Caught in the net: A quaternized wood fiber/chitin nanofibril hydrogel trap for polystyrene nanoplastics

Nanoplastics pollution requires sustainable remediation technologies aligned with green chemistry and circular economy principles. Here, we report a fully biomass-derived, hierarchically structured hydrogel adsorbent for efficient removal of polystyrene nanoplastics (PSNPs). The hydrogel was fabricated by integrating quaternized wood fibers (QWF), derived from lignocellulosic biomass, with chitin nanofibrils (ChNFs), forming an interconnected micro-nano hierarchical porous network. Structural integrity was achieved through physical entanglement and hydrogen bonding, without toxic chemical crosslinkers during hydrogel formation. The cationic hierarchical architecture provided abundant electrostatic anchoring sites, internal diffusion pathways, and excellent mechanical stability, enabling a high adsorption capacity of 1940 mg g^-1 (calculated q_e: 2109 mg g^-1) with rapid adsorption kinetics. The hydrogel also maintained strong performance (>750 mg g^-1) in complex real-water matrices containing competing ions. Moreover, the adsorbent exhibited excellent reusability, retaining over 98% removal efficiency after 30 cycles via acid-assisted mechanical compression. The pristine hydrogel underwent complete biodegradation within 23 days in soil (ISO 17556), whereas the spent adsorbent collected after PSNP capture showed delayed but complete biodegradation within approximately 40 days. This work demonstrates a potentially scalable biomass-derived adsorbent matrix for environmentally responsible nanoplastics remediation. Overall, the design reconciles adsorption performance, regenerability, and end-of-life management in one practical platform.