Agglomeration-Induced Deactivation of Metal Oxide-Based Catalysts by Dissolved Organic Matter in Heterogeneous Fenton Systems

Abstract Heterogeneous Fenton processes are promising for wastewater treatment, yet their performance often deteriorates in dissolved organic matter (DOM)-rich waters. DOM inhibition has conventionally been attributed to reactive-species scavenging and active-site coverage. Here, we identify DOM-induced catalyst agglomeration as an additional deactivation pathway in metal oxide-based heterogeneous Fenton systems. DOM adsorbs onto catalyst surfaces through complexation, alters surface charge, and weakens interparticle electrostatic repulsion, thereby promoting rapid agglomeration and reducing the accessible catalytic surface area. At 30 mgC L–1 DOM, pH 4.0, and 25 °C, the hydrodynamic diameter of ferrihydrite increased from ∼220 nm to over 1300 nm, accompanied by a decrease in specific surface area from 118.1 to 62.8 m2 g–1. Similar DOM-induced inhibition was observed across six metal oxide catalysts, different DOM types, and real water matrices. Immobilizing ferrihydrite on a porous carbon substrate effectively suppressed particle migration and agglomeration, which enabled stable catalytic performance for over 30 h during continuous-flow treatment of landfill leachate. These findings extend the conventional understanding of DOM inhibition from chemical interference to catalyst-state destabilization and highlight particle stability as an important criterion for designing heterogeneous Fenton catalysts for practical water treatment.