Impact of UV‑B\nPhotoaging on Chlorpyrifos Adsorption\nby PET Microplastics: Insights from Experimental and DFT Analysis

Microplastics (MPs) in the environment pose a persistent\nconcern,\nas these plastic particles can adversely impact both aquatic ecosystems\nand human health. MPs are subject to natural weathering and aging\nprocesses, such as photodegradation, which significantly alter their\nsurface morphology and physicochemical properties, thereby influencing\ntheir fate, transport, and sorption behavior. To better understand\nhow aging affects these properties and to elucidate the mechanisms\nbehind the interactions with the chlorpyrifos pesticide, poly(ethylene\nterephthalate) (PET) microplastics (<100 μm) were subjected\nto accelerated photoaging in a UV-B chamber for varying exposure times.\nSeveral characterization techniques were employed, including scanning\nelectron microscopy (SEM), energy dispersive X-ray spectrometry (EDS),\nX-ray diffraction (XRD), infrared spectroscopy (IR), point of zero\ncharge (pHPZC), and thermogravimetric analysis (TGA). Additionally,\nthe percentage of crystallinity and carbonyl index (CI) were calculated.\nThe results demonstrated a decrease in pHPZC following photodegradation,\nlikely due to an increase in δ- (−CO) groups,\nconsistent with the CI findings. SEM revealed surface deterioration\ncaused by aging, while TGA indicated an early thermal degradation\nstage associated with water volatilization, suggesting enhanced hydrophilicity.\nDensity functional theory (DFT) calculations showed that the PET monomer\nabsorbs slightly in the UV-B region, leading to excitation and subsequent\nradical reactions that form Norrish type I products. The adsorption\ncapacity of aged PET increased compared to the pristine material,\nlikely due to the molecular geometry becoming more planar, facilitating\ninteractions between the aged MPs and chlorpyrifos, as confirmed by\nnoncovalent interaction (NCI) analysis. These findings highlight the\nsignificant potential of aged microplastics to adsorb micropollutants\nand act as vectors in aquatic environments.