Potassium humate possesses a wide variety of oxygen-containing functional groups and has good adsorption and complexion properties for many kinds of transition metal ions.

In this work, a simple and separable route had been developed to synthesize Fe3O4/graphene nanocomposite, derived from potassium humate, were employed for the effective adsorption of Cr(VI) in aqueous phase. In addition, the Fe3O4/graphene nanocomposite prepared at 600 °C (S-600) showed a maximum adsorption capacity of 280.6 mg/g for Cr(VI) and good cycling performance, which was much higher than those reported graphene-based adsorbents and other conventional adsorbents.

The adsorptive behavior was well fitted to the Langmuir isotherm model. The adsorption kinetics for removal of Cr(VI) agreed with pseudo-second-order equation, which indicates a kind of chemical adsorption. Its superior adsorption performance might be due to the effective adsorption sites at the surface and formation of FeOH2+ on the surface of Fe3O4/graphene. This work provided a promising approach for the removal of Cr(VI) from wastewater using a Fe3O4/graphene nanocomposite, which shows a huge number of application prospects.