Enhanced photo-Fenton degradation of dyes under visible light with recyclable γ-Fe2O3/CQDs: Catalyst preparation, performance and mechanism insight

Abstract

A low band gap and visible light-responsive heterogeneous Photo-Fenton catalyst of γ-Fe₂O₃/CQDs micron composite was prepared under the one-pot hydrothermal method. The Photo-Fenton degradation of γ-Fe₂O₃/CQDs towards dye solution of rhodamine B(RhB), methyl blue (MB), and methyl orange (MO) was studied comparatively with α-Fe₂O₃. The γ-Fe₂O₃/CQDs exhibited remarkable catalytic performance for various dyes and with a first-order rate (k) of 14 times higher than that of initial α-Fe₂O₃ with a low concentration of H₂O₂ of 0.049 mmol^. L^-1 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-Fe₂O₃/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 ¹O₂ were the major active species during the typical photo-Fenton reaction. What's more, the γ-Fe₂O₃/CQDs also exhibited good stability and magnetic properties. DFT conclusion shows that the mechanism of the potential determination step (PDS) on α-Fe₂O₃(220) is the cleavage of H₂O₂ with an energy barrier of only 0.08 eV, which is 0.54 eV lower than that of OH* on γ-Fe₂O₃(220). Thus it can be deemed that γ-Fe₂O₃/CQDs perform much higher catalytic activity for the dissociation of H₂O₂ than α-Fe₂O₃. This work gives a feasible and economical countermeasure of visible light Photo-Fenton dispose of dye wastewater with a recyclable magnetic γ-Fe₂O₃/CQDs micron catalyst.

Keywords: Carbon quantum dots; Dye removal; Magnetic recovery; Visible light photo-Fenton.