Fluorine-free superhydrophobic cotton fabric for highly-efficient gravity-driven oil/water separation

Abstract
Rapid urbanisation and industrialisation have imposed great environmental impact due to the discharge of oily wastewater and oil spill incidents. The application of superhydrophobic and superoleophilic surfaces in oil/water separation (OWS) has attracted much attention due to their high selectivity of oil which leads to high separation efficiency in OWS. Herein, a fluorine-free superhydrophobic cotton fabric filter was prepared by loading SiO₂ onto the surface from the silica sol and followed by coating with stearic acid through facile dip coating method. The silica sol was prepared using tetraethyl orthosilicate (TEOS) where the loading was manipulated in order to study its effect on hydrophobicity. In the drying process, the effect of the drying temperature on the hydrophobicity was studied. All the pristine and modified cotton fabric samples were characterised by employing FTIR, SEM-EDX and water contact angle measurement. In the preparation process, the optimum TEOS loading was determined to be 4.5 mL. Additionally, the as-prepared superhydrophobic cotton fabric was used to perform OWS, under sole influence of gravity, by using different oil-water mixture solutions and the separation efficiency was above 99%. The results showed that higher drying temperature gives rise in hydrophobicity, and thus lead to more efficient OWS.