Facile preparation of marine carrageenan hydrogel-coated steel mesh with superhydrophilic and underwater superoleophobic performance for highly efficient oil-water separation.

The discharge of oil-laden wastewater from industrial processes and the frequent occurrence of oil spills pose severe threats to the ecological environment and human health. Membrane materials with special wettability have garnered attention for their ability to achieve efficient oil-water separation by leveraging the differences in wettability at the oil-water interface. These materials are characterized by their simplicity, energy efficiency, environmental friendliness, and reusability. Among them, superhydrophilic-underwater superoleophobic membranes inspired by biomimetic fish scale structures have become a focal point of oil-water separation research due to their ability to repel oil contaminants effectively and maintain self-cleaning properties during the separation process. In this study, a stainless steel microporous two-dimensional metal mesh was employed as the substrate, coated with a carrageenan solution, and gelled in situ using sodium periodate as a crosslinking agent to fabricate a membrane with oil-water separation capabilities. The robust hydrophilicity of the carrageenan hydrogel imparts the coated stainless steel mesh with superhydrophilicity and underwater superoleophobicity (underwater oil contact angle ≥ 158°), along with excellent antifouling properties and recyclability. Experimental results demonstrate that the membrane achieved separation efficiencies of 98.87%, 98.08%, 98.14%, and 97.98% for silicone oil, canola oil, cyclohexane, and liquid paraffin, respectively, with a water flux of 1380.75 L/m²·h. Remarkably, the membrane retained its initial separation efficiency even after 20 cycles. Additionally, the hydrogel exhibited exceptional stability under highly alkaline conditions, making it suitable for the treatment of complex oil-contaminated wastewater. PRACTITIONER POINTS: This study extracted a biocompatible and renewable hydrogel from marine red algae for application in oil-water separation. A superhydrophilic/underwater superoleophobic oil-water separation membrane was developed based on biomimetic fish scale structures. The membrane exhibited exceptionally high separation efficiency under pure gravity-driven conditions. The resulting material exhibits excellent oil repellency, self-cleaning capability, and recyclability.