Fabrication of porous metal–organic frameworks via a mixed-ligand strategy for highly selective and efficient dye adsorption in aqueous solution

In our efforts toward the rational design and systematic synthesis of porous 3D MOFs, three 3D frameworks of Zn-MOFs ([Zn(BDC)(TIB)]·3H2O (Zn-MOF-1) (TIB = 1,3,5-tri(1H-imidazol-1-ly) benzene and H2BDC = 1,4-dicarboxybenzene), [Zn(BDA)(TIB)2/3]n (Zn-MOF-2) (H2BDA = 4,4′-biphenyl-dicarboxylic acid) and [Zn3(BDC)2(BDA)(TIB)2]n (Zn-MOF-3)) were successfully synthesized, based on different multicarboxylate ligands through solvothermal reactions. The resulting MOFs show similar 3D structures with different pore sizes which lead to distinct selective adsorption for organic dyes. Remarkably, Zn-MOF-1 exhibits an excellent capacity to adsorb CR (congo red) with high selectivity, and it maintains an almost identical adsorption performance after being recycled several times.