High-Efficiency Adsorption of PS, PE, and PP Microplastics from Environmental Waters Using a Cross-Linked Chitosan/Graphitic Carbon Nitride/ZIF-67 Nanocomposite

Municipal wastewater is a major pathway for the continuous release of microplastics into aquatic environments, making the development of efficient and reusable capture materials essential for advanced water treatment. In this study, a multifunctional ZIF-67/g-C3N4/CS nanocomposite was designed by integrating cobalt-based zeolitic imidazolate framework ZIF-67 with graphitic carbon nitride (g-C3N4) and a chitosan (CS) biopolymer matrix. The novelty of this material lies in combining the high porosity and tunable surface chemistry of ZIF-67, the π-rich layered structure of g-C3N4, and the hydrophilic, amino-rich chitosan framework into a single adsorptive platform for simultaneous removal of chemically different microplastics. The nanocomposite achieved high removal efficiencies for polystyrene (PS), polypropylene (PP), and polyethylene (PE) microplastics with particle sizes of 20–25 μm, reaching 97.4%, 92.1%, and 90.3%, respectively, at pH 7.6 within 25 min. The higher affinity toward PS is attributed to additional π–π interactions between the aromatic PS chains and the conjugated domains of g-C3N4/ZIF-67, whereas PP and PE removal is mainly governed by hydrophobic adhesion, surface trapping, and interfacial interactions with the chitosan-supported porous framework. The equilibrium data were well described by both Langmuir and Freundlich models, with maximum adsorption capacities of 97.69, 94.86, and 93.67 mg g−1 for PS, PP, and PE, respectively. The nanocomposite retained high recyclability, maintaining 95–97 ± 3.1% removal after five adsorption–desorption cycles. These findings demonstrate that ZIF-67/g-C3N4/CS is a durable and high-performance adsorbent for microplastic remediation, with strong potential for application in municipal wastewater treatment, constructed wetlands, and advanced water-polishing systems.