Effect of Fe₃O₄:RGO Ratios in Magnetic Nanocomposites Applied for Dye Discoloration

Nanocomposites of magnetite anchored on reduced graphene oxide with different magnetite:reduced graphene oxide mass ratios were synthesized and evaluated in indigo carmine photo Fenton discoloration. All nanocomposites are magnetic and showed comparable amounts of magnetite and hematite with a higher level of hematite for low iron contents. The highest value of 63.6 emu g⁻¹ was obtained for the nanocomposite with the highest magnetite content. The nanocomposites presented high dispersion of iron oxide particles, at about 12 nm on reduced graphene oxide surface sheets. The samples also showed bandgap energies below that found for bulk magnetite, showing an important effect of reduced graphene oxide. The nanocomposite with an iron nitrate precursors mass ratio of 17:1 showed the best performance (99.7% of indigo carmine discoloration (2.1 × 10⁻⁵ mol L⁻¹) at 30 min of reaction, hydrogen peroxide (2.3 × 10⁻¹ mol L⁻¹), and a catalyst dosage of 0.67 g L⁻¹). Reusability tests were performed, and this nanocomposite was shown to be active for at least three recycles. X-ray photoelectron spectrum of Fe2p_3/2 showed that the Fe^III/Fe^II ratio was maintained even after three recycles (4 runs), meaning that reduced graphene oxide is responsible for stabilizing magnetite particles, thus maintaining its photocatalytic activity.

Keywords:
iron oxides; reduced graphene oxide; heterogeneous photocatalysis; indigo carmine