Efficient removal of cationic dyes from aqueous solutions by polydopamine functionalized NH2-MIL-53(Al)

Polydopamine (PDA) functionalized NH 2 -MIL-53(Al) nanoparticles (NH 2 -MIL-53(Al)@PDA NPs) were successfully prepared by a facile in-situ polymerization method for the first time and characterized by various methods, including transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD) analysis, and Brunauer-Emmett-Teller (BET) analysis.The prepared NH 2 -MIL-53(Al)@PDA NPs were used to remove cationic dyes crystal violet (CV) and malachite green (MG) from aqueous solutions.The maximum removal efficiency of NH 2 -MIL-53(Al)@PDA NPs for CV and MG reached 95.94% and 77.88% at pH 10.0 and 8.0, respectively.Compared with NH 2 -MIL-53(Al), NH 2 -MIL-53(Al)@PDA NPs showed better adsorption capacity and removal efficiency.The adsorption of cationic dyes on NH 2 -MIL-53(Al)@PDA NPs might be attributed to hydrogen bonding, electrostatic, and π-π interactions.The results indicate that pseudo-second-order models and Freundlich isotherm are a better fit for CV and MG adsorption.Adsorption thermodynamic tests showed that the adsorption was spontaneous, irreversible, and endothermic.NH 2 -MIL-53(Al)@PDA NPs can be used for five times with no loss in absorption efficiency.