High-efficiency and selective adsorption of organic pollutants by magnetic CoFe2O4/graphene oxide adsorbents: Experimental and molecular dynamics simulation study

In this work, magnetic CoFe2O4/graphene oxide (GO) adsorbents are synthesized by a facile hydrothermal method, where the structure, morphology and magnetic properties of as-synthesized adsorbents are characterized by XRD, FTIR, Raman spectra, SEM, TGA and VSM. Additionally, the CoFe2O4/GO composites are used to remove methylene blue (MB), rhodamine B (RhB) and methyl orange (MO). Impressively, almost no adsorption of the above three dyes for the as-synthesized CoFe2O4 is detected, which confirms that adsorption performance of organic dyes for the CoFe2O4/GO composite mainly originates from the contribution of GO. Here, an obvious selective adsorption behavior can be observed, where the order of adsorption capacity is MB > RhB > MO. The adsorption process conforms to the pseudo-second-order model and Langmuir isotherm model. Noticeably, from Langmuir model, a superior adsorption capacity q(e(max)) for MB and RhB is obtained as 355.9 and 284.9 mg/g, respectively. Owing to good magnetic properties, the CoFe2O4/GO adsorbents is easy to be separated from the aqueous solution. Additionally, in terms of the molecular dynamics method, we systematically calculated adsorption configurations and adsorption energies to investigate the interaction of dye molecules with GO. Theoretical calculations point out that the dye adsorption of GO is mainly caused by electrostatic interaction and pi-pi stacking interaction. Further, we theoretically explore that the defects and oxygen-containing functional groups of GO have great effects on its adsorption performance of organic dyes. This work gives a profound insight on the adsorption mechanism of CoFe2O4/GO composites, and especially, proposes a new design thought to develop GO-based composite as magnetic adsorbents for the removal of dyes from the wastewater.