Optimizing Fe-Based Metal-Organic Frameworks through Ligand Conformation Regulation for Efficient Dye Adsorption and C2H2/CO2 Separation

Regulating the structure of metal-organic frameworks (MOFs) by adjusting the ligands reasonably is expected to enhance the interaction of MOFs on special molecules/ions, which has significant application value for the selective adsorption of guest molecules. Herein, two tricarboxylic ligands H₃L−Cl and H₃L−NH₂ were designed and synthesized based on the ligand H₃TTCA by replacing part of the benzene rings with C=C bonds and modifying the chlorine and amino groups on the 4-position of the benzene ring. Two 3D Fe-MOFs ( UPC-60-Cl and UPC-60-NH₂ ) with the new topology types were constructed. As the C=C bonds of the ligands have flexible torsion angles, UPC-60-Cl features three types of irregular 2D channels, while UPC-60-NH₂ has a cage with two types of windows on the surface. The synergistic effect of unique channels and modification of functional groups endows UPC-60-Cl and UPC-60-NH₂ with high adsorption capacity for organic dyes. Compound UPC-60-Cl shows high adsorption capacity for CV (147.2 mg g⁻¹), RHB (100.3 mg g⁻¹), and MO (220.9 mg g⁻¹), whereas UPC-60-NH₂ exhibits selective adsorption of MO (158.7 mg g⁻¹). Meanwhile, based on the diverse pore structure and modification of active sites, UPC-60-Cl and UPC-60-NH₂ show the selective separation of equimolar C₂H₂/CO₂. Therefore, reasonable regulation of organic ligands plays a significant role in guiding the structure diversification and performance improvement of MOFs.