Photo-Fenton degradation of methylene blue in the presence of Au-Fe3O4/graphene composites under UV and visible light at near neutral pH: Effect of coexisting inorganic anion

Abstract

Herein, Fe3O4 nanocatalyst composited with Au and graphene (Au-Fe3O4/graphene) has been applied for the photo-Fenton degradation of methylene blue in solution at a near neutral pH value under UV and visible light. The synthesized catalyst was successfully prepared by hydrothermal method and showed a good catalytic performance on H2O2 activation to degrade methylene blue at neutral pH. The Au concentration was set as 15 and 25 wt percentage (wt.%). The degradation efficiency of methylene blue reached 99% and 100% within 2 h under UV light irradiation using Au-Fe3O4/graphene with Au concentrations of 15% and 25 wt.%, respectively, whereas the corresponding percentage under visible light was 60% and 80%, respectively. The Au-Fe3O4/graphene maintained its stability during the repeated batch experiments. Furthermore, the effect of inorganic anions, including chloride, sulfate, nitrate, dihydrogen phosphate, and carbonate ions, on the photo-Fenton degradation of methylene blue was investigated. Results showed that under different concentrations of various inorganic anions, carbonate ions have a significant effect in inhibiting the photo-Fenton process, whereas nitrate and sulfate ions have a negligible effect to inhibit the photo-Fenton activity. The degradation efficiency of methylene blue decreased from 78% to 53% under visible light irradiation and from 100% to 73% under UV light irradiation in the presence of carbonate. The inhibition effect was in the following order: sodium carbonate (vis =32% and UV = 27%) > dihydrogen phosphate (vis =28% and UV = 24%) > chloride (vis =15% and UV = 18%) > nitrate (vis = 6% and UV = 3%) > sulfate (vis = 4% and UV = 3%).