Molecular Mechanisms Governing the Adsorption, Deposition, and Removal of Environmentally Aged Microplastics by Engineered Surfaces

Microplastic (MP) pollution poses escalating environmental and health risks, yet the molecular mechanisms governing the interactions between environmentally aged microplastics (MPs) and engineered surfaces remain largely unresolved, hindering the rational design of remediation materials. Herein, we quantitatively elucidate the interaction forces between aged polystyrene MPs (PSMPs) and self-assembled monolayer (SAM)-functionalized surfaces at the solid/water interface using colloidal probe atomic force microscopy (AFM), complemented by quartz crystal microbalance (QCM) analysis. The results reveal that adhesion forces are strongly influenced by aqueous salinity and pH, with π-π stacking and electrostatic/cation-π interactions likely contributing predominantly on phenyl- and amino-terminated surfaces, respectively. A robust correlation between nanoscale adhesion forces and macroscopic adsorption capabilities is established, enabling predictive understanding of aged MP-surface interactions. Guided by these mechanistic insights, a tannic acid-modified chitosan biomaterial integrating amino and phenyl functionalities is developed, achieving over 92.1% removal efficiency for aged PSMPs across diverse water chemistries at an environmentally relevant initial MP concentration of 1 mg L⁻¹. This work provides an intermolecular force-driven design paradigm that bridges nanoscale intermolecular interaction mechanisms with macroscopic material performance, offering theoretical and practical guidance for next-generation remediation strategies targeting environmentally aged MPs.