Beetle-Exoskeleton-Inspired Fluorine-Free PDA/Chitosan–SiO2/PDMS Coating for Cotton: Durable Self-Cleaning, Self-Healing, Antibacterial Activity, and Oil–Water Separation

A biomimetic, fluorine-free, three-layer aqueous coating for cotton─composed of an Fe2+/Cu2+-catalyzed polydopamine (PDA) primer, a chitosan–SiO2 (CS) aerogel midlayer, and a thin polydimethylsiloxane (PDMS) overcoat─was developed to impart durable superhydrophobicity, rapid photothermal self-healing, antibacterial activity, and efficient oil–water separation. Treated cotton exhibited a static water contact angle (WCA) of 170° and retained a WCA of >155° after 2500 Martindale abrasion cycles or 30 ISO 105-C06 wash cycles; the WCA was restored to ≥160° after ambient storage or within 20 min under natural sunlight as surface temperatures approached ≈50 °C. PDA-mediated Cu2+ chelation (5 mM) produced >99% inhibition of Escherichia coli and Staphylococcus aureus; gravity-driven oil–water separation efficiencies exceeded 98% with >96% retention after 12 cycles. Preliminary scalability and environmental impact analyses, including material inventories and PDMS release estimates, support the potential for industrial translation. This fluorine-free, beetle-exoskeleton-inspired strategy offers a scalable route to multifunctional, sustainable textile finishing and environmental remediation.