Fabrication of Janus Membranes with Gradient Interfacial Pores and Wettability for Robust Antiwetting and Antifouling Membrane Distillation

Robust membrane distillation (MD) membranes with resistance to fouling and wetting are essential for sustainable water recovery from saline oily wastewater; however, achieving both high vapor transport efficiency and antiwetting performance remains challenging. Herein, we developed a Janus membrane with gradient interfacial wettability and pore structure. A carbon nanotube (CNT) interlayer and polyphenol-metal coordination network functionalized surface were constructed using an organic-solvent-free layer-by-layer assembly method. Plant-derived tannic acid (TA), an environmentally benign material, was employed to precisely regulate the surface hydrophilicity and microstructure through its intrinsic reactivity. The CNT interlayer facilitates the adsorption and reaction of TA, enabling the formation of a defect-free TA-metal coating. The optimized membrane exhibits high vapor flux and sustained salt rejection (≥99.9%) through the synergistic effects of the CNT interlayer and TA-metal network. Notably, it maintains stable performance during a prolonged 72 h exposure to actual seawater containing 0.2 mM surfactant, demonstrating exceptional resistance to surfactant-induced wetting. Mechanistic studies reveal that the TA-metal coating synergizes with the CNT interlayer to enhance the capillary forces, thereby creating a significant diffusion barrier against surfactant penetration. Meanwhile, the TA-metal coordination improves surface hydrophilicity, resulting in underwater superoleophobicity (oil contact angle >170°). This wettability confers superior antioil-fouling capability, as validated by the outstanding desalination performance during a 72 h MD test using actual oily seawater. This work establishes a membrane design paradigm through the synergistic integration of carbon nanomaterials and polyphenol chemistry for the sustainable reclamation of water from complex oily wastewater.