Intermediate dual-site confinement recognition in a Cu-based metal–organic framework for efficient capture of trace SO2 over CO2

Effective removal of SO 2 from flue gas is critical for the environment, human health, and the following CO 2 capture process. Conventional flue-gas desulfurization technologies are energy-intensive and insufficient for deep removal of such trace SO 2 . However, even a low concentration of SO 2 (ca. 2000 ppm) can significantly degrade the performance of adsorbents employed in CO 2 capture from flue gas, thus demanding its deep removal from CO 2 -rich gas streams. Herein, we report a metal-organic framework, Cu-tpo-tpt, which possesses ultra-microporous channels functionalized with two oppositely aligned open Cu(II) sites. Upon activation, the geometrically complementary spatial arrangement of two opposing open Cu(II) sites within the channel perfectly fits the bent V-shaped SO 2 molecule, while linear CO 2 exhibits a molecular size exceeding the aperture distance between the dual Cu(II) sites. Benefiting from the geometrically matched dual-site confinement recognition strategy, Cu-tpo-tpt exhibits preferential adsorption of SO 2 over CO 2 . At 298 K and 0.1 bar, the SO 2 adsorption capacity (2.7 mmol g −1 ) is considerably higher than that for CO 2 (1.0 mmol g −1 ), leading to an exceptional IAST selectivity of 264 for SO 2 /CO 2 (0.2/99.8, v/v). Dynamic breakthrough experiment further confirms its outstanding separation performance. Mechanistic analysis reveals that the precise geometric matching between SO 2 and the Cu(II) sites enhances host-guest interactions, facilitating highly selective recognition of trace SO 2 over abundant CO 2 . This finding not only addresses a critical challenge for trace SO 2 capture, but also provides new insights for the rational design of advanced adsorbents targeting industrial gas separation processes.