Dual-Ligand Synergistic Construction of Double-Walled Cage Zn-MOFs: Methyl Modification Regulates Pore Size and Selective C2H2/CO2 Separation Performance

Abstract

Due to the extremely similar molecular sizes and melting and boiling points of acetylene (C2H2) and carbon dioxide (CO2), their efficient separation and purification have long been significant challenges in the field of industrial purification. Based on the ligand construction strategy, this study selected 2,4,6-tris(4-carboxyphenyl)-1,3,5-triazine as the main ligand and coordinated it with 3-methyl-1H-1,2,4-triazole and 3,5-dimethyl-1H-1,2,4-triazole, respectively, to assemble metal-organic frameworks (MOFs), successfully preparing two double-walled MOF crystal materials: Zn-TATB-fmtrz and Zn-TATB-dmtrz. Among them, Zn-TATB-fmtrz has a larger pore size (11.64 × 6.63 Å), while the pore size of the comparative material Zn-TATB-dmtrz is only 4.94 × 4.30 Å; in addition, the specific surface area of Zn-TATB-fmtrz (1403.4 m2/g) is also significantly higher than that of Zn-TATB-dmtrz (826.4 m2/g). Benefiting from the above structural advantages, both MOF materials can achieve efficient separation of C2H2/CO2. Systematic adsorption tests indicate that under conditions of 298 K and 1 bar, the maximum acetylene adsorption capacity of Zn-TATB-fmtrz reaches 58.6 cm3/g, much higher than the 37.5 cm3/g of Zn-TATB-dmtrz; moreover, the adsorption selectivity of Zn-TATB-fmtrz for C2H2/CO2 is 3.0, slightly better than 2.9 for Zn-TATB-dmtrz. Dynamic breakthrough experiments based on real binary mixtures further visually confirm that Zn-TATB-fmtrz shows potential for practical C2H2/CO2 separation.