Unveiling Exceptional Membrane Distillation Performance via a Wettability Transition in Covalent Organic Frameworks

Membrane distillation (MD) leverages the water-energy nexus by using low-grade heat to facilitate water distillation from hypersaline wastewater. To address the challenges of low flux and poor antifouling capabilities facing traditional membranes, we developed a highly aligned covalent organic framework (COF) film featuring pores that transition from hydrophilic to hydrophobic through the in situ growth and reversible hydrolysis of the COF layer under alkaline conditions. This wettability transition, coupled with surface charges, relocates the liquid-vapor interface to a position near the membrane outlet, with a dramatically shortened travel path and lower phase transition energy barrier. The hydrophilic groups introduced during this process also reduce concentration polarization at the evaporation interface while enhancing antifouling properties against oil and surfactants. The engineered COF film surpasses both contemporary commercial membranes and those reported in the literature in terms of permeability, antifouling, and sustainability. The COF membrane achieved an unprecedently high flux of 185.86 L/(m²·h) when treating hypersaline wastewater (driven by a 65 °C temperature differential), approximately 3.9 times greater than that achieved with commercial membranes. These findings hold significant potential to advance MD applications in water recovery from hypersaline wastewater.