Lignin/Poly(vinyl alcohol) Hydrogel for Detecting and Effectively Removing Microplastics

This study presents the synthesis of a biobased hydrogel derived from aminated lignin and poly(vinyl alcohol), where the lignin was extracted from bamboo powder and functionalized through phenolization and ammoniation. The hydrogel was characterized using scanning electron microscopy (SEM), in situ Fourier-transform infrared spectroscopy (FTIR), and N₂ adsorption–desorption isotherms. Its adsorption performance was evaluated for polystyrene microplastics (PSMP), demonstrating a high maximum adsorption capacity of 288.6 mg/g. The adsorption kinetics followed a pseudo-second-order model, while the equilibrium data aligned with the Langmuir isotherm, indicating monolayer adsorption. Remarkably, the hydrogel retained 87.64% of its adsorption efficiency after five regeneration cycles. Beyond PSMPs, the hydrogel also exhibited effective adsorption for four other microplastic types─polyethylene (PEMP), polypropylene (PPMP), polyvinyl chloride (PVCMP), and polyamide (PAMP)─at low concentrations (10 mg/L). In real-world water matrices, the adsorption rates for PSMPs and PAMP were as follows: 92.7% and 96.7% in lake water, 94.7% and 98.5% in pipeline water, 97.1% and 99.2% in river water, and 97.9% and 99.7% in sludge supernatant. This work provides foundational data for microplastic removal across diverse environmental media and proposes an eco-friendly, sustainable, and efficient strategy for designing biobased adsorbents targeting low-concentration, small-sized microplastics.