A switchable wettability coating based on KH550-SiO2-DTMS nanocomposite particles with controllable oil-water separation performance

Intelligently responsive super-wetting coatings have garnered significant attention for their ability to modulate wettability in response to environmental stimuli, enabling efficient oil/water separation. This study presents a novel pH-responsive super-wetting coating fabricated via a simple, cost-effective sol-gel and dip-coating approach on cotton fabric. The coating combines low-surface-energy dodecyl trimethoxysilane (DTMS) with pH-sensitive 3-aminopropyl triethoxysilane (KH550) modified SiO₂ nanoparticles. The coating's structure, morphology, and properties were characterized using Fourier transform infrared (FTIR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), and water contact angle measurements (WCA). Compared to existing pH-responsive systems, this coating exhibits superior switching speed: it transitions rapidly from superhydrophobicity (WCA > 150° at pH 7) to superhydrophilicity (WCA decreases from 50.24° to 0° within 20 s at pH 1) and reversibly back to superhydrophobicity (WCA = 163° at pH 13). The coating demonstrates excellent stability in various salt solutions (NaCl, KCl, KNO₃) and under ultrasonic washing, ensuring robustness in complex aqueous environments. Leveraging this reversible wettability switching, the coating achieves high separation efficiencies for both high-density (98.5 %) and low-density (96 %) oil/water mixtures. Critically, this fabrication strategy eliminates the need for expensive, environmentally hazardous heavy metals (e.g., Ag, Au, Cu) or complex polymerization processes commonly employed in other smart separation materials. The combination of rapid switching, environmental and economic friendliness, salt resistance, durability, and high separation performance underscores the significant potential of this coating for diverse practical oil/water separation applications.