Adsorption of Polyethylene Nanoplastics by Graphene Oxide–Polysaccharide Composites: Kinetic, Isotherm and Thermodynamic Studies

With high mobility, long-term durability, and potential risks to aquatic ecosystems and human health, polyethylene nanoplastics (PE–NPs) are a developing environmental issue. Therefore, graphene oxide (GO) was utilized to functionalize chitosan (CS) and microcrystalline cellulose (MCC) in order to create sustainable polysaccharide-based composites that resulted in graphene oxide–chitosan (GO–CS), graphene oxide–MCC–50 µm and graphene oxide–MCC–90 µm adsorbents in order to evaluate the adsorption performance of sustainable GO–polysaccharide composites toward laboratory-prepared polyethylene nanoplastics under controlled conditions. The novelty of this study lies in the comparative evaluation of GO–chitosan and GO–microcrystalline cellulose composites with two MCC particle sizes (50 μm and 90 μm) for the adsorption of laboratory-prepared polyethylene nanoplastics, providing insight into the influence of adsorbent composition and particle size on adsorption performance. The prepared adsorbents were characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), point of zero charge (pHpzc), and X-ray diffraction (XRD) in order to analyze adsorption behavior by morphology, chemical structure, surface chemistry, and particle crystallinity. According to the results, GO–CS has the maximum adsorption capacity (50.25 mg·g−1), followed by GO–MCC–50 µm (38.31 mg·g−1) and GO–MCC–90 µm (27.02 mg·g−1). Smaller MCC particle sizes of adsorbent resulted in improved adsorption performance, as demonstrated by the increased adsorption capacity of GO–MCC–50 µm as opposed to GO–MCC–90 µm. The difference between the graphene oxide–MCC–50 µm and graphene oxide–MCC–90 µm composites’ adsorption capacities demonstrates that adsorption capacity greatly increases with small adsorbent particle sizes. Stronger interaction sites, hydrophobic contacts, and a large number of functional groups are all responsible for the improved performance. The findings provide insight into the influence of polymer type and particle size on polyethylene nanoplastic adsorption and support the further development of GO-based biopolymer adsorbents.