Graphene-regulated hydrogel distillation membranes with enhanced resistance to fouling, wetting, and scaling

The synergistic coupling of wetting, fouling, and scaling represents a critical bottleneck that limits the practical application of membrane distillation (MD) for hypersaline wastewater treatment. Herein, a Janus membrane (PTG-PTFE) was designed by constructing a compact graphene-regulated hydrogel layer on a hydrophobic polytetrafluoroethylene (PTFE) substrate to achieve simultaneous resistance to these challenges. The introduction of graphene nanosheets regulated the network structure of poly(vinyl alcohol)/tannic acid (PVA/TA) hydrogel through strong π-π interactions and hydrogen bonding, forming a uniform and compact hydrogel network, which exhibited a refined morphology after freeze-drying. Molecular simulations further revealed that graphene bridges PVA and TA, enhancing network compactness and structural integrity. The PTG-PTFE membrane exhibited superior anti-scaling performance by rendering CaSO₄ adhesion thermodynamically unfavorable through a positive interfacial free energy and decreased interaction energy, while possessing an ultrahigh liquid entry pressure (LEP) of 59.6 ± 2.3 bar. As a consequence, the PTG-PTFE exhibited outstanding desalination stability when treating complex saline feeds containing oil, surfactants, and high-concentration calcium sulfate, with high salt rejection consistently maintained at 99.9%. In addition, the PTG-PTFE maintained stable flux and excellent overall salt rejection during long-term treatment of representative real hypersaline wastewaters, including landfill leachate and oilfield-produced water, highlighting its strong potential for practical industrial wastewater management. This work provides new insights and valuable guidance for designing multi-resistant advanced MD membranes for robust desalination, offering strong support for the potential application of MD in treating high-salinity wastewater.