Systematic assessment of the water-matrix effect on the photo-Fenton oxidation of polystyrene micro-nanoplastics

This study systematically evaluates the impact of water-matrix complexity on the photo-Fenton oxidation of polystyrene (PS) nanoplastics (NPs), using operating conditions previously optimized for ultrapure water ([PS NPs] 0 = 20 mg L −1 , [Fe 3+ ] = 1 mg L −1 , pH 0 = 3, and [H 2 O 2 ] 0 = 130 mg L −1 with sequential dosing). Degradation kinetics followed the Prout-Tompkins model, revealing an anionic inhibition trend (H 2 PO 4 − ≫ NO 3 − ≈ SO 4 2− > Cl − ). Phosphate was the main bottleneck due to iron complexation, whereas counter-cations showed negligible effects. The full inorganic matrix reduced the reaction rate by 45% through catalyst complexation and radical scavenging. Dissolved organic matter (DOM) further decreased the kinetic rate constant by 38–44%. Ultimately, the full complex matrix (ions + DOM) induced a 68% reduction in the reaction rate. Despite these constraints, complete mineralization of PS NPs was achieved within 40–140 min. Proof-of-concept applications in real matrices (bottled, tap, reclaimed water, and wastewater effluent) confirmed organic load as the primary kinetic driver, reducing the rate constant by up to 49%. Additionally, expanded polystyrene microplastics (MPs) removal in different real matrices exhibited significant weight loss (50–74%) with negligible final total organic carbon, indicating effective mineralization despite lower specific surface areas. SEM and TEM analyses confirmed a surface-driven degradation pathway for both NPs and MPs, progressing from the particle surface toward the core. Overall, these findings demonstrate the viability of the photo-Fenton process for removing persistent plastic contaminants in water reuse schemes.