Facile synthesis of polyethyleneimine modified magnetic graphite: An effective adsorbent for the removal of humic acid from aqueous solution

In this study, a simple method was introduced to synthesize polyethyleneimine modified magnetic graphite (Fe3O4@GR-PEI(50)), which was used to adsorb humic acid (HA) from aqueous solution. The obtained materials were characterized by field emission scanning electron microscope, X-Ray diffraction, Fourier transform-infrared, and thermogravimetric analysis. The results showed that Fe3O4@GR-PEI(50) was synthesized successfully and PEI uniformly covered on Fe3O4@GR-PEI(50) surface. The adsorption performance was evaluated at different concentration, temperature, pH, and cationic concentration. The maximum adsorption capacity of Fe3O4@GR-PEI(50) was 49.87 mg/g at 293 +/- 1 K and it was greatly affected by the solution pH and the additional cations. This is mainly due to the strong electrostatic interactions between the negatively charged HA molecules and the positively charged adsorbents. The adsorption kinetics were examined using pseudo-first-order, pseudo-second-order and intra-particle diffusion model. The equilibrium adsorption data were analyzed by Langmuir and Freundlich models. The results revealed that the pseudo-second-order model and Freundlich isotherm fit the kinetics and equilibrium data, respectively. Furthermore, Fe3O4@GR-PEI(50) exhibited a good performance of regeneration and reuse, which maintained a high adsorption capacity after six consecutive times of regeneration.