One-step spontaneous grafting via diazonium chemistry for the fabrication of robust bionic multifunctional superhydrophobic fabric

A superhydrophobic cotton fabric with peanut leaf-like nanoplates, 3D flower-like and mulberry-like microstructure surface with varied water adhesion was fabricated via simple one-step spontaneous grafting method at room temperature. The spontaneous covalent grafting of 3,5-di(trifluoromethyl)phenyl functionalities to cotton fibers by the Fe0 reduction of the corresponding 3,5-di(trifluoromethyl)benzene diazonium salt has been studied in aqueous acid, which relates to the homolytic reduction of diazonium salts to produce radicals followed by grafting to the cotton fibers. We adjust the spontaneous grafting process by simply changing the molarity of HCl solutions to control the micro-nanostructures of β-FeOOH on the cotton fabric surfaces. Thus, the superhydrophobic surface adhesion forces to the water droplets can be effectively adjusted from 21.36 μN (lowest) to 159.35 μN (highest) via changing the surface architecture. The modified cotton fabric surface exhibited excellent superhydrophobicity with a water contact angle (WCA) of 167.2 ± 1.6°, sliding angle (WSA) of 1.8 ± 0.3° and superoleophilicity with the n-hexane contact angle (OCA) of 0°. Thus, the superhydrophobic cotton fabric can be used for self-cleaning and oil/water separation with an efficiency of as high as 98.9%, which has good recyclability, laundering and abrasion durability. Moreover, the movement of the superhydrophobic cotton fabric in water can be controlled by the orientation of a magnet without contact. Meanwhile, the micro-nanostructured rough surface with tunable adhesive force to water can be used to detect AgNO3 or NaOH in the aqueous solution, and so other potential applications in the droplet based microreactor can be found.