Janus membranes in membrane distillation: Unveiling the anti-wetting behavior and mechanisms in the presence of nanoplastic-surfactant complexes

Membrane distillation (MD), a novel membrane separation technology, exhibits advantages in treating high-salinity wastewater. However, membrane wetting caused by surfactants remains a major challenge for the large-scale application of MD. Nanoplastics (NPs) commonly coexist with surfactants such as sodium dodecyl sulfate (SDS) in high-salinity industrial wastewater. Their interactions can lead to the formation of nanoplastic-surfactant complexes, thereby altering membrane wetting behavior during MD operation. Herein, we proposed an air-liquid interfacial deposition strategy to fabricate a Janus membrane with high anti-wetting performance. A dense metal-phenolic network hydrophilic layer was constructed on a hydrophobic PVDF substrate via tannic-Fe 3+ co-deposition, followed by polyethyleneimine (PEI) cross-linking. The as-prepared membrane exhibited superior anti-wetting performance in the treatment of high-salinity water containing SDS@NPs complex with stable normalized flux and ∼ 100% NPs rejection. Notably, the coexistence of NPs significantly mitigated membrane wetting, mainly attributed to the adsorption of SDS on NPs, which reduced the concentration of free SDS in feed solution. The effects of the size and surface charge of NPs were investigated. Moreover, the interactions between the membrane and SDS@NPs were calculated using the XDLVO theory to elucidate the mechanisms underlying the enhanced anti-wetting performance. This study provides a promising approach for the fabrication of high-performance Janus membranes and unveils the anti-wetting mechanism of Janus membranes induced by nanoplastic-surfactant complexes.