Biodegradable, superwettable caffeic acid/chitosan polymer coated cotton fibers for the simultaneous removal of oils, dyes, and metal ions from water

Abstract Discharged wastewater is known to contain insoluble oils, soluble pollutants (organic dyes), and metal ions from industry, which can lead to serious ecological problems. Inspired by the strong adhesion behavior of marine mussels to surfaces, polymers have been developed to mimic this behavior. More specifically, such polymers have been applied in the coating of membrane substrates to obtain multifunctional materials for the absorption of wastewater pollutants. In this study, superwettable cotton-based materials for wastewater treatment were constructed by modifying cotton fiber (CF) with caffeic acid (CA) and chitosan (CHI). The as-prepared CA-CHI-CF materials exhibited superhydrophilicity (i.e., a water contact angle of ~ 0°) and underwater superoleophobicity (i.e., an underwater oil contact angle ≥ 160°). Notably, the compressed CA-CHI-CF exhibited an excellent oil-in-water emulsion separation performance, i.e., a flux up to 50,050 L h−1 m−2 bar−1 under 0.1 bar pressure, and a separation efficiency > 99.9%. Interestingly, due to the advantages of the amino, carboxyl, and hydroxyl groups offered by caffeic acid and chitosan, CA-CHI-CF showed excellent adsorption capabilities for cationic dyes (>99%) and heavy metal ions (>99%). To demonstrate the applicability of our system, a benchmark separation experiment was conducted, namely the separation of dye- and metal ion-spiked emulsions. CA-CHI-CF was found to separate all target pollutants from the solution simultaneously. CA-CHI-CF also exhibited a good biocompatibility and biodegradability, thereby confirming its great potential for practical applications.