Divergent aging pathways in polypropylene microplastics: Ionizing radiation induced oxygen containing functional groups govern pollutant adsorption

Conventional approaches for treating microplastics are often characterized as incomplete and insufficient, rendering it challenging to elucidate the aging processes and mechanisms of microplastics. We employed irradiation technology to establish a highly potent oxidation system that achieves complete aging of polypropylene microplastics within a short timeframe. The results demonstrate that gamma ray exhibits remarkably strong microplastics degradation capability, with a mass loss reaching 70.58 %. Moreover, distinct aging mechanisms were observed under varying irradiation conditions, confirming that the aging process of microplastics is influenced by the oxidative capacity of the system. As the oxidative strength changes, the generation and transformation sequence of oxygen-containing functional groups also varies. Specifically, gamma ray initially forms ether bonds, followed by the generation of carbonyl and hydroxyl groups; in contrast, electron beam induces hydroxyl formation primarily through C-H bond cleavage before the emergence of other functional groups. The experiments further identified carbonyl groups as the principal sites for adsorption and transformation during the aging and adsorption processes. Because gamma ray preferentially produces carbonyl functionalities, it significantly enhances both the adsorption performance and the aging degree of polypropylene microplastics. Our findings provide new insights and foundation for understanding the aging and adsorption behaviors of microplastics.