Adsorption Characteristics of Heavy Metals onto Functionalized Microplastics

Microplastics represent a significant environmental threat owing to their persistence and resistance to degradation. Their co-occurrence with heavy metals in aquatic environments exacerbates the risks of complex pollution. While most current research focuses on conventional microplastics such as polyethylene and poly-(vinyl chloride), functionalized microplastics, which exhibit richer functional groups and more complex environmental behaviors, remain insufficiently studied. This research examines the adsorption behaviors of cadmium (Cd² ⁺), copper (Cu² ⁺), and lead (Pb² ⁺) onto three types of functionalized microplastics: polyacrylate (PAT), biobased polyurethane (BPU), and petroleum-based polyurethane (PPU). Analyses based on Langmuir and Freundlich isotherm models indicate that microplastics with a particle size of 150 μm exhibit significantly enhanced adsorption capacities for Cd² ⁺, Cu² ⁺, and Pb² ⁺, showing increases of 5-18.62, 12.91-18.04, and 8.7-12.31%, respectively, compared to larger particles (1-2 mm). Among the tested materials, polyacrylate (PAT) exhibited the strongest adsorption affinity, with Langmuir maximum capacities (<i>q</i> _m) of 34.68, 29.85, and 12.31 mg/g for Pb² ⁺, Cu² ⁺, and Cd² ⁺, respectively, following the order: Pb² ⁺ > Cu² ⁺ > Cd² ⁺. Furthermore, UV aging increased the adsorption capacity of PAT for Cd² ⁺ from 7.07 to 11.22 mg/g, as described by the pseudo-second-order model. However, the rate constant (<i>k</i> ₂) decreased from 0.027 to 0.006 g/(mg·min), indicating slower adsorption kinetics. These findings provide valuable insight into the interaction mechanisms between microplastics and heavy metals, offering a scientific basis for assessing their copollution behavior and ecological risks.