Comprehensive screening of microplastic degradation by photo-Fenton oxidation: A comparative approach between different polymers

Abstract

Microplastics (MPs) are persistent pollutants of growing environmental concern, and advanced oxidation processes (AOPs) have been increasingly investigated as promising routes to accelerate their transformation beyond conventional treatments. In this study, homogeneous photo-Fenton oxidation was applied to cryo-milled commercial MPs (50–100 µm) of polyethylene terephthalate (PET), low-density polyethylene (LDPE), polycarbonate(PC), polyvinyl chloride (PVC), and expanded polystyrene (EPS) to assess polymer-dependent degradation under controlled conditions. Degradation was quantified through a combined solid–liquid carbon assessment based on gravimetric weight loss (solid-phase removal) and aqueous Total Organic Carbon (TOC) (mineralization yield). Scanning Electron Microscopy (SEM) provided insights into particle morphology and surface damage, while Energy-Dispersive X-ray Spectroscopy (EDS) and Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR) were employed to track elemental and chemical changes, respectively. Finally, elemental analysis was used to assess bulk compositional shifts during oxidation. A polymer-dependent degradation trend was observed after 8 h of photo-Fenton treatment, EPS (≈74 %) > LDPE > PC > PET ≈ PVC (≈40 %), accompanied by extensive mineralization (aqueous TOC < 1 mg L- 1). Clear oxidation signatures were also found on MPs surfaces, including the emergence of surface pitting, cavities, and microcracks in SEM, together with increased oxygenated functionalities detected by ATR-FTIR/EDS. The degradation kinetics of EPS and PETwere successfully described by the Shrinking Core Model (SCM) for spherical particles (R2 > 0.99), indicating ash-layer diffusion behavior for EPS and surface chemical control behavior for PET.