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

Conventional Fenton technology is severely bottlenecked by its strict dependence on highly acidic environments. This study develops an acid-free Fenton-like strategy utilizing a structural Fe(II) source (ferrous hydroxyl complex, FHC) to activate a solid H2O2 precursor (nano-calcium peroxide, nCP). Under circumneutral conditions, the FHC-nCP system rapidly degrades >90% of Acid Orange 7 (AO7) within just 5 min. Notably, the system exhibits a negative apparent activation energy (-23.18 kJ mol-1), indicating an unconventional exothermic, surface-mediated degradation pathway. Comprehensive mechanistic investigations-including quenching, chemical probes, and EPR spectroscopy-unveil a significant reaction paradigm shift: •O2- and 1O2, rather than the classical •OH, decisively dominate the degradation process (contributing >85%). Meanwhile, electrochemical analyses (CV and OCP) firmly exclude direct electron transfer. Mechanistically, controlled H2O2 release from nCP hydrolysis regulates a robust Fe(II)/Fe(III)/Fe(IV) cycle and, alongside co-released O2, triggers the synergistic generation of four reactive oxygen species (ROS). Also, hydrogen bonding (O-H···O) acts as the primary interfacial interaction bridging FHC and nCP, while density functional theory (DFT) calculations pinpoint the specific AO7 sites vulnerable to •O2-/1O2 attack. Environmentally, Fe speciation analysis demonstrates that ∼53% of total iron is converted into readily settleable sludge, significantly curtailing secondary pollution compared to homogeneous Fenton systems. This work establishes a novel paradigm for neutral-pH, multi-pathway Fenton-like chemistry and provides design principles for pH-adaptive advanced oxidation technologies.