Performance and potential mechanism of transformation of polycyclic aromatic hydrocarbons (PAHs) on various iron oxides

The abiotic transformation of polycyclic aromatic hydrocarbons (PAHs) is significantly impacted by soil components, especially inorganic redox species like iron oxides. In this study, the catalytic activities of three types of iron oxides in PAHs degradation without light irradiation were evaluated using a combination of experimental techniques. The results showed that α-Fe2O3 possessed the highest transformation rate for anthracene (ANT), with a reaction rate constant (Kobs) up to 0.28 d−1, followed by Fe3O4 (Kobs = 0.06 d−1) and α-FeOOH (Kobs = 0.06 d−1). X-ray photoelectron spectroscopy (XPS) characterization suggested that α-Fe2O3 had the highest oxygen vacancy concentration, which was conducive to the adsorption of O2 by α-Fe2O3, providing sufficient adsorbed oxygen species. Oxygen vacancy contributed to the exposure of Fe(III), and accordingly, more active sites were created that were responsible for ANT degradation. According to these results, two possible pathways for the degradation of PAHs on iron oxides can be concluded: (1) direct oxidation by Fe(III) and (2) oxidation by the O2•− generated onto oxygen vacancies. This study provides significant insights into the environmental fate of PAHs on iron oxides, and raises the possibility that iron oxides may be used as catalytic materials in the remediation PAHs-contaminated soil.