Constructing highly rough skin layer of thin film (nano)composite polyamide membranes to enhance separation performance: A review

The thin-film (nano)composite (TFC or TFN) polyamide membrane prepared by interfacial polymerization method has a wide range of applications in water treatment. The preparation of TFC or TFN membrane with a highly wrinkled morphology in the selective layer can significantly improve the permeability of the membrane and is an effective way to break the "trade-off" effect. However, the formation mechanism of highly rough skin layer and the membrane fouling performance associated with the rough structure have been underexplored. In this review, the formation mechanisms of crumpled membranes were summarized into four aspects: interfacial nanobubbles effect, template method, diffusion-driven instability, and co-solvent effects. On the basis of these mechanisms, researchers have explored different methods to construct membranes with highly rough structures. This article summarized these construction methods including introduction of additives, construction of functional interlayer, sacrificial template and some other strategies. The advantages and disadvantages of these fabrication methods and the separation performance comparison of the crumpled membrane and the original membrane were discussed in detail. Furthermore, the review analyzed the recent research status of the anti-fouling performance of the pleated membrane, and finally put forward the research opinions on the future in fabricating highly roughness membranes.