial feasibility of TIFSIX-2-Ni-i for C2H2/C2H4 separation is confirmed by transient breakthrough tests (611.4 mmol/L C2H2 absorbed for mixtures containing 1% C2H2). The excellent cycle performance and stable structure of TIFSIX-2-Ni-i during multiple breakthrough tests show great potential in industrial separation of light hydrocarbons.