Fluorinated Covalent Organic Framework Membranes with Robust Wetting Resistance for Durable Membrane Distillation.

Membrane distillation (MD) is a promising separation technique for producing pure water from brine using low-grade heat. Covalent organic framework (COF) membranes with high porosity and well-ordered pore structure exhibit excellent flux and salt rejection during MD. However, long-term MD operation is often restricted by the inevitable gradual wetting of COF membranes, which causes deterioration of salt rejection, primarily resulting from the lack of intrinsic hydrophobicity. Herein, a fluorinated COF (TGTf) membrane with intrinsic hydrophobicity and excellent anti-wetting property is reported. Under 65 °C and 12 kPa operation pressure, the TGTf membrane maintained a high water flux of 195 L m h and a salt rejection of 99.80% over 168 h of MD operation, which is the longest operation time ever reported for MD using COF membranes. In addition, the TGTf membrane showed unparalleled resistance to scaling and organic fouling, demonstrating great potential for real-world brine treatment. Experimental and simulation studies revealed that incorporation of fluorine atom not only enhanced the hydrophobicity of the COF membrane, but also created electrostatic barriers within the fluorinated nanochannels, efficiently preventing ion penetration. These results underscore the remarkable potential of fluorinated COF membranes in MD, offering a promising solution for sustainable brine desalination.