Metal-organic framework MIL-100(Fe) for the adsorption of malachite green from aqueous solution

The adsorption of malachite green from aqueous solution on a highly porous metal-organic framework MIL-100(Fe) was studied in view of the adsorption isotherm, thermodynamics, kinetics, and regeneration of the sorbent. The adsorption isotherms of malachite green on MIL-100(Fe) followed the Freundlich model, and MIL-100(Fe) possessed heterogeneous surface caused by the presence of different functional groups on the surface. The adsorption of malachite green on MIL-100(Fe) is controlled by an entropy effect rather than an enthalpy change, and obeyed a pseudo-second-order kinetics. Analysis of the intraparticle diffusion plots revealed that more than one process affected the adsorption, and film (boundary layer) diffusion controlled the adsorption rate at the beginning. Evidence from zeta potential and X-ray photoelectron spectroscopic data showed that the adsorption of malachite green was also driven by electrostatic attraction and the interaction between the Lewis base -N(CH3)(2) in malachite green and the water molecule coordinated metal sites of MIL-100(Fe). MIL-100(Fe) gave much higher adsorption capacity for malachite green than other conventional adsorbents such as activated carbon and natural zeolite. The high adsorption capacity, good solvent stability, and excellent reusability make MIL-100(Fe) attractive for the removal of MG from aqueous solution.