Mechanism of Ag-enhanced Bi₂Fe₄O₉ photocatalytic Fenton system for inactivation of marine microorganisms

In this work, Ag was compounded with Bi₂Fe₄O₉ to form a composite photocatalyst by photoreduction method. Structural characterization by XRD, XPS and SEM revealed that Ag was loaded on the surface of Bi₂Fe₄O₉ in the form of monomers. UV–Vis and electrochemical characterization revealed that the composite photocatalysts had improved carrier separation efficiency. Under visible light irradiation and accompanied by a small amount of H₂O₂ assisted to constitute a photocatalytic-Fenton coupling system, Photocatalytic inactivation experiments showed that the highest inactivation ratio of 90.8% was observed in BFO-Ag-1 BFO-Ag-1 (BFO refers to Bi₂Fe₄O₉, -Ag-1 refers to the silver concentration of 0.1 mol/L carried on the surface of BFO, named -Ag-1) at a concentration of H₂O₂ of 3 × 10^–4 mol/L and 30 min of light exposure. This is mainly due to the increased efficiency of the Fe(III)/Fe(II) Fenton cycle and H₂O₂ utilization due to the loading of monatomic silver. Comprehensive radical trapping experiments showed that ^·OH and holes were the main active substances for inactivating marine microorganisms. In this work, by loading Ag nanoparticles on the surface of Bi₂Fe₄O₉, the efficiency of the effective conversion of H₂O₂ to ^·OH was improved, which provided a new idea for the development of photocatalytic-Fenton coupling technology and ballast water treatment.