Visible-light-driven photocatalytic degradation of Metalaxyl by reduced graphene oxide/Fe3O4/ZnO ternary nanohybrid: Influential factors, mechanism and toxicity bioassay

Abstract

A heterogeneous photocatalyst, reduced graphene oxide (rGO)/Fe3O4/ZnO (GFZ) nanocatalyst, was synthesized for the oxidative degradation of Metalaxyl (MX) in aqueous solution under Vis-light irradiation. For the characterization of the synthesized catalyst FTIR, XRD, FE-SEM, EDS, BET, VSM, PL spectra and UV–Vis DRS techniques were applied. The influence of operating parameters, including solution pH, catalyst concentration, ZnO percentage in the catalyst structure, MX concentration and Vis-light intensity on the oxidative degradation of MX was studied. A probable mechanism for the degradation of MX was also proposed. Reusability, stability, intermediate products identification and quenching studies were done too. Under optimized conditions, the degradation and mineralization rates of MX were obtained 92.11 and 51.38% within 120 min, respectively. The ROS scavenging experiments confirmed the participation of •OH and O2•− radicals as reactive species in the oxidation process. Degradation rate in the presence of scavenger agents was decreased in order of t-BuOH > BQ > EDTA-2Na > AgNO3. Therefore, •OH radicals were the main species in the oxidation process. MX degradation rate in real agricultural runoff sample was 58.3%, which has been lower than that of deionized water. The kinetic experiments were in good agreement with pseudo-first-order kinetic model. The GFZ catalyst showed a good reusability after five successive runs. The toxicity bioassay by D. Magna showed that the toxicity of MX significantly decreased in the GFZ/Vis process. Finally, the application of GFZ catalyst under Vis-light for the degradation of organic materials, such as pesticides in wastewater seems to be a practical and effective process because the GFZ catalyst exhibits excellent catalytic activity and can be easily recovered from aqueous solutions.