Combined effect of amino nitrogen and pyridine nitrogen for tetracycline adsorption on aminopyridine modified MIL-101(Cr)

MIL-101(Cr) has demonstrated promising potential for tetracycline (TC) adsorption owing to its exceptional water stability. In this study, polymers with nitrogenous organic ligands were incorporated in the framework of MIL-101(Cr) using a post-synthetic modification approach to enhance the adsorption properties of MIL-101(Cr) for TC. We used the grafting reagent 4-aminopyridine (4-Apy), which contains two types of nitrogen species (amino nitrogen and pyridine nitrogen), to create a series of stable MOF composite materials, xApy-MIL-101(Cr), through interaction with the exposed Cr(iii) sites in MIL-101(Cr). The high nitrogenous organic ligand content in the framework of xApy-MIL-101(Cr) contributes to its high TC adsorption capacity. The results showed that 30%Apy-MIL-101(Cr) adsorbed far more than MIL-101(Cr), reaching a maximum adsorbed amount of 264.5 mg g⁻¹, nearly five times greater. Importantly, adsorption equilibrium can be reached within 50 minutes. Moreover, the primary adsorption mechanisms of xApy-MIL-101(Cr) for TC removal involve hydrogen bonding, π-π interactions, and electrostatic interactions. Additionally, 30%Apy-MIL-101(Cr) demonstrated excellent adsorption cycle stability, maintaining a regeneration rate of 74% even after four cycles of TC adsorption and desorption.