Visible-light-driven photo-Fenton oxidation enhanced by Fe/Bi-nanocrystal phase transformation as a universal way for various organic pollutants mineralization

Emerging organic pollutants (EOPs), such as azoxystrobin (AZX) fungicide, have been an increasingly serious problem in aquatic environments. Here, a novel Fe/Bi-nanocrystal (bismuth ferrite polymorphism composites, BFPCs) driven a new photo-Fenton system in visible light (λ >420 nm) irradiation (LED/BFPCs/H₂O₂) remarkably accelerates hydroxyl radical (HO^•) formation with excellent efficiencies of both AZX and other 18 EOPs (especially for AZX 100 % degradation rarely reported). The system outperforms in mineralization rate, saving H₂O₂ usage (85 %) and reaction time (50 %) compared to the alike Fenton-like system. A phenomenon in BFPCs crystal structure observed on the crystal phase transformation from FeO₆ octahedron into FeO₄ tetrahedron that implied/uncovered a new finding of crystal-phase restructuring for enhancing Fe³⁺/Fe²⁺ circulation in Fenton chemistry. The stability of crystal structure and chemical composition of BFPCs catalysts was evaluated by HAADF imaging coupling with EDX mapping at atomic level. The mechanism on AZX degradation pathway in LED/BFPCs/H₂O₂ system is proposed for the first time by monitoring HO^• and its source, and intermediates at a control condition.