Photolysis of polycyclic aromatic hydrocarbons (PAHs) on Fe3+-montmorillonite surface under visible light: Degradation kinetics, mechanism, and toxicity assessments

- Fe3+-montmorillonite has great potential to catalytic photo-degradation of PAHs.
- Photolysis rate of PAHs is highly dependent on their interaction with surface cation.
- Potential photolysis mechanism of various PAHs was systematically explored.
- Acute toxicities initially increase and then gradually reduce with irradiation time.

Photochemical behavior of various polycyclic aromatic hydrocarbons (PAHs) on Fe3+-modified montmorillonite was explored to determine their potential kinetics, pathways, and mechanism under visible light. Depending on the type of PAH molecules, the transformation rate follows the order of benzo[a]pyrene ≈ anthracene > benzo[a]anthracene > phenanthrene. Quantum simulation results confirm the crucial role of “cation-π” interaction between Fe3+ and PAHs on their transformation kinetics. Primary intermediates, including quinones, ring-opening products and benzene derivatives, were identified by gas chromatography-mass spectrometer (GC-MS), and the possible photodegradation pathway of benzo[a]pyrene was proposed. Meanwhile, radical intermediates, such as reactive oxygen species (ROS) and free organic radicals, were detected by electron paramagnetic resonance (EPR) technique. The photolysis of selected PAHs, such as anthracene and benzo[a]pyrene, on clay surface firstly occurs by electron transfer from PAHs to Fe3+-montmorillonite, followed by degradation involving photo-induced ROS such as ·OH and ·O2−. To investigate the acute toxicity of photolysis products, the Microtox® toxicity test was performed during the photodegradation processes of various PAHs. As a result, the photo-irradiation initially induces increased toxicity by generating reactive intermediates, such as free organic radicals, and then the toxicity gradually decreases with increasing of reaction time. Overall, the present study provides useful information to understand the fate and photo-transformation of PAHs in contaminated soils.