Structural ferrous hydroxyl complex unlocks neutral-pH Fenton-like chemistry via multi-pathway ROS generation from...

Area of Science:

• Environmental Chemistry
• Advanced Oxidation Processes
• Catalysis

Background:

• Conventional Fenton technology requires highly acidic conditions, limiting its practical application.
• Developing efficient and environmentally friendly oxidation methods for pollutant degradation is crucial.

Purpose of the Study:

• To develop an acid-free Fenton-like strategy for pollutant degradation under neutral conditions.
• To elucidate the degradation mechanism and identify the dominant reactive oxygen species.

Main Methods:

• Utilized ferrous hydroxyl complex (FHC) as a structural Fe(II) source and nano-calcium peroxide (nCP) as a solid H2O2 precursor.
• Employed quenching experiments, chemical probes, EPR spectroscopy, electrochemical analyses (CV, OCP), and DFT calculations for mechanistic studies.
• Analyzed iron speciation to assess environmental impact.

Main Results:

• The FHC-nCP system rapidly degraded >90% of Acid Orange 7 (AO7) within 5 minutes under circumneutral conditions.
• The reaction exhibited a negative apparent activation energy, indicating an exothermic, surface-mediated pathway.
• Superoxide radical anion (•O2-) and singlet oxygen (1O2) were identified as the dominant ROS (>85%), not hydroxyl radicals (•OH).
• Controlled H2O2 release from nCP hydrolysis facilitated a Fe(II)/Fe(III)/Fe(IV) cycle and synergistic ROS generation.
• Approximately 53% of iron converted into settleable sludge, reducing secondary pollution.

Conclusions:

• Established a novel Fenton-like paradigm operating effectively at neutral pH.
• Demonstrated the dominance of •O2- and 1O2 in the degradation pathway, shifting from classical •OH.
• Provided design principles for pH-adaptive advanced oxidation technologies with reduced secondary pollution.