Binding mechanisms dictate distinct interactions of iron oxides with nanoplastics under structural feature constraints

Interactions with iron (oxyhydr)oxides govern the mobility and fate of nanoplastics in freshwater systems, yet the mechanisms underlying mineral-phase-dependent binding remain unclear. Here, we investigated the binding processes and mechanisms of representative iron oxides (ferrihydrite, lepidocrocite, and goethite) toward nanoplastics with varied sizes, surface functionalities, and aging states. Binding rates and capacities differ by up to 15.9- and 43.6-fold, respectively. Ferrihydrite achieves the fastest kinetics through surface attachment facilitated by its rough, heterogeneous interface and binding-induced interfacial restructuring. In contrast, goethite maintains higher, less condition-sensitive binding capacities because its macropores promote pore entrapment. Nanoplastic aging involving size reduction and surface functionalization inhibits mineral-nanoplastic interactions by enhancing post-binding charge reversal, thereby weakening subsequent electrostatic attraction. These findings highlight interfacial interactions and pore entrapment as key mechanisms driving divergent nanoplastic binding by iron oxides, providing a mechanistic framework for predicting nanoplastic immobilization and transport in freshwater sediments. Ferrihydrite bound nanoplastics fastest while goethite retained the highest, most robust capacity; nanoplastic aging reduced binding, with surface attachment and pore entrapment driving differences, according to kinetic and mechanistic comparisons of iron oxides and nanoplastics.