Multifunctional MOF-based superhydrophobic quartz sand: Interfacial interactions for durable and efficient microplastic removal in stormwater

Urban stormwater runoff is a primary source of microplastic pollution in aquatic environments, and its efficient removal is critical for maintaining water ecological security. In this study, a superhydrophobic silica sand composite with MOF structure (HDTMS@ZIF-8@PDA@QS) was developed to enhance microplastic removal through hydrophobic interaction. The adhesion of the substrate was enhanced by polydopamine (PDA) coating, the rough structure and adsorption sites were provided by in-situ growth of ZIF-8 nanoparticles, and the superhydrophobicity was improved by HDTMS modification. Stability tests demonstrated that the material retained superhydrophobicity (WCA > 150°) under extreme temperature (−20 °C), high salinity (3.5 wt% NaCl), and a broad pH range (1−13). After mechanical abrasion, the WCA decreased by only 5 %. Self-cleaning experiments confirmed superior anti-fouling performance against both solid and liquid contaminants. Adsorption experiments revealed that the removal efficiencies of HDTMS@ZIF-8@PDA@QS for polypropylene (PP), polyethylene (PE), and polyethylene terephthalate (PET) microplastics (25 μm) were 98 %, 96 %, and 86 %, respectively, following the order of PP > PE > PET. The maximum adsorption capacity reached 67 mg/g, and after five cycles, the removal efficiency remained above 90 %. AFM and XDLVO theoretical analysis indicated that hydrophobic interaction was the main mechanism of microplastic adsorption, and the adhesion force between modified quartz sand and microplastic was more than four times that of pristine quartz sand. The MOF-based functional filter material proposed offers an efficient and sustainable strategy for mitigating microplastic pollution in urban stormwater runoff. This material holds significant potential for application in green infrastructure systems such as constructed wetlands and bioretention facilities.