Interfacial capture of microplastics by a superhydrophobic COF-zeolite medium: Performance and multiscale mechanisms

Urban stormwater runoff is an important pathway for microplastics entering aquatic environments, while conventional bioretention media have limited interfacial capture capacity for hydrophobic microplastics (MPs). To construct a medium with a superhydrophobic surface and enhanced MP capture ability, this study fabricated a superhydrophobic medium, HDA@COF-LZU1@PDA@Zeolite, through polydopamine anchoring, in situ growth of COF-LZU1, and hexadecylamine hydrophobic modification. Its structural composition, wetting stability, MP removal performance, and interfacial interaction mechanism were systematically investigated. The results showed that the modified material achieved a WCA of 160° and retained superhydrophobicity under saline, acidic/alkaline, and mechanical abrasion conditions. Compared with pristine zeolite, the modified medium increased PP, PE, and PET removal from 3.27%, 5.63%, and 6.89-83.06%, 96.52%, and 99.16%, respectively. Kinetic data were best described by the PSO model, while the Langmuir model provided the best fit to the isotherm data, with capture capacity tending toward saturation at higher MP concentrations. The material also maintained effective MP removal at lower initial concentrations and under different ionic conditions. AFM, XDLVO, DFT calculations, and AIMD simulations were further used to explain the origin of the different capture behaviors from the perspectives of interfacial mechanics and molecular interactions. The differentiated capture behavior was associated with hydrophobic interactions, van der Waals interactions, local polar interactions, and possible π-π interactions. Among them, PET exhibited the highest capture efficiency, possibly due to additional contributions from its benzene rings and ester groups to interfacial interactions with the COF-LZU1 framework. This study suggests the differentiated capture mechanism of different MPs by the superhydrophobic COF-zeolite medium and provides guidance for the interfacial design of media in bioretention systems.