Insights into the enhanced flux and robust desalination of hydrogel composite Janus membrane in membrane distillation: overlooked interfacial compatibility

Janus membranes demonstrate promising potentials in membrane distillation (MD); however, the critical role of interfacial compatibility between their hydrophilic and hydrophobic layers has been largely overlooked, limiting membrane mass transfer and effectiveness. Here, this study developed an innovative interfacial bridging-anchoring strategy to enhance the interfacial compatibility. A polydopamine–polyethyleneimine bridging layer was applied to the hydrophobic PTFE substrate via amino‑fluorine hydrogen bonding, enhancing the interfacial homogeneity. Subsequently, a protocatechuic acid (PCA)@iron ions–polyvinyl alcohol (PVA) hydrogel layer in situ engineered based on the polyphenol-metal networks was anchored to the bridging layer through hydrogen bonding, π–π stacking, and iron ions-hydroxyl coordination. The resultant membrane exhibitedincreased interfacial peel strength that facilitated water transport to the evaporation interface and incorporated a metal-phenolic network that reduced the evaporation enthalpy to enhance the confined interfacial evaporation, effectively overcoming the so-called “flux constraints” caused by the formation of extra-dense Janus layer, achieving a 14.87 % higher flux than the PTFE substrate. Moreover, regulating interfacial compatibility benefited from to eliminating interfacial gaps, suppressing surfactant diffusion, while introducing a metal-phenolic network improved the adhesion energy barriers for mineral oil and gypsum through competitive hydration interactions. Consequently, the anti-fouling, anti-wetting, and anti-scaling properties of Janus membranes were significantly enhanced, achieving over 90 % flux recovery and 99.90 % salt rejection in treating real shale gas-produced wastewater (SGPW). Importantly, techno-economic assessment confirmed the obviously economic feasibility of this strategy. This study provides a facile and economical approach to designing high-performance and durable membranes for MD applications in SGPW treatment.