Natural polyelectrolyte-functionalized superhydrophilic and antibacterial wood for efficient oil/water separation

As the amount of oily wastewater discharged from industrial and domestic sources increases, materials used for oil/water separation have received widespread research attention in recent years. However, many reported separation materials with special wetting properties require complex and environmentally unfriendly preparation processes. Therefore, green and efficient materials for oily wastewater and emulsion separation are urgently needed. In this paper, inspired by the scrobiculate and honeycomb-shaped porous structure of natural balsa wood, functionalized wood was designed as an oil/water separation and emulsion purification material by delignification and a simple surface modification process. A deep eutectic solvent (DES) was used to remove the lignin and hemicellulose components. Sodium carboxymethyl cellulose (CMC) and chitosan quaternary ammonium salt (CQA) were used to functionalize and obtain the superhydrophilic/underwater superoleophobic wood material. The water contact angle of the functionalized wood in air reached 0 degrees, while the underwater contact angles for different kinds of oil were greater than 150 degrees. Various oils were effectively separated with a high separation efficiency (> 99.2%). Moreover, the separation efficiency of kerosene from water still reached 99.5% after 30 separation test cycles. After long-term immersion in different pH and salt solutions, the separation efficiency for a kerosene/water mixture was still greater than 99%. Rapid and continuous oil/water separation was achieved conveniently. More importantly, the selective wetting properties and complex porous structure of the functionalized wood enabled the purification of unstable and surfactant-stabilized oil-in-water emulsions with high separation efficiencies. The functionalized wood material also showed promising antibacterial properties, with a good inhibitory effect on the growth of both Gram-positive S.aureus and Gram-negative E.coli. This will effectively prevent contamination and the decrease in separation efficiency caused by mold on the surface. Therefore, this green, efficient, easily prepared, and durable functionalized wood shows excellent potential for application as a separation material for oily wastewater.