Immobilization of Cr(VI) from solution by a graphene oxide-nZVI/biochar composite.

A graphene oxide (GO)-nanoscale zerovalent iron (nZVI)-biochar composite (GO-nZVI/BC) was synthesized prior to characterization by X-ray diffraction (XRD), vibrating sample magnetometer (VSM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy analyses. Batch experiments were performed at different initial Cr(VI) concentrations, contact times, and solution pH values. The effects of coexisting anions and chelating agents were also examined. The results indicated that the removal of Cr(VI) was highly pH-dependent and reached a maximum capacity at pH of 2. The equilibrium data were fitted well with the Langmuir isotherm model, and the kinetic data fitted better with the pseudo-second-order kinetic model. The increasing concentrations of EDTA in aqueous solutions were favorable to the removal of Cr(VI), while significantly inhibited adsorption. Furthermore, the GO-nZVI/BC maintained ~84.5% of its original capacity after aging in the air for 25 weeks. Based on the removal efficiency, GO-nZVI/BC can be considered to be an effective material for water treatment applications. PRACTITIONER POINTS: Biochar-supported graphene oxide-coated nanoscale zerovalent iron (GO-nZVI/BC) was synthesized and used to treat Cr(VI) from solution. Cr(VI) removal was pH-dependent and obeyed the Langmuir isotherm model and pseudo-second-order model. GO-nZVI/BC maintained ~84.5% of its original capacity after aging for 25 w in the air.