[Adsorption Characteristics of Arsenic on UV-aged Polypropylene Microplastics in Aqueous Solution]

The adsorption characteristics of microplastics （MPs） for pollutants in the aqueous environment have received extensive attention； however， the adsorption characteristics of UV-aged MPs for arsenic （As） are not yet fully understood. In this study， the adsorption kinetics and isothermal adsorption of As（Ⅴ） from aqueous solutions by pristine and UV-aged MPs were investigated in static adsorption mode. Polypropylene microplastics （PP MPs） were used as the adsorbent， and the effects of environmental factors （pH， dissolved organic matter， and NO₃^-） on the adsorption process were also explored. The results showed that UV aging produced a substantial number of rough folded structures with irregular protrusions and pores on the surface of PP MPs. Furthermore， an enhancement in the prevalence of oxygen-containing functional groups， concomitant with an escalation in the crystallinity of the MPs， was observed. The adsorption of As（Ⅴ） by PP MPs tended to reach equilibrium within 12 h， and the adsorption kinetics of As（Ⅴ） on UV-aged MPs exhibited a stronger correlation with the pseudo-second-order model （R²=0.980）， indicating that the adsorption of As（Ⅴ） by UV-aged PP MPs was dominated by chemisorption. The Freundlich and Langmuir models were found to be applicable to the isothermal adsorption of As（Ⅴ） by aged MPs， with the Freundlich model providing a superior fit to the data. This finding suggests that the adsorption of As（Ⅴ） on aged MPs was predominantly influenced by surface complexation and van der Waals forces. The theoretical maximum adsorption （Q_m） of As（Ⅴ） by UV-aged MPs fitted by the Langmuir model increased by 11.8% compared to that by the pristine MPs. In addition， the adsorption of As（Ⅴ） by aged PP MPs exhibited an increasing trend， followed by a decrease， with elevated NO₃^- and dissolved organic matter concentrations. This study provides a significant theoretical foundation for investigating the biogeochemical cycling and ecological risk assessment of As from aging MPs.