Magnetic
ZnFe2O4–C3N4 hybrids
were successfully synthesized through a simple reflux
treatment of ZnFe2O4 nanoparticles (NPs) (ca.
19.1 nm) with graphitic C3N4 sheets in methanol
at 90 °C, and characterized by X-ray diffraction, Fourier transform
infrared spectroscopy, thermogravimetric and differential thermal
analysis, X-ray photoelectron spectroscopy, high-resolution transmission
electron microscopy, and UV–vis diffuse reflectance spectroscopy.
Also, the catalytic activities of heterogeneous ZnFe2O4–C3N4 catalysts were evaluated
in photo-Fenton discoloration toward Orange II using H2O2 as an oxidant under visible light (λ > 420
nm)
irradiation. The reaction kinetics, degradation mechanism, and catalyst
stability, as well as the roles of ZnFe2O4 and
C3N4 in photoreaction, were comprehensively
studied. It was found that the ZnFe2O4–C3N4 photocatalysts presented remarkable catalytic
ability at neutral conditions, which is a great advantage over the
traditional Fenton system (Fe2+/H2O2). The ZnFe2O4–C3N4 hybrid (mass ratio of ZnFe2O4/g-C3N4 = 2:3) exhibits the highest degradation rate of 0.012
min–1, which is nearly 2.4 times higher than that
of the simple mixture of g-C3N4 and ZnFe2O4 NPs. g-C3N4 acted as not
only a p-conjugated material for the heterojunction formation with
ZnFe2O4, but also a catalyst for the decomposition
of H2O2 to ·OH radicals. The heterogeneous
ZnFe2O4–C3N4 hybrid
exhibited stable performance without losing activity after five successive
runs, showing a promising application for the photo-oxidative degradation
of organic contaminants.
Magnetic
cobalt nanoparticles (NPs) at a size of approximately
29.9 nm anchored on graphene sheets were prepared and tested for heterogeneous
oxidation of a dyeing pollutant, Orange II, with peroxymonosulfate
(PMS) in aqueous solutions. The physicochemical properties of Co–graphene
hybrids were investigated by various characterization techniques,
such as powder X-ray diffraction (XRD), thermogravimetric analysis
(TGA), field emission scanning electron microscopy (FESEM), transmission
electron microscopy (TEM), energy-dispersive X-ray spectrometer (EDS),
Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The
incorporation of Co NPs and graphene sheets produces much higher catalytic
activity of Orange II degradation than pure Co. The Orange II decomposition
rate increases with increasing temperature (25–45 °C),
pH (4–10), and PMS dosage (0.04–0.60 g/L) but decreases
with its increased concentration (30–120 mg/L). Kinetic studies
show decomposition of Orange II on Co–graphene can be described
by a pseudo-first-order kinetic model with activation energy of 49.5
kJ/mol.
A magnetic ZnFe2O4-reduced graphene oxide (rGO) hybrid was successfully developed as a heterogeneous catalyst for photo-Fenton-like decolorization of various dyes using peroxymonosulfate (PMS) as an oxidant under visible light irradiation. Through an in situ chemical deposition and reduction, ZnFe2O4 nanoparticles (NPs) with an average size of 23.7 nm were anchored uniformly on rGO sheets to form a ZnFe2O4-rGO hybrid. The catalytic activities in oxidative decomposition of organic dyes were evaluated. The reaction kinetics, effect of ion species and strength, catalytic stability, degradation mechanism, as well as the roles of ZnFe2O4 and graphene were also studied. ZnFe2O4-rGO showed to be a promising photocatalyst with magnetism for the oxidative degradation of aqueous organic pollutants and simple separation. The combination of ZnFe2O4 NPs with graphene sheets leads to a much higher catalytic activity than pure ZnFe2O4. Graphene acted as not only a support and stabilizer for ZnFe2O4 to prevent them from aggregation, largely improving the charge separation in the hybrid material, but also a catalyst for activating PMS to produce sulfate radicals at the same time. The ZnFe2O4-rGO hybrid exhibited stable performance without losing activity after five successive runs.
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