Superhydrophilic and Underwater Superoleophobic Cotton Fabric for Oil–Water Separation and Removal of Heavy-Metal Ion

Superhydrophilic and underwater superoleophobic cotton fabric (named CS-CF-PDA, or m-CF) was prepared by modifying the cotton fabric (CF) with dopamine (DA) and chitosan (CS). The oil-water separation and heavy-metal ion (e.g., Cu(II)) adsorption performances of m-CF were investigated, and m-CF was characterized by field emission scanning electron microscopy (FE-SEM), energy-dispersive spectroscopy (EDS), Fourier transform infrared (FT-IR), and thermogravimetric analysis (TGA). The results showed that the underwater oil contact angle (UWOCA) of m-CF was more than 156°. The m-CF was used to treat artificial oily wastewater containing Cu(II) under room temperature and atmospheric pressure and gravity, by which the separation efficiency, water flux, and Cu(II) removal rate could reach 99%, 17 400 L·m^-2·h^-1, and 89%, respectively. Additionally, in the process of continuous treatment of oily wastewater, the water flux slightly decreased; on the contrary, the Cu(II) removal rate decreased significantly to 67% within 120 s. Cu(II) was one of the reasons for the decrease of water flux. The m-CF of adsorbed Cu(II) could be leached with HCl (0.1 mol·L^-1) solution, and the Cu(II) desorption rate could reach over 95% within 120 s. After strong acid, strong alkali, high salt, and abrasion treatment, the UWOCAs of m-CF were still higher than 150°. In a word, in terms of oil-water separation, m-CF exhibited good acid, alkali, salt, and abrasion resistances. Also, it is an underwater superoleophobic material involving simple preparation, low cost, and environmental friendliness, which could remove the floating oil and heavy-metal ions from wastewater and has good industrial application prospects.