Preparation of omniphobic membrane by anchoring hydrophobic islands at fixed-points for treating hypersaline wastewater

With a high rejection rate for salts and non-volatile organic compounds, membrane distillation (MD) is widely used in in the treatment of hypersaline wastewater. However, the performance degradation of membranes caused by pore-wetting, mineral scaling or structural instability greatly limits their development potential. Improving the durability of service performance in MD process has become the focus of the scientific community. Herein, we anchored the fluor‑silicon island structure with low-surface-energy onto the poly(vinylidene fluoride- co -chlorotrifluoroethylene) (PVDF-CTFE) membrane surface by covalent bonding based on C Cl, so as to construct an omniphobic membrane with excellent anti-fouling and anti-wetting performance. Through the characterization of the surface morphology, element composition and basic physicochemical properties of the membrane, it was demonstrated that the discontinuous island-structure was successfully anchored on the membrane surface through chemical bonds, endowing the modified membrane with a higher gas-permeability coefficient and liquid entry pressure (LEP w  > 4.0 bar), and exhibiting outstanding gas-permeability and water-impermeability. Meanwhile, it has a high contact angle for water (154.0°), brine (152.2°), Sodium Dodecyl Sulfonate (SDS) salt solution (150.5°), and soybean oil emulsion (123.1°), showing excellent lyophobic properties. Experimentally, it was demonstrated that the modified membrane had higher vapor-flux (≥ 23.0 kg m −2  h −1 ), lower irreversible flux decay rate (< 8.8 %), and could be continuously and stably operated for 60 h with excellent performance compared with the original membrane, homogeneous coating or electrostatic adsorption modified membranes. Treating hypersaline wastewater with complex components, it still exhibits excellent stability, anti-wetting, and anti-fouling performance after long-term operation.