Adsorbing nanoplastics through high-resilience lignin-polyurethane foam

Nanoplastics (NPs) are emerging contaminants that need to be urgently removed from water. In this study, a compression-resistant polyurethane foam modified by lignin is used to remove NPs from aqueous media via two mechanisms: (1) macropore transport in the polyurethane foam and (2) electrostatic, hydrogen bond and π–π conjugation interactions between NPs and the lignin-polyurethane foam. The roles of these two mechanisms change with the variation of the lignin content. When the lignin content was 2%, the resulting PU–Ln (2%) foam had an excellent adsorption capacity for NPs at pH 9. The results of the adsorption kinetics indicated that the adsorption of NPs on the polyurethane foam fitted the pseudo-second-order kinetic model, indicating that the adsorption process mainly proceeded via chemical adsorption. The adsorption isotherms at different temperatures and the calculation of thermodynamic parameters showed that the adsorption of NPs conformed to the Langmuir isotherm model, and the maximum adsorption capacity of PU–Ln (2%) for NPs was calculated to be 38.06 mg/g. Even after five adsorption–desorption cycles, the adsorbents showed high NPs removal efficiency. Therefore, the lignin-modified polyurethane foam has a promising potential for application in NPs removal.