Methyl orange removal by a magnetic Fe0/Fe3O4/graphene composite: influencing factors, desulfurization, and mechanism

A magnetic Fe-0/Fe3O4/graphene composite was used to remove methyl orange from water, and its operation was studied in detail. The effects of important parameters were investigated. The results showed that an excellent synergetic effect among Fe-0, Fe3O4, and graphene existed in the composite. The composite could remove methyl orange in acidic and alkali conditions as well. In fact, 95.60% of the methyl orange was removed within 20 min. The desulfurization of methyl orange involved cleavage of the azo bond and mineralization of the sulfuric groups; 70% desulfurization efficiency was achieved after 40 min, indicating good detoxification abilities of Fe-0/Fe3O4/graphene. The addition of H2O2 significantly inhibited the removal efficiency, indicating that reduction was the main role of Fe-0/Fe3O4/graphene. X-ray photoelectron spectroscopic analysis showed that O2- groups increased after use, indicating that more lattice oxygen was generated in the form of iron oxides. The increase in Fe2+ and decrease in Fe-0 and Fe3+ further verified that the oxygen functional groups on graphene were reduced to lattice oxygen in iron oxides by Fe-0. The reaction mechanism was proposed to involve adsorption, surface complexation, cleavage of the azo bond, and mineralization.