Adsorption behavior of magnetic amino-functionalized metal-organic framework for cationic and anionic dyes from aqueous solution

As organic dyes are a major group of water pollutants, the development of materials for removal of dyes is of great significance for the environment. Here we report a kind of magnetic metal-organic framework (MOF) for the adsorption of different kinds of anionic and cationic dyes. Magnetic NH₂-MIL-101(Al) was synthesized and characterized with Fourier-transform infrared spectrometry (FT-IR), physical property measurement system (PPMS), X-ray diffraction (XRD), a transmission electron microscope (TEM), a thermogravimetric analyzer (TGA) and nitrogen adsorption/desorption measurements. Adsorption isotherms and thermodynamic studies indicated that the maximum adsorption capacities of malachite green (MG) and indigo carmine (IC) were 274.4 and 135 mg g^-1, respectively. The mechanisms of interaction such as electrostatic interaction, hydrogen bonding, π-π stacking interaction, and hydrophobic interaction are discussed for the adsorption of cationic and anionic dyes onto magnetic NH₂-MIL-101(Al). Also, magnetic separation in this method shortened separation time, and the magnetic material can be reused at least five times without obvious decrease in the removal efficiency. Moreover, the synthesis of the magnetic NH₂-MIL-101(Al) is easy to control and the good solvent stability makes this material promising as a novel adsorbent for the adsorption and removal of dyes from aqueous solution.