Multifunctional superwetting positively charged foams for continuous oil/water emulsion separation and removal of hazardous pollutants from water

The discharge of anionic surfactants stabilized oily wastewater is harmful to aquatic plants and animals, and the treatment of the wastewater is urgent. However, on account of the high stability of the oil-water interface, the wastewater is hard to be efficiently disposed. To destabilize the stability, superhydrophilic positively charged polyurethane (PU) sponge was fabricated by a simple cross-linking reaction between chitosan and glutaraldehyde. Through the electrostatic interaction, the positively charged PU sponge could absorb anionic surfactants molecules (sodium dodecyl sulfate, SDS) absorbed on the oil surface, resulting in the decline of the stability of the oil-water interface, sequentially the oil droplets could collide and coalesce in the three-dimensional pores of PU sponge. For SDS stabilized oil-in-water emulsion, the positively charged PU sponge can constantly work for 100 min to separate above 3500 mL emulsion with a favorable separation efficiency. Furthermore, the positively charged PU sponge can absorb dyes and metal ions in wastewater, due to a large number of amino groups and hydroxyl groups of the positively charged coating. Therefore, the prepared positively charged PU sponge could continuously separate oil/water emulsion and remove the dyes and metal ions in wastewater, which could be a promising candidate for oily wastewater treatment.