Heterogeneous Fenton catalyst based on clay decorated with nano-sized amorphous iron oxides prevents oxidant scavenging through surface complexation

Heterogeneous Fenton catalysts based on iron-oxides are of great interest due to their low cost and high reactivity. Herein, the activity of nano-sized amorphous iron-oxide particles deposited on montmorillonite clay (MMT) was compared to crystalline hematite and magnetite-coated MMT. Hematite, magnetite, and their respective clay composites showed little catalytic activity and almost no phenanthrene (PHE) oxidation at circumneutral pH - in part, due to the decomposition of hydrogen peroxide. In contrast, the amorphous iron oxide (Fe)-MMT, showed very high catalytic activity (over 60% PHE degradation in 60 min) with only minimal consumption of H2O2 (3.3%). In-depth characterization of the Fe-MMT coupled with kinetic and mechanistic experiments was performed to understand the reaction pathway and mechanism. The results suggest that initially H2O2 is complexed to the nano-sized iron oxide catalytic sites on the surface, forming a stable Fe-MMT-H2O2 complex that is activated primarily when the pollutant is introduced. The reactive species, & BULL;OH and O-1(2), were detected upon the diffusion of PHE to the surface leading to oxidation and mineralization with a minimal decomposition of H2O2. Quenching experiments further revealed that O-1(2) played an important role in the extensive mineralization of PHE. The amorphous Fe-MMT also exhibited high stability and performance in semi continuous cycle batch experiments. Thus, this low-cost and simple Fe-MMT catalyst was found to be highly efficient towards the activation of H2O2, oxidizing PHE rapidly while reducing radical scavenging and unwanted side reactions. These findings, regarding the role of amorphous phases in the reactivity of iron-oxides, have the potential to improve the design and implementation of solid Fenton catalysts for pollutant remediation in engineered and natural systems.

Automated summary

This study investigates heterogeneous Fenton catalysts based on iron-oxides and finds that nano-sized amorphous iron-oxide particles have high degradation activity towards pollutants with minimal consumption of H2O2. The mechanism involves complexation of H2O2 to the catalytic sites on the iron oxide surface, leading to oxidation and mineralization of pollutants through the production of reactive species such as •OH and O-1(2). The amorphous Fe-MMT catalyst exhibits high stability and performance.