Fabrication and characterization of degradable and durable fluoride-free super-hydrophobic cotton fabrics for oil/water separation

A simple and mild low-cost method for fabricating fluoride-free super-hydrophobic cotton fabrics is presented. The two-step method involves the decoration of the cotton fabrics by ZnO nano-rods to construct rough surface and the grafting of low surface energy stearic acid (SA) onto the as-decorated cotton fabrics via an immersion route. The as-prepared ZnO/SA modified cotton fabrics were characterized by X-ray powder diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, atomic force microscopy and Fourier transform infrared spectroscopy. The wetting behavior of coffee, milk, tea, water dyed by methylene blue, strong acid (HCl), strong alkali (NaOH), and saturated salt solution (NaCl) on the ZnO/SA modified cotton fabrics was evaluated with a contact angle tester, and the durability of the ZnO/SA modified cotton fabrics in corrosive liquids and under ultraviolet (UV) irradiation was tested. In addition, the oil/water separation efficiency of the ZnO/SA modified cotton fabrics towards the oil/water mixed solutions of n-hexane, liquid paraffin, dichloromethane, chloroform and motor oil with different density and viscosity was investigated; and their degradation rate under harsh conditions (e.g., immersion in acid and alkali or exposure to UV irradiation) was calculated. Results demonstrate that ZnO and SA are chemically bonded onto the surface of cotton fabrics to achieve super-hydrophobicity. The as-prepared ZnO/SA modified cotton fabrics exhibit a water contact angle of over 164; and they retain the super-hydrophobicity after immersion in acid and alkali solutions or under UV irradiation. Besides, they have an oil/water separation efficiency of over 96.5% for all the tested liquids as well as a biodegradability rate of 59.0% after immersion in phosphate buffer saline solution containing cellulase (pH = 4.8) for 15 days. Therefore, the present approach could be applicable to constructing durable super-hydrophobic cotton fabrics with promising potential for oil/water separation in industry.