Preparation of caffeic acid-polyethyleneimine modified sponge for emulsion separation and dye adsorption

Abstract Water pollution has become a serious problem in aquatic ecology due to the oil spills and the consistent release of industrial pollutants, such as dyes. Herein, we report a simple method to fabricate superwetting caffeic acid (CA)-polyethyleneimine (PEI)-modified melamine sponges (CA-PEI-MS) for oil-in-water emulsion separation and dye adsorption. The as-fabricated CA-PEI-MS exhibited superhydrophilicity with an approximately zero water contact angel (WCA) and underwater superoleophobicity with an underwater oil contact angel (UWOCA) greater than 150°. The compressed CA-PEI-MS showed an excellent oil-in-water emulsion separation performance with a separation efficiency greater than 97% and a water flux of up to 25,480 L h−1 m−2 bar−1. The recyclability test was used to study the stability of the compressed CA-PEI-MS, after washing with acetone; the flux did not show any significant change during the 12-cycle separation test. The separation efficiency in every cycle was greater than 97%. Due to the availability of rich positive charged amino groups, the as fabricated CA-PEI-MS exhibited adsorption ability towards negatively charged dyes such as, rose bengal (RB) and direct red (DR) with 96% adsorption efficiency. Therefore, the as designed low-cost and eco-friendly preparation of CA-PEI-MS has a great potential for practical application as it shows high separation performances and excellent efficiency.