Acoustic Cavitation-Assisted Ag/Fe Bimetallic Nanoparticle-Based Integrated Heterocatalytic System Synergistically Promotes Rapid Degradation of Polybrominated Diphenyl Ethers

Polybrominated diphenyl ethers (PBDEs), widely used brominated flame retardants, have been classified as a new persistent organic pollutant by the Stockholm Convention. Among them, decabrominated diphenyl ether (BDE-209) exhibits strong oxidative resistance due to its symmetrical structure, making its oxidative degradation challenging. An acoustic cavitation (AC)-assisted bimetallic nanoparticle (BMNP)-based integrated heterocatalytic system (AC/BMNP) was explored for achieving the rapid degradation of BDE-209, the highest congener of PBDEs, a group of persistent organic pollutants. The BMNP catalyst comprises Ag–Fe nanoparticles uniformly dispersed and stabilized within a ferroso-ferric oxide framework (Fe0@Ag0/FeFe2O4), exhibiting an urchin-like structure. The AC/BMNP system facilitated rapid degradation of BDE-209 within 15 min, significantly outperforming only AC (∼14%) or BMNP catalyst (∼34% in 6 h) alone. Supported by the experimental and computational analyses, this breakthrough degradation efficiency was attributed to the synergistic interactions between AC and BMNP that promoted in situ generation of H2O2 in the mM range through a dual-catalytic pathway involving the recombination of *OH and hydrogenation of *OOH species on the catalyst surface, thereby eliminating the need for any external oxidants. To the best of our knowledge, this represents the first instance of achieving such rapid degradation of BDE-209 without adding any oxidant, which is at least ∼2 × 102-fold faster than previously reported methods (48 h). A three-phase degradation mechanism of PBDEs is proposed based on (1) reductive debromination by metallic nanoparticles, (2) hydrodynamic effect and transient cavitation hot-spot model, and (3) sono-oscillation of the Fe2+/Fe3+ system, and the charging–discharging of Ag nanoparticles. Identified degradation byproducts indicated that BDE-209 degradation involved both sequential reductive debromination of higher congeners and oxidative degradation of lower congeners, ultimately leading to the ring-opening of PBDEs. The in situ oxidant generation ability of the integrated system makes it a promising tool for the effective removal of emerging pollutants and advancement of next-generation remediation technologies.