Photo- and Photo-Fenton-like Catalytic Degradations of Malachite Green in a Water Using Magnetically Separable ZnFe2O4-reduced Graphene Oxide Hybrid Nanostructuresa

ZnFe2O4 nanoparticles and ZnFe2O4-reduced graphene oxide (ZnFe2O4-rGO) hybrid nanostructures with rGO/ZnFe2O4 ratio of 0.05, and 0.10 were hydrothermally synthesized. The microstrutrual and photocatalytic activities of nanoparticles and hybrids were studied in the photodegradation of malachite green in the water. The ZnFe2O4 nanoparticles and theirhybrids showed uniform granular morphology and average particle sizes below ~16 nm. Because higher valence band energy of the ZnFe2O4, the photogenerated electrons can be transformed from the ZnFe2O4 to the rGO. Therefore, the sunlight-excited photocatalytic and Fenton-like photocatalytic activities of hybrids in the dye degradation showed obviously greater than the nanoparticles and increased with increasing rGO/ZnFe2O4 ratio. Moreover, the photodegradation rate is larger at higher initial solution pH=5 than at pH=7, whereas the photo-Fenton-like reaction is intenser at higher H2O2 concentration. The quasi-kinetic rate constants of the photocatalysis systems are in the range of ~0.412–0.96 h-1 and increase to ~3.86–7.53 h-1 by synthetically using H2O2. The nanoparticles and hybrids also showed strong ferromagnetic property with the saturation magnetization of ~25.15–26.28 emu/g, which provides a well magnetic separation performance of the nanoparticles and hybrids from the degraded solution.