Title：
Mechanism of interaction between ascorbic acid and soil iron-containing minerals for peroxydisulfate activation and organophosphorus flame retardant degradation
Soil constituents may play an important role in peroxydisulfate (PDS)-based oxidation of organic contaminants in
soil. Iron-containing minerals (Fe-minerals) have been found to promote PDS activation for organics degradation.
Our study found that ascorbic acid (H2A) could enhance PDS activation by soil Fe-minerals for triphenyl
phosphate (TPHP) degradation. Determination and characterization analyses of Fe fractions showed that H2A
could induce the reductive dissolution of solid Fe-minerals and the increasing of oxygen vacancies/hydroxyl
groups content on Fe-minerals surface. The increasing of divalent Fe (Fe(II)) accelerated PDS activation to
generate reactive oxygen species (ROS). Electron paramagnetic resonance (EPR) and quenching studies showed
that sulfate radicals (SO4
？？ ) and hydroxyl radicals (HO？) contributed significantly to TPHP degradation. The
composition and content of Fe-minerals and soil organic matter (SOM) markedly influenced ROS trans_x0002_formations. Surface-bond and structural Fe played the main role in the production of Fe(II) in reaction system.
The high-concentration SOM could result in ROS consumption and degradation inhibition. Density functional
theory (DFT) studies revealed that H2A is preferentially adsorbed at α-Fe2O3(012) surface through Fe–O–C
bridges rather than hydrogen bonds. After absorption, H atoms on H2A may further be migrated to adjacent O
atoms on the α-Fe2O3(012) surface. With the transformation of H atoms to the α-Fe2O3(012) surface, the Fe–O–C
bridge is broken and one electron is transferred from the O to Fe atom, inducing the reduction of trivalent Fe (Fe
(III)) atom. MS/MS2 analysis, HPLC analysis, and toxicity assessment demonstrated that TPHP was transformed
to less toxic 4-hydroxyphenyl diphenyl phosphate (OH-TPHP), diphenyl hydrogen phosphate (DPHP), and
phenyl phosphate (PHP) through phenol-cleavage and hydroxylation processes, and even be mineralized in reaction system.
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