[Effect of Photoaging on Adsorption of Cu(Ⅱ) by Polystyrene Microplastics with Different Particle Sizes]

In order to evaluate the effect of aging and particle size on the adsorption of heavy metals by microplastics, the adsorption behavior of Cu(Ⅱ) by three different particle sizes of polystyrene (PS; 1, 50, and 100 μm) under UV irradiation was systematically studied. The results demonstrated that UV aging significantly changed the surface morphology and physicochemical properties of PS, and 1 μm PS had the strongest aging degree. The adsorption kinetics of PS on Cu(Ⅱ) conformed to the pseudo-second-order kinetic model, and the Freundlich model was more suitable for the experimental data of isothermal adsorption of Cu(Ⅱ) by PS. These results indicated that the adsorption of Cu(Ⅱ) by PS occurred on the non-uniform surface of PS, and the adsorption behavior was multilayer adsorption. Parameter "n" of the Freundlich model was less than 1, indicating that the adsorption behavior of PS on Cu(Ⅱ) was a higher intensity physical adsorption behavior. The order of theoretical maximum adsorption capacity of different particle sizes PS for Cu(Ⅱ) was as follows:1 μm > 50 μm > 100 μm, indicating that the size of PS was an important influence factor for the adsorption capacity of PS to pollutants. For the same particle size PS, aging enhanced its adsorption capacity for Cu(Ⅱ). The results on the adsorption of Cu(Ⅱ) by PS under different environmental conditions indicated that the adsorption capacity of PS for Cu (II) increased with the increase in pH, whereas an increase in salinity had the opposite effect. Surface complexation and electrical adsorption were the main mechanisms of adsorption of Cu(Ⅱ) by PS. This study provides an important scientific basis for understanding the adsorption behavior of microplastics to heavy metals in the environment.