Dense Janus membranes (JMs) are potential candidates in hypersaline wastewater treatments for membrane distillation (MD). However, dense surface layers generally add obvious membrane mass transfer resistance, limiting its practical application. In this study, a novel dense JM was facilely developed by controlled interfacial polymerization utilizing a phosphonium functional monomer (THPC) on hydrophilic polyvinylidene fluoride (PVDF) substrate. MD desalination performance results showed that the optimized THPC/PVDF JM surprisingly achieved a flux even 21.3% higher than that of its substrate and exhibited robust stability to surfactants, oil, and gypsum. Importantly, potential mechanism of remarkable flux enhancement of dense JMs was revealed. Raman and DSC analyses showed that THPC/PVDF JM with elevated intermediate water content had minimal enthalpy for water evaporation, thus facilitating water vaporization. Dynamic water contact angle measurements, advanced microstructural characterization by positron annihilation spectroscopy and water permeability experiments etc. showed that THPC/PVDF JM with high hydrophilicity and appropriately enlarged effective pore sizes provided strong water-absorption capacity and water permeability, contributing to rapid water replenishment. Both synergistically contributed to an incredible increase in membrane flux. Meanwhile, the dense surface layer, featured by its strong hydrophilicity and abundant hydroxyl groups, effectively prevented complex contaminants from intruding hydrophobic substrate and discouraged oil/gypsum adhesion, ensuring stable MD operation. This study shall provide useful insights and strategies to design high-flux dense JMs with minimal membrane failure propensity, highlighting its great potential for efficient hypersaline wastewater treatments.

中文翻译：

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构建高度水合和可渗透的致密 Janus 膜，用于快速、稳定的膜蒸馏脱盐


致密 Janus 膜 （JM） 是用于膜蒸馏 （MD） 的高盐废水处理的潜在候选者。然而，致密的表层通常会增加明显的膜传质阻力，限制了其实际应用。在本研究中，通过在亲水性聚偏二氟乙烯 （PVDF） 基材上利用鏻功能单体 （THPC） 进行受控界面聚合，轻松开发了一种新的致密 JM。MD 海水淡化性能结果表明，优化的 THPC/PVDF JM 出人意料地实现了比其基材高 21.3% 的磁通量，并且对表面活性剂、油和石膏表现出强大的稳定性。重要的是，揭示了致密 JMs 显着通量增强的潜在机制。拉曼和 DSC 分析表明，中间含水量较高的 THPC/PVDF JM 对水分的蒸发焓最小，从而促进了水的蒸发。动态水接触角测量、正电子湮没光谱和透水实验的高级微观结构表征等表明，具有高亲水性和适当扩大有效孔径的 THPC/PVDF JM 具有较强的吸水和透水性，有助于快速补水。两者协同作用促成了膜通量的惊人增加。同时，致密的表层具有很强的亲水性和丰富的羟基，有效防止复杂污染物侵入疏水基材，阻止油/石膏粘附，确保 MD 稳定运行。 本研究将为设计具有最小膜失效倾向的高通量密度 JM 提供有用的见解和策略，突出其在高效高盐废水处理方面的巨大潜力。