Removal of CO₂ impurity from C₂H₂ by physical-adsorption separation is energy-saving but extremely challenging because the two gases have very similar molecular dimensions and physicochemical properties. CO₂-selective (inverse) separation is more efficient, yet suitable adsorbents are scarce. Moreover, the stability, cost, and practical efficiency of adsorbents for gas separation must be addressed. This work employs two low-cost, stable porous coordination frameworks—Zn₃[Fe³⁺(CN)₆]₂ (ZnHCF) and K₂Zn₃[Fe²⁺(CN)₆]₂ (KZnHCF)—to overcome these obstacles. Their cage-like pore structures possess appropriate window sizes, enabling selective adsorption of CO₂ over C₂H₂. In KZnHCF, the K⁺ ions residing in the cavities electrostatically orient incoming CO₂ or C₂H₂ molecules differently, markedly enhancing CO₂ uptake and selectivity and partially mitigating the usual trade-off between capacity and selectivity. The material exhibits a remarkable saturated CO₂ adsorption capacity of 111.5 cm³•g⁻¹ at 298 K, and high CO₂-selective performance for 1∶1 (V/V) CO₂/C₂H₂ mixture, with an ideal adsorption solution theory (IAST) selectivity of 23.4 at 298 K and 0.1 MPa. More importantly, dynamic breakthrough experiments demonstrate that KZnHCF maintains highly efficient CO₂/C₂H₂ separation over a broad temperature range. From 50/50 (V/V) CO₂/C₂H₂ mixture at 298 K, the process yields C₂H₂ of >99.9 % purity with a dynamic productivity of 1915 mmol•kg⁻¹ in a single step—only slightly below the newly reported record. At 323 K, the productivity (1450 mmol•kg⁻¹) remains higher than most reported values at 298 K. This outstanding separation performance, combined with excellent stability, recyclability, low-cost, and facile scalable synthesis, positions KZnHCF as a promising adsorbent for efficient CO₂/C₂H₂ separation in practical applications.

Key words: porous framework, CO₂-selective, inverse, separation, low-cost