Nanofoamed\nPolyamide Membranes: Mechanisms, Developments,\nand Environmental Implications

Thin film composite (TFC) polyamide\nmembranes have been widely\napplied for environmental applications, such as desalination and water\nreuse. The separation performance of TFC polyamide membranes strongly\ndepends on their nanovoid-containing roughness morphology. These nanovoids\nnot only influence the effective filtration area of the polyamide\nfilm but also regulate the water transport pathways through the film.\nAlthough there have been ongoing debates on the formation mechanisms\nof nanovoids, a nanofoaming theorystipulating the shaping\nof polyamide roughness morphology by nanobubbles of degassed CO<sub>2</sub> and the vapor of volatile solventshas gained much\nattention in recent years. In this review, we provide a comprehensive\nsummary of the nanofoaming mechanism, including related fundamental\nprinciples and strategies to tailor nanovoid formation for improved\nmembrane separation performance. The effects of nanovoids on the fouling\nbehaviors of TFC membranes are also discussed. In addition, numerical\nmodels on the role of nanovoids in regulating the water transport\npathways toward improved water permeance and antifouling ability are\nhighlighted. The comprehensive summary on the nanofoaming mechanism\nin this review provides insightful guidelines for the future design\nand optimization of TFC polyamide membranes toward various environmental\napplications.