Aging of Polystyrene Micro/Nanoplastics Enhances Cephalosporin Phototransformation via Structure-Sensitive Interfacial Hydrogen Bonding

Beyond their roles in adsorbing and transporting pollutants, microplastics (MPs) and nanoplastics (NPs), particularly polystyrene variants (PS-M/NPs), have emerged as potential accelerators for the transformation of coexisting contaminants. This study uncovered a novel environmental phenomenon induced by aged PS-M/NPs and delved into the underlying mechanisms. Our findings revealed that the aged PS-M/NP particles significantly amplified the photodegradation of common cephalosporin antibiotics, and the extent of enhancement was tightly correlated to the molecular structures of cephalosporin antibiotics. Notably, the results confirmed that the hydroxyl radical (OH•) acted as the primary agent to drive the accelerated degradation. Furthermore, in-depth analysis utilizing <i>in situ</i> Fourier transform infrared spectroscopy, batch adsorption experiments, and theoretical calculations underscored that the structure-dependent enhancement stemmed from the specific hydrogen bonding sites, rather than mere adsorption capacity. Specifically, the -OOH group (hydroperoxyl group) on the PS surface exhibited a greater potential to generate OH• compared to the -OH group. Therefore, cephalosporins that formed hydrogen bonds with -OOH moieties on the aged PS surfaces, as opposed to -OH, would experience a more pronounced degradation enhancement. Thus, the unique interaction pattern between contaminants and PS-M/NPs transforms aged PS into a selective reactor, facilitating the targeted degradation of pharmaceuticals in aquatic ecosystems.