Cellulose nanofiber-coated delignified wood as an efficient filter for microplastic removal

Microplastics (MPs) are a new type of emerging pollutant in the aquatic environment that pose a tremendous risk to aquatic organisms and human health. Although many studies have focused on the removal of MPs, most of the materials used are non-renewable, non-degradable, and relatively costly. The development of green, renewable, and cost-effective materials for the removal of MPs presents a significant challenge. In this work, cellulose nanofiber-coated, delignified wood (CNF-CDW) was prepared and used as an efficient filter to remove MPs for the first time. Balsa wood chip was delignified through three approaches using NaClO2, Na2SO3/NaOH, and a deep eutectic solvent (DES) consisting of choline chloride/lactic acid. Delignified wood (DW) with desirable mechanical properties and a high pore structure was successfully prepared by optimizing the delignification method and reaction conditions. Subsequently, the CNF-CDW was prepared through immersion of DW in a suspension of cellulose nanofiber (CNF), followed by crosslinking with CaCl2 solutions. The effects of CNF concentration, CaCl2 concentration, and wood chip thickness on the removal efficiency and flux of CNF-CDW towards polystyrene (PS) MPs were systematically studied. Under the optimal conditions of 0.5 ​wt% CNF, 1 ​mol/L CaCl2, and 10 ​mm in thickness, the CNF-CDW exhibited superior MPs removal performance, with a removal efficiency of 95.97% and a flux of 1146 ​L/m2·h. Morphological analysis revealed that CNF formed compact films on the surface DW, and MPs were efficiently blocked both on the surface and internal cellular structure of CNF-CDW. Therefore, with its exceptional filtration efficiency, high flux, and sustainable nature, CNF-CDW has a broad application prospect in the field of removing MPs from aquatic environment, promoting a brighter and cleaner future for aquatic ecosystems and human well-being.