Photoassisted Ultralow-Fe Fenton Degradation of Organic Pollutants Based on Photocatalytic Fe ³⁺ Reduction by Zn-Doped BiVO ₄

The Fenton process is an important option in the treatment of organic wastewaters, yet its wide application remains difficult due to the high level of consumption of chemicals and the production of iron-containing sludge. Herein, we develop an ultralow-Fe Fenton system based on the great enhancement of Fe³⁺/Fe²⁺ cycling promoted by Zn-doped bismuth vanadate (Zn/BiVO₄) under visible light and H₂O₂ in multiple roles. This study first revealed that Zn/BiVO₄ with an oxygen vacancy has high photocatalytic performance with respect to the reduction of dissolved Fe³⁺ to Fe²⁺ and H₂O₂ redox. As Zn/BiVO₄ photocatalysis was introduced into the Fenton system, excellent degradation of various organic pollutants was realized even with only 2.0 mg L⁻¹ Fe³⁺. The degradation of ofloxacin for 120 min was nearly 100% efficient, and moreover, this system removed 86.1% chemical oxygen demand (COD) and 84.2% total organic carbon (TOC) from the refuse leachate. Density functional theory (DFT) calculations together with photocurrent, photoluminescence, open circuit potential (OCP), and electron spin resonance (ESR) measurements revealed the Fe³⁺ reduction mechanism and showed that the synergistic effect exists in the ultralow-Fe Fenton system. The synergistic effect is mainly manifested as follows. Photocatalytic Fe³⁺ reduction can greatly enhance the Fenton reaction, generating the dominant reactive species hydroxyl radical (•OH) by accelerating Fe³⁺/Fe²⁺ cycling, and concurrently, H₂O₂ can serve as not only an electron acceptor but also an important electron donor. Overall, this study offers comprehensive insights into the developed system and highlights its potential application in wastewater treatment.