Removal of methylene blue from aqueous solution using humic-acid coated magnetic nanoparticles

In this paper, magnetic Fe3O4/HA nanoparticles (MHA) were synthesized using a coprecipitation method. The structure and properties of the MHA were characterized by Fourier transform infrared spectroscopy, TG, transmission electron microscope, zeta potential, X-ray diffraction, and vibration sample magnetometer. MHA is proven to be stable in water and can be easily separated from solution under an external magnetic field. Adsorptive removal of methylene blue (MB) from aqueous solution using MHA was systematically studied. The fundamental adsorption experiments reveals that MHA is more efficient in dye removal when initial solution pH is higher than 4.0. The theoretical maximal adsorption capacity, which is based on the simulation results from the isothermal equilibrium study, is 200 mg/g. The adsorption kinetic and equilibrium behaviors of MHA are in agreement with pseudo-second-order model and Langmuir model, respectively. The value of activation energy (Ea) indicates that the adsorption of MB onto MHA is a physical process. The Gibbs free energy of the adsorption process (△G) is negative, indicating that the adsorption of MB onto MHA is thermodynamically favorable. Furthermore, MHA could be easily regenerated and reused with almost no loss of adsorption capacity, which is satisfactory for practical applications.