Cobalt-based MOF-modified multidimensional cotton with ethanol-responsive wettability for on-demand oil–water separation

Industrial wastewater discharge and oil spills pose significant threats to both ecological systems and human health. However, conventional hydrophobic materials with a single functional capability are often inadequate for addressing the diverse challenges associated with complex oil–water mixtures encountered in oily wastewater treatment. Herein, two-phase material with ethanol-triggered, switchable surface wettability was successfully fabricated. Cotton balls were Co-modified with a hydrothermally synthesized cobalt-based metal-organic framework and polydimethylsiloxane, a low-surface-energy polymer. The surface wettability of the modified cotton balls reversibly transitions from a hydrophobic and oleophilic state to a hydrophilic and underwater oleophobic state upon ethanol impregnation, and is fully restored to the original hydrophobic state after drying. Benefiting from this unique switching mechanism, the modified cotton balls enable the on-demand separation of diverse oil-water mixtures. Beyond two-dimensional cotton substrates, the hydrophobicity of three-dimensional cotton fabrics was significantly enhanced via surface coating with a cobalt-based metal-organic framework and hexadecyltrimethoxysilane. The resulting three-dimensional cotton fabrics exhibit a high water contact angle of 142.3 ± 2°, along with excellent self-cleaning performance and mechanical stability. This work demonstrates the effective application of cobalt-based metal–organic frameworks in regulating surface wettability across multidimensional materials.