Unlocking inherent superoxide production from potassium peroxoborate for efficient PAHs degradation

Conventional Fenton-like systems for in-situ chemical oxidation (ISCO) face significant challenges, including non-productive consumption of reactive oxygen species (ROS) and inefficient Fe(III)/Fe(II) circulation. This study developed a novel Fenton-like system for polycyclic aromatic hydrocarbons (PAHs) remediation employing potassium peroxoborate (PPB) as oxidant coupled with iron nitrilotriacetic acid (Fe(III)/NTA). The proposed PPB/Fe(III)/NTA system achieved 6.34-folds higher degradation efficiency of pyrene comparing with the H₂O₂/Fe(III)/NTA system. Sustainable H₂O₂ generation from PPB reduced the non-productive loss of ROS. Crucially, this system generated superoxide radicals (•O₂^-) at a rate 7 orders of magnitude greater than the H₂O₂ counterpart. Integrated analysis via electron paramagnetic resonance, isotopic tracing (¹⁸O-labeling), and density functional theory calculations revealed that •O₂^- originates from PPB's water-mediated O-O bond cleavage, with oxygen atoms derived exclusively from PPB. Endogenous •O₂^- accelerated Fe(III) reduction to Fe(II), bypassing the rate-limiting step in traditional Fenton-like system. Moreover, actual contaminated soil remediation experiments verified the feasibility of PPB/Fe(III)/NTA in a real polluted site, in which total PAHs removed by 66 %, outperforming the H₂O₂/Fe(III)/NTA system (29 % removal). These findings highlight PPB's dual function as a ROS reservoir and endogenous activator, expanding the understanding of the activation mechanisms of Fenton-like reactions and presenting a promising strategy for efficient ISCO remediation.