Enhanced photo-Fenton degradation of dyes under visible light with recyclable γ-FeO/CQDs: Catalyst preparation, performance and mechanism insight.

A low band gap and visible light-responsive heterogeneous Photo-Fenton catalyst of γ-FeO/CQDs micron composite was prepared under the one-pot hydrothermal method. The Photo-Fenton degradation of γ-FeO/CQDs towards dye solution of rhodamine B(RhB), methyl blue (MB), and methyl orange (MO) was studied comparatively with α-FeO. The γ-FeO/CQDs exhibited remarkable catalytic performance for various dyes and with a first-order rate (k) of 14 times higher than that of initial α-FeO with a low concentration of HO of 0.049 mmol L and a wider pH range of 3.1-7.1. The microstructure of the compounds was observed by XRD, SEM, TEM, FT-IR, and XPS characterization results suggested that the γ-FeO/CQDs nanocomposite was formed through the stable Fe-O-C bonds, thus, the band gap decreased, and it is more favorable for the distance of holes and electrons. The free radical trapping experiment and EPR analysis indicated that •OH and O were the major active species during the typical photo-Fenton reaction. What's more, the γ-FeO/CQDs also exhibited good stability and magnetic properties. DFT conclusion shows that the mechanism of the potential determination step (PDS) on α-FeO(220) is the cleavage of HO with an energy barrier of only 0.08 eV, which is 0.54 eV lower than that of OH* on γ-FeO(220). Thus it can be deemed that γ-FeO/CQDs perform much higher catalytic activity for the dissociation of HO than α-FeO. This work gives a feasible and economical countermeasure of visible light Photo-Fenton dispose of dye wastewater with a recyclable magnetic γ-FeO/CQDs micron catalyst.