Enhanced catalytic degradation of methylene blue by Α-Fe₂O₃/graphene oxide via heterogeneous photo-Fenton reactions

Novel hybrid nanostructures or nanocomposites are receiving increasing attention due to their newly evolved properties. In this work, α-Fe₂O₃anchored to graphene oxide (GO) nanosheet (α-Fe₂O₃@GO) was synthesized through a facile hydrolysis process and its photo-catalytic performances and durability in heterogeneous Fenton system were fully evaluated. The decolorization rates of methylene blue in α-Fe₂O₃@GO + H₂O₂ + UV system within a wide pH range were approximately 2.9-fold that of classical Degussa P25 TiO₂ + UV and 2.4-fold that of α-Fe₂O₃ + H₂O₂ + UV. This enhanced decolorization of methylene blue (MB) in α-Fe₂O₃@GO + H₂O₂ + UV system were attributed to the unique incorporation of GO into the catalyst which not only mediated the morphology of active sites α-Fe₂O₃nanoparticles but also offered high electron conductivity and electrostatic attraction between negatively charged GO with positively charged MB. High efficiencies of degradation were achieved on various surface charged organic pollutants (around 96–100%), such as cationic compounds of MB and rhodamine B (RhB), anionic compound Orange II (OII) and Orange G (OG), neutral compounds of phenol, 2-nitrophenol (2-NP) and endocrine disrupting compound 17β-estradiol (E2). The dominant reactive oxygen species (ROS) responsible for decolorization, such as hydroxyl radicals ([rad]OH) and superoxide anion radicals (O₂ ^[rad]−) generated by activation of H₂O₂on the surface of α-Fe₂O₃@GO were detected and quantified by free radical quenching methods. The possible degradation mechanism of MB involved the rupture of phenothiazine ring by desulfurization and the rupture of phenyl ring due to the attack of ROS, which was analyzed by LC/MS/MS. The reduction of MB and its intermediates was consistent with the decreasing trend of the acute toxicity towards luminous bacteria with the increasing irradiation time. The results lay a foundation for highly effective and durable photo-Fenton technologies for organic wastewater within wider pH ranges than the conventional photo-Fenton reaction.